Single-photon single-flux coupled detectors

Patent metadata

Field	Value
Publication number	US-11024790-B2
Application number	US-202017000959-A
Country	US
Kind code	B2
Filing date	Aug 24, 2020
Priority date	Oct 22, 2019
Publication date	Jun 1, 2021
Grant date	Jun 1, 2021

Abstract

A device that is a combination of a superconducting nanowire single-photon detector and a superconducting multi-level memory. These devices can be used to count a number of photons impinging on the device through single-photon to single-flux conversion. Electrical characterization of the device demonstrates single-flux quantum (SFQ) separated states. Optical measurements using attenuated laser pulses with different mean photon number, pulse energies and repetition rates are shown to differentiate single-photon detection from other possible phenomena, such as multiphoton detection and thermal activation. Array devices and methods are also discussed.

First claim

The invention claimed is:

1. A method of optical detection, comprising:
applying a bias current to an input arm of a photodetector, the photodetector including a superconducting loop having a constriction in series with the input arm, the bias current flowing through the constriction;
for each photon in a set of photons sequentially impinging on the constriction:
switching the constriction from a superconducting state to a resistive state, thereby diverting a portion of the bias current into a remaining portion of the superconducting loop;
returning the constriction to the superconducting state while retaining the portion of the bias current in the superconducting loop as a loop current such that the loop current is a cumulative measure of detection of the set of photons; and
reducing the loop current with a shunt electrically and thermally coupled to the superconducting loop;

reading the loop current;
determining, based on the loop current, a number of photons in the set of photons.

2. The method of claim 1 , the reading further comprising reading the loop current based on a current crowding effect.

3. The method of claim 1 , wherein the set of photons includes at least two photons.

4. The method of claim 1 , the returning the constriction to the superconducting state including attaining, by the constriction, a subsequent superconducting state, wherein the constriction is switchable to sequentially attain up to twenty five subsequent superconducting states.

5. The method of claim 1 , wherein at least a portion of the superconducting loop includes a nanowire, and wherein the nanowire includes the constriction.

6. The method of claim 1 , further comprising, after the reading, resetting the loop current by modifying the bias current to be at least twice a switching current of the constriction.

7. The method of claim 1 , further comprising, prior to the applying, characterizing the photodetector by:
setting the constriction to a first superconducting state of the set of superconducting states by applying the bias current at a first predetermined magnitude;
measuring the loop current;
increasing, in a stepwise manner, the magnitude of the bias current while monitoring the loop current; and
identifying, as a transition from the first superconducting state to a second superconducting state of the set of superconducting states, when an increase in the bias current results in an increase in the loop current.

8. A system, comprising:
a biasing circuit to supply a biasing current;
a photodetector, comprising:
an input arm, in electrical communication with the biasing circuit, to receive the biasing current;
a superconducting loop in series with the input arm and including a constriction, wherein the constriction is configured to sequentially attain a set of superconducting states in response to a corresponding set of photons sequentially impinging on the constriction, wherein:
a) in each superconducting state, the bias current flows through the constriction;
b) in response to absorption of a corresponding photon of the set of photons, the constriction attains a resistive state, wherein the bias current is diverted to a remaining portion of the superconducting loop; and
c) the constriction attains a subsequent superconducting state, wherein the constriction returns to its superconducting form, wherein a portion of the bias current is retained in the superconducting loop as a loop current,

such that the loop current is a cumulative measure of detection of the set of photons;
a shunt electrically and thermally coupled to the superconducting loop to reduce the portion of the bias current that is retained at step (b);

a readout arm coupled to the remaining portion of the superconducting loop;
a detection circuit, coupled to the readout arm, to detect the loop current; and
a processor operably coupled to the detection circuit, to determine, based on the detected loop current, a number of photons of the set of photons.

9. The system of claim 8 , wherein the shunt is thermally and electrically isolated from the readout arm.

10. The system of claim 8 , wherein the readout arm is configured to detect the loop current based on a current crowding effect.

11. The system of claim 8 , wherein the set of photons includes two photons or more.

12. The system of claim 8 , wherein the set of superconducting states includes up to twenty five superconducting states.

13. The system of claim 8 , wherein the photodetector is a superconducting nanowire single-photon detector (SNSPD), and wherein the SNSPD includes the constriction.

14. The system of claim 8 , further comprising a photodetector array, wherein the photodetector is a first photodetector of a set of photodetectors of the photodetector array.

15. A photodetector, comprising:
an input arm to supply a bias current;
a superconducting loop in series with the input arm and including a constriction, wherein the constriction is switchable among:
a) a first superconducting state in which the bias current flows through the constriction; to
b) in response to absorption of a first photon, a resistive state, wherein the bias current is diverted to a remaining portion of the superconducting loop; and to
c) a second superconducting state, wherein the constriction returns to its superconducting form, wherein a portion of the bias current is retained in the superconducting loop as a loop current,

wherein the portion of the bias current is a measure of detection of the first photon, and wherein steps (a)-(c) are repeatable for each photon of a set of photons including the first photon sequentially impinging on the constriction, such that the loop current is a cumulative measure of detection of the set of photons;
a shunt electrically and thermally coupled to the superconducting loop to reduce the portion of the bias current that is retained at step (b); and
an output arm in series with the superconducting loop to receive the bias current or a remainder portion thereof.

16. The photodetector of claim 15 , wherein the set of photons includes two photons or more.

17. The photodetector of claim 15 , wherein the set of superconducting states includes up to twenty five superconducting states.

18. The photodetector of claim 15 , wherein the output arm is isolated from the shunt.

19. The photodetector of claim 15 , wherein a cross-sectional area of the constriction is at most 25% of a cross-sectional area of any other portion of the superconducting loop.

20. The photodetector of claim 15 , wherein the superconducting loop includes a meandering nanowire, and wherein the nanowire includes the constriction.

Assignees

• Massachusetts Inst Technology

Inventors

• Onen Oguzhan Murat
• Turchetti Marco
• Berggren Karl K
• Butters Brenden
• Bionta Mina
• Keathley Phillip Donald

Classifications

• H10F30/21

  the devices being sensitive to infrared, visible or ultraviolet radiation · CPC title

• G01J1/44

  Electric circuits {(for command of an exposure part G03B7/02)} · CPC title

• G01J2001/442

  Single-photon detection or photon counting · CPC title

• G01J1/42 Primary

  using electric radiation detectors (optical or mechanical part G01J1/04; by comparison with a reference light or electric value G01J1/10) · CPC title

• H01L39/10 Primary

  Electricity · mapped topic