EP-4736074-A1 - BOSON SAMPLER PARAMETER CONFIGURATION

Abstract

Methods, systems, and computer-readable media are provided for configuring a boson sampler. The method includes operating the boson sampler to produce a batch of samples. The method further includes determining, from the batch of samples, an estimate of a partial derivative of an objective function. The method further includes configuring the parameter of the boson sampler based on the determined estimate. Determining the estimate includes: determining from the batch of samples, for each observable of a set of observables, a corresponding first value representative of a partial derivative of the objective function with respect to the expectation value of the observable; determining, for each observable of the set of observables, a corresponding second value representative of a partial derivative of the expectation value of the observable with respect to a parame ter value of the configurable parameter; and determining the estimate from the first values and the second values.

Inventors

• MARTIN, ALEX
• WALLNER, Hugo
• CLEMENTS, WILLIAM

Assignees

• ORCA COMPUTING LIMITED

Dates

Publication Date

20260506

Application Date

20240624

Claims (20)

1. 1. A method for configuring a boson sampler, the method comprising: operating the boson sampler to produce a batch of samples; determining, from the batch of samples, an estimate of a partial derivative of an objective function with respect to a parameter value of a configurable parameter of the boson sampler; wherein determining the estimate comprises: determining from the batch of samples, for each observable of a set of observables, a corresponding first value representative of a partial derivative of the objective function with respect to an expectation value of the observable; determining, for each observable of the set of observables, a corresponding second value representative of a partial derivative of the expectation value of the observable with respect to the parameter value of the configurable parameter; and determining the estimate from the first values and the second values ; and configuring the configurable parameter of the boson sampler based onthe determined estimate.
2. 2. The method of claim 1 , wherein an observable of the set of observables comprises a number of photons in an output mode of the boson sampler.
3. 3. The method of claim 2, wherein every observable of the set of observables comprises a number of photons in a corresponding output mode of the boson sampler.
4. 4. The method of claim 1, wherein an observable of the set of observables comprises a product of a number of photons in a first output mode of the bo son samplerand a number of photons in a second output mode of the boson sampler.
5. 5. The method of claim 4, wherein eve ly observable of the set of observables comprises either a number of photons in an output mode of the boson sampleror a product of a number of photons in a first output mode and a second output mode of the boson sampler.
6. 6. The method of claim 1, wherein, for at least one observable of the set of observables, determining the corresponding first value comprises: determining, from the batch of samples, the expectation value of the observable; separating the batch of samples into two groups; determining, for each group, an average value for the objective function; determining a difference between the average values of the two groups; and determining, fromthe difference and the expectation value of the observable, the corresponding first value.
7. 7. The method of claim 6, further comprising: li- determining, from the batch of samples, a median value for the objective function; wherein a first group of the two groups comprises samples thatproduce an objective function value that is greater than the median value; and wherein a second group of the two groups comprises samples thatproduce an objectivefunction value that is less than the median value.
8. 8. The method of claim 1, wherein, for at least one observable of the set of observables, determining the corresponding first value comprises: generating, from the batch of samples, an affine fitofthe objective function with respectto the observables.
9. 9. The method of claim 1 , wherein, for at least one observable of the set of observables, determining the corresponding first value comprises: generating, from the batch of samples, a non-linear fit of the objective function with respectto the observables.
10. 10. The method of claim 1, wherein, for at least one observable of the set of observables, determining the corresponding second value comprises determining the corresponding second value from an analytic function of a relationship between the expectation value of the observable and the configurable parameter.
11. 11. The method of claim 1, wherein, for at least one observable of the set of observables, determining the corresponding second value comprises determining the corresponding secondvalue from the batch of samples.
12. 12. The method of claim 1, wherein the configurable parameter comprises an effective transmission coefficient of a reconfigurable beamsplitter of the boson sampler.
13. 13. The methodof claim 1 , whereinthe configurable parameter comprises a phase imparted by a phase shifter of the boson sampler.
14. 14. The method of claim 1, further comprising: determining, fromthe batchof samples, a secondestimate of apartial derivative of the objective function with respect to a second parameter value of a second configurable parameter of the boson sampler; and configuring the second configurable parameterof the boson sampler based on the determined second estimate.
15. 15. A non-transitory computer-readable medium comprising stored instmctions that, when executed by a computing device, cause the computing device to perform operations including: operating a boson sampler to produce a batch of samples; determining, from the batch of samples, an estimate of a partial derivative of an objective function with respect to a parameter value of a configurable parameter of the boson sampler; and configuring the configurable parameter of the bo son sampler based on the determined estimate; wherein determining the estimate comprises: determining from the batch of samples, for each observable of a set of observables, a corresponding first value representative of a partial derivative of the objective function with respect to an expectation value of the observable; determining, for each observable of the set of observables, a corresponding second value representative of a partial derivative of the expectation value of the observable with respect to a parameter value of the configurable parameter; and determining the estimate from the first values and the second values.
16. 16. A system comprising: a boson sampler; and control logic configured to: operate the boson sampler to produce a batch of samples; determine, fromthe batchof samples, an estimate of apartial derivative of an objective function with respect to a parameter value of a configurable parameter of the boson sampler, and configure the configurable parameter of the boson sampler based on the determined estimate; wherein determining the estimate comprises: determining from the batch of samples, for each observable of a set of observables, a corresponding first value representative of a partial derivative of the objective function with respect to an expectation value of the observable; determining, for each observable of the set of observables, a corresponding second value representative of a partial derivative of the expectation value of the observable with respect to a parameter value of the configurable parameter; and determining the estimate from the first values and the second values.
17. 17. The system of claim 16, wherein the boson sampler comprises a light source, an interferometer, and one or more photodetectors.
18. 18. The system of claim 16, wherein the boson sampler is a single -photon boson sampler.
19. 19. The system of claim 16, wherein the boson sampler is a Gaussian boson sampler.
20. 20. The systemof claim 16, furthercomprisingprocessingcircuitry coupledto the boson sampler and the control logic and configured to provide an artificial neural network (ANN).

