international conference on quantum optics 2016 - … · international conference on quantum optics...
TRANSCRIPT
International conference on
Quantum Optics 2016Obergurgl, Tirol, Austria
February 21-27, 2016
Book of Abstracts
Chair:Hanns-Christoph Nägerl (University of Innsbruck)
Co-chairs:Helmut Ritsch (University of Innsbruck)
Jörg Schmiedmayer (TU Vienna)
ContentsConference Schedule 3
Talks 5Monday, February 22 . . . . . . . . . . . . . . . . . . . . . . . . . . 5Tuesday, February 23 . . . . . . . . . . . . . . . . . . . . . . . . . . 11Wednesday, February 24 . . . . . . . . . . . . . . . . . . . . . . . . 18Thursday, February 25 . . . . . . . . . . . . . . . . . . . . . . . . . 24Friday, February 26 . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Posters 37
Sponsors 83
Index 85
Conference Schedule
Conference Schedule
3
Talks
TalksMonday, February 22
Invited TalkMeasurements not bounded by the Heisenberg uncertainty
principle
Eugene PolzikNiels Bohr Institute, University of CopenhagenBlegdamsvej 17, 2100 Copenhagen, Denmark
Measurements of one quadrature of an oscillator with precision beyond itsvacuum state uncertainty have occupied a central place in quantum physicsfor decades. We have recently reported the first experimental implementationof such measurement with a magnetic oscillator [1]. However, a much moreintriguing goal is to trace an oscillator trajectory with the precision beyondthe vacuum state uncertainty in both position and momentum, a feat naivelyassumed not possible due to the Heisenberg uncertainty principle. We havedemonstrated that such measurement is possible if the oscillator is entangledwith a quantum reference oscillator characterized by an effective negativemass [2,3]. Progress towards such a measurement involving a macroscopicmechanical oscillator will be reported. The key element is the cancellation ofthe back action of the measurement on the composite system of two oscilla-tors. Applications include measurements of e.-m. fields, accelleration, forceand time [4] with practically unlimited accuracy. In a more general sense, thisapproach leads to trajectories without quantum uncertainties and to achiev-ing new fundamental bounds on the measurement precision.[1] Generation of a squeezed state of an oscillator by stroboscopic back-action-evading measurement. G. Vasilakis, H. Shen, K. Jensen, M. Balabas, D.Salart, B. Chen, and E. S. Polzik. NaturePhysics, (2015)doi:10.1038/nphys3280.[2] Establishing Einstein-Podolsky-Rosen channels between nanomechanicsand atomic ensembles. K. Hammerer, M. Aspelmeyer, E.S. Polzik, P. Zoller.Phys. Rev. Lett. 102, 020501 (2009).[3] Trajectories without quantum uncertainties. E.S. Polzik and K.Hammerer.Annalen der Physyk. 527, No. 1–2, A15–A20 (2015).[4] Entanglement and spin-squeezing in a network of optical lattice clocks. E.S. Polzik and J. Ye. arXiv:1508.02540
5
Talks
Invited TalkHybrid Quantum Processing with Cavity Photons and Single
Atoms
Axel KuhnUniversity of Oxford
Clarendon Laboratory, OX1 3PU Oxford, [email protected]
Cavity-mediated interfacing of stationary with flying quantum bits in theform of atoms and photons is combined with on-chip linear optics quantumcomputing to an hitherto unprecedented approach to quantum networking.This hybrid scheme operates on-chip photonic quantum gates and entanglingoperations with photons delivered on demand from a non-probabilistic atom-photon interface. Non-classical correlations are observed between events sep-arated by periods exceeding the travel time across the chip by three orders ofmagnitude. This paves the way to novel quantum technologies that exploitboth narrowband cavity photons and integrated quantum photonics, such asscalable photonic quantum computing and narrow linewidth atomic memo-ries.
6
Talks
Overlapping a Cs Mott insulator with superfluid Rb at tunableinterspecies interactions
Andreas SchindewolfUniversity Innsbruck
Technikerstraße 25/4, 6020 Innsbruck, [email protected]
Ultracold dipolar systems are of high interest for quantum chemistry, pre-cision spectroscopy, quantum many-body physics, and quantum simulation.The goal of our project is to prepare an ultracold sample of dipolar RbCsground-state molecules in an optical lattice with a high filling factor. To thisend, atomic Rb and Cs samples are mixed in an optical lattice to efficientlyform Rb-Cs atom pairs as precursors to ground-state molecules. The basicidea is to go through the superfluid-to-Mott-insulator phase transition twice,first for Cs to create a sample with single-site occupancy, then for Rb on topof Cs to create a homogenous distribution of atom pairs.We investigate the transport properties of superfluid Rb samples while theyare moved on top of a strongly interacting sample of Cs atoms. Overlappingis realized in the vicinity of a Feshbach-resonance zero crossing to tune theinterspecies interactions. We find a breakdown of the superfluid current forsufficiently strong attractive interspecies interactions. For even stronger at-tractive interactions the samples are immiscible and superfluidity is restored.Our experiments show that atom-pair formation is optimized for nulled in-teractions. We estimate the filling fraction to be 30% in the center of ourtrap.
7
Talks
Invited TalkMany-body localization and symmetry protected topology
Norman YaoUC Berkeley
510 Beloit Ave., 94708 Kensington, [email protected]
Owing to their natural isolation, quantum optical systems of atoms, ions andmolecules offer an attractive platform to study out-of-equilibrium quantumdynamics and localization. Recent progress on many-body localized phaseshas demonstrated that they can exhibit symmetry breaking and/or topolog-ical orders in dimensions normally forbidden by Mermin-Wagner arguments.In this talk, I will describe how to coherently prepare, protect and detectsymmetry protected topological order in a non-equilibrium setting. I willexplore a 1D transverse-field Ising model with periodically driven two-bodyterms whose Floquet dynamics mirror those of the celebrated Haldane phase.Even in the presence of generic interactions, I will show that disorder lead-ing to many-body localization prevents arbitrary heating of the system andleads to an exponential enhancement of the edge spin coherence at infinitetemperature. Finally, I will describe a natural realization in a Rydberg en-semble, leveraging the blockade to controllably toggle between ferromagneticand antiferromagnetic Ising interactions.
Far-Field Optical Nanoscopy with Ultrashort Pulses
Oriol Romero-IsartIQOQI and UNI Innsbruck
IQOQI Technikerstraße 21a, 6020 Innsbruck, [email protected]
The Abbe diffraction limit applies to monochromatic light. Here we addresswhether polychromatic light can be used for far-field optical microscopy. Weshow that an ultrashort pulse can be focused to a spot size smaller than theoptical wavelength and can be used for far-field optical nanoscopy.
8
Talks
Invited TalkCoherent Orbital Manipulation of SU(N) Fermi gases
Jacopo CataniLENS and INO-CNR
via Nello Carrara, 1, I-50019 Sesto Fiorentino, [email protected]
In this talk I will report on recent results obtained in a SU(N) quantum de-generate Fermi gas of Yb by exploiting its orbital degree of freedom . Firstly,I report on the evidence of inter-orbital coherent spin-exchange dynamicsachieved by a coherent manipulation of the orbital degree of freedom, ex-ploiting the ultranarrow clock transition of 173Y b. Secondly, I will show howthe orbital degree of freedom can be efficiently employed in order to achievemagnetic tunability of interactions in this non-magnetic atom. A new kindof Feshbach resonance (orbital Feshbach resonance) is observed in the openchannel involving different electronic orbitals. Noticeably, the behavior whichis observed in the position of resonance centers as a function of the relativespin projection of the scattering particles reflects the SU(N) character ofinteractions in the Yb atom. The strong interacting regime is achieved bytuning the scattering length via this novel kind of resonance.
Hottopic TalkSuperradiant Mott insulator in the Dicke-Hubbard model
Andreas HemmerichInst. für Laser-Physik, Uni Hamburg
Luruper Chaussee 149, 22761 Hamburg, [email protected]
It is well known that the bosonic Hubbard model possesses a Mott insulatorphase. Likewise, it is known that the Dicke model exhibits a self-organizedsuperradiant phase. By implementing an optical lattice inside of a high fi-nesse optical cavity both models are merged such that an extended Hubbardmodel with cavity-mediated infinite range interactions arises. In addition toa normal superfluid phase, two superradiant phases are found, one of themcoherent and hence superfluid and one incoherent Mott insulating.
9
Talks
Solving a quantum many-body problem by experiment
Thomas SchweiglerAtominstitut, TU Wien
Stadionallee 2, 1020 Vienna, [email protected]
We experimentally study a pair of tunnel-coupled one-dimensional atomic su-perfluids, which realize the quantum sine-Gordon/massive Thirring modelsrelevant for a wide variety of disciplines from particle to condensed-matterphysics. From measured interference patterns we extract phase correlationfunctions and analyze if, and under which conditions, the higher-order corre-lation functions factorize into lower ones. This allows us to characterize theessential features of the model solely from our experimental measurements,detecting the relevant quasiparticles, their interactions and the topologicallydistinct vacua. The method is also used to investigate the non-equilibriumdynamics following a quench in the tunnel-coupling between the superfluids.
Invited TalkRosensweig instability and quantum droplets in a strongly dipolar
BEC.
Igor Ferrier-Barbut5. Physikalisches Institut Stuttgart
Pfaffenwaldring 57, 70569 Stuttgart, [email protected]
Quantum many-body systems with dipole interactions are expected to fea-ture many novel phenomena. In this talk we will report on the observation oftwo of them, one expected and one unexpected. Our team explores dipolarBECs of 164Dy, characterized by a domination of the dipole interaction overthe contact interaction at the background level (away from resonances). Wefirst observe a finite wavelength instability of a BEC driven by the anisotropiclong-range interaction. This instability was expected and is related the “ro-ton” minimum of the elementary excitations, it is in close similarity with theRosensweig instability of classical ferrofluids. Following this instability weobserve the formation of long-lived droplets in contradiction with the mean-field prediction that they should subsequently collapse. By systematicallystudying these droplets in a waveguide configuration, we demonstrate thatquantum fluctuations play a strong role and in fact stabilize the dropletsagainst collapse.
10
Talks
Tuesday, February 23Invited Talk
Controlling long-range interactions by Rydberg dressing
Christian GrossMPQ
Hans-Kopfermann-Str. 1, 85748 Garching, [email protected]
Controlling strong long-range interactions in quantum gases enables the ex-perimental study of rich quantum many-body physics, such as frustratedquantum magnets or supersolids. One possibility to achieve this goal is nearresonant laser coupling to Rydberg states, thus, transferring the dipolar inter-action between Rydberg atoms to the dressed atomic ground states. Here wereport on the observation of coherent Rydberg dressing by directly "imaging"the induced interaction phase shift via many-body Ramsey interferometry.We track the growth of correlations in a 2d array of 200 atoms and demon-strate control over the range and shape of the induced interaction potential.Finally, we identify black body radiation induced coupling to nearby Ryd-berg states as the main source of decoherence in our system.
11
Talks
Invited TalkFinding almost conserved local quantities in non-integrable
quantum systems
Maria Carmen BanulsMax Planck Institut fuer Quantenoptik
Hans Kopfermann Str. 1, 85748 Garching, [email protected]
The question of thermalization of closed quantum systems refers to whetherlocal expectation values attain stationary values, independent of the details ofthe initial state, and it is of fundamental interest. Generically, non-integrablesystems, in which the only conserved local quantity is the energy density, areexpected to reach thermalization. But experimental and numerical resultshave hinted at the existence of very slow time scales in systems without localconserved quantities. Using tensor network techniques and exact diagonaliza-tion, we have shown how very large time scales can appear in the dynamicsof one dimensional spin chains. Our method finds operators evolving slowerthan the slowest energy mode in a non-integrable system. The same methodcan be applied to other scenarios, as that of many body localization, to findlocal conserved quantities.
12
Talks
Hottopic TalkOptimal shaking of optical lattices
Florian MintertImperial College London
Imperial College London, London, [email protected]
We discuss the optimal design of driving patterns for optical lattices. Thereare geometry dependent selection rules that limit the realisation of imple-mentable dynamics, but Hamiltonians in accordance with these rules can beimplemented in a clean fashion with the help of polychromatic driving as wedemonstrate with the example of a Chern insulator in a deep optical lattice.
Invited TalkPhoton propagation by dipolar exchange
Thomas PohlMax-Planck-Institute for the Physics of Complex Systems
Noethnitzer Str. 38 , D-01187 Dresden, [email protected]
In this talk I will consider the propagation of light through a medium thatfeatures strong dipolar interactions. Such interactions induce exchange ofexcitations, i.e. spin wave components generated by propagating photons.Already, the simple case of a single photon interacting with a single spinwave reveals a number of surprising features, which will be discussed in thistalk. Recent experiments, utilizing exchange of high-lying atomic states ina cold gas, demonstrate these effects and suggest promising applications forthe processing of single photons.
13
Talks
Invited TalkMany-Body Physics in Cavity Quantum Electrodynamics
Giovanna MorigiSaarland University
Campus E26, 66123 Saarbruecken, [email protected]
In this talk I will review recent works on the dynamics of ultracold atoms inthe long-range potential mediated by the photons of a single-mode cavity. Iwill highlight the features that emerge from the interplay between the long-range interaction and the wave nature of matter at low temperatures.
Invited TalkCompeting Quantum Phases in Bosonic Lattice Systems with
Rydberg Dressing
Walter HofstetterInstitut für Theoretische Physik
Max-von-Laue-Str. 1, 60438 Frankfurt, [email protected]
Recent experiments have shown that (quasi-)crystalline phases of Rydberg-dressed quantum many body systems in optical lattices (OL) are withinreach. While conventional neutral atomic OL gases lack strong long-rangeinteractions, they arise naturally in Rydberg systems, due to the large po-larisability of Rydberg atoms. In combination with the bosonic character ofthe systems considered in our work, a wide range of quantum phases havebeen predicted. Among them are a devil’s staircase of lattice-incommensuratedensity waves, as well as the more exotic supersolid lattice order. High exper-imental tunability opens up a wide range of parameters to be studied. Basedon our previous analysis of the "frozen" gas case, we have studied the groundstate phase diagram at finite hopping amplitudes and in the vicinity of reso-nant Rydberg driving. Since different types of lattice-incommensurate orderare to be expected, we have applied a real-space extension of bosonic dynam-ical mean-field theory (RB-DMFT). This method allows a non-perturbativetreatment of local quantum correlations and also takes lowest-order nearest-neighbour correlations into account. It therefore improves upon basic mean-field theories such as the Gutzwiller approximation (GA), yielding a richphase diagram which illustrates the competition between interaction andcondensation.
