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Dark Current Measurements of a Submillimeter Photon Detector

Dark Current Measurements of a Submillimeter Photon Detector. John Teufel Department of Physics Yale University. Yale: Minghao Shen Andrew Szymkowiak Konrad Lehnert Daniel Prober Rob Schoelkopf. NASA/GSFC Thomas Stevenson Carl Stahle Ed Wollack Harvey Moseley.

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Dark Current Measurements of a Submillimeter Photon Detector

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  1. Dark Current Measurements of a Submillimeter Photon Detector John Teufel Department of Physics Yale University Yale: Minghao Shen Andrew Szymkowiak Konrad Lehnert Daniel Prober Rob Schoelkopf NASA/GSFC Thomas Stevenson Carl Stahle Ed Wollack Harvey Moseley Funding from NASA Explorer Tech., JPL, GSFC

  2. Overview The “SQPC” – a high-sensitivity sub-mm detector Contributions to dark currents Aluminum Junction Characterization Implications on overall sensitivity Future Work

  3. Sub-mm: ~ 100 mm -- 1 mm Sub-mm detectors today: Future NASA missions will require : Detectors should also be: Fast High quantum efficiency Scalable for arrays Motivation

  4. Antenna-coupled Superconducting Tunnel Junction (STJ) Photoconductor direct detector Each Photon with excites 2 quasiparticles Nb Al Al Au AlOx The SQPC: Single Quasiparticle Photon Counter Nb antenna Al absorber (Au) m ~ 1 STJ detector junction sub-mm photon Responsivity=2e/photon=e/D=5000A/W

  5. Rb V en SQPC Electrical Circuit Model and Noise Shot Noise Johnson Noise Amplifier Noise

  6. Temperature Thermal energy breaks Cooper pairs and excites quasiparticles BCS Predicts: Supercurrent Cooper pair tunneling affects the subgap current both at zero and finite voltages Due to rectification of the AC Jospephson Effect: Contributions to the Dark Current

  7. Bow Tie Antenna Detector 140 µm 1 µm Experimental Set-up and Testing • Small area junctions fabricated using double angle evaporation Device mounted in pumped He3 cryostat (T~250mK)

  8. X B Supercurrent Suppression SQUID w/ Rtot = 44 kW Al/AlOx/Al Junctions: ~ 60 x 100 nm

  9. Thermal Dark Current Measurements BCS Predicts: Tc =1.4 K I @ 50 mV Current [pA] Voltage [µV]

  10. Future Work: Detecting Photon Use a low thermal conductance blackbody to shine photons on detector

  11. Conclusions • SQPC: a sub-mm detector capable of NEP < • Characterized two sources dark current • Measured dark current < 0.5 pA • Tests with Blackbody source underway

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