1. Gesine Steudle, Ingmar Müller, and Oliver Benson Humboldt-Universität zu Berlin Institut für Physik, AG Nano-Optik http://www.physik.hu-berlin.de/nano SFB 787 – Teilprojekt C2 19.06.2009 Superconducting Single Photon Detectors

2. Outline Motivation Working Principle Experimental Realization Results Current Research / Outlook

3. Motivation Single photon detection is essential for any experiment with single photons.

4. Motivation single photon detectors: avalanche photodiodes (APDs) - commercially available single photon detectors

5. Motivation Single photon detection is essential for any experiment with single photons. single photon detectors: avalanche photodiodes (APDs) - commercially available single photon detectors superconducting single photon detectors (SSPDs) - new kind of photodetectors - different types of SSPDs, in our case: meander-type SSPD

6. Motivation Single Photon Detectors APDs Si-APDs -high efficiencies in the visible (70 % at 700 nm)  -low dark count rates  -long dead times (40 ns)  -not working in the IR 

7. Motivation Single Photon Detectors APDs Si-APDs -high efficiencies in the visible (70 % at 700 nm)  -low dark count rates  -long dead times (40 ns)  -not working in the IR  InGaAs-APDs -working in the IR  -high dark count rates  -long dead times (100ns) 

8. Motivation Single Photon Detectors APDs Si-APDs -high efficiencies in the visible (70 % at 700 nm)  -low dark count rates  -long dead times (40 ns)  -not working in the IR  InGaAs-APDs -working in the IR  -high dark count rates  -long dead times (100ns)  SSPDs meander-type SSPDs -working in the IR  -low dark count rates  -short dead times (5 ns)  -working at 4.2 K 

9. Working Principle Absorption of light can distruct superconductivity. [L. Testardi, Phys. Rev. B 4, p. 2355 (1971)]

10. Working Principle [G. N. Gol‘tsman et al., phys. stat. sol. c 2, p. 1480 (2005)] Absorption of light can distruct superconductivity. [L. Testardi, Phys. Rev. B 4, p. 2355 (1971)] a) absorption of a photon superconducting wire biased close to critical current (I = 0.9 I C )

11. Working Principle [G. N. Gol‘tsman et al., phys. stat. sol. c 2, p. 1480 (2005)] Absorption of light can distruct superconductivity. [L. Testardi, Phys. Rev. B 4, p. 2355 (1971)] a) absorption of a photon b) absorbed photon causes “hot spot“ superconducting wire biased close to critical current (I = 0.9 I C )

12. Working Principle [G. N. Gol‘tsman et al., phys. stat. sol. c 2, p. 1480 (2005)] Absorption of light can distruct superconductivity. [L. Testardi, Phys. Rev. B 4, p. 2355 (1971)] a) absorption of a photon b) absorbed photon causes “hot spot“ c) current is repelled to the sidewalks - critical current density is exceeded superconducting wire biased close to critical current (I = 0.9 I C )

13. Working Principle [G. N. Gol‘tsman et al., phys. stat. sol. c 2, p. 1480 (2005)] Absorption of light can distruct superconductivity. [L. Testardi, Phys. Rev. B 4, p. 2355 (1971)] a) absorption of a photon b) absorbed photon causes “hot spot“ c) current is repelled to the sidewalks - critical current density is exceeded d) a resistive state appears across the whole strip superconducting wire biased close to critical current (I = 0.9 I C )

14. Detector Layout Detectors are made at TU Delft by Sander Dorenbos and Val Zwiller. [S. Dorenbos, Master Thesis, TU Delft (2007)] NbN on sapphire (T C, NbN =11K) wire width: 100 nm wire height: 4-6 nm filling factor: 50% wire length: ≈ 100 µm active area: 10 x 10 µm 2

15. Fiber Coupling scheme of the fiber coupling theoretical coupling factor: k = 0.87 experimental coupling factor: k = 0.61 k = 0.333 in [W. Słysz et al., Appl. Phys. Lett. 88, 261113 (2006)] backside view frontside view

16. Setup

17. Setup

18. Setup

19. Setup

20. Setup

21. Quantum Efficiency quantum efficiencies between 2% - 10% quantum efficiency increases with bias current and photon energy

22. Dark Counts exponential increase of the dark counts with the bias current

23. Noise Equivalent Power (NEP) R dark count rate QE quantum efficiency with

24. Noise Equivalent Power (NEP) R dark count rate QE quantum efficiency with NEP at 1550nm: ~10 -15 W·Hz -1/2 (InGaAs-APDs: NEP = 10 -13 W·Hz -1/2 )

25. Single Photon Detection Hanburry-Brown and Twiss setup with APD and SSPD source: single N-V center in a diamond nanocrystal (emission around 637 nm)

26. Single Photon Detection

27. Outlook I Outlook I Antibunching With One Detector detector dead time: 5 ns life times of N-V defect centers in nano-diamonds: 40-60 ns  It is possible to see antibunching with one detector.

28. Outlook I Outlook I Antibunching With One Detector detector dead time: 5 ns life times of N-V defect centers in nano-diamonds: 40-60 ns  It is possible to see antibunching with one detector. current problem: more sophisticated electronics necessary

29. Outlook II Outlook II Photon Number Resolution In principle SSPDs provide information about the energy absorbed by the detector. This information is can be obtained e.g. by looking at the shape of the detector pulses. [A. D. Semenov et al., Physica C 351, p. 349 (2001)]

30. Outlook II Outlook II Photon Number Resolution Our approach: Measurements at different bias currents Idea: At low bias currents one single photon does not have enough energy to trigger the detector.  Reduction of the bias current makes the detector sensitive for multi-photon events (because single photon events are suppressed).

31. Outlook II Outlook II excitation with attenuated lasers pulses (repetition rate: 82 MHz) first test of muti-photon absorption: Photon Number Resolution

32. Thank you!