14
Talks
Hottopic TalkA self-interfering clock as a "which path" witness
Ron FolmanBen-Gurion University
Physics Department (POB 653), 84105 Beer Sheva, [email protected]
In Einstein’s general theory of relativity, time depends locally on gravity; instandard quantum theory, time is global all clocks tick uniformly. We demon-strate a new tool for investigating time in the overlap of these two theories:a self-interfering clock, comprising two atomic spin states. We prepare theclock in a spatial superposition of quantum wave packets, which evolve co-herently along two paths into a stable interference pattern. If we make theclock wave packets tick at different rates, to simulate a gravitational time lag,the clock time along each path yields "which path" information, degradingthe pattern’s visibility. In contrast, in standard interferometry, time cannotyield "which path" information.Published in Science 349, 1205 (2015).
15
Talks
Invited TalkInteracting photons using Rydberg atoms
Paul HuilleryDepartment of Physics
Stockton Road, DH1 3LE Durham, [email protected]
If photons are ideal carriers of information, they hardly interact together,which makes the information difficult to process. This problem could be over-comed by mapping back and forth photons onto electronic states of atomsand engenering suitable interactions between the latters. The field of Rydbergnon-linear optics aims to adress this challenge using two main ingredients.Electromagnetically Induced Transparency (EIT) on one hand, which pro-vides a way to coherently map photons onto atoms. The use of Rydbergstates on the other hand which provides strong atomic interactions. Duringthis talk, we will present some of the main results that have been obtainedin this field, including the observation of optical non-linearity at the singlephoton level [1,2], generation of non-classical light [3] and realisation of singlephoton optical transistors [4,5]. We will also present experimental progresstoward the realisation of interactions between photons which are spatiallyseparated.[1] J.D. Pritchard et al, Phys. Rev. Lett. 105, 193603 (2010)[2] T. Peyronel et. al., Nature 488, 57-60 (2012)[3] Y. O. Dudin et al, Science 336, 887-889 (2012)[4] H. Gorniaczyk et. al., Phys. Rev. Lett. 113, 053601 (2014)[5] D. Tiarks et al, Phys. Rev. Lett. 113, 053602 (2014)
16
Talks
Quantum Simulation of a Wilson lattice gauge theory
Christine MuschikIQOQI
Technikerstrasse 21a, 6020 Innsbruck, [email protected]
The quantum simulation of models from high-energy physics is a rapidlygrowing field. A major interest is the simulation of gauge theories.Wilson’s lattice gauge theory represents the most advanced, non-perturbativetechnique to investigate the physics of strongly coupled gauge theories. How-ever, numerical calculations are severely limited by the sign problem, whichhas motivated intensive research on the question how gauge theories couldbe simulated on a quantum simulator. We propose and experimentally studythe quantum simulation of a Wilson lattice gauge theory with trapped ions.The scheme will build a strong bridge to the high-energy physics communityand allow for the direct comparison with quantities discussed in the latticegauge theory literature.
17
Talks
Wednesday, February 24Invited Talk
Progress in quantum information processing with trapped ions atNIST
Dietrich LeibfriedNIST
325 Broadway, 80305 Boulder, [email protected]
Most basic requirements for quantum information processing and quantumsimulation have been demonstrated for trapped ions, with two big challengesremaining: Improving operation fidelity and scaling up to larger numbers ofqubits. In the last few years, operation fidelities have steadily increased withsingle qubit rotation errors per π-pulse close to 10−6 for microwave opera-tions and 10−4 for laser-based Raman-transitions on hyperfine ground statequbits. Laser-based two-qubit entanglement schemes have demonstrated fi-delities of deterministically produced Bell states of larger than 0.998. Entan-glement operations with microwaves in miniaturized surface electrode trapshave recently demonstrated Bell state fidelities of 0.993. At NIST, scalingtowards larger systems is based on moving ion-qubits through a multi-zonetrap array and sympathetically cooling them with a second ion species. Micro-fabrication approaches to ion-trap-arrays have yielded structures that shouldbe capable of holding and manipulating large numbers of ions. I will give abrief overview over technical developments and recent experiments in quan-tum information processing and quantum simulation with trapped ions atNIST, highlighting the progress due to improved laser sources, better laser-beam control by utilizing high-power single-mode UV fibers, reductions inanomalous heating and improvements of cooling, transport and quantumcontrol of multi-species ion crystals.This work has been supported by IARPA, DARPA, ONR, and the NISTQuantum Information Program.
18
Talks
Invited TalkQuantum logic with molecular ions
Piet SchmidtPTB/Leibniz Universität Hannover
Bundesallee 100, 38116 Braunschweig, [email protected]
Precision spectroscopy is a driving force for the development of our physicalunderstanding. However, only few atomic and molecular systems of interesthave been accessible for precision spectroscopy in the past, since they miss asuitable transition for laser cooling and internal state detection. This restric-tion can be overcome in trapped ions through quantum logic spectroscopy.I will show how the internal state of a molecular ion can be detected non-destructively on a co-trapped cooling ion by implemented a quantum logicalgorithm involving only coherent laser manipulation on the molecular ion.This represents a first step towards extending the exquisite control achievedover selected atomic species to much more complex molecular ions.
An enhanced quantum interface through collective ion-cavitycoupling
Tracy NorthupExperimentalphysik Innsbruck
Technikerstrasse 25, 6020 Innsbruck, [email protected]
Optical cavities offer a coherent interface between matter and light, enablingthe transfer of quantum information onto photons for long-distance distribu-tion. For example, a quantum state can be faithfully mapped from a trappedion onto the polarization state of a cavity photon [1]. I will describe how thistransfer can be improved by taking advantage of a collective effect betweenmultiple ions, namely, superradiant emission into the cavity. By construct-ing an interface based on entangled ions, one can thus relax the technicalrequirements for the faithful mapping of quantum information [2]. Finally,prospects for linking together distant ions in cavities via a quantum networkwill be discussed.[1] A. Stute et al., Nature Photon. 7, 219 (2013)[2] B. Casabone et al., Phys. Rev. Lett. 114, 023602 (2015)
19
Talks
Hottopic TalkTopological phases due to density dependent tunnelings in
periodically driven systems
Jakub ZakrzewskiJagiellonian University
Lojasiewicza 11, 30-348 Krakow, [email protected]
Two species of attractively interacting fermions in optical lattice are con-sidered. Using periodic driving, role of density-dependent s – p tunnelingsis enhanced while standard tunnelings are killed. Composites of two speciesform then an emergent lattice in which excess fermions move.For 1D system at half filling, composites form a density wave and excessfermions move in the effective Hamiltonian (dimer Rice-Mele) with controlleddefects where topologically protected localized modes appear [1].For 2D triangular lattice [2] at 1/3-filling the excess fermions move in anemergent Dice lattice. One may realize either anomalous Hall effect or itsquantized version.[1] A. Przysiezna et al., New. J. Phys. 17, 013018 (2015).[2] O. Dutta et al. Sci. Rep. 5, 11060 (2015).
Invited TalkMany-body quantum optics with fermions
Philipp StrackUniversity of Cologne
Zülpicher Str. 77a, 50937 Cologne, [email protected]
We propose and describe far-from-equilibrium phases of matter by interfac-ing quantum degenerate fermionic atoms with quantized, optical light fields.
20
Talks
Invited TalkQuantum phases emerging from competing short- and long-range
interactions in an optical lattice
Manuele LandiniETH zurich
Otto-Stern-weg 1, 8093 Zurich, [email protected]
Examples of competition between interactions acting on different lengthscales range from the folding mechanisms of proteins to the appearance ofstripe phases in quantum matter. Theoretical characterization of such emerg-ing structures is often challenging even if simple models are used. Here weexperimentally realize a bosonic lattice model with competing short- andinfinite-range interactions, and observe the appearance of four distinct phases- a superfluid, a supersolid, a Mott insulator and a charge density wave. Oursystem is based on an atomic quantum gas trapped in an optical lattice insidea high finesse cavity. When probing the transition between the Mott insula-tor and the charge density wave, we discovered a behaviour characteristic ofa first order phase transition.
21
Talks
Hottopic TalkSupermode-polariton condensation in a multimode cavity
QED-BEC system
Alicia KollarStanford University
969 Lawrence Lane, Unit 2, 94303 Palo Alto, [email protected]
Investigations of many-body physics in an AMO context often employ a staticoptical lattice to create a periodic potential. Such systems, while capable ofexploring, e.g., the Hubbard model, lack the fully emergent crystalline orderfound in solid state systems whose stiffness is not imposed externally, butarises dynamically. Our multimode cavity QED experiment is introducing anew method of generating fully emergent and compliant optical lattices tothe ultracold atom toolbox and provides new avenues to explore quantumliquid crystalline order. Looking forward, spin glasses may arise due to theoscillatory, frustrated, and tunable-range interactions mediated by the pho-tons in the multimode optical cavity. It will thus be possible to use spinfulatoms in cavities to realize models of frustrated and/or disordered spin sys-tems, including neuromorphic computation in the context of the Hopfieldassociative memory. We will present our first experimental result, the obser-vation of a supermode-polariton condensate via a supermode superradiantphase transition.
22
Talks
Invited TalkLight, sound, and topology
Florian MarquardtInstitute for Theoretical Physics II
Staudtstr. 7 , 91058 Erlangen, [email protected]
The interaction between radiation and mechanical motion on the nanoscaleis now being studied intensively. Known as optomechanics, this field promisesapplications in quantum communication, sensitive measurements, and funda-mental studies of quantum physics. After a general introduction, I will turnto some recent ideas of ours that envisage controllable transport of photonsand phonons in so-called optomechanical arrays. Once realized, these systemscould e.g. feature engineered chiral edge channels for light and sound thatare topologically protected against disorder-scattering.[1] Cavity optomechanics, M. Aspelmeyer, T. Kippenberg, and F. Marquardt,Reviews of Modern Physics 86, 1391 (2014)[2] Topological Phases of Sound and Light, V. Peano, C. Brendel, M. Schmidt,and F. Marquardt, Phys. Rev. X 5, 031011 (2015)
23
Talks
Thursday, February 25Invited Talk
Breaking Quantum and Thermal Limits on PrecisionMeasurements
James ThompsonJILA
JILA/Univ. of Colorado, 440UCB, 80309 Boulder, [email protected]
We are exploring how to use collective correlations and entanglement be-tween many atoms to overcome quantum and thermal limits on precisionmeasurements. In the first portion of my talk, I will present a path toward a10000 times reduced sensitivity to the thermal mirror motion that limits thelinewidth of today’s best lasers. By utilizing narrow atomic transitions [1],the laser’s phase information is primarily stored in the atomic gain mediumrather than in the vibration-sensitive cavity field [2]. To this end, I will presentthe first observation of lasing based on the 7.5 kHz [3] and 1 mHz linewidthoptical-clock transitions in a laser-cooled ensemble of strontium atoms. Inthe second portion of my talk, I will describe how we use collective measure-ments to surpass the standard quantum limit on phase estimation 1/
√N
for N unentangled atoms. We achieve a directly observed reduction in phasevariance relative to the standard quantum limit of as much as 17.7(6) dB[4,5]. I will discuss first steps toward applying the same technique to createentanglement on the mHz optical-clock transition in strontium via measure-ments of the magnitude of a well-resolved collective vacuum Rabi splittingon the 7.5 kHz transition [6].[1] Prospects for a millihertz-linewidth laser, D. Meiser, J. Ye, D. R. Carlson,M. J. Holland, Phys. Rev. Lett. 102, 063601 (2009)[2] A steady-state superradiant laser with less than one intracavity photon, J.G. Bohnet, Z. Chen, J. M. Weiner, D.Meiser, M. J. Holland, J. K. Thompson,Nature 484, 78-81 (2012)[3] A Cold-Strontium Laser in the Superradiant Crossover Regime , M. A.Norcia, J. K. Thompson, arXiv:1510.06733 (2015)[4] Reduced spin measurement back-action for a phase sensitivity ten timesbeyond the standard quantum limit, J. G. Bohnet, K. C. Cox, M. A. Norcia,J. M. Weiner, Z. Chen, J. K. Thompson, Nature Photonics, 8, 731 (2014)[5] Deterministic Squeezed States with Joint Measurements and Feedback, K.C. Cox, G. P. Greve, J. M. Weiner, J. K. Thompson, arXiv:1512.02150 (2015)[6] Strong Coupling on a Forbidden Transition in Strontium and Nondestruc-tive Atom Counting, M. A. Norcia, J. K. Thompson, arXiv:1506.02297 (2015)
24
Talks
Invited TalkCavity Quantum Electrodynamics: A Quantum Optics Chameleon
Gerhard RempeMax Planck Institute of Quantum Optics
Hans-Kopfermann-Str. 1, 85748 Garching, [email protected]
Electromagnetic resonators provide unparalleled possibilities in controllingthe interaction between single atoms and single photons. The recently devel-oped techniques for controlling also the position and the momentum of theatoms inside an optical resonator now open up new experimental avenues forgenuine quantum-mechanical experiments. Particularly exciting possibilitiesconcern long-distance quantum networking and scalable quantum computa-tion. The talk will highlight some recent achievements like the nondestructivedetection of an optical photon, the heralded and efficient storage of a flyingoptical qubit in a stationary atomic qubit, and – arguably most interesting– the realization of quantum gates with individually addressable atomic andphotonic qubits.
