superconducting photodetectors david schuster assistant professor university of chicago figures...
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Superconducting Photodetectors
David SchusterAssistant ProfessorUniversity of Chicago
Figures from:
Yale:
Schoelkopf GroupProber Lab
NIST:
S.W. Nam
J.M. Martinis
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Manipulating microwaves one photon at a time
?
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Outline
• Applications of superconducting photodetectors
• Overview of superconducting photodetectors
• Kinetic Inductance Detectors
• Nanowire Superconducting Single Photon Detectors
• Practical considerations
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Applications for superconducting detectors
• Astronomy– Low dark noise
– High absorption efficiency
– Multi-pixel
• X-ray analysis– Good energy resolution
• Quantum Computing / Quantum Key Distribution– Low dark noise
– Fast response/recovery time
– Broadband
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SC detectors have great performance!
0 1 2 3 4 5 6 7 80
5
10
15
20
25
30
35
40
45
50
Photon number
Counts
[th
ousa
nds]
Histogram of photon number for a pulsed laser
-5 0 5 10 15 20time [s]
Out
put
sign
al [
a.u.
]
Signal from a TES for 0, 1, 2, 3, 4 photons
1
10
100
1000
0 2 4 6 8 10
time (ns)
cou
nts SiAPD
SSPD
High resolution
Photon number resolving High throughput > 1Gbps
LLE review vol 101
S.W. Nam, NIST
Martinis, NIST
S.W. Nam, NIST
Low noise
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Most SC detectors work like calorimeters
R
T
Rn
Absorber, C
Thermometer
Weak thermal link, g
Thermal sink
Energydeposition
• Many types of detectors: Transition Edge/Tunnel Junction/KID/nanowire• Operating temperatures range from ~ 0.1-60K• Large spectral range THz - Xray • Rely heavily on microfabrication
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Cascade of broken Cooper pairs
•Photon breaks a cooper pair
•Thermalizes making h qp’s
•# gain but no E gain yet
•E resolution / photon # counting determined by shot noise
•Gain comes from change R or L
e-e interactionPhoton h
phonons
Cooper pairs
e-e interaction
Quasi particles
kbT
10-3
10-1
100
eV
phonons
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Quasiparticles change surface impedance
Shunted normal resistance Kinetic inductance
R
LK
R
T
Rn
Day, et. Al. Nature (2003)
Broadband Resonant
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Multiplexing Kinetic Inductance Detectors
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Nanowire Superconducting Single Photon Detector (SSPD)
• Current Biased• Very fast ( 10’s of ps)• Usually cooled by phonons
NbN
4nm thick<100nm wide
Annunziata JAP 2010
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Other innovations…
Williams IEEE ASC Proc. 2010
High Tc
Multiwire detectors
Lincoln labs
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But is it practical?
Already in use for some applications:• X-ray analysis• Ground based telescopes
Major limitations:• Cryogenic operation• Not enough pixels
Way forward:• Closed-cycle Cryo systems• Multiplexed detection, SC cameras• Even better performance
NIST NbN detector
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Summary• Lots of SC detector technologies
• Kinetic Inductance Detectors, Nanowire Single Photon Detectors
• Transition Edge Sensors/Bolometers/Tunnel Junction
• Many applications• Astronomy• Analysis• Quantum computing / cryptography
• Excellent Performance• Wide spectral coverage (Terahertz – X-ray)• Fast (10 ps)• Sensitive (10-21 W/Hz1/2 NEP)• Multiplexable (cameras)
• Cryogenic operation still a limitation but getting better
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Additional slides follow
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Outline
• Types of superconducting photodetectors
• Speed limitations of SC detectors
• Super-sensitive level meter and preliminary measurements of electrons on helium
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10 m
Cavity QED with circuits and floating electrons
2g = vacuum Rabi freq.
= cavity decay rate
= “transverse” decay rate
L = ~ 2.5 cm
Trapped electron10 GHz in
out
Transmission line “cavity”
Theory: Blais, Huang, et al., Phys. Rev. A 69, 062320 (2004)
Strong coupling: 2g > ,
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What to do with hybrid systems and cavity QED?
