Error reduction and, or, correction in analog computing including quantum processor-based computing
The systems, devices, articles, and methods described herein generally relate to analog computers, for example quantum processors comprising qubits, couplers, and, or cavities. Analog computers, for example quantum processor based computers, are the subject of various sources of error which can hinder operation, potentially reducing computational accuracy and speed. Sources of error can be broadly characterized, for example as i) a background susceptibility do to inherently characteristics of the circuitry design, ii) as an h/J ratio imbalance, iii) bit flip errors, iv) fidelity, and v) Anderson localization, and various combinations of the aforesaid.
1. A method of operation in a computational annealing device that comprises both a quantum processor and at least one processor-based device communicatively coupled to one another, the quantum processor comprising a plurality of qubits and a plurality of coupling devices, wherein each coupling device is operable to provide controllable communicative coupling between two of the plurality of qubits, the method comprising:
identifying a problem type of a first submitted problem;
determining whether the identified problem type of the first submitted problem is a problem type that is relatively sensitive to background susceptibility error χ or is a problem type that is relatively insensitive to background susceptibility error χ; and
in response to a determination that the problem type of the first submitted problem is one that is relatively sensitive to background susceptibility error χ, employing existing hardware of the quantum processor to compensate for background susceptibility error χ when generating solutions to the first submitted problem via the quantum processor;
wherein:
employing the existing hardware of the quantum processor to compensate for background susceptibility error χ when generating solutions to the first submitted problem via the quantum processor includes employing a number of the qubits of the quantum processor as ancilla qubits to compensate for background susceptibility error χ when generating solutions to the first submitted problem via the quantum processor; and
employing a number of the qubits of the quantum processor as ancilla qubits to compensate for background susceptibility error χ when generating solutions to the first submitted problem via the quantum processor includes embedding a problem graph of the first submitted problem in a hardware graph of the quantum processor along with setting one or more values of one or more ancilla qubits to compensate for the background susceptibility error χ without contributing to solutions to the first submitted problem.
2. The method of claim 1 wherein setting one or more values of one or more ancilla qubits to compensate for the background susceptibility error χ without contributing to solutions to the first submitted problem includes setting a bias H of one or more ancilla qubits to zero.
3. The method of claim 1 , wherein employing the existing hardware of the quantum processor to compensate for background susceptibility error χ when generating solutions to the first submitted problem via the quantum processor includes determining which pairs of a plurality of problem qubits need to be coupled by a respective ancilla qubit; and recasting a problem graph of the first submitted problem for embedding the first submitted problem in a hardware graph of the quantum processor based at least in part on the determination of which pairs of a plurality of problem qubits need to be coupled by a respective ancilla qubit.
4. The method of claim 1 wherein determining whether the identified problem type of the first submitted problem is a problem type that is relatively sensitive to background susceptibility error χ or is a problem type that is relatively insensitive to background susceptibility error χ includes determining whether the first submitted problem is an optimization problem and hence is relatively sensitive to background susceptibility error χ.
5. The method of claim 1 wherein determining whether the identified problem type of the first submitted problem is a problem type that is relatively sensitive to background susceptibility error χ or is a problem type that is relatively insensitive to background susceptibility error χ includes determining whether the first submitted problem is a machine learning problem and hence is relatively insensitive to background susceptibility error χ.
6. The method of claim 1 wherein determining whether the identified problem type of the first submitted problem is a problem type that is relatively sensitive to background susceptibility error χ or is a problem type that is relatively insensitive to background susceptibility error χ includes querying at least one of a data schema or a piece of metadata, logically associated with the first submitted problem via one or more stored relationships.
7. The method of claim 1 wherein determining whether the identified problem type of the first submitted problem is a problem type that is relatively sensitive to background susceptibility error χ or is a problem type that is relatively insensitive to background susceptibility error χ includes analyzing the first submitted problem to determine a broad class of problems to which the first submitted problem belongs.
8. The method of claim 1 , the method further comprising:
identifying a problem type of a second submitted problem;
determining whether the identified problem type of the second submitted problem is a problem type that is relatively sensitive to background susceptibility error χ or is a problem type that is relatively insensitive to background susceptibility error χ; and
in response to a determination that the problem type of the second submitted problem is a problem type that is relatively insensitive to background susceptibility error χ, employing the existing hardware of the quantum processor to embed a problem graph of the second submitted problem without using the existing hardware to compensate for background susceptibility error χ when generating solutions to the second submitted problem via the quantum processor,
wherein employing the existing hardware of the quantum processor to embed the problem graph of the second submitted problem without using the existing hardware to compensate for background susceptibility error χ when generating solutions to the second submitted problem via the quantum processor includes embedding the problem graph of the second submitted in the hardware graph of the quantum processor without any ancilla qubits to compensate for background susceptibility error χ.