25
Talks
One, two and three photons from a nanowire
Gregor WeihsExperimentalphysik Innsbruck
Technikerstrasse 25, 6020 Innsbruck, [email protected]
Producing advanced quantum states of light is a priority in quantum in-formation technologies. While remarkable progress has been made on singlephotons and photon pairs, multipartite correlated photon states are usu-ally produced in purely optical systems by postselection or cascading, withextremely low efficiency and exponentially poor scaling. Multipartite statesenable improved tests of the quantum mechanics foundations as well as im-plementations of complex quantum optical networks and protocols. It wouldbe favorable to generate these states directly using solid-state systems, forbetter scaling, simpler handling, and the promise of reversible transfer ofquantum information between stationary and flying qubits.In our work, we have shown that quantum dots in nanowires are extremely ef-ficient sources of single photons and entangled photon pairs. Most recently, weused ground states of two optically active coupled InAsP quantum dot inser-tions in an InP nanowire to directly produce photon triplets. The formationof a triexciton leads to a triple cascade recombination and sequential emis-sion of three photons with measurable correlations. This source surpasses therates of all earlier reported sources, in spite of the moderate efficiency of ourdetectors. Our structure and data represent a breakthrough towards imple-menting multipartite photon entanglement and multi-qubit readout schemesin solid state devices, suitable for integrated quantum information process-ing.
26
Talks
Hottopic TalkMicro- and nano-optomechanics towards quantum state and
hybrid devices
Tristan BriantUPMC, LKB
LKB, Campus Jussieu, BC74, 75252 Paris, [email protected]
Reaching the quantum ground state of macroscopic and massive mechanicalobjects is a major experimental challenge at the origin of the rapid emer-gence of cavity optomechanics. We develop a new generation of optomechan-ical devices, either based on microgram 1-mm long quartz micropillar withvery high mechanical quality factor or on 100-pg photonic crystal suspendednanomembranes. We expect to reach the ground state of such optomechan-ical resonators combining cryogenic and radiation-pressure cooling. We alsoinvestigate the possibility to develop an hybrid platform which may be veryhelpful for quantum engineering and quantum information processing, bycoupling our suspended nanomembranes to cold atoms or to microwave cir-cuits.
Invited TalkQuantum optics width deterministically fabricated quantum dot
microlenses
Stephan ReitzensteinTU Berlin
Hardenbergstrasse 36, 10623 Berlin, [email protected]
Bright non-classical light sources emitting single and indistinguishable pho-tons on demand constitute essential building blocks towards the realizationof quantum communication networks. In this talk, I will report on efficientsingle photon sources based on deterministically fabricated single quantumdot (QD) microlenses. Close to ideal performance of the non-classical light-sources in terms of photon extraction efficiency, high suppression of multi-photon events and a high degree of indistinguishability is ensured by applyingin-situ electron beam lithography [1] with process yield higher than 90%.[1] M. Gschrey et al., Nature Communications 6, 7662 (2015).
27
Talks
Invited TalkSuperfluidity and interactions in topologically and geometrically
non-trivial bands
Päivi TörmäAalto University
Department of Applied Physics, P.O.Boz 15100, 76 Aalto, [email protected]
Fermions in flat bands are predicted to reach non-zero pairing gaps at hightemperatures. Superfluidity, however, has been an open question in flat bandssince the usual group velocity is zero. We provide a general expression for thesuperfluid weight D s of a multiband superconductor that is applicable also totopologically nontrivial bands with nonzero Chern number C [1]. We find thatan invariant calculated from the Bloch functions gives the superfluid weight ina flat band, with the bound Ds ≤ |C|. Thus, even a flat band can carry finitesuperfluid current, provided the Chern number is nonzero. Intriguingly, wefind that the superfluid density is connected to the quantum geometric tensorand quantum metric. As an example, we provide Ds for the time-reversalinvariant attractive Harper-Hubbard model that can be experimentally testedin ultracold gases. We have recently shown that also geometric effects canlead to C=0 flat bands that may support superfluidity [2]. Furthermore,we study the effect of repulsive interactions on the Haldane-Hubbard modelrecently realized in ultra-cold gases [3]. By a combined dynamical mean-fieldtheory and exact diagonalization study, we find a new phase with the Chernnumber C=1 [4]. This phase is associated with a spontaneous symmetrybreaking where one of the spin-components is in the Hall state and the otherin the band insulating state.[1] S. Peotta and P. Törmä, Nat. Comm. 6, 8944 (2015)[2] A. Julku, S. Peotta, T.I. Vanhala, D-H. Kim, and P. Törmä, in preparation[3] G. Jotzu, M. Messer, R. Desbuquois, M. Lebrat, T. Uehlinger, D. Greif,and T. Esslinger, Nature 515, 237 (2014)[4] T.I. Vanhala, T. Siro, L. Liang, M. Troyer, A. Harju, and P. Törmä,Topological phase transitions in the repulsively interacting Haldane-Hubbardmodel, arXiv:1512.08804 (2015)
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Talks
Hottopic TalkDemonstration of Deterministic Photon-Photon Interactions
based on Single-Photon Raman Interaction
Barak DayanWeizmann Institute of Science
Weizmann Institute of Science, 76100 Rehovot, [email protected]
I will present our demonstration of a passive scheme for deterministic inter-actions between a single photon and a single atom. Relying on single-photonRaman interaction (SPRINT), this control-fields free scheme swaps a flyingqubit, encoded in the two possible input modes of a photon, with a station-ary qubit, encoded in the two ground states of the atom, and can be alsoharnessed to perform universal quantum gates. Using SPRINT we experi-mentally demonstrated all-optical switching of single photons by single pho-tons, and deterministic extraction of a single photon from an optical pulse.Applicable to any atom-like Lambda system, SPRINT provides a versatilebuilding block for scalable quantum networks based on completely passivenodes interconnected and activated solely by single photons.
A significant-loophole-free test of Bell’s theorem with entangledphotons
Sören WengerowskyIQOQI Vienna and University of ViennaBoltzmanngasse 3, 1090 Vienna, Austria
Local realism is the worldview in which physical properties of objects existindependently of measurement and where physical influences cannot travelfaster than the speed of light. Bell’s theorem states that this concept is in-compatible with the predictions of quantum mechanics, as is expressed inBell’s inequalities. Previous experiments strongly supported the quantumpredictions. Yet, every experiment requires assumptions that provide loop-holes for a local realist explanation. We report a Bell test that closes the mostsignificant of these loopholes simultaneously. Using an optimized source ofentangled photons, rapid setting generation, and highly efficient detectors,we observe a violation of a Bell inequality with high statistical significance,equivalent to 11.5 standard deviations.
29
Talks
Dynamical Self-Ordering of Superfluids and Light
Francesco PiazzaITP Innsbruck
Technikerstrasse 25, 6020 Innsbruck, [email protected]
The strong back-action of an optically dense medium onto the electromag-netic field gives rise to interesting phenomena. One example is atomic self-ordering, whereby the particles spontaneously form a stationary Bragg pat-tern maximising the light scattering. It has been experimentally observedwith thermal gases and more recently also with Bose-Einstein condensates(BECs) inside optical resonators. In this talk, we present some new regimes ofself-ordering with BECs, extending the so far explored regimes to two novelscenarios. Firstly, we will introduce a situation in which self-ordering appearsas a dynamical limit-cycle phase evolving into chaos, whereby the superfluidnature of the BEC manifests itself through phase-slippage and turbulence.Secondly, we will consider a free-space configuration where no pre-selectedlight modes are imposed, so that self-ordering amounts to a real crystallisa-tion of both the BEC, into a supersolid, and the light field, into an opticallattice with phonons.
30
Talks
Friday, February 26Invited Talk
Frequency ratios of optical lattice clocks at the 17th decimal place
Hidetoshi KatoriThe University of Tokyo
7-3-1 Hongo, Bunkyo-ku, 113-8656 Tokyo, [email protected]
Optical lattice clocks [1] benefit from a low quantum-projection noise by si-multaneously interrogating a large number N of atoms, which are trapped inan optical lattice tuned to the “magic wavelength” to largely cancel out lightshift perturbation in the clock transition. N ≈ 103 atoms enable the clocks toachieve 10−18 instability in a few hours of operation, allowing intensive inves-tigation and control of systematic uncertainties. Optical lattice clocks havereached inaccuracies approaching 10−18 [2, 3]. It is now the uncertainty of theSI second (∼ 10−16) itself that restricts the measurement of the absolute fre-quencies of such optical clocks [4, 5]. Direct comparisons of optical clocks are,therefore, the only way to investigate and utilize their superb performancebeyond the current SI second. In this presentation, we report on frequencycomparisons of optical lattice clocks with neutral strontium (87Sr), ytterbium(171Yb) and mercury (199Hg) atoms. By referencing cryogenic Sr clocks [2], wedetermine frequency ratios, νYb/νSr and νHg/νSr [6], of a cryogenic Yb clockand a Hg clock with uncertainty at the mid 10−17 level. Such ratios providean access to search for a temporal variation of the fundamental constants.We also present remote comparisons between cryogenic Sr clocks located atRIKEN and the University of Tokyo over a 30-km-long phase-stabilized fibrelink [7]. The gravitational red shift ∆ν/ν0 ≈ 1.1× 10−18∆h(cm)−1 reads outthe height difference ∆h ∼ 15 m between the two clocks with uncertainty of5 cm, which demonstrates a step towards relativistic geodesy [8].[1] H. Katori, Nature Photon. 5, 203 (2011).[2] I. Ushijima et al., Nature Photon. 9, 185 (2015).[3] B. J. Bloom et al., Nature 506,71 (2014).[4] R. Le Targat et al., Nature Commun. 4, 2109 (2013).[5] S. Falke et al., New J. Phys. 16, 073023 (2014).[6] K. Yamanaka et al., Phys. Rev. Lett. 114, 230801 (2015).[7] T. Akatsuka et al., Jpn. J. Appl. Phys. 53, 032801 (2014).[8] A. Bjerhammar, J. Geod. 59, 207 (1985).
31
Talks
Invited TalkSearching for ultralight dark matter with atomic spectroscopy
and nuclear resonance
Dmitry BudkerHelmholtz Institute Mainz
Friedrichsstraße 33, 55124 Mainz, [email protected]
Axions, axion-like particles (ALPs), dilatons, and other ultralight (massesfrom 10−4 down to 10−22 eV) particles have been discussed as possible can-didates for dark matter. An interesting feature of these ideas is that theylead to predictions of potentially observable transient and oscillating effects.I will describe how we are looking for these as well as the relation of suchexperiments to tests of fundamental symmetries (P, CP, T, CPT . . . ).
Inhibition of superradiance and light-matter decoupling in circuitQED
Peter RablAtominstitut, TU Wien
Stadionallee 2, 1020 Vienna, [email protected]
The existence or non-existence of a superradiance phase transition in theground state of a multi-atom cavity QED systems has generated many de-bates and contradicting conclusions. In view of recent experiments with su-perconducting qubit-cavity systems operated in the ultra-strong couplingregime, this question is no longer only of theoretical relevance. Here I willpresent a microscopic derivation of the Dicke model in circuit QED and showthat the usually neglected qubit-qubit interaction (rather than the often dis-cussed A2-term) cause a suppression of superradiance and can further lead toa complete light-matter decoupling in the limit of very strong interactions.
32
Talks
Hottopic TalkWeak measurements and quantum optical lattices for ultracold
bosons and fermions
Igor MekhovUniversity of Oxford
Parks Road, Dep of Physics, OX1 3PU Oxford, [email protected]
We show that the quantum backaction of weak global measurement con-stitutes a novel source of competitions in many-body systems (in additionsto standard short-range tunnelling and interactions in lattices). This leadsto novel dynamical effects: multimode oscillations of macroscopic superpo-sition states, nonlocal non-Hermitian Zeno dynamics, long-range correlatedpair tunnelling, protection and break-up of fermion pairs, as well as gener-ation of antiferromagnetic states. Quantization of optical lattice potentialsenables quantum simulations of various long-range interacting systems un-obtainable using classical optical lattices. It leads to new quantum phases(dimers, trimers, etc. of matter waves) beyond density orders (e.g. super-solids) utilizing collective light-matter interaction.
Invited TalkThe Quantum Pigeonhole Principle
Sandu PopescuUniversity of Bristol
Tyndall Av, BS8 1TL Bristol, [email protected]
The pigeonhole principle: "If you put three pigeons in two pigeonholes at leasttwo of the pigeons end up in the same hole" is an obvious yet fundamentalprinciple of Nature as it captures the very essence of counting. Here howeverwe show that in quantum mechanics this is not true! We find instances whenthree quantum particles are put in two boxes, yet no two particles are in thesame box. Furthermore, we show that the above ”quantum pigeonhole prin-ciple” is only one of a host of related quantum effects, and points to a veryinteresting structure of quantum mechanics that was hitherto unnoticed. Ourresults shed new light on the very notions of separability and correlations inquantum mechanics and on the nature of interactions. It also presents a newrole for entanglement, complementary to the usual one. Finally, interferomet-ric experiments that illustrate our effects are proposed.
33
Talks
Quantum Simulation with Superconducting Qubits
Gerhard KirchmairIQOQI Innsbruck
Technikerstrasse 21a, 6020 Innsbruck, [email protected]
In this talk I want to present the research activities of the SuperconductingQuantum Circuits group at the Institute for Quantum Optics and Quan-tum Information in Innsbruck towards quantum simulation with Transmonqubits. I will give an introduction to circuit quantum electrodynamics andthe 3D architecture. I will show how we want to use this architecture to re-alize a platform for quantum many body simulations of dipolar XY modelsusing state of the art circuit QED technology. Our basic building blocks are3D Transmon qubits where we use the naturally occurring dipolar interac-tions to realize interacting spin systems.
Hottopic TalkControlled Ensembles of Ultracold Formaldehyde Molecules
Martin ZeppenfeldMPI for Quantum Optics
Hans Kopfermann Str. 1, 85748 Garching, [email protected]
Cooling molecules to ultracold temperatures enables fascinating applicationssuch as ultracold chemistry and investigation of dipolar quantum gases. Weapply opto-electrical Sisyphus cooling, a general cooling technique for po-lar molecules, to formaldehyde. We thereby generate an ensemble of roughly300000 electrically trapped molecules at a temperature of about 400µK. Thecombination with optical pumping via a vibrationally excited state providescontrol of the rotational state, resulting in over 80% of molecules in a singlerotational M-sublevel. Our experiment provides excellent conditions for pre-cision spectroscopy and investigation of ultracold collisions.
34
Talks
Quantum enhancements of learning agents
Vedran DunjkoInstitute for Theoretical Physics
Technikerstrasse 21a, 6020 Innsbruck, [email protected]
The interplay between classical learning theory and quantum mechanics hasbeen gaining an ever increasing interest in the recent years. In this talk, wewill discuss some of the recent results of the research community, which haveexplored both directions of this interplay. In one direction, we will considerthe advantages of utilizing machine learning to enhance quantum experi-ments. In the reverse direction, we will consider the potential of utilizingquantum effects to enhance learning performance. Following this, we will fo-cus on some of our more recent results, which concern quantum speed-ups ofactive learning in the Projective Simulation model for Artificial Intelligence,and also the general capacity of quantum interactions to enhance the learn-ing properties of artificial learning agents.
