First-Order Crosstalk Mitigation in Parallel Quantum Gates Driven With Multi-Photon Transitions

TL;DR

This paper presents a simple frequency offset technique to significantly reduce optical crosstalk in parallel quantum gates on trapped-ion qubits, improving gate fidelity with minimal overhead.

Contribution

The authors introduce a first-order crosstalk mitigation method using drive frequency offsets for two-photon Raman gates, applicable to various quantum computing architectures.

Findings

Crosstalk error reduced from 0.185 to ≤0.006

Phase-agnostic composite gates mitigate rotation errors

Method is simple, effective, and widely applicable

Abstract

We demonstrate an order of magnitude reduction in the sensitivity to optical crosstalk for neighboring trapped-ion qubits during simultaneous single-qubit gates driven with individual addressing beams. Gates are implemented via two-photon Raman transitions, where crosstalk is mitigated by offsetting the drive frequencies for each qubit to avoid first-order crosstalk effects from inter-beam two-photon resonance. The technique is simple to implement, and we find that phase-dependent crosstalk due to optical interference is reduced on the most impacted neighbor from a maximal fractional rotation error of 0.185(4) without crosstalk mitigation to $\leq$ 0.006 with the mitigation strategy. Further, we characterize first-order crosstalk in the two-qubit gate and avoid the resulting rotation errors for the arbitrary-axis M{\o}lmer-S{\o}rensen gate via a phase-agnostic composite gate. Finally, we demonstrate holistic system performance by constructing a composite CNOT gate using the improved single-qubit gates and phase-agnostic two-qubit gate. This work is done on the Quantum Scientific Computing Open User Testbed (QSCOUT); however, our methods are widely applicable for individual-addressing Raman gates and impose no significant overhead, enabling immediate improvement for quantum processors that incorporate this technique.