WP1.4: Single trapped Atoms

M 1.4.5 Establish stable optical fiber link for long-distance applications (M27)

M 1.4.6: Observation of single atoms in second mobile trap (M36)

D 1.4.3: Observation of long-distance atom-photon entanglement (M30)

General Objectives– Generate entanglement between quantum memory

and single photon over large distance (several 100 m).

– Perform “read/write” operations via

quantum teleportation protocols.

– Generate atom-atom entanglement over

large distances (quantum repeater).

– Loophole-free test of Bell’s inequality

D 1.4.3: Observation of long-distance atom-photon entanglement M 1.4.5: Establish stable optical fiber-link for long-distance applications

W. Rosenfeld et al., arXiv:0808.3538v1 [quant-ph]

atomic basisx

atomic basisy

atom-photon correlations over 300 m

WP1.4: Single trapped Atoms

WP1.4: Single trapped Atoms

M 1.4.6: Observation of single atoms in second mobile dipole trap

new setup

Improved photon detection efficiency = 0.21 %

Planning for period 4

M 1.4.7: Theoretical calculation of expected atom-atom entanglement fidelity (M 39)

M 1.4.8: Observation of atom-photon entanglement in second mobile dipole trap (M 42)

D 1.4.4: Observation of quantum interference of photon pairs from two trapped atoms (M 48)

WP1.5: Room-T Atomic Vapour Objective

– A Memory for a quantum state of light in an atomic ensemble of Cs atoms with a fidelity of up to 70%, had previously been demonstrated. The goal in this WP is to investigate further approaches to the memory, all based on gas in glass cells.

M1.5.6 Implementation of and conclusion on storage of squeezed and entangled light states in thermal atomic ensembles – partly achieved:

storage of displaced, squeezed light states two-mode storage of displaced, squeezed light states identical to storage of two entangled states storage of one part of entangled beams

D1.5.3 Application of improved fidelity storage to non-classical light states – partly achieved: storage of non-classical light states (displaced, squeezed states) improved fidelity by technical means:

flat-top beam profile digital feedback improved detection efficiency

improved fidelity by optimized temporal mode functions improved storage fidelity by atomic squeezing

New milestones (month 42 and 48)M1.5.7 protocols for atomic - atomic state teleportationM1.5.8 technical and physical limitations to performance of atomic - atomic state teleportationNew deliverable (month 48)D1.5.4 Conclusion on performance of light-to-atoms and atoms-to- atoms Hi-Fi state transfer

storage fidelity classical

limit

M.Owari, M.Plenio, E.Polzik, A.Serafini, M.M.Wolf, arXiv:0808:2260, accepted by NJP.

11 12 2

1

11 1F

η – added noise in vacuum units,ξ-1 – squeezed variance

X̂

P̂ξ-1

Best classical fidelity vs degree ofsqueezing for arbitrary displacedstates

ξ-1

D1.5.3 Classical benchmark memory fidelity derived for a new class of states

Classical benchmark

5 dB0 dB

atomic statetomography

preliminary

data

D1.5.3 Preliminary results: deterministic quantum memory for displaced squeezed states with fidelity better than classical benchmark

light statetomography

Proposed Objectives

• Characterize fidelity of deterministic storage and retrieval of broadband weak coherent states using an ancillary control field in Cesium vapor (# 9)

• Characterize and implement heralded single-phonon excitation of bulk diamond (# 12)• Implement spatial entanglement of optical phonon excitations in bulk diamond (see diagram)• Develop quantum dot samples with waveguides for an ensemble quantum memory

[1] F. Waldermann et al., submitted to PRB. [2] F. Waldermann et al., Diam. Relat. Mater. 16, 1887-1895 (2007). [3] J. Nunn et al., Phys. Rev. A 78, 033806 (2008).

