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Superconducting Photodetectors

David Schuster Assistant Professor University of Chicago. Superconducting Photodetectors. Figures from: Yale: Schoelkopf Group Prober Lab NIST: S.W. Nam J.M. Martinis. Manipulating microwaves one photon at a time. ?. Outline. Applications of superconducting photodetectors

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Superconducting Photodetectors

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  1. David SchusterAssistant ProfessorUniversity of Chicago Superconducting Photodetectors Figures from: Yale: Schoelkopf GroupProber Lab NIST: S.W. Nam J.M. Martinis

  2. Manipulating microwaves one photon at a time ?

  3. Outline • Applications of superconducting photodetectors • Overview of superconducting photodetectors • Kinetic Inductance Detectors • Nanowire Superconducting Single Photon Detectors • Practical considerations

  4. 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

  5. SC detectors have great performance! High resolution Low noise LLE review vol 101 Martinis, NIST High throughput > 1Gbps Photon number resolving S.W. Nam, NIST S.W. Nam, NIST

  6. Most SC detectors work like calorimeters Energy deposition Thermometer Rn Absorber, C R Weak thermal link, g Thermal sink T • 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

  7. e-e interaction Photon h n 0 10 -1 10 phonons phonons eV e-e interaction Quasi particles 2D -3 10 k T b Cooper pairs Cascade of broken Cooper pairs • Photon breaks a cooper pair • Thermalizes making hn/D qp’s • # gain but no E gain yet • E resolution / photon # counting determined by shot noise • Gain comes from change R or L

  8. Quasiparticles change surface impedance LK Shunted normal resistance Kinetic inductance R Broadband Resonant R Rn T Day, et. Al. Nature (2003)

  9. Multiplexing Kinetic Inductance Detectors

  10. Nanowire Superconducting Single Photon Detector (SSPD) NbN 4nm thick <100nm wide • Current Biased • Very fast ( 10’s of ps) • Usually cooled by phonons Annunziata JAP 2010

  11. Other innovations… High Tc Williams IEEE ASC Proc. 2010 Multiwire detectors Lincoln labs

  12. 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

  13. 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

  14. Additional slides follow

  15. Outline • Types of superconducting photodetectors • Speed limitations of SC detectors • Super-sensitive level meter and preliminary measurements of electrons on helium

  16. Cavity QED with circuits and floating electrons 2g = vacuum Rabi freq. k= cavity decay rate g= “transverse” decay rate Strong coupling: 2g > k, g out L = l ~ 2.5 cm Transmission line “cavity” 10 mm Trapped electron 10 GHz in Theory: Blais, Huang, et al., Phys. Rev. A 69, 062320 (2004)

  17. What to do with hybrid systems and cavity QED? Quantum Optics • Measure individual photon # states • Produce single photon states • Tomography of arbitrary quantum states DIS*, Houck*, et. al., Nature, (2007) Fundamental Quantum physics • Measurement of field quantization • Tests of quantum gravity, etc. Bishop, Chow, et. al.,Nature Physics, (2009) Quantum Computing • Two qubit gates • Quantum algorithms • Process tomography DiCarlo, Chow, et. al., Nature, (2009)

  18. Hybrid quantum systems Nanomechanics Solid-state spins Y. Kubo, F. Ong, P. Bertet et. al. PRL (2010)DIS, A. Sears, E. Ginossar, et. al. PRL (2010) Teufel, et al., Nature (2011) See SYHQ 2! Ultracold atoms Verdu, Zoubi, et. al. PRL (2009)Hunger, Camerer, Hänsch, et. al. PRL (2010) Electrons on helium See SYHQ 3-5! Polar Molecular Ions DIS, Bishop, et. al. PRA (2011) DIS, Fragner, et. al. PRL (2010)

  19. Seeing a puddle of electrons on helium Low energy electrons get stuck on the surface Force from positive electrode causes a dimple M.W. Cole. Rev. Mod. Phys. 46, 3 1974

  20. An electron on helium? See Jackson 4.4 Electron bound at < 8K He Levitates 8nm above surface (in vacuum) Clean 2DEG :Mobility = 1010 cm2/Vs Bare electron: meff = 1.005 me, g = 2 <1 ppm 3He nuclear spins + e = 1.057 a0 = 7.6 nm QC Proposal w/ vertical states: Dykman, Science 1999

  21. 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 ~ 1mm)

  22. CCD’s for electrons on helium • 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 Courtesy Lyon group

  23. 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)

  24. Cavity-electron coupling An electron in a cavity • Electron motion couples to cavity field • Can achieve strong coupling limit of cavity QED • Couple to other qubits through cavity bus Predicted decay rate <10 kHz Schuster, Dykman, et. al. Phys. Rev. Lett. 105, 040503 (2010)

  25. Accessing spin: Artificial spin-orbit coupling • Electricaly tunable spin-motion coupling! • With no flux focusing and current geometry: 100 kHz/mA

  26. Motional Decoherence Mechanisms • Relaxation through bias electrodes • Dephasing from level fluctuations • Emission of (two) ripplons • Emission of phonons dephasing relaxation • 10 us motional decoherence time … 10,000x longer than GaAs • Spin coherence time predicted > 100s

  27. Anatomy of an “eon” trap Cavity level meter Drive plate Gate plate Guard ring Sense plate

  28. Experiment I II III V IV Superconducting Cavities as liquid He-Meters Q~105

  29. Detecting trapped electrons on helium Electrons No electrons

  30. Making an eonhe transistor (eonFET) DVgate Modulate density without losing electrons Measure density ~109 e/cm2 (~few e/um2)

  31. 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

  32. Additional slides follow

  33. Experimental Setup Pulse-tube cooled dilution refrigerator Hermetic sample holder top bottom • Indium sealing & stainless capillary • No superfluid leaks down to 10mK

  34. Additional slides follow

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