Suppressing Counter-Rotating Errors for Fast Single-Qubit Gates with Fluxonium

TL;DR

This paper introduces two protocols to suppress counter-rotating errors in fast single-qubit gates with fluxonium, achieving fidelities exceeding 99.997% and advancing high-speed quantum control.

Contribution

It develops and demonstrates two novel, platform-independent methods to mitigate counter-rotating errors in fast qubit gates, improving fidelity without extra calibration.

Findings

Achieved single-qubit gate fidelities over 99.997%.

Demonstrated effective error suppression with circularly polarized drives.

Provided platform-independent protocols for high-fidelity quantum control.

Abstract

Qubit decoherence unavoidably degrades the fidelity of quantum logic gates. Accordingly, realizing gates that are as fast as possible is a guiding principle for qubit control, necessitating protocols for mitigating error channels that become significant as gate time is decreased. One such error channel arises from the counter-rotating component of strong, linearly polarized drives. This error channel is particularly important when gate times approach the qubit Larmor period and represents the dominant source of infidelity for sufficiently fast single-qubit gates with low-frequency qubits such as fluxonium. In this work, we develop and demonstrate two complementary protocols for mitigating this error channel. The first protocol realizes circularly polarized driving in circuit quantum electrodynamics (QED) through simultaneous charge and flux control. The second protocol -- commensurate pulses -- leverages the coherent and periodic nature of counter-rotating fields to regularize their contributions to gates, enabling single-qubit gate fidelities reliably exceeding $99.997\%$. This protocol is platform independent and requires no additional calibration overhead. This work establishes straightforward strategies for mitigating counter-rotating effects from strong drives in circuit QED and other platforms, which we expect to be helpful in the effort to realize high-fidelity control for fault-tolerant quantum computing.