Abstract: In a general aspect, a tunable qubit device is identified that exhibits a frequency-dependent energy relaxation process in a quantum processor cell. The frequency-dependent energy relaxation process is produced by a material defect in the quantum processor cell. A first qubit frequency associated with a first relaxation time of the tunable qubit device is identified and a second qubit frequency associated with a second relaxation time of the tunable qubit device is identified. The second relaxation time is shorter than the first due to the frequency-dependent energy relaxation process produced by the material defect. The tunable qubit device is operated at the first qubit frequency while processing quantum information in the quantum processor cell. The tunable qubit device is tuned from the first qubit frequency to the second qubit frequency. A qubit state of the qubit device is reset by the frequency-dependent energy relaxation process produced by the material defect.

Abstract: In some aspects, a hybrid quantum-classical computing platform may comprise: a first quantum processor unit (QPU); a second QPU; and a shared classical memory, the shared classical memory being connected to both the first QPU and the second QPU, wherein the shared classical memory is configured to share data between the first QPU and the second QPU. In some embodiments, the first QPU operates at a higher repetition rate and/or clock rate than the second QPU and the second QPU operates with a higher fidelity than the first QPU.

Abstract: In a general aspect, a quantum logic gate is performed in a quantum computing system. In some cases, a pair of qubits are defined in a quantum processor; the pair of qubits can include a first qubit defined by a first qubit device in the quantum processor and a second qubit defined by a tunable qubit device in the quantum processor. A quantum logic gate can be applied to the pair of qubits by communicating a control signal to a control line coupled to the tunable qubit device. The control signal can be configured to modulate a transition frequency of the tunable qubit device at a modulation frequency, and the modulation frequency can be determined based on a transition frequency of the first qubit device.

Abstract: In a general aspect, calibration is performed in a quantum computing system. In some cases, domains of a quantum computing system are identified, where the domains include respective domain control subsystems and respective subsets of quantum circuit devices in a quantum processor of the quantum computing system. Sets of measurements are obtained from one of the domains and stored in memory. Device characteristics of the quantum circuit devices of the domain are obtained based on the set of measurements, and the device characteristics are stored in a memory of the control system. Quantum logic control parameters for the subset of quantum circuit devices of the domain are obtained based on the set of measurements and stored in memory.

Abstract: In a general aspect, quantum computing system performance is tested. Systems and methods for testing hardware in a quantum computing system are described. The methods may include certification/decertification of data produced by the quantum computing system, detection of faults, correction of errors and/or recalibration/replacement of the quantum computing system or a quantum computing subsystem.

Abstract: In a general aspect, a quantum logic gate is performed in a quantum computing system. In some cases, a pair of qubits are defined in a quantum processor; the pair of qubits can include a first qubit defined by a first qubit device in the quantum processor and a second qubit defined by a tunable qubit device in the quantum processor. A quantum logic gate can be applied to the pair of qubits by communicating a control signal to a control line coupled to the tunable qubit device. The control signal can be configured to modulate a transition frequency of the tunable qubit device at a modulation frequency, and the modulation frequency can be determined based on a transition frequency of the first qubit device.

Abstract: In a general aspect, calibration is performed in a quantum computing system. In some cases, domains of a quantum computing system are identified, where the domains include respective domain control subsystems and respective subsets of quantum circuit devices in a quantum processor of the quantum computing system. Sets of measurements are obtained from one of the domains and stored in memory. Device characteristics of the quantum circuit devices of the domain are obtained based on the set of measurements, and the device characteristics are stored in a memory of the control system. Quantum logic control parameters for the subset of quantum circuit devices of the domain are obtained based on the set of measurements and stored in memory.

Abstract: In a general aspect, calibration is performed in a quantum computing system. In some cases, domains of a quantum computing system are identified, where the domains include respective domain control subsystems and respective subsets of quantum circuit devices in a quantum processor of the quantum computing system. Sets of measurements are obtained from one of the domains and stored in memory. Device characteristics of the quantum circuit devices of the domain are obtained based on the set of measurements, and the device characteristics are stored in a memory of the control system. Quantum logic control parameters for the subset of quantum circuit devices of the domain are obtained based on the set of measurements and stored in memory.

