1. Infrared superconducting single-photon detectors
Robert Hadfield
Heriot-Watt University, Edinburgh, UK
Chandra Mouli Natarajan, Mike Tanner, John O’Connor Heriot-Watt University, UK
Burm Baek, Marty Stevens, Sae Woo Nam NIST, USA
Shigehito Miki, Zhen Wang, Masahide Sasaki NICT, Japan
Sander Dorenbos, Val Zwiller TU Delft, The Netherlands
Jonathan Habif, Chip Elliot BBN Technologies, USA
Hiroke Takesue NTT, Japan
Qiang Zhang, Yoshihisa Yamamoto Stanford, USA
Alberto Peruzzo, Damien Bonneau, Mirko Lobino, Mark Thompson, Jeremy O’Brien U. Bristol, UK

2. Infrared superconducting single-photon detectors
Introduction to photon counting
Superconducting nanowire single photon detectors (SNSPDs): device concept and evolution.
Applications of SNSPDs in quantum information science:
measurements of quantum emitters, quantum key distribution, quantum waveguide circuits.
Outlook: challenges and opportunities for this technology.
Robert Hadfield – RIT Detector Virtual Workshop 2011

3. Robert Hadfield – RIT Detector Virtual Workshop 2011
What is a Photon?
The term ‘Photon’ coined in 1926 following Einstein’s explanation of the photoelectric effect. Quantum of electromagnetic radiation E=hn.
Robert Hadfield – RIT Detector Virtual Workshop 2011

4. Robert Hadfield – RIT Detector Virtual Workshop 2011
What is a Photon?
The term ‘Photon’ coined in 1926 following Einstein’s explanation of the photoelectric effect. Quantum of electromagnetic radiation E=hn.
Some prominent detractors:
Willis Lamb ‘Anti-Photon’ Appl. Phys. B (1995)
Indian Proverb:
Six wise men went to see an elephant (though all of them were blind)..
Robert Hadfield – RIT Detector Virtual Workshop 2011

5. Robert Hadfield – RIT Detector Virtual Workshop 2011
What is a Photon?
The term ‘Photon’ coined in 1926 following Einstein’s explanation of the photoelectric effect. Quantum of electromagnetic radiation E=hn.
Some prominent detractors:
Willis Lamb ‘Anti-Photon’ Appl. Phys. B (1995)
The following definition appears to cut the Gordian Knot:
‘A photon is what a photodetector detects’ (Roy Glauber)
Robert Hadfield – RIT Detector Virtual Workshop 2011

6. Photon-counting detectors
Human eyes are sensitive down to the (few) photon level.
Photomultipliers photocathode + dynode multiplication
Semiconductor single-photon avalanche photodiodes (SPADs)
Superconductors
numerous detector examples, including superconducting nanowires
Robert Hadfield – RIT Detector Virtual Workshop 2011

7. Photon-counting detectors
Human eyes are sensitive down to the (few) photon level.
Photomultipliers photocathode + dynode multiplication
Semiconductor single-photon avalanche photodiodes (SPADs)
Superconductors
numerous detector examples, including superconducting nanowires
Robert Hadfield – RIT Detector Virtual Workshop 2011

8. Photon-counting detectors
Human eyes are sensitive down to the (few) photon level.
Photomultipliers photocathode + dynode multiplication
Semiconductor single-photon avalanche photodiodes (SPADs)
Superconductors
numerous detector examples, including superconducting nanowires
Robert Hadfield – RIT Detector Virtual Workshop 2011

9. Photon-counting detectors
Human eyes are sensitive down to the (few) photon level.
Photomultipliers photocathode + dynode multiplication
Semiconductor single-photon avalanche photodiodes (SPADs)
Superconductors
numerous detector examples, including superconducting nanowires
Robert Hadfield – RIT Detector Virtual Workshop 2011

10. Single-photon detectors & applications
Astronomy
Applications
Life Sciences
FLIM/FRET
Quantum Optics
Free space comms and LIDAR
IC Testing
Quantum cryptography
in fibre
Atmospheric Sensing
Wavelength
Photomultipliers
IR PMTs
Detectors
Si SPADs
InGaAs SPADs
Superconducting detectors
Robert Hadfield – RIT Detector Virtual Workshop 2011