Achievements

• Set up components for and achieved efficient optical pumping in Cesium for state preparation

• Tested repeatability of optical phonon coherence measurement in bulk diamond

• Developed a quantum-optical interpretation of optical phonon excitations [1,2]

• Enhanced a paper on multimode storage using the off-resonant Raman scheme; accepted for publication [3]

• Characterized the Zeeman splitting inhomogeneity and Schottky-contact charging of quantum dot samples

|Ψ>=|01>±|10>Pump

Herald

Read-out

Schematic of spatial entanglement of optical phonon excitations in bulk diamond

WP1.5: Room-T Atomic Vapour

WP1.6: Cold Atoms Objective

– The general goal of this WP is to develop interfaces between light and cold atoms. In addition to a memory of single photon qubits, we want to demonstrate spin squeezing at Cs clock transition based on atom light interaction with the ultimate goal to improve the sensitivity of atom clocks.

M1.6.6: Assessment of decoherence rates for Rubidium and Cesium atomic samples trapped in state insensitive potentials. (due: month 30) . Partly achieved, to be continued

M1.6.7: Assessment of conditional state preparation in the few excitation regime for trapped Cesium and Rubidium atomic samples; Choice of the target system (due: month 33).Partly achieved

M1.6.8: Implementation of atomic state tomography on the chosen target system(due: month 36) . Partly achieved ( to be continued)

D1.6.3: Investigation of quantum properties of light coupled to the Rb BEC(due: month 24) . Partly achieved, to be continued

D1.6.4: Application of atomic state tomography to excitations in quantum memories(due: month 36) . Partly achieved, to be continued

D1.6.4 Spin Squeezing and Entanglement in the Cs Clock – tomography of the nonclassical atomic state

3.3 dB of spectroscopically relevant pseudo-spin squeezing (projection noise corrected for decoherence from probing)

WP1.7: Comparison• Objective– The objective of this WP is to compare, evaluate and analyse the different

approaches to quantum memory for applications in quantum communication and computation.

• M1.7.4: Assessment of status of quantum memory implementation (M36)

• D1.7.3: Updated results on the comparison, evaluation and analysis of the different approaches to quantum memory for applications in quantum communication and computation (M36)

Approaches to Quantum Memories 08(Copenhagen: 10 - 11 July)

Approaches to Quantum Memories 07

(Stuttgart: 21 - 22 June)

Approaches to Quantum Memories 06

(Geneva: 29 - 30 June)

Goals:– Develop a common means of

characterising and comparing the different quantum systems.

– Developing collaborations

– Structuring the Community

• Revised vision!

• Comparison table

ALL SP1

Copenhagen ComparisonALL SP1

Copenhagen Comparison

RE AFC

RE CRIB

NV

QD

Single atomsFree space

Room-temp.gas

Cold gas

Raman gasdiamond

SPS, QRepLOC4

SPS, QRepLOC4

Approach PotentialApplications

QRep, SPS

SPS

LHF, QRep

LOC4,Prec.msmt.

Prec.msmt.,LOC4, QRep

SPS, QRep

EfficiencyWrite-in Retrieval

inout~ 0.01 ~1

not yet ~1

~1withcavity

not yet

~0.2~1

~0.2~1

low~1

withcavity

1

notyet

~1

notyet

~1 ~1

notyet

notyet

notyet ~1 ~1

Measurement

retrieval

retrieval

retrieval

retrieval

?

Entanglemt.with light

not yet

not yet

Yes with PDC

Yes with PDC

?

not yetyes

done!

done!

not yet

not yet

yes

yes

Fidelity

0.97cond.

not yet

?

not yet

Write 0.94 condRead 0.9 uncond

Write 0.7 (uncond.)Msmt 0.6

Write not yetRead 0.75?

not yet

Bandwidth

10 MHz

1GHz10 MHz

100 MHz

?

>GHz

6 MHz

kHz

100 kHz

1 MHz

0.5 GHz

not yet

GHz CsTHz diam

StorageTime

MM capacity Dim.

1 s

30 s

not yet

30 s

not yet

1 s

150 s

>ms

4 ms

200 ms

not yet

100 ms

not yet

1 s Cs10 ps diam

4

high

moderate

moderate(spatial)

moderate

low

low

low

low

high

low

low

low

high

high

high

high

ALL SP1