Abstract: In a general aspect, a quantum logic gate is performed in a quantum computing system. In some cases, a pair of qubits are defined in a quantum processor; the pair of qubits can include a first qubit defined by a first qubit device in the quantum processor and a second qubit defined by a tunable qubit device in the quantum processor. A quantum logic gate can be applied to the pair of qubits by communicating a control signal to a control line coupled to the tunable qubit device. The control signal can be configured to modulate a transition frequency of the tunable qubit device at a modulation frequency, and the modulation frequency can be determined based on a transition frequency of the first qubit device.

Abstract: In a general aspect, calibration is performed in a quantum computing system. In some cases, domains of a quantum computing system are identified, where the domains include respective domain control subsystems and respective subsets of quantum circuit devices in a quantum processor of the quantum computing system. Sets of measurements are obtained from one of the domains and stored in memory. Device characteristics of the quantum circuit devices of the domain are obtained based on the set of measurements, and the device characteristics are stored in a memory of the control system. Quantum logic control parameters for the subset of quantum circuit devices of the domain are obtained based on the set of measurements and stored in memory.

Abstract: In example implementations, an apparatus includes a bus waveguide, a plurality of optical gates coupled to the bus waveguide and an injection coupler. The bus waveguide receives a plurality of constraint signals. Each optical gate outputs an internal state via a local phase shift when at least one of the plurality of constraint signals has a wavelength that matches a respective resonant wavelength. The injection coupler combines the at least one of the plurality of constraint signals with additional constraint signals that are injected. An error is detected in a bit of a message when an overall phase shift has occurred to the at least one of the plurality of constraint signals causing a power level to exceed a power level threshold of an optical gate when the at least one of the plurality of constraint signals constructively interferes with the additional constraint signals that are injected.

Abstract: In a general aspect, a quantum logic gate is performed in a quantum computing system. In some cases, a pair of qubits are defined in a quantum processor; the pair of qubits can include a first qubit defined by a first qubit device in the quantum processor and a second qubit defined by a tunable qubit device in the quantum processor. A quantum logic gate can be applied to the pair of qubits by communicating a control signal to a control line coupled to the tunable qubit device. The control signal can be configured to modulate a transition frequency of the tunable qubit device at a modulation frequency, and the modulation frequency can be determined based on a transition frequency of the first qubit device.

Abstract: In example implementations, an apparatus includes a bus waveguide, a plurality of optical gates coupled to the bus waveguide and an injection coupler. The bus waveguide receives a plurality of constraint signals. Each optical gate outputs an internal state via a local phase shift when at least one of the plurality of constraint signals has a wavelength that matches a respective resonant wavelength. The injection coupler combines the at least one of the plurality of constraint signals with additional constraint signals that are injected. An error is detected in a bit of a message when an overall phase shift has occurred to the at least one of the plurality of constraint signals causing a power level to exceed a power level threshold of an optical gate when the at least one of the plurality of constraint signals constructively interferes with the additional constraint signals that are injected.

Abstract: In a general aspect, calibration is performed in a quantum computing system. In some cases, domains of a quantum computing system are identified, where the domains include respective domain control subsystems and respective subsets of quantum circuit devices in a quantum processor of the quantum computing system. Sets of measurements are obtained from one of the domains and stored in memory. Device characteristics of the quantum circuit devices of the domain are obtained based on the set of measurements, and the device characteristics are stored in a memory of the control system. Quantum logic control parameters for the subset of quantum circuit devices of the domain are obtained based on the set of measurements and stored in memory.

Abstract: In a general aspect, a quantum computing method is described. In some aspects, a control system in a quantum computing system assigns subsets of qubit devices in a quantum processor to respective cores. The control system identifies boundary qubit devices residing between the cores in the quantum processor and generates control sequences for each respective core. A signal delivery system in communication with the control system and the quantum processor receives control signals to execute the control sequences, and the control signals are applied to the respective cores in the quantum processor.