9. The method of claim 1 , the method further comprising:
identifying a problem type of a second submitted problem;
determining whether the identified problem type of the second submitted problem is a problem type that is relatively sensitive to background susceptibility error χ or is a problem type that is relatively insensitive to background susceptibility error χ; and
in response to a determination that the problem type of the second submitted problem is a problem type that is relatively insensitive to background susceptibility error χ, employing the existing hardware of the quantum processor to embed a problem graph of the second submitted problem without using the existing hardware to compensate for background susceptibility error χ when generating solutions to the second submitted problem via the quantum processor,
wherein employing the existing hardware of the quantum processor to embed the problem graph of the second submitted problem without using the existing hardware to compensate for background susceptibility error χ when generating solutions to the second submitted problem via the quantum processor includes embedding the problem graph of the second submitted in the hardware graph of the quantum processor employing one or more of the qubits of the quantum processor that were used as ancilla qubits when generating solutions for the first submitted problem as problem qubits when generating solutions for the second submitted problem.
10. A method of operation in a computational annealing device that comprises both a quantum processor and at least one processor-based device communicatively coupled to one another, the quantum processor comprising a plurality of qubits and a plurality of coupling devices, wherein each coupling device is operable to provide controllable communicative coupling between two of the plurality of qubits, the method comprising:
identifying a problem type of a first submitted problem;
determining whether the identified problem type of the first submitted problem is a problem type that is relatively sensitive to background susceptibility error χ or is a problem type that is relatively insensitive to background susceptibility error χ;
in response to a determination that the problem type of the first submitted problem is one that is relatively sensitive to background susceptibility error χ, employing existing hardware of the quantum processor to compensate for background susceptibility error χ when generating solutions to the first submitted problem via the quantum processor; and
in response to a determination that the problem type is one that is relatively insensitive to background susceptibility error χ, employing the existing hardware to embed a problem graph of the first submitted problem in a hardware graph of the quantum processor without using the existing hardware of the quantum processor to compensate for background susceptibility error χ.
11. The method of claim 10 wherein employing the existing hardware to embed a problem graph of the first submitted problem in a hardware graph of the quantum processor without using the existing hardware of the quantum processor to compensate for background susceptibility error χ includes embedding the problem graph of the first submitted problem in the hardware graph of the quantum processor without any ancilla qubits to compensate for background susceptibility error χ.
12. A quantum computing system comprising:
a first qubit communicatively coupled to a second qubit via a first coupler set to a first coupling strength;
a third qubit communicatively coupled to the second qubit via a second coupler set to a second coupling strength;
a fourth qubit communicatively coupled to the third qubit via a third coupler set to a third coupling strength, the fourth qubit further communicatively coupled to the first qubit via a fourth coupler set to a fourth coupling strength, wherein the fourth coupling strength is proportional to a group comprising: a background susceptibility, the first coupling strength, and the second coupling strength;
a first bias applied to the first qubit;
a second bias applied to the second qubit;
a third bias applied to the third qubit; and
a fourth bias applied to the fourth qubit, wherein the fourth bias is equal to zero.
13. The quantum computing system of claim 12 wherein the first qubit is indirectly communicatively coupled to the third qubit with a fifth coupling strength proportional to the group comprising: the background susceptibility, the first coupling strength, and the second coupling strength.
14. The quantum computing system of claim 13 wherein the third coupling strength at least partially compensates the fifth coupling strength.
15. The quantum computing system of claim 14 wherein the fourth coupling strength at least partially compensates the fifth coupling strength.
16. The quantum computing system of claim 12 wherein the third coupling strength is at least as strong as at least one of: the first coupling strength, the second coupling strength, and the fourth coupling strength.
17. The quantum computing system of claim 12 wherein the first qubit, the second qubit, the third qubit, and the fourth qubit each correspond to a set of bipartite graph vertices.
18. The quantum computing system of claim 17 wherein the first qubit and the third qubit correspond to a first subset of bipartite graph vertices, and the second qubit and the fourth qubit correspond to a second subset of bipartite graph vertices.
19. The quantum computing system of claim 12 wherein the first qubit is directly communicatively coupled to the second qubit.
20. The quantum computing system of claim 12 wherein the third qubit is directly communicatively coupled to the second qubit.