Invited TalkDicke subradiance in a large cloud of cold atoms
Robin KaiserCNRS
1361 route des Lucioles, 6560 Valbonne, [email protected]
Since Dicke’s seminal paper on coherence in spontaneous radiation by atomicensembles, superradiance has been extensively studied. Subradiance, on thecontrary, has remained elusive, mainly because subradiant states are weaklycoupled to the environment and are very sensitive to nonradiative decoher-ence processes.Here we report the direct observation of subradiance in anextended and dilute cold-atom sample containing a large number of parti-cles. We use a far detuned laser to avoid multiple scattering and observe thetemporal decay after a sudden switch-off of the laser beam. After the fastdecay of most of the fluorescence, we detect a very slow decay, with timeconstants as long as 100 times the natural lifetime of the excited state ofindividual atoms. This subradiant time constant scales linearly with the co-operativity parameter, corresponding to the on-resonance optical thicknessof the sample, and is independent of the laser detuning, as expected from acoupled-dipole model.
35
Posters
PostersQuantum Superposition at the half-meter scale
Peter AsenbaumStanford University
382 Via Pueblo Mall, 94305 Stanford, [email protected]
In matter wave interferometers, large wave packet separation is impeded bythe need for long interaction times and large momentum beam splitters,which cause susceptibility to dephasing and decoherence. We use light-pulseatom interferometry to realize quantum interference with wave packets sep-arated by up to 54 cm on the time scale of 1 s. Large quantum superpositionstates are vital to exploring gravity with atom interferometers in greaterdetail, e.g. tests of the equivalence principle.
Magnetic double slits for a magnetic skatepark
Prasanna Venkatesh BalaIQOQI
Technikerstrasse 21a, 6020 Innsbruck, [email protected]
In this poster we discuss a key component of a proposal for an on-chip all mag-netic set up to create large superposition and observe the quantum interfer-ence of a massive superconducting sphere (mass ∼ 1014 amu). The idea is tocreate a magnetic double slit by allowing the superconducting sphere, whichis a perfect diamagnet below its critical temperature, to dispersively interactwith a transmon qubit such that a flux-dependent coupling proportional tothe squared position of the sphere is realized. A homodyne measurement ofthe output field of the transmon actualizes a continuous measurement of thesquared position of the sphere – a magnetic double slit. In contrast to usualdouble slits for massive quantum mechanical objects in this scenario, theslit separation is a dynamical variable set by the measurement outcome andpost-selection can be used to restrict to a given range of slit sizes required forthe proposal. The larger aim of the proposal is to show that interference ofsuch massive objects can be used to falsify gravity-induced decoherence andother paradigmatic collapse models that predict a breakdown of quantumsuperposition principle at large mass scales.
37
Posters
Bell Correlations in a Bose-Einstein Condensate
Jean-Daniel BancalUniversity of Basel
Klingerlbergstrasse 82, CH-4056 Basel, [email protected]
Tremendous progress has been made recently in characterizing many-bodysystems through the quantum correlations between their constituent parti-cles. While entanglement is routinely observed in many systems, we reporthere the detection of stronger correlations - namely Bell correlations - be-tween the spins of about 480 atoms in a Bose-Einstein condensate. We de-rive a Bell correlation witness from a recent many-particle Bell inequalityinvolving one- and two-body correlation functions only. Our measurementon a spin-squeezed state exceeds the threshold for Bell correlations by 3.8standard deviations. Concluding the presence of Bell correlations is unprece-dented for an ensemble containing more than a few particles.
Majorana fermions in atomic-molecular systems at finitetemperature and in the presence of a noise.
Mikhail BaranovIQOQI
Technikerstraße 21a, 6020 Innsbruck, [email protected]
The effects of quantum and thermal fluctuations, as well as of global andlocal noises, on the Majorana edge states in networks of topological atomic-molecular wires are discussed.
38
Posters
Atomic clocks and interferometers with a PLL on the coherentatomic superposition
Andrea BertoldiLP2N - Institut d’Optique
rue Mitterrand, 33400 Talence, [email protected]
In an atomic interferometer the phase evolution of a local oscillator is com-pared to that of an atomic superposition state. A tradeoff must be found be-tween the duration of the comparison interval, if longer sensitivity increases,and the avoidance of readout ambiguities, the measurement gives the phaseprojection so phase wraps go undetected. This issue limits the sensitivityof optical lattice clocks and of atomic gravimeters. We bypassed the tradeoffusing coherence preserving measurements and phase corrections, and demon-strate the phase lock of a clock oscillator to an atomic superposition state[PRX 5, 021011 (2015)]. The protocol could improve the sensitivity of atomicclocks limited by local oscillator noise and could be applied in inertial sensorsbased on atom interferometry.
Incompressible polaritons in a flat band
Matteo BiondiETH Zurich
Wolfgang-Pauli-Str. 27, 8093 Zurich, [email protected]
We present theoretical and experimental results on geometrically frustratednon-equilibrium photonic lattices. In a theoretical work (PRL 115,143601)we study the interplay of frustration and interactions in a polaritonic flatband system. We engineer correlations in such a driven, dissipative systemby quenching the kinetic energy through frustration. This produces an in-compressible state of photons characterized by short-range density-wave or-der with period doubling. We propose a circuit QED realization tunable in-situ. We also discuss the first experiment on polariton condensation in a flatband (arXiv 1505.05652). Due to the infinite effective mass, the condensateis highly sensitive to disorder and fragments in localized modes, identified byinterferometric and spectral measurements.
39
Posters
Microscopic observation of degenerate fermionic lattice gases
Martin BollMPQ
Hans-Kopfermann Straße 1, 85748 Garching, [email protected]
We report on local observation of degenerate gases of fermions in an opticallattices. We probe the gas with single-site resolution using a new genera-tion quantum gas microscope avoiding the common problem of light inducedlosses. In the band insulating regime, we measure a strong local suppressionof particle number fluctuations and a low local entropy per atom. Our workopens a new avenue for studying quantum correlations in fermionic quantummatter both in and out of equilibrium.
Developing portable ion trap magnetic field quantum sensors
Harry BostockSussex University
Falmer road, BN1 9RH Brighton, [email protected]
Highly sensitive magnetometers in the DC - GHz frequency range have usessuch as detecting explosives and drugs and can be a biological scanner. Singletrapped ytterbium ions have already successfully been used to sense magneticfields with sensitivities of 4pTH−1/2 for AC magnetic fields. We will presentprogress towards making a portable, highly sensitive device based on saidmethod. For quantum sensing of magnetic fields with trapped ions, increasingthe number of trapped ions and coherence time improves sensitivity. We willdescribe a design capable of trapping more than 100 ions along with progresstowards miniaturized ion trap sub systems technologies that are required fora portable device.
40
Posters
New physics searches with atomic systems
Loukourgos BougasHelmholtz Institut-Mainz
Johann Joachim Becherweg 36, 55128 Mainz, [email protected]
The nature of dark matter and dark energy is one of the most exciting openquestions in physics today. Our recent work has shown that atomic systemsare excellent candidates for constraining a theoretical models where darkmatter is an ultralight particle with a macroscopic de Broglie wavelength. Wepresent initial constraints on such models from radio-frequency spectroscopyof dysprosium, and discuss how these constraints may be improved by opticalclocks based on ions or atoms.
Local probing of the Hubbard model in two-dimensions
Ferdinand BrenneckeUni Bonn
Wegelerstrasse 8, 53115 Bonn, [email protected]
Quantum gases of interacting fermionic atoms in optical lattices promise toshed new light on the low-temperature phases of Hubbard-type models, suchas spin-ordered phases or possible d-wave superconductivity. We experimen-tally study the physics of the Hubbard model by loading a quantum degener-ate two-component Fermi gas of 40K atoms into a three-dimensional opticallattice geometry. Using high-resolution absorption imaging combined withradio-frequency spectroscopy we are able to resolve the in-situ distributionof singly and doubly occupied lattice sites within a single two-dimensionallayer. We will report on the observation of the fermionic Mott insulator anda measurement of the equation of state for the repulsive Hubbard model intwo dimensions.
41
Posters
Atom-field dressed states in slow-light waveguide QED
Giuseppe CalajoTu Wien, atomic institute
Stadionallee 2, 1020 Vienna, [email protected]
We discuss the properties of atom-photon bound states in waveguide QEDsystems consisting of single or multiple atoms coupled strongly to a finite-bandwidth photonic channel. Such bound states are formed by an atom anda localized photonic excitations and represent the continuum analog of thefamiliar dressed states in single-mode cavity QED. In this work we presenta detailed analysis of the linear and nonlinear spectral features associatedwith single- and multi-photon dressed states and show how the formation ofbound states affects the waveguide-mediated dipole-dipole interactions be-tween separated atoms. Our results provide a both qualitative and quantita-tive description of the essential strong-coupling processes in waveguide QEDsystems.
Ultracold atoms on a superconducting atomchip
Fritz DioricoAtominsitut TU Wien
Stadionallee 2, 1020 Vienna, [email protected]
We present the realization of a robust magnetic transport scheme to bring3 × 108 ultracold 87Rb atoms into a 4K cryostat. The sequence starts withstandard laser cooling and trapping of 87Rb atoms, transporting first hor-izontally and then vertically through the radiation shields into a cryostatby a series of normal- and superconducting magnetic coils. After subsequentprecooling in a QUIC trap, about 3 × 106 atoms at 30µK are loaded ona superconducting atomchip. This can be built from any superconductingmaterial. Currently, we have various designs of Niobium and YBCO atom-chips fabricated with features either for cQED with microwave resonatorsand ultracold atoms or novel superconducting traps using the remnant mag-netization of the superconducting surface (vortex-like traps).
42
Posters
Symmetric Suppression in Many-Body Quantum Interferences
Christoph DittelInstitut für Experimentalphysik
Technikerstraße 25d, 6020 Innsbruck, [email protected]
We investigate how symmetry considerations in many-boson scattering ex-periments allow the formulation of symmetry suppression laws which predictevents occurring with zero probability due to constructive interference. Inparticular, we theoretically formulate and experimentally test a suppressionlaw, based uniquely on the symmetries of the setup, leaving the exact form ofthe scattering matrix open. Since this suppression relies on genuine N-bodyinterference, it represents a stringent certification criterion that can be usedto ensure the functionality of boson-samplers. Moreover, calculating whichevents are suppressed and testing the suppression for a few such events isefficient and scalable to very large particle numbers in practice.
Quantum Criticality of Coherently Driven Open Systems
Peter DomokosHungarian Academy of Sciences
Konkoly Thege Miklós út 29-33, 1121 Budapest, [email protected]
Quantum critical behavior can appear in coherently driven dissipative sys-tems which cannot be, in general, mapped onto an effective Hamiltoniansystem. It is thus unclear how their critical behavior is related to universal-ity classes of known quantum and thermal phase transitions. We will discussthis question in the case of the Dicke model realized by means of ultracoldatom gases strongly coupled to the electromagnetic radiation field of an opti-cal resonator. We will show that the critical exponent of the recently observedself-organization quantum phase transition is determined by the spectral den-sity function of the reservoir and has a continuously tunable value.
43
Posters
Time-domain interferometry with nanoparticles
Nadine DörreUniversity of Vienna
Boltzmanngasse 5, 1090 Wien, [email protected]
The wave/particle duality of matter is one of the fundamental and most in-triguing concepts in quantum physics. De Broglie interferometers allow test-ing the superposition principle for mesoscopic objects, such as large clustersand molecules. They serve to establish new bounds on theoretical predictionsthat modify standard quantum mechanics and are interesting for measuringmolecular properties.We discuss the principle of a time domain matter-wave interferometer fornanoparticles which uses pulsed optical gratings and show in particular howphoto-fragmentation can used for beam-splitting. We further discuss our ef-forts towards and possible scenarios for breaking mass records in nanoparticleinterferometry with the aim of testing the validity of quantum theory on largecomplexity scales.
Towards an optical phase shift based on Rydberg blockade
Stephan DürrMax-Planck Institute for Quantum Optics
Hans-Kopfermann-Str. 1, 85748 Garching, [email protected]
Controlling the interaction between single photons is important for quantuminformation technology. Recently we demonstrated that an opaque mediumin which single photons are converted into stationary Rydberg excitationscan be used to control the transmission of a subsequent light pulse by usingelectromagnetically induced transparency. Manipulation of coherent super-positions requires, however, non-dissipative interactions that only affect thephase of the light. In this work we report on our recent progress towards re-alizing controlled phase shifts of single photons. We store photons in highlyexited Rydberg states which changes the refractive properties of the mediumdue to Rydberg blockade. A subsequent light pulse will thus experience asignificant phase shift.
44
Posters
Manipulating High-Dimensional Orbital-Angular-MomentumEntanglement
Manuel ErhardIQOQI
Boltzmanngasse 3, 1090 Wien, [email protected]
We discuss the development of a interferometric beam splitter that splits lightbased on the two-dimensional parity of its spatial mode structure. We demon-strate a near-unit sorting efficiency of classical light as well as single photonscarrying orbital angular momentum (OAM). This device is implemented ina double Sagnac configuration that allows stable operation over several days.This capability is crucial for its use in high-dimensional multi-photon ex-periments as an OAM parity beam splitter that mixes high-dimensionallyentangled photons from two independent nonlinear crystals.
Demonstration of the reversed dissipation regime in cavityelectro-mechanics
Alexey FeofanovEPFL (Swiss Federal Institute of Technology in Lausanne)
EPFL-SB-ICMP-LPQM, 1015 Lausanne, [email protected]
Cavity optomechanical phenomena, such as cooling, amplification or optome-chanically induced transparency, emerge due to a strong imbalance in the dis-sipation rates of the parametrically coupled electromagnetic and mechanicalresonators. Here we explore experimentally for the first time the reversed dis-sipation regime where the mechanical energy relaxation rate exceeds the en-ergy decay rate of the electromagnetic cavity. We demonstrate optomechani-cally induced modifications of the microwave cavity resonance frequency anddecay rate as well as mechanically-induced amplification of the electromag-netic mode and self-sustained oscillations (maser action) with high spectralpurity of emitted microwave tone.