Quantum Optics Measure individual photon # states Produce single photon states Tomography of arbitrary quantum states
Quantum Computing Two qubit gates Quantum algorithms Process tomography
DiCarlo, Chow, et. al., Nature, (2009)
Fundamental Quantum physics Measurement of field quantization Tests of quantum gravity, etc.
Bishop, Chow, et. al.,
Nature Physics, (2009)
DIS*, Houck*, et. al., Nature, (2007)
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Hybrid quantum systems
Ultracold atoms
Polar Molecular Ions
Nanomechanics
Electrons on helium
Solid-state spins
DIS, Fragner, et. al.
PRL (2010)
Y. Kubo, F. Ong, P. Bertet et. al. PRL (2010)DIS, A. Sears, E. Ginossar, et. al. PRL (2010)
Verdu, Zoubi, et. al. PRL (2009)Hunger, Camerer, Hänsch, et. al. PRL (2010)
DIS, Bishop, et. al. PRA (2011)
Teufel, et al., Nature (2011)
See SYHQ 3-5!
See SYHQ 2!
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Seeing a puddle of electrons on helium
M.W. Cole. Rev. Mod. Phys. 46, 3 1974
Low energy electrons get stuck on the surface
Force from positive electrode causes a dimple
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An electron on helium?
See Jackson 4.4
= 1.057
2
0
1
4
eV
z
/ 157GHzR h
a0 = 7.6 nm
2n
RE
n
Electron bound at < 8K
Levitates 8nm above surface (in vacuum)
+
He
Clean 2DEG :Mobility = 1010 cm2/Vs
Bare electron: meff = 1.005 me, g = 2
<1 ppm 3He nuclear spins
QC Proposal w/ vertical states: Dykman, Science 1999
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An electron in an anharmonic potential
• DC electrodes to define trap for lateral motion
• Nearly harmonic motion with transitions at a few GHz
• Anharmonicity from small size of trap (w ~ d ~ 1m)
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• Massive CCD of electrons on helium
• Control many electrons withjust a control inputs
• Needed: to load/detect exactly 1 electron/pixel• Needed: way to entangle pairs of pixels together
CCD’s for electrons on helium
Courtesy Lyon group
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Detection of single electrons on helium
Electrons transferred 1 at a time from a resevoir into a 10 micron size trap
Charge is quantized but no detection of coherent motion or spin
Rousseau, et. al. PRB 79 045406 (2009)
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An electron in a cavity
Schuster, Dykman, et. al. Phys. Rev. Lett. 105, 040503 (2010)
00
VE
w
00~ ~ 25MHzV
g ex hw
Cavity-electron coupling• Electron motion couples to cavity field
• Can achieve strong coupling limit of cavity QED
• Couple to other qubits through cavity busPredicted decay rate
<10 kHz
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Accessing spin: Artificial spin-orbit coupling
• Electricaly tunable spin-motion coupling!
• With no flux focusing and current geometry: 100 kHz/mA
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• Relaxation through bias electrodes
• Dephasing from level fluctuations
• Emission of (two) ripplons
• Emission of phonons
Motional Decoherence Mechanisms
dephasingrelaxation
10 us motional decoherence time … 10,000x longer than GaAs Spin coherence time predicted > 100s
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Anatomy of an “eon” trap
Cavity level meter
Guard ring
Gate plateDrive plate
Sense plate
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Experiment
I II III IV
Superconducting Cavities as liquid He-Meters
V
Q~105
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Detecting trapped electrons on helium
No electrons
Electrons
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Making an eonhe transistor (eonFET)
Vgate
Modulate density without losing electrons
Measure density ~109 e/cm2 (~few e/um2)
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Conclusions
Electrons on Helium:
•Rich physics - single electron dynamics, motional and spin coherence, superfluid excitations, etc.
• Strong coupling limit easily reached
• Good coherence times for motion and spin
We see electrons on helium!!
• Can trap at 10 mK without much heating (~100mK)
• Can hold them for hours
Next up: Trapping single electrons
Recruiting! Check out: schusterlab.uchicago.edu for more info
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Additional slides follow
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Experimental Setup
Pulse-tube cooled dilution refrigerator
• Indium sealing & stainless capillary• No superfluid leaks down to 10mK
top
bottom
Hermetic sample holder
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Additional slides follow