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Patent US10469087
Issued 2019-11-05
Bayesian Tuning For Quantum Logic Gates
A method for tuning a quantum gate of a quantum computer comprises interrogating one or more qubits of the quantum computer using stored control-parameter values and yielding new data. The method further comprises computing an objective function quantifying operational quality of the quantum gate at the stored control-parameter values, such computing employing the new data in addition to a prior distribution over features used to compute the objective function. Here, the prior distribution may be obtained by previous adaptive or non-adaptive interrogation of the one or more qubits, for instance. The method further comprises updating the stored control-parameter values, expanding the prior distribution to incorporate uncertainty in the objective function at the updated control-parameter values, re-interrogating the one or more qubits using the updated control-parameter values, and re-computing the objective function using the expanded prior distribution.
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- 1. A method for tuning a quantum gate of a quantum computer, the method comprising:
interrogating one or more qubits of the quantum computer using stored control-parameter values and yielding new data; computing an objective function quantifying fidelity of the quantum gate at the stored control-parameter values, such computing employing the new data in addition to a prior distribution over features used to compute the objective function, wherein the prior distribution is obtained by previous adaptive or non-adaptive interrogation of the one or more qubits; updating the stored control-parameter values; expanding the prior distribution to incorporate uncertainty in the objective function at the updated control-parameter values; re-interrogating the one or more qubits using the updated control-parameter values; re-computing the objective function using the expanded prior distribution; and accepting and subsequently using the stored control-parameter values for the quantum gate if the fidelity quantified by the objective function exceeds a threshold fidelity, wherein the threshold fidelity is determined based on an estimate of a posterior uncertainty in the fidelity as quantified by the objective function.
- 8. A method for tuning one or more quantum gates of a quantum computer, the method comprising:
manipulating one or more qubits of the quantum computer to effect a Clifford-gate sequence on the one or more qubits using stored control-parameter values; manipulating the one or more qubits to reverse the Clifford-gate sequence on the one or more qubits using the stored control-parameter values; interrogating the one or more qubits to measure a quantum state of the one or more qubits, yielding new data; computing an objective function quantifying fidelity of the reversed Clifford-gate sequence at the stored control-parameter values, such computing employing the new data in addition to a prior distribution obtained by prior interrogation of the one or more qubits using prior control-parameter values; updating the stored control-parameter values; expanding the prior distribution to incorporate uncertainty in the objective function at the updated control-parameter values; repeating said manipulating, interrogating, and computing the objective function employing the expanded prior distribution and the updated control-parameter values; and accepting and subsequently using the stored control-parameter values for the Clifford-gate sequence if the fidelity quantified by the objective function exceeds a threshold fidelity, wherein the threshold fidelity is determined based on an estimate of a posterior uncertainty in the fidelity as quantified by the objective function.
- 16. A quantum computer comprising:
a register including a plurality of qubits; a modulator configured to implement a quantum-logic operation on the plurality of qubits according to stored control-parameter values; a demodulator configured to reveal data reflecting a quantum state of the plurality of qubits; a controller operatively coupled to the modulator and to the demodulator; and associated with the controller, computer memory holding the stored control-parameter values and holding instructions that cause the controller to:
interrogate the plurality of qubits using stored control-parameter values and yielding new data,
compute an objective function quantifying fidelity of the quantum-logic operation at the stored control-parameter values, such computing employing the new data in addition to a prior distribution over features used to compute the objective function,
update the stored control-parameter values,
expand the prior distribution to incorporate uncertainty in the objective function at the updated control-parameter values,
re-interrogate the plurality of qubits using the updated control-parameter values,
re-compute the objective function using the expanded prior distribution; and
accent and subsequently use the stored control-parameter values for the quantum-logic operation if the fidelity quantified by the objective function exceeds a threshold fidelity, wherein the threshold fidelity is determined based on an estimate of a posterior uncertainty in the fidelity as quantified by the objective function.
