Abstract: In a general aspect, input data for a computer process are preprocessed by a preprocessor unit that includes a quantum processor. In some aspects, a preprocessor unit obtains input data for a computer process that is configured to run on a computer processing unit. Randomized parameter values are computed for variable parameters of a quantum logic circuit based on the input data. A classical processor in the preprocessor unit computes the randomized parameter values from the input data and a set of random numbers. A quantum processor in the preprocessor unit produces quantum processor output data by executing the quantum logic circuit having the randomized parameter values assigned to the variable parameters. Preprocessed data generated based on the quantum processor output data are then provided as the input for the computer process configured to run on the computer processing unit.

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.

Abstract: In a general aspect, a surface code syndrome measurement is performed on a superconducting quantum processing unit. In some implementations, the superconducting quantum processing unit is caused to apply a quantum error correction code including X-type and Z-type stabilizer check patches. Each of the X-type and Z-type stabilizer check patches includes a stabilizer check qubit device and data qubit devices of the superconducting quantum processing unit. Applying the quantum error correction code includes iteratively twirling the data qubit devices in a stabilizer check patch; and evolving the stabilizer check qubit device in the stabilizer check patch and the data qubit devices in the stabilizer check patch under an interaction Hamiltonian. The interaction Hamiltonian includes a plurality of terms interactions between the stabilizer check qubit device in the stabilizer check patch and a respective one of the data qubit devices in the stabilizer check patch.

Abstract: In some aspects, a heterogeneous computing system includes a quantum processor unit and a classical processor unit. In some instances, variables defined by a computer program are stored in a classical memory in the heterogeneous computing system. The computer program is executed in the heterogeneous computing system by operation of the quantum processor unit and the classical processor unit. Instructions are generated for the quantum processor by a host processor unit based on values of the variables stored in the classical memory. The instructions are configured to cause the quantum processor unit to perform a data processing task defined by the computer program. The values of the variables are updated in the classical memory based on output values generated by the quantum processor unit. The classical processor unit processes the updated values of the variables.

Abstract: In a general aspect, parametric amplification is performed in a quantum computing system. In some cases, a traveling wave parametric amplifier (TWPA) includes a plurality of Josephson junctions connected in series. The plurality of Josephson junctions includes a first Josephson junction, which includes a first superconducting electrode on a surface of a substrate, a second superconducting electrode that overlaps the first superconducting electrode, and a barrier sandwiched between overlapping sections of the first and second superconducting electrodes. The barrier defines a footprint with a tapered shape over the surface of the substrate.

Abstract: In a general aspect, a machine learning process is performed using data-parallel quantum processing. In some cases, a machine learning model is operated in a hybrid computing system. The hybrid computing system includes a quantum computing resource and a classical computing resource. The quantum computing resource includes quantum processing unit (QPU) sublattices, each including a subset of qubit devices.

Abstract: In a general aspect, a gate is formed for a quantum processor. In some implementations, an arbitrary program is received. The arbitrary program includes a first sequence of quantum logic gates, which includes a parametric XY gate. A native gate set is identified, which includes a set of quantum logic gates associated with a quantum processing unit. A second sequence of quantum logic gates corresponding to the parametric XY gate is identified, which includes a parametric quantum logic gate. Each of the quantum logic gates in the second sequence is selected from the native gate set. A native program is generated. The native program includes a third sequence of quantum logic gates. The third sequence of quantum logic gates corresponds to the first sequence of quantum logic gates and includes the second sequence of quantum logic gates. The native program is provided for execution by the quantum processing unit.

Abstract: In a general aspect, a quantum process for execution by a quantum processor is generated. In some instances, test data representing a test output of a quantum process are obtained. The test data are obtained based on a value assigned to a variable parameter of the quantum process. An objective function is evaluated based on the test data, and an updated value is assigned to the variable parameter based on the evaluation of the objective function. The quantum process is provided for execution by a quantum processor, and the quantum process provided for execution has the updated value assigned to the variable parameter.

Abstract: In a general aspect, information is encoded in data qubits in a three-dimensional device lattice. The data qubits reside in multiple layers of the three-dimensional device lattice, and each layer includes a respective two-dimensional device lattice. A three-dimensional color code is applied in the three-dimensional device lattice to detect errors in the data qubits residing in the multiple layers. A two-dimensional color code is applied in the two-dimensional device lattice in each respective layer to detect errors in one or more of the data qubits residing in the respective layer.