11. Characteristics of single-photon detectors
High quantum detection efficiency at wavelength of interest.
Probability of noise-triggered ‘dark counts’ low.
Time between detection of photon and generation of electrical signal should be constant – low jitter.
Short recovery time (‘dead time’).
Ability to resolve photon number.
Review article: Hadfield RH ‘Single-photon detectors for optical quantum information applications’ Nature Photonics 3 (12) 696 (2009)
Robert Hadfield – RIT Detector Virtual Workshop 2011

12. Superconducting nanowire single photon detectors (SSPDs or SNSPDs)
Key Properties:
Wide spectral range (visible – mid IR)
Free running (no gating required)
Low dark counts
Low timing jitter
Short recovery time
Gol’tsman et al Applied Physics Letters (2001)
Considerable scope for further improvements!
Robert Hadfield – RIT Detector Virtual Workshop 2011

13. Superconducting nanowire single-photon detector
Bias Current
Incident
Photon
Hot spot
(R > 0)
T~ 4K
Bias Current
R > 0
Bias Current
R = 0
→ Voltage Drop = 0
Bias Current
Current density
above critical
Hot spot
(R > 0)
Sapphire
substrate
100 nm
3.5 nm
NbN
Gol’tsman et al., Applied Physics Letters 79, 705 (2001)
Robert Hadfield – RIT Detector Virtual Workshop 2011

14. Superconducting nanowire single-photon detector
T~ 4K
Bias Current Reduced
R > 0
→ Voltage Pulse Out
Sapphire
substrate
Hotspot Growth
NbN
V(t)
Gol’tsman et al., Applied Physics Letters 79, 705 (2001)
Robert Hadfield – RIT Detector Virtual Workshop 2011

15. Superconducting nanowire single-photon detector
Bias current suppressed
Bias Current
Sapphire
substrate
NbN
V(t)
Recovery:
Hotspot shrinks as heat is dissipated into substrate
Current builds up limited by inductance of nanowire
Robert Hadfield – RIT Detector Virtual Workshop 2011

16. Evolution of SNSPD design
Efficient optical coupling is a challenge:
Practical detection efficiency
= coupling efficiency x intrinsic quantum efficiency
=> Increase active area
Verevkin APL 2002
Meander
100 nm wide wire,
~10 mm x 10 mm area
Gol’tsman APL 2001
100 nm wide wire,
~5 mm long
Single wire
Robert Hadfield – RIT Detector Virtual Workshop 2011

17. Evolution of SNSPD design
Next step:
Practical detection efficiency
= coupling efficiency x intrinsic quantum efficiency
=> Boost absorption to increase intrinsic QE
Verevkin APL 2002
Meander
100 nm wide wire,
~10 mm x 10 mm area
Optical Cavity
nanowire
mirror
Light
substrate
Rosfjord OX 2006
Robert Hadfield – RIT Detector Virtual Workshop 2011

18. Evolution of SNSPD design
Single wire
Meander
Increase coupling
Optical Cavity
Increase absorption
Practical detection
efficiency low
Max intrinsic efficiency ~20% at 1550 nm
Best reported intrinsic efficiency 57% at 1550 nm
Robert Hadfield – RIT Detector Virtual Workshop 2011

19. Other developments in SNSPD design
Photon number resolution with spatial multiplexing (SINPHONIA, MIT)
Dichovy et al Nature Photonics 2008
Dauler et al J. Modern Optics 2009
SNSPDs on Si substrates (Delft)
Detector embedded in waveguide (MIT, Yale, TUe)
Dorenbos et al APL 2008
Hu IEEE Trans Appl. Supercon. 2009;
Sprengers arXiv ; Pernice arXiv
Robert Hadfield – RIT Detector Virtual Workshop 2011

20. Superconducting nanowire single-photon detector system
High efficiency SNSPDs from TU Delft
Tanner et al Applied Physics Letters (2010)
4 or more fiber-coupled SNSPDs can be implemented into a practical, closed-cycle refrigerator system
Hadfield et al Optics Express 13 (26) (2005)
SNSPD system at Heriot-Watt
Robert Hadfield – RIT Detector Virtual Workshop 2011

21. Robert Hadfield – RIT Detector Virtual Workshop 2011
Superconducting nanowire single-photon detector system: practical performance
Tanner et al Applied Physics Letters (2010)
Robert Hadfield – RIT Detector Virtual Workshop 2011

