Google Inc.

Alexander Nikolaevich Korotkov

Julian Shaw Kelly

Vadim Smelyanskiy

Paul Victor Klimov

Kevin Joseph Satzinger

Rami Barends

Matthew James McEwen

Hartmut Neven

Sergio Boixo Castrillo

Yu Chen

Zhang Jiang

Yuezhen Niu

Charles Neill

Zijun Chen

Kostyantyn Yevgenovych Kechedzhi

Xiao Mi

Kevin Chenghao Miao

Juan Carlos Atalaya-Chavez

Charles James Neill

Methods, systems and apparatus for estimating the fidelity of quantum logic gates. In one aspect, a method includes defining multiple sets of random quantum circuits; for each set of random quantum circuits: selecting an observable for each element in the set of random quantum circuits, wherein each selected observable corresponds to a respective element of the set of random quantum circuits and is dependent on the element to which it corresponds; estimating a value of a polarization parameter for the set of random quantum circuits, comprising performing a least mean squares minimization based on multiple expectation values, wherein each expectation value comprises an expectation value of a respective selected observable with respect to an output of an experimental implementation of a random quantum circuit corresponding to the respective selected observable; and processing the estimated polarization parameter values to obtain an estimate of the fidelity of the n-qubit quantum logic gate.

Estimating the fidelity of quantum logic gates and quantum circuits

Systems and methods for composite quantum gate calibration for a quantum computing system are provided. In some implementations, a method includes accessing a unitary gate model describing a composite quantum gate. The unitary gate model includes a plurality of gate parameters. The method includes implementing the composite quantum gate for a plurality of gate cycles on the quantum system to amplify the plurality of gate parameters. The method includes obtaining a measurement of a state of the quantum system after implementing the composite quantum gate for the plurality of gate cycles. The method includes determining at least one of the plurality of gate parameters based at least in part on the measurement of the state of the quantum system. The method includes calibrating the composite quantum gate for the quantum computing system based at least in part on the plurality of gate parameters.

Composite quantum gate calibration

Systems and methods for measuring quantum states of qubits with more than two levels are provided. A method can include, for a plurality of shuffling sequences, applying, by a quantum computer, one or more quantum gates to the one or more qubits to execute a quantum algorithm; applying, by the quantum computer, a shuffling sequence to the one or more qubits; and measuring, using a readout apparatus, the state of the one or more qubits to determine a readout state. The method can further include determining, by a classical computer or the quantum computer, an average occupation for one or more of the quantum states of the one or more qubits using the readout states for each of the shuffling sequences. The readout states can correspond to a state in a subset of the quantum states of the one or more qubits.

Multi-state qubit readout with permutation sequences

Methods, systems and apparatus for resetting a qubit. In one aspect, an apparatus includes a qubit, wherein the state of the qubit occupies a plurality of levels comprising two computational levels and one or more non-computational levels; a resonator that operates at a resonator frequency; control electronics that control a frequency of the qubit such that during a reset operation the qubit frequency is adjusted from a holding frequency that is lower than the resonator frequency to an idling frequency that is higher than the resonator frequency, and during the adjustment a first derivative of the qubit frequency at a first time is positive, at a second time that occurs after the first time is zero, and at a third time that occurs after the second time is positive, where the qubit frequency achieves the idling frequency at a fourth time that occurs after the third time.

Rapid multi-level qubit reset

A quantum computing system configured for removal of leakage states can include quantum hardware including a first qubit and a second qubit, wherein the first qubit is configured to have a first transition frequency and wherein the second qubit is configured to have a second transition frequency, the first transition frequency being greater than the second transition frequency. The quantum computing system can include one or more quantum control devices configured to control operation of at least the first qubit and the second qubit, wherein the one or more quantum control devices are configured to implement a quantum gate operation on the first qubit and the second qubit based at least in part on the first transition frequency and the second transition frequency, and wherein the one or more quantum control devices are configured to periodically reset a quantum state of the first qubit.

Frequency configuration in quantum gates for leakage removal

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Riverside, CA, United States of America

Alexander Nikolaevich Korotkov