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 Superconducting Single Photon Detectors Single Photon Detectors

OutlineOutline

MotivationMotivation

Working PrincipleWorking Principle

Experimental RealizationExperimental Realization

ResultsResults

Current Research / OutlookCurrent Research / Outlook

MotivationMotivation

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

MotivationMotivation

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

single photon detectors:

• avalanche photodiodes (APDs) - commercially available single photon detectors

MotivationMotivation

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

MotivationMotivation

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

MotivationMotivation

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)

MotivationMotivation

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

Working PrincipleWorking Principle

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

Working PrincipleWorking 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 IC)

Working PrincipleWorking 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 IC)

Working PrincipleWorking 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 IC)

Working PrincipleWorking 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 IC)

Detector LayoutDetector Layout

Detectors are made at TU Delft by Sander Dorenbos and Val Zwiller.

[S. Dorenbos, Master Thesis, TU Delft (2007)]

• NbN on sapphire (TC, NbN =11K)• wire width: 100 nm• wire height: 4-6 nm• filling factor: 50%• wire length: ≈ 100 µm• active area: 10 x 10 µm2

Fiber CouplingFiber 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

SetupSetup

SetupSetup

SetupSetup

SetupSetup

SetupSetup

Quantum EfficiencyQuantum Efficiency

• quantum efficiencies between 2% - 10%• quantum efficiency increases with bias current and photon energy

Dark CountsDark Counts

exponential increase of the dark counts with the bias current

Noise Equivalent Power (NEP)Noise Equivalent Power (NEP)

R dark count rate QE quantum efficiency

with

Noise Equivalent Power (NEP)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)

Single Photon DetectionSingle Photon Detection

• Hanburry-Brown and Twiss setup with APD and SSPD

• source: single N-V center in a diamond nanocrystal (emission around 637 nm)

Single Photon DetectionSingle Photon Detection

Outlook I Outlook I

Antibunching With One DetectorAntibunching 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.

Outlook I Outlook I

Antibunching With One DetectorAntibunching 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

Outlook II Outlook II

Photon Number ResolutionPhoton 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)]

Outlook II Outlook II

Photon Number ResolutionPhoton 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).

Outlook II Outlook II

excitation with attenuated lasers pulses (repetition rate: 82 MHz)

first test of muti-photon absorption:

Photon Number ResolutionPhoton Number Resolution

Thank you!Thank you!