45
Posters
Interferometric laser cooling of atomic rubidium
Tim FreegardeUniversity of Southampton
School of Physics & Astronomy, SO20 6AG Highfield, Southampton, [email protected]
When the beamsplitters of an atom interferometer change the atom’s mo-mentum, the difference in kinetic energy between the coupled states gives avelocity dependence to the interferometric phase. The interferometer can beused not only to determine the atomic velocity, but also to impart a velocity-dependent impulse which can cool a cloud of atoms. We report the 1-Dcooling of 85Rb atoms using a velocity-dependent optical force based uponRamsey matter-wave interferometry. Using stimulated Raman transitions be-tween ground hyperfine states, 12 cycles of the interferometer sequence coola freely moving atom cloud from 21 to 3 µK. This pulsed analogue of c-wDoppler cooling is effective down to the recoil limit, and will be more suitablefor species that lack a closed radiative transition.
46
Posters
Quantum decoherence of a single-ion qubit induced by singleoptical photons
Konstantin FriebeExperimentalphysik Innsbruck
Technikerstr. 25/4, 6020 Innsbruck, [email protected]
Quantum measurement is based on the interaction between a quantum ob-ject and a meter entangled with the object. While the information stored inthe object is being extracted by the interaction, the measurement leads todecoherence of the object due to the intrinsic quantum fluctuations of themeter. Here, we report the observation of measurement-induced dephasingof a single-ion qubit with single optical photons. We employ a single 40Ca+ion that is dispersively coupled to a high-finesse cavity. The cavity is drivenby a weak laser field to populate the cavity with mean photon numbers upto five. Spectroscopy is performed on the 729 nm qubit transition to identifythe shift and broadening of the atomic energy levels. The information storedin the qubit is extracted by photons escaping the cavity, which, in turn, leadsto dephasing of the qubit owing to photon-number fluctuations. This mea-surement represents the first demonstration of such quantum decoherenceeffects in the optical domain. Furthermore, heterodyne measurements of thecavity output photons will make it possible to probe quantum trajectories ofthe qubit nondestructively.
47
Posters
Fermi-Bose Mixture of 6Li and 41K
Isabella FritscheInstitut for Experimental Physics, University of Innsbruck
Technikerstraße 25, 6020 Innsbruck, [email protected]
We report on the production of a 41K Bose-Einstein condensate (BEC) im-mersed in a degenerate two-component 6Li Fermi sea. After evaporation inan optical dipole trap, we obtain 104 41K atoms with a 33% BEC fractionand a Fermi sea of 105 6Li atoms with a T/TF ≈ 0.1 This facilitates thestudy of the collective modes of a mass-imbalanced mixture of two coupledsuperfluids. Using loss spectroscopy, we observe the 335.8G Feshbach reso-nance, which is comparable to the one between 6Li and the fermionic 40Kisotope. We exploited the latter in previous studies on the quantum many-body dynamics of a Fermi impurity in a Fermi sea. Investigating interactingbosonic impurities complements this work and enables the direct comparisonof the role of quantum statistics for bosonic/fermionic impurities.
48
Posters
Superfluidity of light : semiconductor microcavities andpropagation geometry
Quentin GlorieuxLaboratoire Kastler Brossel
4 Place Jussieu, 75252 Paris Cedex 5, [email protected]
Historically, research in many body-physics deals with massive material par-ticules. It is known since the early days of quantum mechanics, that photonsin a box can be interpreted as a massless Bose gas of non-interacting partic-ules. Recently, it has been realized that under suitable circumstances photonscan acquire an effective mass and will behave as a quantum fluid of light withphoton-photon interactions.Experimental demonstrations of superfluidity and other quantum hydrody-namical effects will be presented in a confined geometry using semi-conductorplanar micro-cavities.An alternative to the confined geometry will also be introduced: the use ofa monochromatic light field propagating in a non-linear medium showing anintensity dependent an intensity dependent refractive index.
Enhanced Nonlinearity in an Atom-Driven Cavity QED System
Christoph HamsenMax-Planck-Institute of Quantum Optics
Hans-Kopfermann-Str. 1, 85748 Garching bei München, [email protected]
Optical nonlinearities at the single- to few-photon level are essential to quan-tum optics. An atom strongly coupled to the light field of an optical cav-ity provides such nonlinearity. Here we investigate a cavity QED systemwhere the coherent drive resonantly excites the emitter. Compared to thecavity-driven case, we expect an enhanced nonlinearity since the transitionelements from the first to higher Jaynes-Cummings manifolds are reduced.This has distinct implications on the photon statistics of the cavity emission,as demonstrated experimentally: Driving the emitter on the normal modesyields an improved photon-blockade effect. In contrast, driving to the secondmanifold shows a novel photon-concatenation effect reflecting the internaldynamics of the system.
49
Posters
Dark energy search using atom interferometry
Philipp HaslingerUniversity of California, Berkeley
Department of Physics, 311 Le Conte Hall MS 7300, 94720 Berkeley, [email protected]
If dark energy, which drives the accelerated expansion of the universe, consistsof a light scalar field it might be detectable as a "fifth force" between normal-matter objects. In order to be consistent with cosmological observation andlaboratory experiments, some leading theories use a screening mechanism tosuppress this interaction. However, atom-interferometry presents a tool toreduce this screening [1] and has allowed us to place tight constraints on acertain class of these theories, the so-called chameleon models [2]. Recentmodifications to our cavity-enhanced atom interferometer have improved thesensitivity by a hundredfold and we expect new results soon.[1] C. Burrage et al., J. Cosmol. Astropart. Phys. 2015, 042 (2015).[2] P. Hamilton et al., Science 349, 849 (2015).
Non-staggered magnetic flux in optical lattices usingmulti-frequency light
Gediminas JuzeliunasVilnius University
A. Gostatuto 12, LT01108 Vilnius, [email protected]
We explore a novel way of creating a non-staggered magnetic flux for ultra-cold atoms by using a properly chosen periodic sequence of counter-propagatinglaser pulses representing a multi-frequency perturbation. The laser fieldsdrive optical transitions between a pair of atomic internal states. The ener-gies of the two internal states have opposite gradients in one spatial direction,while the multi-frequency driving radiation propagates in a direction perpen-dicular to the energy gradient. This effectively creates a square optical latticeaffected by a non-staggered magnetic flux. The topological properties of sucha lattice have been explored.
50
Posters
Three photon energy-time entanglement
Thomas KautenInstitut für Experimentalphysik
Technikerstraße 25, 6020 Innsbruck, [email protected]
Creating entangled photon pairs is a long known and widely used technique inmodern quantum optics. Those photon pairs are used for various applicationssuch as quantum cryptography and optical quantum computation. For someapplication it would be useful to have more than two photons entangled witheach other. We developed a scheme to create energy-time entangled photontriplets from a cascaded parametric down conversion source. Our source cre-ates approximately 2000 entangled photon triplets per hour. We analyze thephoton triplets with three imbalanced Mach-Zehnder interferometers wherewe were able to observe higher order correlations in the triplet rate. In orderto prove entanglement we try to violate Mermin’s inequality, the generalizedBell inequality for more than two particles.
Universal sign-control of coupling in tight-binding lattices
Robert KeilInstitut for Experimental Physics
Technikerstraße 25, 6020 Innsbruck, [email protected]
We present a method of locally inverting the sign of the coupling term intight-binding systems, by means of inserting an ancillary site and eigenmodematching of the resulting vertex triplet. Our technique can be universallyapplied to all lattice configurations and physical platforms, as long as indi-vidual sites can be detuned. We experimentally verify this scheme in photonicwaveguide lattices and confirm the inverted sign of the coupling by interfer-ometric measurements. Based on these findings, we demonstrate how suchuniversal sign-flipped coupling links can be embedded into extended latticestructures to impose arbitrary Z2-gauge transformations. This opens a newavenue for investigations on topological effects arising from magnetic fieldswith aperiodic flux patterns or disorder.
51
Posters
Unified nonclassicality criteria and continuous sampling
Semjon KöhnkeUniversity of Rostock
Ulmenstr. 1, 18057 Rostock, [email protected]
A number of nonclassicality criteria have been formulated to certify quan-tum features of states. One hierarchy is based on Bochner’s theorem and thecharacteristic function of the Glauber-Sudarshan representation (P function).Another hierarchy is formulated in terms of the matrix of moments. We com-bine the advantages of both, resulting in a generalization of Bochner’s the-orem. For applications of the generalized nonclassicality probes, we providedirect sampling formulas for balanced homodyne detection. Furthermore wepresent a continuous phase sampling technique. In contrast to discrete phase-locked measurements, the continuous sampling of a regularized P functionallows an unconditional verification of nonclassicality, as we demonstrate forthe phase-sensitive squeezed vacuum state.
Optimized geometries for future generation optical lattice clocks
Sebastian KrämerInstitute for Theoretical Physics
Technikerstrasse 21a, 6020 Innsbruck, [email protected]
Atoms deeply trapped in magic wavelength optical lattices provide a Doppler-and collision-free dense ensemble of quantum emitters ideal for high preci-sion spectroscopy and they are the basis of some of the best optical atomicclocks to date. However, despite their minute optical dipole moments theinherent long range dipole-dipole interactions in such lattices still generateline shifts, dephasing and modified decay. We show that in a perfectly filledlattice line shifts and decay are resonantly enhanced depending on the latticeconstant and geometry. Potentially, this yields clock shifts of many atomiclinewidths and reduces the measurement By optimizing the lattice geometry,such collective effects can be tailored to yield zero effective shifts and pro-long dipole lifetimes beyond the single atom decay. In particular, we identifydense 2D hexagonal or square lattices as most promising configurations foran accuracy and precision well below the independent ensemble limit. Thisgeometry should also be an ideal basis for related applications such as super-radiant lasers, precision magnetometry or long lived quantum memories.
52
Posters
Automated Search for new Quantum Experiments
Mario KrennUniversity Vienna
Boltzmanngasse 5, 1090 Vienna, [email protected]
Quantum mechanics predicts a number of at first sight counterintuitive phe-nomena. It is therefore a question whether our intuition is the best way to findnew experiments. Here we report the development of a computer algorithmwhich is able to find new experimental implementations for the creation andmanipulation of complex quantum states. And indeed, the discovered ex-periments extensively use unfamiliar and asymmetric techniques which arechallenging to understand intuitively. The results range from the first imple-mentation of a high-dimensional Greenberger-Horne-Zeilinger (GHZ) state,to new types of high-dimensional cyclic transformations. The algorithm au-tonomously learns from solutions for simpler systems, which significantlyspeeds up the discovery rate of more complex experiments.
Correlation spreading in spin systems after a quench
Carlo KrimphoffITP, Uni Innsbruck
Technikerstraße 21a, 6020 Innsbruck, [email protected]
We numerically investigate the time evolution of the correlation density ma-trix and other correlation measures after a quantum quench in various onedimensional spin systems. For integrable systems, dynamics is expected tobe dominated by linear quasiparticle propagation with light cones showingalgebraic decay. However in the non-integrable case, quasiparticle scatteringis expected to lead to an exponential decay and a hydrodynamical propa-gation pattern. Our goal is to quantify the transition of these two pictures,when performing quenches to different non-integrable systems.
53
Posters
Single-photon Michelson Fringes from Entangled Photon Pairs
Mayukh LahiriIQOQI, University of Vienna
Boltzmanngasse 3, 1090 Wien, [email protected]
We observe a novel single-photon interference pattern that resembles Michel-son fringes but has some remarkable properties. We use non-degenerate en-tangled photon pairs (signal and idler) created by spontaneous parametricdown-conversion at two spatially separated nonlinear crystals. The fringesare obtained by superposing the two beams of signal photons from the crys-tals, while the idler beams are aligned to induce coherence between the signalbeams. If the phase is modulated using the idler photons, wavelengths of bothsignal and idler characterize the fringe spacing. The visibility of the fringesdecreases when the momentum correlation between the photons of each pairis reduced. Our results show that the fringes can be created only if the pho-tons of each pair are momentum-correlated.
Gravity gradiometer
Mehdi LangloisSYRTE
61 avenue de l’Observatoire, 75014 Paris, [email protected]
The principle of this experiment is to measure the Earth gravity gradientby atomic interferometry. The interferometer is realised on two atomic cloudwith the same laser. By subtracting the phases of the two interferometers wecan extract the gravity gradient and reject common mode phase fluctuations.The atoms are trap and cool on atomic chips by a magneto-optical trapand evaporative cooling. After that we launch them with a Bloch elevatorin a tube and we realise the interferometer with large momentum transferbeamsplitter. It allows to reach large separations between the two arms ofthe interferometer, and increase the sensitivity of the interferometer up to afew 10−11s−2/
√Hz.
54
Posters
Quantum decoherence of a single-ion qubit induced by singleoptical photons
Moonjoo LeeExperimentalphysik Innsbruck
Technikerstr. 25/4, 6020 Innsbruck, [email protected]
Quantum measurement is based on the interaction between a quantum ob-ject and a meter entangled with the object. While the information stored inthe object is being extracted by the interaction, the measurement leads todecoherence of the object due to the intrinsic quantum fluctuations of themeter. Here, we report the observation of measurement-induced dephasingof a single-ion qubit with single optical photons. We employ a single 40Ca+ion that is dispersively coupled to a high-finesse cavity. The cavity is drivenby a weak laser field to populate the cavity with mean photon numbers upto five. Spectroscopy is performed on the 729 nm qubit transition to identifythe shift and broadening of the atomic energy levels. The information storedin the qubit is extracted by photons escaping the cavity, which, in turn, leadsto dephasing of the qubit owing to photon-number fluctuations. This mea-surement represents the first demonstration of such quantum decoherenceeffects in the optical domain. Furthermore, heterodyne measurements of thecavity output photons will make it possible to probe quantum trajectories ofthe qubit nondestructively.
Rotation of quantum impurities in the presence of a many-bodyenvironment
Mikhail LemeshkoIST Austria
Am Campus 1, 3400 Klosterneuburg, [email protected]
We present the first systematic treatment of quantum rotation coupled toa many-particle environment. We approach the problem by introducing thequasiparticle concept of an "angulon" - a quantum rotor dressed by a quan-tum field and reveal its properties using a combination of variational anddiagrammatic techniques. The theory can be applied to a wide range of sys-tems described by the angular momentum algebra, from Rydberg atoms im-mersed into BECs, to cold molecules solvated in helium droplets, to ultracoldmolecular ions.
