Single-flux-quantum probabilistic digitizer

Patent metadata

Field	Value
Publication number	US-9793913-B2
Application number	US-201715437043-A
Country	US
Kind code	B2
Filing date	Feb 20, 2017
Priority date	Dec 17, 2015
Publication date	Oct 17, 2017
Grant date	Oct 17, 2017

Abstract

A probabilistic digitizer for extracting information from a Josephson comparator is disclosed. The digitizer uses statistical methods to aggregate over a set of comparator readouts, effectively increasing the sensitivity of the comparator even when an input signal falls within the comparator's gray zone. Among other uses, such a digitizer may be used to discriminate between states of a qubit.

First claim

What is claimed is:

1. A method comprising:
receiving a plurality of sample sets, with each sample set including N sequential samples;
for each given sample set of the plurality of sample sets:
estimating a probability p(j) of an output pulse being produced from a Josephson comparator based on the N sequential samples of the given sample set, and
estimating an analog input current Ix(j) corresponding to the given sample set based on an inverse function of p(j) for the given sample set using a probability curve Prob(I x ); and

extracting a signal from output of the Josephson comparator based, at least in part upon the analog input current I x (j) values respectively corresponding to the sample sets.

2. The method of claim 1 wherein the inverse function is expressed by the following equation: I x (j)=Prob −1 (p(j)).

3. The method of claim 1 further comprising:
performing empirical calibration tests to determine the probability curve Prob(I x ).

4. The method of claim 1 further comprising:
computing probability curve Prob(I x ) based on: (i) empirical or theoretical properties of the Josephson comparator, and (ii) operating conditions of the Josephson comparator.

5. The method of claim 1 wherein, for each given sample set, N is approximately equal to an fclk value for the given sample set divided by an fsig value for the given sample set.

6. The method of claim 1 wherein sampling is done at a higher frequency than the input signal rate/frequency.

7. A computer program product comprising:
a machine readable storage device; and
computer code stored on the machine readable storage device, with the computer code including instructions for causing a processor(s) set to perform operations including the following:
receiving a plurality of sample sets, with each sample set including N sequential samples,
for each given sample set of the plurality of sample sets:
estimating a probability p(j) of an output pulse being produced from a Josephson comparator based on the N sequential samples of the given sample set, and
estimating an analog input current I x (j) corresponding to the given sample set based on an inverse function of p(j) for the given sample set using a probability curve Prob(I x ); and

extracting a signal from output of the Josephson comparator based, at least in part upon the analog input current I x (j) values respectively corresponding to the sample sets.

8. The computer program product of claim 7 wherein the inverse function is expressed by the following equation: I x (j)=Prob −1 (p(j)).

9. The computer program product of claim 7 further comprising:
performing empirical calibration tests to determine the probability curve Prob(I x ).

10. The computer program product of claim 7 further comprising:
computing probability curve Prob(I x ) based on: (i) empirical or theoretical properties of the Josephson comparator, and (ii) operating conditions of the Josephson comparator.

11. The computer program product of claim 7 wherein, for each given sample set, N is approximately equal to an fclk value for the given sample set divided by an fsig value for the given sample set.

12. The computer program product of claim 7 wherein sampling is done at a higher frequency than the input signal rate/frequency.

13. A computer system comprising:
a processor(s) set;
a machine readable storage device; and
computer code stored on the machine readable storage device, with the computer code including instructions for causing the processor(s) set to perform operations including the following:
receiving a plurality of sample sets, with each sample set including N sequential samples,
for each given sample set of the plurality of sample sets:
estimating a probability p(j) of an output pulse being produced from a Josephson comparator based on the N sequential samples of the given sample set, and
estimating an analog input current I x (j) corresponding to the given sample set based on an inverse function of p(j) for the given sample set using a probability curve Prob(I x ); and

extracting a signal from output of the Josephson comparator based, at least in part upon the analog input current I x (j) values respectively corresponding to the sample sets.

14. The computer system of claim 13 wherein the inverse function is expressed by the following equation: I x (j)=Prob −1 (p(j)).

15. The computer system of claim 13 further comprising:
performing empirical calibration tests to determine the probability curve Prob(I x ).

16. The computer system of claim 13 further comprising:
computing probability curve Prob(I x ) based on: (i) empirical or theoretical properties of the Josephson comparator, and (ii) operating conditions of the Josephson comparator.

17. The computer system of claim 13 wherein, for each given sample set, N is approximately equal to an fclk value for the given sample set divided by an fsig value for the given sample set.

18. The computer system of claim 13 wherein sampling is done at a higher frequency than the input signal rate/frequency.

Assignees

• IBM

Inventors

• Bulzacchelli John F
• Ketchen Mark B
• Lirakis Christopher B
• Lvov Alexey Y
• Polonsky Stanislav
• Ritter Mark B

Classifications

• H03M1/1245 Primary

  Details of sampling arrangements or methods · CPC title

• G11C27/02

  Sample-and-hold arrangements (G11C27/04 takes precedence) · CPC title

• H03M1/1071

  Measuring or testing · CPC title

• H03M1/1009

  Calibration · CPC title

• H03M1/08

  of noise {(H03M1/0617 takes precedence)} · CPC title