22. Quantum information science with single photons
Quantum systems can be used to encode and manipulate information.
QIST promises dramatic improvements in secure communications metrology, and computation.
In principle many candidate quantum systems (trapped ions, spins in semiconductor quantum dots, superconducting circuits..)
Optical photon makes an ideal ‘flying qubit’
Photons have low decoherence even at room temperature, easy to route and manipulate
|0 +|1
e.g. polarization of photon

23. Robert Hadfield – RIT Detector Virtual Workshop 2011
Superconducting single-photon photon detectors for quantum information science
Faithful detection of single photons is a key challenge.
Hadfield Nature Photonics 3 (12) 696 (2009)
Superconducting nanowire single-photon detectors (SSPDs or SNSPDs) have are an important emerging photon-counting technology.
SNSPDs have an important role in new QIS applications:
Characterization of quantum emitters
Quantum Key Distribution (QKD)
Operation of quantum waveguide circuits
Robert Hadfield – RIT Detector Virtual Workshop 2011

24. Characterization of quantum emitters
Ti:Sapphire
Laser
1 ps, 780 nm
Fast Photodiode
Start
TAC/MCA
Timing Electronics BS
82 MHz
Mono-
chromator
@ 935 nm
Fiber
Stop
SSPD
Dichroic BS
Sample
Sample
InGaAs/GaAs QW, Room Temp
Cryostat
Instrument
Responses
Decays
Stevens et al Applied Physics Letters (2006)

25. Quantum dot single-photon sources for quantum information science applications
Self-assembled quantum dots in III-V semiconductor are a promising source of single photons for optical QIS.
Michler et al Nature (2001)
Single photon emission is verified by g(2)(0) measurement.
These measurements were on emitters at l ~900 nm; SNSPDs would also enable measurements on telecom wavelength single-photon sources
Hadfield et al Optics Express (2005)
Hadfield et al Journal of Applied Physics (2007)

26. Long wavelength characterization of quantum emitters using SNSPDs
Si single photon avalanche photodiodes do not work at l>1 mm.
SNSPDs can be used for characterization of long wavelength emitters.
InGaAs grown on InP
lDetect = 1650 nm
Stevens et al Applied Physics Letters (2006)
These measurements were carried out on semiconductor single-photon emitters; this technique would be equally applicable to studies of single photon emission from diamond defect centers, FLIM and FRET for single molecules and singlet oxygen detection.
Robert Hadfield – RIT Detector Virtual Workshop 2011

27. Quantum Key Distribution
(Bennett & Brassard, 1984) hn
Alice
Bob
Eve
R. Liechtenstein
Quantum Key Distribution is a method for two parties (‘Alice’ and ‘Bob’) to create a ‘key’ for encrypting subsequent messages.
Information encoded on single photons via phase or polarization
Any attempted eavesdropping introduces errors and is therefore detectable.
Robert Hadfield – RIT Detector Virtual Workshop 2011 27

28. Robert Hadfield - Heriot-Watt Quantum Photonics Workshop
Quantum Key Distribution – range limitations
Above a certain error rate (QBER) threshold, secure key can no longer be generated.
There are two contributions to the error rate (QBER):
QBER total = QBER interferometer + QBER dark counts
Fixed ~1%
Dark count rate / Sifted bit rate
As the transmission distance increases, the number of detected bits falls, so the error rate rises, causing the secret bit rate to eventually fall to zero.
Log(Key Rate)
Distance
Sifted
Secret
Distance
QBER
11 %
Robert Hadfield - Heriot-Watt Quantum Photonics Workshop

29. Superconducting nanowire single-photon detectors
in Quantum Key Distribution
Superconducting nanowire single-photon detectors: benefits for QKD in optical fibre:
- Single-photon sensitivity at 1550 nm
- Low dark counts
- Low timing jitter
- Gaussian instrument response function
=>Long distances
=>High bit rates
Robert Hadfield – RIT Detector Virtual Workshop 2011 29

30. First QKD demonstration with SNSPDs in the DARPA quantum network
A collaboration between NIST and BBN Technologies (Jonathan Habif, Chip Elliot) sponsored by the DARPA QuIST programme.
First prototype SNSPD system delivered to BBN end 2005.
Clock rate 3.3 MHz
Bob
42.5 km spool
Alice
(behind)
Bit rate (bits/s)
25 km spool
Link loss (dB)
SNSPD Closed-cycle system
Hadfield et al Applied Physics Letters (2006)