55
Posters
Coherent interaction of a Bose-Einstein condensate with twocrossed cavity modes
Julian LeonardETH Zürich
Otto-Stern-Weg 1, 8093 Zürich, [email protected]
Coupling a quantum gas to the field of a single high-finesse cavity gives riseto interactions of infinite range between the atoms, which can create a self-organized state when exceeding a critical strength. It is desirable to tunerange and directionality of these interactions, which enables explorations ofmore complex self-organized states or quantum soft matter physics, such assuperfluid glasses and associative memory. However, this requires extendingthe one-cavity system to higher dimensions. We report on the realizationof such an extended system, involving a Bose-Einstein condensate coupledto two crossed cavities modes. This already allows to spatially shape theinteractions, leading to multiple new crystalline phases, e.g. with hexagonal,triangular or stripe order.
Fermi-Bose Mixture of 6Li and 41K
Rianne LousIQOQI and Institute for Experimental PhysicsTechnikerstrasse 21a, 6020 Innsbruck, Austria
We report on the production of a 41K Bose-Einstein condensate (BEC) im-mersed in a degenerate two-component 6Li Fermi sea. After evaporation inan optical dipole trap, we obtain 104 41K atoms with a 33% BEC fractionand a Fermi sea of 105 6Li atoms with a T/TF ≈ 0.1 This facilitates thestudy of the collective modes of a mass-imbalanced mixture of two coupledsuperfluids. Using loss spectroscopy, we observe the 335.8G Feshbach reso-nance, which is comparable to the one between 6Li and the fermionic 40Kisotope. We exploited the latter in previous studies on the quantum many-body dynamics of a Fermi impurity in a Fermi sea. Investigating interactingbosonic impurities complements this work and enables the direct comparisonof the role of quantum statistics for bosonic/fermionic impurities.
56
Posters
Multi-photon entanglement in high dimensions
Mehul MalikIQOQI
Boltzmanngasse 3, 1090 Vienna, [email protected]
Forming the backbone of quantum technologies today, entanglement has beendemonstrated in physical systems as diverse as photons, ions, and super-conducting circuits. While steadily pushing the boundary of the number ofparticles entangled, these experiments have remained in a two-dimensionalspace for each particle. Here we show the experimental generation of thefirst multi-photon entangled state where both—the number of particles anddimensions—are greater than two. Two photons in our state reside in a three-dimensional space, while the third lives in two dimensions. This asymmet-ric entanglement structure only appears in multi-particle entangled stateswith d > 2. Our method relies on combining two pairs of photons, high-dimensionally entangled in their orbital angular momentum. Additionally,we show how this state enables a new type of "layered" quantum communi-cation protocol. Entangled states such as these serve as a manifestation ofthe complex dance of correlations that can exist within quantum mechanics.(Malik et al, arXiv:1509.02561, (2015))
57
Posters
Controlling many-body tunneling dynamics in a stronglycorrelated quantum gas
Florian MeinertInnsbruck
Technikerstraße 25, 6020 Innsbruck, [email protected]
Atomic gases at ultralow temperatures prepared in optical lattice potentialsprovide an exquisite platform to study many-body quantum systems out ofequilibrium. Moreover, system parameters can be coherently controlled viaperiodic driving as has been demonstrated for e.g. the single-particle tunnel-ing amplitude. Here, we present a series of experiments in the context of theBose-Hubbard model for which we independently control the tunneling rateJ and the on-site interaction energy U. For 1D chains of bosons preparedin a Mott insulator and subject to a tilt E, we study correlated tunnel-ing dynamics between neighboring lattice sites (and beyond), and identifythe role of bond-charge interactions in modifying the overall tunneling rate,i.e. giving rise to a tunneling rate that depends on the local site occupa-tion in the lattice. We then demonstrate the controlled implementation ofsuch occupation-dependent tunneling in the framework of Floquet theoryvia periodic modulation of interactions. This opens a new platform for theexploration of phenomena in Hubbard models with occupation-dependenthopping, including the possibility of dynamical synthetic gauge fields.
Coherent controlization using transmon qubits
Alexey MelnikovInstitute for Theoretical Physics, University of Innsbruck
Technikerstraße 21a, 6020 Innsbruck, [email protected]
Coherent controlization is a process by which priori unspecified (or unknown)operations on subsystems are coherently conditioned on the state of a con-trol qubit. The practical realization of coherent controlization requires anauxiliary system in addition to the control and target qubits. However, thedetails of the implementation depend on the nature of the ancilla systemand the type of qubit used. Here, we propose a method that allows coherentcontrolization in a register of superconducting transmon qubits coupled toan auxiliary microwave resonator.
58
Posters
The equation of state of a weakly interating 3D Bose gas
Carmelo MordiniBEC Center – University of Trento
Via Sommarive 14, 38123 Povo - Trento, [email protected]
We report on the progress towards the measurement of the equation of stateof a homogeneous 3D interacting Bose gas, focusing on the effects of mean-field interactions on the chemical potential across the transition. While thetopic has been widely discussed, yet no direct measurement was reported sofar. The physics of uniform gases is studied in a trapped sample through theLocal Density Approximation. We developed a new data acquisition tech-nique based on a sequence of partial extractions of fractions of the samplethrough an output coupling mechanism and the reconstruction of the originalspatial profile. This allows for the extraction of the in-situ, column-integrateddensity profile of the partially condensed sample, in the full range, withoutsaturation effects on the CCD camera.
Quantumness Quantification
Melanie MrazUniversity of Rostock
Albert-Einstein-Str. 23, 18057 Rostock, [email protected]
To study the amount of nonclassicality, we propose a degree of nonclassical-ity being a nonclassicality measure. It is determined by the decomposition ofa quantum state into superpositions of coherent states. The more quantumsuperpositions of coherent states are needed, the more quantum interferencesarise. A method for such a decomposition of quantum states is presented the-oretically. Following this approach the next step is to apply this measure toan experiment. But how can we extract the information necessary to esti-mate the amount of quantumness in our system? Therefore pattern functionsare used to reconstruct a density matrix in coherent state basis. Using thismethod we will try to witness the amount of nonclassicality in our system.
59
Posters
Dissipative quantum phase transitions in cavity QED
David NagyWigner Research Centre of the Hungarian Academy of Sciences
29-33 Konkoly-Thege M. Street, 1121 Budapest, [email protected]
A laser-driven Bose-Einstein condensate interacting with the field of a high-finesse optical cavity proves to be a versatile simulation tool, which helps usunderstand quantum phase transitions in driven-dissipative systems [PRA 84,043637 (2011)]. The cavity photon loss inhibits the observation of the super-radiant quantum phase transition in the ground state. Instead, a dissipativephase transition takes place in the steady state. Moreover, the atom field isalso subjected to dissipative decay that originates from Landau- and Beliaev-type scattering processes [PRA 89, 051601 (2014)]. This system serves as ageneric example that exhibits quantum criticality with dissipation to un-conventional reservoirs having non-trivial noise spectrum [PRL 115, 043601(2015)].
Hybrid thermo-mechanical machines powered by quantumnon-thermal baths
Wolfgang NiedenzuWeizmann Institute of Science
234 Herzl Street, 7610001 Rehovot, [email protected]
Diverse models of engines energised by quantum-coherent, hence non-thermal,baths allow the engine efficiency to transgress the standard thermodynamicCarnot bound. These transgressions call for an elucidation of their underly-ing mechanism. Here we show that non-thermal baths may impart not onlyheat, but also mechanical work to the machine. Hence, the Carnot bound isinapplicable to such a hybrid machine. Intriguingly, it may exhibit dual ac-tion, concurrently as engine and refrigerator, with up to 100% efficiency. Thegeneral criteria for their quantumness are revealed. We conclude that evenwhen these machines are quantum or unconventional in their performance,they still abide by the traditional principles of thermodynamics.
60
Posters
Towards strong ion-photon coupling in an ion-trap fibercavityapparatus
Florian OngUniversität Innsbruck
Technikerstrasse 25/4, 6020 Innsbruck, [email protected]
A single atom coupled to an optical cavity can be used as a coherent quantuminterface between stationary and flying qubits in a quantum network. Usingfiber-based cavities, it may be possible to reach the strong coupling regime ofcavity QED with a single trapped ion. This regime would enhance the fidelityand efficiency of protocols useful for quantum communication. The challengeof integrating fiber cavities with ion traps is that the dielectric fibers shouldbe far enough from the ions so that they do not significantly alter the trappotential. Using the CO2-laser ablation technique, we have built fiber cavitieswith finesses up to 70,000 at 854nm and at a length of 550um. We will reporton the integration and interplay of such a fiber cavity with a calcium ionstored in a Paul trap.
Twisting tensor and spin squeezing
Tomas OpatrnyPalacky University Olomouc
17. listopadu 12, 77146 Olomouc, Czech [email protected]
A unified tensor description of quadratic spin squeezing interactions is pro-posed, covering the single- and two-axis twisting as two special cases of ageneral scheme [PRA 91, 053826 (2015)]. Equations of motion of the firsttwo moments are derived and conditions for the fastest squeezing generationare found. The optimum rate of squeezing generation is proportional to thedifference between the largest and the smallest eigenvalues of the twistingtensor. Examples of possible experimental realization are proposed in theform of a cascaded optical interferometer with Kerr nonlinear media, and ofa toroidal Bose-Einstein condensate with spatially modulated nonlinearity[PRA 91, 053612 (2015)].
61
Posters
Spontaneous crystallization of light and ultracold atoms
Stefan OstermannInstitute for Theoretical Physics, University of Innsbruck
Technikerstraße 21a, 6020 Innsbruck, [email protected]
Coherent scattering of light from ultracold atoms involves an exchange of en-ergy and momentum introducing a wealth of non-linear dynamical phenom-ena. As a prominent example particles can spontaneously form stationary pe-riodic configurations which simultaneously maximize the light scattering andminimize the atomic potential energy in the emerging optical lattice. Herewe study a regime of periodic pattern formation for a BEC in free space,driven by far off-resonant counterpropagating and non-interfering lasers oforthogonal polarization. In this case, no spatial light modes are preselectedby any boundary conditions and the transition from homogeneous to periodicorder amounts to a crystallization of both light and ultracold atoms breakinga continuous symmetry. In the crystallized state the BEC acquires a phasesimilar to a supersolid with an emergent intrinsic length scale whereas thelight-field forms an optical lattice allowing phononic excitations. The studiedsystem constitutes a novel configuration allowing the simulation of syntheticsolid state systems with ultracold atoms including long-range phonon dy-namics.
Trapping ions on two generations of surface ion trap chips
Baoquan OuDepartment of Physics, Science College, NUDT109 DeYa Road, 410000 Changsha City, China
The first and the second generation surface ion trap chips built in our groupand the ion trapping experiments are reportted. The Gen I surface trap con-sisted of five gold platted electrodes on glass substrate(SiO2), all the elec-trodes are distributed symmetrically , and ions are trapped 140 um above thesurface. The Gen II surface trap are built on standard PCB, five electrodesare distributed asymmetrically, and the ions are trapped 570um above thesurface. Both surface traps are suffered heavily by heating effects, we measurethe life-time of the trapped ions and discuss the probale heating mechanics,and the Gen III cryogenic ion trap is under constructted.
62
Posters
Experimental realization of stimulated Raman adiabatic passagein a transmon
Sorin ParaoanuDepartment of Applied Physics, Aalto University
Puumiehenkuja 2B,P.O. BOX 1510, FI-00076 AALTO Espoo, [email protected]
In recent years, standard quantum-optics effects have been observed withsuperconducting circuits. Our results in Helsinki include the Autler-Towneseffect, motional narrowing, Landau-Zener interference in the strong nona-diabatic regime, the dynamical Casimir effect, and the STIRAP protocol.A fundamental prediction of quantum field theory is the existence of vac-uum fluctuations. Here I will present an experiment demonstrating how thevacuum fluctuations of a resonant superconducting circuit can be harnessedto produce quantum coherence by employing a double parametric pumpingscheme. The existence of these correlations is a consequence of absence ofwhich-color information and it opens the prospect of realizing cluster statesin superconducting circuits.The adiabatic manipulation of quantum states is a powerful technique fromquantum optics and atomic physics. Our previous work on the Autler-Towneseffect in superconducting phase qutrits [1], on Stueckelberg interference [2],and on the effect of motional averaging in transmons [3] has added up ev-idence that superconducting circuits truly behave as controllable artificialatoms. Here we benchmark the stimulated Raman adiabatic passage processfor circuit quantum electrodynamics, by using the first three levels of a trans-mon qubit [4].To realize this coherent transfer, we use two adiabatic Gaussian-shaped con-trol microwave pulses coupled to the first and the second transition. In thisladder con guration, we measure a population transfer efficiency above 80%between the ground state and the second excited state. The advantage ofthis technique is robustness against errors in the timing of the control pulses.By doing quantum tomography at successive moments during the Ramanpulses, we investigate the transfer of the population in time-domain. We alsoshow that this protocol can be reversed by applying a third adiabatic pulse.Furthermore, we study the e ffect of applying the adiabatic Raman sequenceto a superposition between the ground and the first excited state, and wepresent experimental results for the case of a quasi-degenerate intermediatelevel. The result is one step towards the realization of holonomic quantumcomputing and quantum simulators with superconducting circuits [5].[1] Mika A. Sillanpää, et. al., Phys. Rev. Lett. 103, (2009) 193601; Jian Li
63
Posters
et. al., Phys. Rev. B 84, (2011) 104527; Jian Li et. al. , Sci. Rep. 2, (2012)45;[2] M.P. Silveri, K.S. Kumar, J. Tuorila, J. Li, A. Veps""al""ainen, E.V.Thuneberg, G.S. Paraoanu, New J. Phys. 17 (2015) 043058.[3] Jian Li, M. P. Silveri, K. S. Kumar, J.-M. Pirkkalainen, A. Vepsäläinen,W. C. Chien, J. Tuorila, M. A. Sillanpää, P. J. Hakonen, E. V. Thuneberg,G. S. Paraoanu, Nat. Commun. 4, 1420 (2013);[4] K. S. Kumar, A. Vepsalainen, S. Danilin, G. S. Paraoanu, arXiv:1508.02981.[5] G. S. Paraoanu, Recent progress in quantum simulation using supercon-ducting circuits, J. Low. Temp. Phys. 175, (2014) 633-654.
