PhotonNumber Resolving Detectors for Quantum Communications

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Photon-Number Resolving Detectors for Quantum
Communications
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Optical Photon Detectors

• Sae Woo Nam, D. Rosenberg,
• A. J. Miller, A. Salminen,
• E. Grossman, J. M. Martinis

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Conventional vs. Photon Number Resolving Detectors
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Transition Edge Sensor (TES) Technology
Energy deposition
Thermometer
Rn
Absorber, C
R
Weak thermal link, g
Thermal sink (50 mK)
T

• Calorimetric detection of UV/optical/IR photons
• Photon(s) absorbed by a heat capacity C
  connected to a thermal sink by a weak thermal
  link g.
• Temperature of the absorber is monitored by an
  ultra-sensitive thermometer (superconducting-to-no
  rmal transition).
• Temperatures are 100 mK to ensure low noise and
  high sensitivity.
• Our absorber and thermometer are the same

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Historical Note

• CDMS direct detection of dark matter
• X-ray microanalysis
• Constellation-X
• SCUBA II Submillimeter detector array
• Optical Spectrophotometer with timestamping

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TES Readout
Output signal is proportional to number of
absorbed photons

• Device is voltage biased
• Current through device is pre-amplified using a
  cryogenic SQUID array amplifier
• Signal can then be processed using RT electronics

• Optimized now for photon-number resolution, not
  speed (trise100 ns, tfall10 ms)
• Absorption events show good distinguishability
• Much slower than APDs

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Devices and Optical Coupling
W TES
Si
25 µm
Al wiring

• TES is 35 nm thick tungsten film, Tc100 mK
• Wiring is 80 nm thick superconducting Al
• Central pixel is 25 µm 25 µm
• Optical photolithographic process

• Optical fiber is 9 µm core SM fiber
• Coupling is lens-free, expect low-loss
• Losses are dominated by reflection and
  inefficient optical alignment
• Target efficiency gt80 at 1550 nm

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• Cryostat
• Commercially available
• Portable (70 kg)
• All electronic cooling
• LN2 fill every 24 hrs.
• LHe fill every 3 days
• Base Tlt100mK for 24 hrs.
• 1.5 hour regeneration time
• Next version, Cryogen Free!

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1310 nm Weak Coherent Source
PNR
SM Fiber
Pulsed Laser

65 dB
Fiber attenuator
1310 nm or 1550 nm 100 ns wide pulses
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1550 nm Weak Coherent Source
l1.550 mm
Pulse Height a.u.
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BU Quantum Optical Setup
Doubles
Coincident

PNR 1
CW Laser
Dichroic
351 nm

BBO

Doubles
PNR 2
3 nm IF
l/2
PBS
Delay
Coincident Rate
Zero Delay
Counts/sec
Delay time
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LANL Fiber QKD

• Phase encoding
• 1310 nm link
• 1550 nm bright pulse for timing

• Timing / Optical switches
• GPS link for timing
• Stray light

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Unique Features of TES detectors

• Photon Number Resolution
• Low Noise
• NEP lt 10-19 W/vHz (limited by stray light)
• No Dark Counts
• High QE at telecommunication wavelengths
• 40 intrinsic, gt20 end-to-end measured
• AR coatings give no limit, in principle
• Target of gt80 w/ single layer at 1550 nm
• Crude Spectrometer
• Slow trise100 ns, tfall10 ms
• Cryogenic

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Work In Progress

• Improving the Quantum Efficiency
• Anti-reflection coatings
• Materials compatibility work
• Speed (MHz)
• Improvements to existing materials, new materials
• New biasing technique
• Putting together systems for broader use

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Superconducting Fabrication Facility

• 2700 sq ft class 100 space
• I-line 5x lithography
• E-beam lithography
• Reticle generation
• Sputter deposition (x2)
• ECR PECVD deposition
• LPCVD (x2)
• Thermal oxide / diffusion (x2)
• Thermal deposition (x2)
• RIE (x2)
• Plasma etching
• Ion mill etching
• 3 inch wafers

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Improving the Quantum Efficiency

• Optical coatings
• Thin film dielectrics
• Detector material compatibility
• Tungsten deposition
• Optical characterization and simulation tools
• Spectrophotometer

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Path to Moores Law

• Combination of electrical circuit, thermal
  circuit, and noise sources
• More Power speed
• but lower discrimination
• New materials with higher conductance
• Modulate electrical bias

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System Assembling

• Cryogen based system
• Major parts arriving soon
• No longer borrowing equipment
• Cryogen free system for NIST DARPA QuIST testbed
  and Boulder Labs
• Cryogenic platform for other detector technologies

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Next Experiments / Systems

• Source Characterizations
• Weak coherent at 1550nm
• SPDC on demand, NIST Physics Lab
• SPT (now available at NIST EEEL)
• Quantum Optics, BU
• QKD experiments, LANL
• Demonstration of multi-channel system
• Detector loophole free tests of Bells inequality
• Full Bell-State analyzer

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Conclusion

• Demonstration of first true photon-counting
  detector at telecomm wavelengths for quantum
  information science and applications
• Verification of the Poisson nature of a weak
  coherent source
• Demonstration of the only telecommunications-wavel
  ength system with zero dark counts
• Prospects are good for improving QE to gt80 at
  1550nm
• Truly unique among telecommunication-wavelength
  instruments
• Ideal for a NIST metrological tool