Abstract: In a general aspect, a method executed in a quantum computing system includes performing a calibration process in the quantum computing system to identify a value of a parameter of the quantum computing system. The method also includes analyzing a variation of the value in response to a change in a condition of the quantum computing system, thereby determining a stability of the parameter. The method additionally includes scheduling a recalibration of the parameter based on the stability of the parameter and executing a quantum algorithm in the quantum computing system based on the value of the parameter identified by the calibration process.

Abstract: In a general aspect, user requests for access distributed quantum computing resources in a distributed quantum computing system are managed. In a general aspect, a job request for accessing a quantum computing resource is received. The job request includes a user id and a program. On authentication of a user associated with the job request, a job identifier is assigned to the job request, and a particular quantum computing resource is selected for the job request. The job request is individualized based on user permissions and pushed onto a queue to be processed for execution by the quantum computing resource.

Abstract: In a general aspect, two-qubit quantum gate operations are performed in a superconducting quantum processing unit. In some cases, a flux modulation signal is generated. The flux modulation signal is configured to modulate a transition frequency of a first tunable-frequency qubit device in a superconducting quantum processing unit such that a time average of the transition frequency of the first tunable-frequency qubit device over a duration of the flux modulation signal is on resonance with a transition frequency of a second qubit device in the superconducting quantum processing unit. A two-qubit quantum logic gate is applied to a pair of qubits defined by the first tunable-frequency qubit device and the second qubit device. Applying the two-qubit quantum logic gate includes communicating the flux modulation signal to a flux bias control line coupled to the first tunable-frequency 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: Interactions between a classical computing system and a quantum computing system can be structured to increase the effective memory available to hold instructions for a quantum processor. The system stores a schedule of compiled quantum processing instructions in a memory storage location on a classical computing system. A small program memory is included in close proximity to a control system for the quantum processor on the quantum computing system. The classical computing system sends a subset of instructions from the schedule of quantum instructions to the program memory. The control system manages execution of the instructions by accessing them at the program memory and configuring the quantum processor accordingly. While the quantum processor executes the instructions, additional instructions are transferred from the classical computing system to the program memory to await execution.

Abstract: In a general aspect, a quantum streaming kernel processes a data stream. In some aspects, an input stream of data is converted to an output stream of data by repeatedly receiving new portions of the input stream; encoding each new portion into an internal quantum state of a quantum processor; measuring a first part of the internal quantum state while maintaining coherence of a second part of the internal quantum state; and producing the output stream of data based on the measurements. In some cases, a history of the input stream is preserved by the coherence of the internal quantum state, and the measurements contain information based on the history of the input stream.

Abstract: In a general aspect, an integrated quantum circuit includes a first substrate and a second substrate. The first substrate includes a first surface and a recess formed in the first substrate along the first surface. The recess has a recess surface and is configured to enclose a quantum circuit element. The first substrate includes a first electrically-conductive layer disposed on the first surface and covering at least a portion of the recess surface. The first electrically-conductive layer includes a first superconducting material. The second substrate includes a second surface and a quantum circuit element. The second substrate includes a second electrically-conductive layer on the second surface that includes a second superconducting material. The first substrate is adjacent the second substrate to enclose the quantum circuit device within the recess. The first electrically-conductive layer of the first substrate is electrically-coupled to the second electrically-coupled layer of the second substrate.

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, user requests for access distributed quantum computing resources in a distributed quantum computing system are managed. In a general aspect, a job request for accessing a quantum computing resource is received. The job request includes a user id and a program. On authentication of a user associated with the job request, a job identifier is assigned to the job request, and a particular quantum computing resource is selected for the job request. The job request is individualized based on user permissions and pushed onto a queue to be processed for execution by the quantum computing resource.

Abstract: In a general aspect, a quantum streaming kernel processes a data stream. In some aspects, an input stream of data is converted to an output stream of data by repeatedly receiving new portions of the input stream; encoding each new portion into an internal quantum state of a quantum processor; measuring a first part of the internal quantum state while maintaining coherence of a second part of the internal quantum state; and producing the output stream of data based on the measurements. In some cases, a history of the input stream is preserved by the coherence of the internal quantum state, and the measurements contain information based on the history of the input stream.

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.