Single-shot, complete characterization of a single-photon state
Sergey PolyakovNIST
100 Bureau Dr., 20877 Gaithersburg, [email protected]
We simultaneously determine the single photon purity, photon indistinguisha-bility, and reconstruct higher-order statistical distribution of photon-numberstates of a light source, characterizations that up to now have used multi-ple sequential measurements. This new method takes advantage of photon-number resolved detection, and extracts more information about the sourceper one measurement than a conventional method for any single-photon state.We assess the measurement efficiency of available characterization methodsand find the most advantageous strategy as a function of light source param-eters. For demonstration, we characterize the light from a single quantumdot. The platform can be used as a metrology testbed, or as an elementaryblock of a boson sampling protocol.
64
Posters
Symmetry-protected topologically ordered states for universalquantum computation
Hendrik Poulsen NautrupInstitute for Theoretical Physics
Technikerstraße 21a, 6020 Innsbruck, [email protected]
Measurement-based quantum computation is a model for quantum informa-tion processing utilizing local measurements on suitably entangled resourcestates for the implementation of quantum gates. A complete characterizationfor universal resource states is still missing. It has been shown that symmetry-protected topological order in one dimension can be exploited for the protec-tion of certain quantum gates in measurement-based quantum computation.I will illustrate that the two-dimensional plaquette states on arbitrary latticesexhibit nontrivial symmetry-protected topological order in terms of symme-try fractionalization and that they are universal resource states for quantumcomputation.
Excitations in Dense Bose Gases of Tilted Dipoles in Coupled2D-Layers
Michael RaderInstitute for Theoretical Physics
Technikerstr. 21a, 6020 Innsbruck, [email protected]
In this work excitations in strongly interacting dipolar Bose gases, that aretrapped in coupled 2D-layers, are investigated. Equations of motion are de-rived using a least-action principle equivalent to the Schrödinger equation.We solve the equations of motion to determine the density-density linearresponse matrix in a very general way for inhomogeneous multi-componentsystems. This result is a generalisation of the work of Clements et al. [PRB53, 12253 (1996)] for multi-component systems. We discuss how the generalformalism can be applied to homogeneous systems. Based on ground stateresults, obtained with the hypernetted-chain Euler-Lagrange method, numer-ical evaluations of the density-density response matrix are performed for one-and two-layer systems, that have either a polarisation perpendicular to thelayers or a tilted polarisation. We find systems with tilted dipoles, that areabout to solidify in the direction orthogonal to thepolarisation of the system.
65
Posters
Quantum error correction by engineered dissipation
Florentin ReiterInstitute for Quantum Optics and Quantum Information
Technikerstr. 21a, 6020 Innsbruck, [email protected]
Performing advanced quantum information protocols in the presence of de-coherence requires quantum error correcting codes. Harnessing dissipation tocorrect for errors represents a conceptually different approach which allowsfor features different from established approaches. We present a quantumerror correcting code based on engineered dissipation built from always-oncouplings and sources of noise. Our scheme operates in an autonomous andcontinuous manner, without the need to perform measurements or unitaryoperations on the system, and can be implemented using couplings which areavailable in standard quantum optical systems, e.g. trapped ions.
Levitated Single-Magnetic-Domain Nanospheres in the QuantumRegime
Cosimo Carlo RusconiIQOQI and UNI Innsbruck
Technikerstr. 21a, 6020 Innsbruck, [email protected]
We propose to magnetically levitate a single-magnetic-domain nanosphere inthe vicinity of a quantum circuit. We develop the theoretical background todescribe the rich dynamics of the nanosphere in the highly prolarized regime:tightly confined in position, nearly not rotating and with the macrospin anti-aligned to the magnetic field. The parameter regime for the stability of thehighly polarized regime is obtained. A magnetic on-chip set-up for coolingthe system in the quantum regime is discussed.
66
Posters
Single shot simulations of dynamic quantum many-body systems
Kaspar SakmannAtominstitut, TU Wien
Stadionallee 2, 1020 Vienna, [email protected]
Single experimental shots of ultracold quantum gases sample the many-particle probability distribution. In some cases single shots could be suc-cessfully simulated from a given many-body wave function [1-4]. However,for realistic time-dependent many-body dynamics this has long been elusive.Here, we show how single shots can be simulated from numerical solutionsof the time-dependent many-body Schr""odinger equation. Using this tech-nique we provide first principle explanations of several many-body phenom-ena, including fluctuating many-body vortices, partially destructive imagingas well as full counting distributions of center of mass fluctuations of attrac-tive BECs.
Quantum error correction with trapped ions
Philipp SchindlerInstitute for Experimental Physics
Technikerstrasse 25/4, 6020 Innsbruck, [email protected]
It seems out of question that a large-scale quantum information processorwill require quantum error correction procedures to run a long quantum al-gorithm. In our trapped ion quantum information processor we have realizedrepetitive three qubit error correction and encoded a logical qubit in a 7qubit Color Code. Building on this, we demonstrate operations on the en-coded qubit. A major milestone for quantum error correction would be alogical qubit that outperforms the bare physical qubits in any respect. Aprerequisite for this is to model the effect of noise on the system with highaccuracy. For this, we use robust methods for characterizing the noise in oursystem.
67
Posters
Quantum State Tomography for Optical Soliton Molecules
Oskar SchlettweinUniversity of Rostock
Albert-Einstein-Straße 24, 18059 Rostock, [email protected]
Bright pulses in optical fibers mainly experience dispersion, the Kerr-effectas well as (stimulated) Brillouin and Raman scattering. The scattering pro-cesses introduce phase noise which becomes important for applications at orbelow the shot noise limit. In contrast to Brillouin scattering the impact ofthe Raman effect on quantum states is not clear. Numerical simulation aswell as a quantum state tomographic setup for bright pulsed signals will bepresented to provide deeper insight about it. Extending our system to a twomode quantum state tomograph will lead the way to probe correlation effectsin soliton molecules. This stable configuration of two or more DM-solitonscould provide a fruitful source for new fiber based quantum communicationapplication.
From the transverse field Ising model to conformal field theory in2+1D
Michael SchulerInstitut für theoretische Physik, University of Innsbruck
Technikerstraße 21a, 6020 Innsbruck, [email protected]
Conformal field theories (CFTs) have been a useful tool to describe systemsat quantum critical points. Already some time ago, Cardy pointed out thatthe infinite Rd can be conformally mapped to Sd−1×R. If the dimension R isthen interpreted as time direction, this means, that the energy spectrum ofan appropriate quantum Hamiltonian on Sd−1 can be directly related to thescaling dimensions of the corresponding CFT. This approach turned out tobe very successful for d = 2, where the quantum Hamiltonian is defined on aperiodic chain. For d = 3, however, Hamiltonians have to be simulated on thegeometry of a 2D sphere, where finite-size scaling turns out to be extremelydifficult. By replacing the sphere with a torus and using large-scale exactdiagonalization and quantum Monte Carlo methods, we show that the low-energy spectrum after finite-size scaling is universal even in that case andcan serve as a fingerprint for the underlying CFT.
68
Posters
Detailed characterization of three-qubit linear optical quantumToffoli gate
Michal SedlakInstitute of Physics, Slovak Academy of SciencesDubravska cesta 9, 845 11 Bratislava, Slovakia
We report on a detailed characterization of three-qubit linear optical quan-tum Toffoli gate by two efficient methods. The first method provides a boundon quantum process fidelity that is determined by average output state fideli-ties for three partially conjugate product bases. A distinct advantage of thisapproach is that only fidelities with product states need to be measured whilekeeping the number of measurements much smaller than for other methods(192 two-photon coincidences suffice). For the second method we measured4032 different two-photon coincidences which allow us to estimate the fidelityof the gate to be 90%. Although these data are not tomographically com-plete, we show that they are sufficient for a reliable reconstruction of thequantum process matrix of the gate.
Optical tweezer
Seyedeh Sahar Seyed HejaziOIST Okinawa Institute of Science and Technology)
Tancha Onna-son, 1919-1 Okinawa, [email protected]
Optical tweezer and plasmic trap of nano-particle.
69
Posters
Cavity-induced chiral states of fermionic quantum gases
Ameneh Sheikhan SoudaniUniversity of Bonn
Nussallee 14-16, 53115 Bonn, [email protected]
We investigate ultracold fermions placed into an optical cavity and subjectedto optical lattices which confine the atoms to ladder structures. A transverserunning-wave laser beam induces together with the cavity field a two-photonRaman-assisted tunneling process with spatially dependent phase imprintalong the rungs of the ladders. We investigate the steady states which canarise by the feedback mechanism between the cavity and the atoms. We findthat a spontaneous occupation of the cavity field can arise which leads to theself-organization of an artificial magnetic field felt by the fermionic atoms.These form a chiral insulating or chiral liquid state which carries a chiralcurrent. We explore the rich state diagram on different parameters of themodel.
Vacuum-Induced Quantum Brownian Motion of a MagneticParticle Near a Surface
Kanupriya SinhaInstitute for Quantum Optics and Quantum Information (IQOQI)
Technikerstraße 21a, 6020 Innsbruck, [email protected]
We study the quantum Brownian motion (QBM) of a magnetic particle near asurface as induced by its coupling to the vacuum electromagnetic (EM) field.We derive a general QBM master equation for a magnetic particle includingits interactions with a surface via the quantum fluctuations of the vacuumEM field. We then apply our analysis to the specific case of a superconductingmicrosphere in an all magnetic on-chip setup and study the vacuum induceddecoherence of its center of mass motion and Casimir friction. Our analysis isgenerally applicable to all magnetic on-chip architectures with nanomagnetsand superconducting microspheres and our results are relevant for recentproposals on on-chip matter-wave interferometers of microspheres.
70
Posters
A trapped atom interferometer for short range forcesmeasurement
Cyrille SolaroSYRTE Système de Référence Temps Espace
61 Avenue de l’Observatoire, 75014 PARIS, [email protected]
We demonstrate a trapped ultracold atom interferometer in a vertical opti-cal lattice. For shallow depths of the lattice, stimulated Raman transitionscan be used to induce coherent transport between adjacent Wannier-Starkstates, allowing us to perform atom interferometry. This short range forcessensor shows state of the art relative sensitivity on the Bloch frequency of1.8× 10−6 at 1s. Using ultracold atoms allowed reducing coupling and phaseinhomogeneities and increased the interrogation time up to several secondsvia a spin self-rephasing mechanism (ISRE) originating from particle indistin-guishability. In this specific configuration, where the two partial wavepacketsare spatially separated and do not perfectly overlap, we test self-rephasingas a function of this overlap.
71
Posters
Radiation Forces in Time-Dependent Optical Fields
Matthias SonnleitnerSchool of Physics and Astronomy, University of GlasgowKelvin Building, Uni Glasgow, G128QQ Glasgow, UK
The mechanical interaction between light and atoms, molecules or nanopar-ticles is usually described in two terms: the dipole force, dragging particlesalong the gradient of the light intensity; and the radiation pressure, push-ing particles along the direction marked by the Poynting vector. However, ifsome parameters of the radiation field vary in time, like in a light pulse oran amplitude-modulated standing wave, additional force terms appear whichare not fully covered by a time-dependent dipole force or radiation pressure.In fact, they sometimes even act against the intuitively expected forces. Theorigin of these forces lies in the so called Röntgen interaction term, althoughour treatment involving time-dependent fields goes beyond the usually dis-cussed modifications regarding moving atoms. Obviously these additionalterms are very small compared to usual radiation interactions, but given therapid advancement of the field and proposals to use optically trapped atomsas sensors for other weak forces, we believe it is important to study thesesmall terms as well. Here we present the general idea, some simple resultsand possible applications for this surprising and fascinating extension to op-tical forces, which we believed to understand so well.
72
Posters
Chip Integrated Nano-Fiber Atom-Photon Interface
Florian SteinerAtominstitut, TU Wien
Stadionallee 2, 6020 Vienna, [email protected]
Micro-Optics on Atom chips; The experiment concerns the combination oftwo established concepts in Ultracold-Atompyhsics. The first is trappingatoms magnetically on atom-chips in a one dimensional fashion. The sec-ond is using nanofiber based elongated cavities which are integrated closeto the chip. Together, this constitutes a unique platform to probe atom-photon interactions. The intrinsically mode-matched resonator consists oftwo fiber Bragg gratings (FBG) that are being lased onto the fiber. I willpresent the newest measurements which show strong coupling of atoms froma magnetic trap to the cavity. A few exemplary applications for our systemare: Self-organization of atoms due to Bragg Scattering into the cavity mode;Frequency selective fluorescence spectroscopy of atoms in the surface-inducedpotential of the fibre; Strong nonlinear interactions between individual pho-tons; Realizing a Photon-Transistor.
Moving single atoms
Dustin StuartUniversity of Oxford
22 Nursery Close, OX3 7AG Oxford, [email protected]
Single neutral atoms are promising candidates for qubits, which can be inter-faced with high-finesse optical cavities to form quantum networks. We havebuilt a set of optical tweezers for trapping and moving single Rubidium atomswithin such cavities. We use a digital micromirror device (DMD) to produceholograms of the desired arrangement of traps. The DMD has a frame rateof 20 kHz which, when combined with fast algorithms [1], allows for rapidreconfiguration and transport. We demonstrate trapping of up to 20 atomsin arbitrary arrangements, and single-atom transport over a distance of 14um with continuous laser cooling, and 5 um without.[1] Fast algorithms for generating binary holograms - (http://arxiv.org/abs/1409.1841)
73
Posters
Appearance and disappearance of quantum correlations inmeasurement-based feedback
Vivishek SudhirSwiss Federal Institute of Technology (EPFL)
BM 2116, Station 17, LPQM1, 1007 Lausanne, [email protected]
We implement a measurement-based feedback protocol to cool a solid-statemechanical oscillator to its ground state. Correlations between the oscillatorand the light used to measure it, are recorded via sideband asymmetry. Asthe oscillator is cooled, the scattered sidebands become asymmetric. Furtherincrease in the feedback gain leads to a decrease in the asymmetry due toamplified shot-noise dominating the error signal.
