Superconducting Photodetectors

David SchusterAssistant ProfessorUniversity of Chicago

Figures from:

Yale:

Schoelkopf GroupProber Lab

NIST:

S.W. Nam

J.M. Martinis

Manipulating microwaves one photon at a time

?

Outline

• Applications of superconducting photodetectors

• Overview of superconducting photodetectors

• Kinetic Inductance Detectors

• Nanowire Superconducting Single Photon Detectors

• Practical considerations

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

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

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

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

Quasiparticles change surface impedance

Shunted normal resistance Kinetic inductance

R

LK

R

T

Rn

Day, et. Al. Nature (2003)

Broadband Resonant

Multiplexing Kinetic Inductance Detectors

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

Other innovations…

Williams IEEE ASC Proc. 2010

High Tc

Multiwire detectors

Lincoln labs

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

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

Additional slides follow

Outline

• Types of superconducting photodetectors

• Speed limitations of SC detectors

• Super-sensitive level meter and preliminary measurements of electrons on helium

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 > ,

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)

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!

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

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

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)

• 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

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)

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

Accessing spin: Artificial spin-orbit coupling

• Electricaly tunable spin-motion coupling!

• With no flux focusing and current geometry: 100 kHz/mA

• 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

Anatomy of an “eon” trap

Cavity level meter

Guard ring

Gate plateDrive plate

Sense plate

Experiment

I II III IV

Superconducting Cavities as liquid He-Meters

V

Q~105

Detecting trapped electrons on helium

No electrons

Electrons

Making an eonhe transistor (eonFET)

Vgate

Modulate density without losing electrons

Measure density ~109 e/cm2 (~few e/um2)

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

Additional slides follow

Experimental Setup

Pulse-tube cooled dilution refrigerator

• Indium sealing & stainless capillary• No superfluid leaks down to 10mK

top

bottom

Hermetic sample holder

Additional slides follow