31. Robert Hadfield – RIT Detector Virtual Workshop 2011
World record result for long distance QKD in optical fiber using SNSPDs
Demonstration carried out end 2006 in Yamamoto lab, Stanford University (Stanford/NTT/NIST)
10 GHz clocked QKD system at l= 1550 nm using superconducting detectors
10 GHz
1 GHz
Takesue et al Nature Photonics (2007)
Robert Hadfield – RIT Detector Virtual Workshop 2011 31

32. New directions in QKD: ground to space
Vision of European Space Agency SpaceQUEST topical team
(led by Prof. Anton Zeilinger, University of Vienna):
QKD from the International Space Station (ISS).
Photon flux
Microlens
array
Cavity enhanced nanowire pixels
Role for SNSPDs?
R Ursin et al Europhysics News 40 (3)
Robert Hadfield – RIT Detector Virtual Workshop 2011

33. Quantum waveguide circuits
Jeremy O’Brien, University of Bristol
Optical waveguide circuits can be used to replace conventional optics.
Politi et al Science (2008)
Robert Hadfield – RIT Detector Virtual Workshop 2011

34. Operating quantum waveguide circuits with SNSPDs
with Jeremy O’Brien, University of Bristol, UK
CW laser, 402nm, 60mW
μm actuator
SNSPDs
Waveguide Circuit
BiBO
PMF
SMF
Filter
TCSPC
Card a b c d
804nm photon pairs
Robert Hadfield – RIT Detector Virtual Workshop 2011

35. Robert Hadfield – RIT Detector Virtual Workshop 2011
Operating quantum waveguide circuits with SNSPDs: initial experiments at l=805 nm
First generation quantum waveguide circuits: silica on silicon waveguides, downconversion pair source at l=850 nm (as used in Politi et al Science (2008))
SNSPDs replace Si SPADs
Demonstrations:
-Two photon interference (Hong-Ou-Mandel dip)
-Tuned two phonon interference with resistive phase shift
-CNOT gate
F=90.4%
VSNSPD %
Natarajan et al Applied Physics Letters (2010)
Robert Hadfield – RIT Detector Virtual Workshop 2011

36. Robert Hadfield – RIT Detector Virtual Workshop 2011
Operating quantum waveguide circuits with SNSPDs: migrating to telecom wavelengths
First generation quantum waveguide circuits: silica on silicon waveguides, downconversion pair source at l=850 nm and Si SPAD detectors
Politi et al Science (2008)
A much wider range of high performance waveguide components (compact low loss waveguides, high speed switches and modulators)
SNSPDs allow operation of next generation quantum waveguide circuits at 1550 nm.
Recent reports show that SNSPDs can also be integrated on-chip with the waveguide. This is crucial for the scalabilty of circuits in demanding applications such as optical quantum computing.
Robert Hadfield – RIT Detector Virtual Workshop 2011

37. Heralded source with fast lithium niobate switch
Switching efficiency
MZI driven with a 4 ns rising time pulse
Bonneau et al Fast path and polarization manipulation of telecom wavelength single photons in lithium niobate waveguide devices arXiv (2011)

38. Fast switching of quantum interferenceb c d
Signal generator
Counting logic C1 C2
SPDC
q =p/2
q = 0 C2 C1
Counting logic with toggle between two separate counters
Square waves 4MHz
Interleaved measurement. Both curves taken at the same time.
Bonneau et al Fast path and polarization manipulation of telecom wavelength single photons in lithium niobate waveguide devices arXiv (2011)

39. Infrared superconducting single-photon detectors Outlook
Superconducting nanowire single-photon detectors (SNSPDs) offer very good practical performance at telecom wavelengths and have successfully been used in challenging quantum information science experiments.
Prospects and challenges for SNSPD development:
Achieving high efficiency at mid IR wavelengths
Reducing the timing jitter
Increasing the active area
Integrating devices on-chip with optical and electrical elements (optical waveguide circuits, readout electronics)
Potential breakthroughs:
Large area single photon detectors/detector arrays with high efficiency, picosecond timing resolution and gigahertz count rates from UV to mid IR wavelengths
Adoption in new application areas: quantum communications and computing, LiDAR, astronomy, life sciences, integrated circuit testing
Robert Hadfield – RIT Detector Virtual Workshop 2011