Dynamical effects in electromagnetic induced transparency
Klara TheophiloUniversity of Oxford
Clarendon Lab., Parks Roads, OX1 3PU Oxford, [email protected]
The electromagnetic induced transparency (EIT) is one of the most exploredeffects in quantum optics research. However, the dynamical effects of EIT stillmajorly uncharted. Our research focused on a better understanding of atomicdynamics, investigating a transient interaction of cold rubidium atoms in aLambda EIT system,using noise correlation spectroscopy. We characterisedthe system for a broad range of experimental parameter, including observa-tions of its temporal evolution. Moreover, we developed a theoretical modelto explain our results, showing a coupling between internal and externalatomic degrees of freedom. Unraveling this feature in EIT systems was onlypossible due to noise spectroscopy, highlighting the importance of exploringtechniques beyond mean intensity spectroscopy.
74
Posters
Nonlinear Quantum Optics Using Interacting Rydberg Atoms
Christoph Tresp5. Physikalisches Institut, Universität StuttgartPfaffenwaldring 57, 70569 Stuttgart, Germany
Mapping the strong interactions between Rydberg atoms in ultracold atomicensembles onto single photons via EIT enables realizing huge optical non-linearities. We report the realization of a free-space single-photon transistor,where a single gate photon controls the transmission of many source photons[1]. We show that the gain of the transistor can be enhanced using Stark-tuned Förster resonances and might be suitable as a quantum device wherethe gate input is retrieved after the transistor operation. We also present ourwork investigating the interaction between individual polaritons coupled toRydberg D-states, where the anisotropy leads to state-mixing interactions[2].[1] H. Gorniaczyk et al: Phys. Rev. Lett. 113, 053601 (2014)[2] C. Tresp et al: Phys. Rev. Lett 115, 083602 (2015)
Fermi-Fermi mixtures of dysprosium and potassium
Slava TzanovaInstitut for Experimental Physics, University of Innsbruck
Technikerstraße 25, 6020 Innsbruck, [email protected]
Ultracold Fermi-Fermi mixtures with tunable interactions represent an in-triguing test bed for exploring the physics of strongly interacting many-bodyquantum systems and few-body quantum states. Two-species Fermi gases ex-tend the variety of phenomena thanks to mass imbalance. This motivates usto construct a dysprosium - potassium experiment exploiting the favorablemass ratio of 4. The strong magnetic moment of dysprosium allows elasticdipolar scattering between identical fermions and offers an additional degreeof freedom to our system.
75
Posters
Towards quantum nonlinearities in an intracavity Rydbergmedium
Imam UsmaniInstitut d’Optique Graduate School
2 avenue augustin fresnel, 91127 palaiseau, [email protected]
The realization of a strong deterministic photon-photon interaction is a chal-lenging task, but could enable the implementation of a two-photon phasegate. Nonlinearities in standard media are however too weak to induce sucheffects. One approach is to sent a photon in a cold atomic ensemble to tempo-rally convert it into a dark-state polariton and use the Rydberg blockade fora deterministic interaction. Here, our atomic cloud is placed into an opticalcavity which increases the light-matter coupling and translates a nonlineardispersion into a shift of the cavity resonance. We will present the intracav-ity nonlinear absorptions we observed, with a comparison to our theoreticalmodels. Then, with some improvements on the setup, we aim at observingbunching or anti-bunching of light.
76
Posters
Internal State Coupling of a Micromechanical Resonator to anAtomic Ensemble
Berit VogellIQOQI/Universität Innsbruck
Technikerstrasse 21a, 6020 Innsbruck, [email protected]
Combining AMO physical systems with newly developed solid state devicesinto so-called hybrid quantum systems is motivated by the idea to combinethe advantages of both, AMO and solid state systems, while compensate theirdisadvantages. We present two realizations of such hybrid quantum systemsthat implement the coupling of a mechanical resonator, such as a microme-chanical membrane, to an atomic system by coupling to the internal statesof the atoms. In the first part a hybrid quantum system consisting of a mov-ing micromechanical resonator coupled to a spin wave of a distant atomicensemble of three-level atoms is discussed. The interaction of the motionalstates of the mechanical oscillator to the internal states of the atomic ensem-ble is mediated by a polarized light field. The coupling works via translatingthe phase shift caused by a displacement of the mechanical resonator intoa polarization rotation, and is enhanced by the square root of the numberof atoms. As a second hybrid system, we propose a scheme to engineer aJaynes-Cummings interaction between a moving membrane and the internaldegrees of freedom of a Rydberg superatom, which models an effective twolevel system. Exploiting the collective enhancement of the superatom Rabifrequency strong coupling is feasible within accessible parameter regimes.This hybrid system provides a broad toolbox for strong coupling in an AMOhybrid mechanical system. As an extension of a membrane-superatom insidea cavity setup, the alternative of long distance coupling between the systemsis also discussed.
77
Posters
Photon pairs from microcavity polaritons
Zoltán VörösInstitute for Experimental Physics
Technikerstraße 25/d, 6020 Innsbruck, [email protected]
Interacting photons can be created by dressing them with material excita-tions. This interaction can be the basis for producing non-classical photoncorrelations, such as squeezed or entangled light. In our case, the dressedstates, called polaritons, are created by enclosing a quantum well in a λ cavity.In this contribution, we discuss our work on photon scattering in a polaritonsample with ultralow photonic and excitonic disorder. We demonstrate, howthe photon statistics depends on a number of experimental parameters, e.g.,excitation density, and temporal filtering, and identify a parameter range,where quantum correlations can be observed. We also compare our experi-mental findings to analytical and numerical models and calculations.
Quantum information processing with long-wavelength radiation
Simon WebsterUniversity of Sussex
Pevensey 2, Falmer Campus, BN1 9QH Brighton, [email protected]
Trapped ion quantum computation will require scaling systems to a largenumber of qubits. The use of long-wavelength radiation is a powerful scalingtechnology due to the ability to use a single set of global control fields todrive an arbitrary number of gates in parallel, with ions selected for gateoperations by locally applied magnetic fields. I will report the experimen-tal demonstration of important tools towards this end such as the demon-stration of ground state cooling using long wavelength radiation and thedemonstration of a high-fidelity long-wavelength two-ion quantum gate us-ing a quantum-engineered clock qubit with fidelity of 0.985(12). Finally, Iwill present results concerning the development of ion microchips that canbe used as an architecture for such a quantum computer.
78
Posters
Optimal measurement strategies for the lifted trine states
Graeme WeirUniversity of Glasgow
Kelvin Building, G12 8QQ University of Glasgow, [email protected]
We investigate measurement strategies for the three symmetric quantumstates which comprise the so-called lifted trine ensemble, parameterised bya lifting angle. We then introduce a measurement which will always pro-vide either an unambiguous outcome or an eliminatory outcome, and is thusguaranteed to provide some degree of certainty in state discrimination. Thesemeasurements are compared against one another using two common figuresof merit: probability of error and mutual information. We also find that thismeasurement becomes unfeasible at a certain lifting angle; beyond this angle,some inconclusive outcome which provides no information about the state isrequired.
Exploiting light-shift effects for atomic magnetometry
Arne WickenbrockUni Mainz
Kurfuerstenstrasse 35, 55118 Mainz, [email protected]
We demonstrate a selection of experiments exploiting vector light shift ef-fects for atomic magnetometry. The fictitious magnetic fields of two circularpolarized laser beams are used to transform a scalar magnetometer with fTsensitivity to an all-optical vector magnetometer. The sensor exhibits a pro-jected sensitivity of 12fT/Hz1/2 and 5microrad/Hz1/2. A second experimentdemonstrates a novel approach to all-optical magnetometry with potentialadvantages for magnetometer arrays and magnetically sensitive fundamentalphysics experiments. Intensity modulation of a laser beam at the Larmorfrequency directly drives a narrow magnetic resonance in alkali vapor. As amagnetometer the setup achieves a projected shot-noise-limited sensitivityof 1.7fT/Hz1/2 and measures a technical noise floor of 40fT/Hz1/2. Theseresults are essentially identical to a coil-driven scalar magnetometer usingthe same setup. In a third experiment we demonstrate that the long spincoherence time in paraffin-coated cells leads to spatial averaging of the lightshifts over the entire cell volume, which renders the averaged light shift in-dependent, under certain approximations, of the light-intensity distributionwithin the sensor cell.
79
Posters
Some improved techniques in trapped ion quantum computing
Yi XieNational University of Defense Technology
#109 Deya Road, 86-410073 Changsha City, [email protected]
We will introduce the experiment progress of Ion trap Quantum Computingprogram in National University of Defense Technology. Ground state cool-ing was preliminary performed on one Calcium ion trapped in a blade-trapreaching < 0.5. Some improved techniques will also be reported. A threesteps photo-ionization experiment was performed on Calcium atoms by twolasers containing one violet laser and one red laser in order to prevent theUV contamination. Fluorescence revival under low magnetic field by mixedrepump lasers will also be described. We also provide a method to improvethe optical pump efficiency despite the laser polarization is not pure enough.
Efimov States in Lithium-Rubidium-Mixtures
Claus ZimmermannUni Tübingen
Dürrstraße, 72070 Tübingen, [email protected]
We study collisional heating in a cold 7Li-87Rb mixture near a broad Fesh-bach resonance at 661 G. At the high field slope of the resonance, we find anenhanced three-body recombination rate that we interpret as a heteronuclearEfimov resonance. With improved Feshbach spectroscopy of two further res-onances, a model for the molecular potentials has been developed that nowconsistently explains all known Feshbach resonances of the various Li-Rb iso-tope mixtures. With this model, we determine the scattering length of theobserved Efimov state. Its value of -1870a0 supports the currently discussedassumption of universality of the three-body parameter also in heteronuclearmixtures.
80
Posters
Single Photon Source based on Room Temperature Vapor Cells
Michael ZugenmaierNiels Bohr Institute, University of CopenhagenBlegdamsvej 17, 2100 Kobenhavn, Denmark
The DLCZ protocol for long distance quantum communication is based on thestorage of single collective excitations, superposition quantum states whereone of many indistinguishable atoms is excited. We report on the progress ofour experiment applying room temperature vapor cells to create and storea single collective excitation. A weak laser pulse excites one of the Cesiumatoms inside the vapor. The single excitation will be heralded by the de-tection of a single forward-scattered photon. The paraffin-coated cell wallspreserve coherence times over milliseconds. The readout of the single excita-tion deterministically creates a single photon with high efficiency. Scalabilityand fast reinitialization allow to combine such cells to create a quantum in-formation network.
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Sponsors
SponsorsWe gratefully acknowledge support from our industrial sponsors:
83
Index
IndexAsenbaum Peter, 37
Bala Prasanna Venkatesh, 37Bancal Jean-Daniel, 38Banuls Maria Carmen, 12Baranov Mikhail, 38Bertoldi Andrea, 39Biondi Matteo, 39Boll Martin, 40Bostock Harry, 40Bougas Loukourgos, 41Brennecke Ferdinand, 41Briant Tristan, 27Budker Dmitry, 32
Calajo Giuseppe, 42Catani Jacopo, 9
Dayan Barak, 29Diorico Fritz, 42Dittel Christoph, 43Doerre Nadine, 44Domokos Peter, 43Duerr Stephan, 44Dunjko Vedran, 35
Erhard Manuel, 45
Feofanov Alexey, 45Ferrier-Barbut Igor, 10Folman Ron, 15Freegarde Tim, 46Friebe Konstantin, 47Fritsche Isabella, 48
Glorieux Quentin, 49Gross Christian, 11
Hamsen Christoph, 49Haslinger Philipp, 50Hemmerich Andreas, 9
Hofstetter Walter, 14Huillery Paul, 16
Juzeliunas Gediminas, 50
Kaiser Robin, 35Katori Hidetoshi, 31Kauten Thomas, 51Keil Robert, 51Kirchmair Gerhard, 34Koehnke Semjon, 52Kollar Alicia, 22Krämer Sebastian, 52Krenn Mario, 53Krimphoff Carlo, 53Kuhn Axel, 6
Lahiri Mayukh, 54Landini Manuele, 21Langlois Mehdi, 54Lee Moonjoo, 55Leibfried Dietrich, 18Lemeshko Mikhail, 55Leonard Julian, 56Lous Rianne, 56
Malik Mehul, 57Marquardt Florian, 23Meinert Florian, 58Mekhov Igor, 33Melnikov Alexey, 58Mintert Florian, 13Mordini Carmelo, 59Morigi Giovanna, 14Mraz Melanie, 59Muschik Christine, 17
Nagy David, 60Niedenzu Wolfgang, 60Northup Tracy, 19
85
Index
Ong Florian, 61Opatrny Tomas, 61Ostermann Stefan, 62Ou Baoquan, 62
Paraoanu Sorin, 63Piazza Francesco, 30Pohl Thomas, 13Polyakov Sergey, 64Polzik Eugene, 5Popescu Sandu, 33Poulsen Nautrup Hendrik, 65
Rabl Peter, 32Rader Michael, 65Reiter Florentin, 66Reitzenstein Stephan, 27Rempe Gerhard, 25Romero-Isart Oriol, 8Rusconi Cosimo Carlo, 66
Sakmann Kaspar, 67Schindewolf Andreas, 7Schindler Philipp, 67Schlettwein Oskar, 68Schmidt Piet, 19Schuler Michael, 68Schweigler Thomas, 10Sedlak Michal, 69Seyed Hejazi Seyedeh Sahar, 69Sheikhan Soudani Ameneh, 70Sinha Kanupriya, 70
Solaro Cyrille, 71Sonnleitner Matthias, 72Steiner Florian, 73Strack Philipp, 20Stuart Dustin, 73Sudhir Vivishek, 74
Theophilo Klara, 74Thompson James, 24Toermae Paeivi, 28Tresp Christoph, 75Tzanova Slava, 75
Usmani Imam, 76
Voeroes Zoltán, 78Vogell Berit, 77
Webster Simon, 78Weihs Gregor, 26Weir Graeme, 79Wengerowsky Sören, 29Wickenbrock Arne, 79
Xie Yi, 80
Yao Norman, 8
Zakrzewski Jakub, 20Zeppenfeld Martin, 34Zimmermann Claus, 80Zugenmaier Michael, 81
86
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