Analog processor comprising quantum devices
View Patent ↗Analog processors for solving various computational problems are provided. Such analog processors comprise a plurality of quantum devices, arranged in a lattice, together with a plurality of coupling devices. The analog processors further comprise bias control systems each configured to apply a local effective bias on a corresponding quantum device. A set of coupling devices in the plurality of coupling devices is configured to couple nearest-neighbor quantum devices in the lattice. Another set of coupling devices is configured to couple next-nearest neighbor quantum devices. The analog processors further comprise a plurality of coupling control systems each configured to tune the coupling value of a corresponding coupling device in the plurality of coupling devices to a coupling. Such quantum processors further comprise a set of readout devices each configured to measure the information from a corresponding quantum device in the plurality of quantum devices.
1. A method of determining a result of a computational problem using a quantum processor, wherein the quantum processor comprises:
a plurality of quantum devices,
a plurality of coupling devices wherein each coupling device in the plurality of coupling devices is operable to tunably couple a respective pair of quantum devices in the plurality of quantum devices,
a coupling device control system comprising a respective coupling controller for each coupling device wherein each respective coupling controller in the coupling device control system is operable to tune a coupling strength of a corresponding coupling device;
a quantum device control system comprising a respective node controller for each quantum device wherein each respective node controller in the quantum device control system is operable to control an effective bias applied to a corresponding quantum device; and
at least one readout device operable to readout a state of at least one quantum device in the plurality of quantum devices;
the method comprising:
setting a state of at least one quantum device in the plurality of quantum devices via the quantum device control system and setting a coupling strength of at least one of the coupling devices in the plurality of coupling devices via the coupling device control system to initialize the quantum processor to an initial state;
allowing the quantum processor to evolve to a final state, wherein allowing the quantum processor to evolve to a final state comprises at least one of decreasing an effective temperature of the quantum processor and evolving the quantum processor adiabatically; and
reading out a final state of at least one quantum device in the plurality of quantum devices via the at least one readout device to determine the result of the computational problem.
2. The method of claim 1 wherein at least one quantum device in the plurality of quantum devices comprises a loop of superconducting material interrupted by at least one Josephson junction.
3. The method of claim 2 , further comprising tuning an effective critical current of the at least one Josephson junction interrupting the superconducting loop.
4. The method of claim 1 wherein at least one quantum device in the plurality of quantum devices comprises an rf-SQUID.
5. The method of claim 1 wherein the computational problem is selected from the group consisting of a problem having a complexity of P, a problem having a complexity of NP, a problem having a complexity of NP-Hard and a problem having a complexity of NP-Complete.
6. The method of claim 5 wherein the computational problem is a maximum independent set problem.
7. The method of claim 1 wherein setting a state of at least one quantum device in the plurality of quantum devices comprises:
setting a zero effective local field bias at a first quantum device via the quantum device control system, and wherein setting a coupling strength of at least one of the coupling devices in the plurality of coupling devices comprises setting a coupling strength of a first coupling device to ferromagnetically couple the first quantum device to a second quantum device in the plurality of quantum devices via the coupling device control system.
8. The method of claim 1 wherein setting a state of at least one quantum device in the plurality of quantum devices comprises setting a local field bias at the at least one quantum device via the quantum device control system.
9. The method of claim 1 wherein setting a state of at least one quantum device in the plurality of quantum devices comprises setting a global field bias across the plurality of quantum devices via the quantum device control system and waiting for a certain period of time.
10. The method of claim 1 wherein setting a state of at least one quantum device in the plurality of quantum devices comprises applying a current to a superconducting coil in close proximity to the at least one quantum device via the quantum device control system to generate a local magnetic field bias in the at least one quantum device.
11. The method of claim 1 wherein allowing the quantum processor to evolve to a final state comprises increasing a temperature of the quantum processor from a base temperature and then decreasing the temperature of the quantum processor to the base temperature.
12. The method of claim 11 wherein allowing the quantum processor to evolve to a final state comprises increasing a temperature of the quantum processor from a base temperature to a temperature between 30 mK-3K and then decreasing the temperature of the quantum processor to the base temperature.
13. The method of claim 1 wherein allowing the quantum processor to evolve to a final state includes allowing the quantum processor to evolve to a final state that at least approximates a ground state of the computational problem.
14. A computational system comprising:
a digital computer; and
a quantum processor in communication with the digital computer, wherein the quantum processor comprises:
a plurality of quantum devices;
a plurality of coupling devices wherein each coupling device in the plurality of coupling devices is operable to tunably couple a respective pair of quantum devices in the plurality of quantum devices;
a coupling device control system comprising a respective coupling controller for each coupling device wherein each respective coupling controller in the coupling device control system is operable to tune a coupling strength of a corresponding coupling device;
a quantum device control system comprising a respective node controller for each quantum device wherein each respective node controller in the quantum device control system is operable to control an effective bias applied to a corresponding quantum device; and
at least one readout device that is operable to readout a state of at least one quantum device in the plurality of quantum devices.
15. The computational system of claim 14 wherein the digital computer comprises a quantum processor interface module comprising:
an initialization module that initializes the quantum processor to an initial state, wherein the initialization module determines appropriate values of bias for the quantum devices and values of coupling for the coupling devices, and sends appropriate signals to the quantum device control system and the coupling device control system;
an evolution module that allows the quantum processor to evolve to a final state, wherein the evolution module determines appropriate values of bias for the quantum devices and values of coupling for the coupling devices, and sends appropriate signals to the quantum device control system and the coupling device control system; and
an output module to readout a final state of at least one quantum device in the plurality of quantum devices, wherein the output module operates in conjunction with the at least one readout device of the quantum processor to read a result of the computational problem.