Description

Boson Sampler Parameter Configuration Technical Field [0001] The present disclosure relates to hybrid quantum-classical systems that include a boson sampler, and associated methods for use with such systems. Background [0002] A boson sampler is a non-universal quantum computer that relies on the interference of photons to generate its output. More particularly, a boson sampler comprises a network of optical components or elements (an interferometer) in which photons interfere with one another. As photons are quantum objects, the output of this network is described by a quantum superposition of all the possible outcomes. When a measurement is performed at the output of this network using one or more photodetectors, a single measurement outcome is realised from this superposition. For example, if photon number resolving (PNR) detectors are used, then each sample or measurement outcome may be describedby an array or string or sequence of integers indicating how many photons were found in each output mode of the output state; if threshold detectors are used, then each measurement outcome may be described by an array or string or sequence of integers, for example a binary sequence, indicatingwhetherphotonswerepresentorabsentineachoutput mode of theoutput state. By repeatedly samp ling measurement outcomes, one canbuild up a picture of the probability distribution governingthe quantum superposition. [0003] The photonic superposition states output from an interferometer of a boson sampler can be highly entangled. Accordingly, the output probability distributions generated by a boson sampler may have a complex structure and simulating this sampling task is understood to be intractable classically. Modern supercomputers fail to simulate boson sampler distributions generated from more than a few tens of modes. Summary [0004] According to an aspect of the present disclosure, a method for configuring a boson sampler is provided. The method comprisesoperatingthebosonsamplerto produce abatchof samples. The methodfurthercomprises determining, from thebatchof samples, an estimate of a partial derivative of an objective function with respect to a parameter value of a configurable parameter of the boson sampler. Determining the estimate comprises determining from the batch of samples, for each observable of a set of observables, a corresponding first value representative of a partial derivative of the objective function with respect to the expectation value of the observable. Determiningthe estimate further comprises determining, for each observable of the set of observables, a corresponding second value representative of a partial derivative of the expectation value of the observable with respect to a parameter value of the configurable parameter. Determining the estimate further comprises determiningthe estimate from the first values and the second values. The method further comprises configuring the parameter of the boson sampler based on the determined estimate . [0005] Advantageously, the methodsdescribedhereinenable parameters ofabosonsamplerto be updated based on a single batch of samples produced by the boson sampler. This means that some computational tasks, particularly those involving the determination of gradients such as gradient descent, canbe performedfar more efficiently than other known methods, scalingwell with the numberof parameters ofthebosonsamplerwhile still remaining considerably accurate compared to e.g. finite difference methods. Conventional methods typically require multiple, often overlapping, distributions to be sampled in order to determine a single gradient or update a single parameter, whichcanbe slow and inaccurate (due to the difficulty in distinguishing between the multiple distributions unless extremely large numbers of samples are collected). [0006] The method may further comprise determining, from the batch of samples, a second estimate of a partial derivative of the objective function with respect to a second parameter value of a second configurable parameter of the boson sampler. The method may further comprise configuring the parameter of the boson sampler based on the determined second estimate. [0007] An observable of the set of observables may comprise a number of photons in an output mode of the boson sampler. In some examples, eveiy observable of the set of observables may comprise a number of photons in a corresponding output mode of the boson sampler. [0008] An observable of the set of observables may comprise a product of a number of photons in a first output mode of the boson sampler and a number of photons in a second output mode of the boson sampler. In some examples, every observable of the set of ob servables may comprise either a number of photons in an output mode of the boson sampler or comprise a productof a number of pho to ns in a first output mode and a second output mode of the boson sampler. [0009] An observable of the set of observablesmay comprise a parity (