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arXiv · 2607.24050

Pound-Drever-Hall Feedforward for Trapped-Ion Optical Qubits

Jia-Yang Gao·Jianwei Lee·Morteza Ahmadi·Manas Mukherjee
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Abstract

Laser phase noise is one of the limiting factors that dictate gate fidelities and coherence times in trapped-ion quantum systems. Previous studies have reported that when the Rabi frequency of an ion qubit is close to the servo-bump phase-noise frequency, the driving laser limits the fidelity and coherence time. This issue has typically been mitigated by choosing a Rabi frequency outside the servo-bump region. However, this constrains the usable range of gate speeds and can limit the achievable fidelity. To address this issue, we developed an active phase-noise stabilization system for a barium-ion optical-qubit laser at 1762 nm, employing a fiber electro-optic modulator (EOM) with an electrical feedforward servo. Our results demonstrate that this setup, based on the Pound-Drever-Hall (PDH) feedforward method, can suppress servo-bump phase noise by 15 dB near the bump peak frequency in our locking system. The laser phase noise is analyzed using delayed self-heterodyne interferometry (DSHI). We further tested the stabilized laser on an optical qubit and observed a clear improvement in coherence time based on the measured amplitude decay of Rabi oscillations, even when the Rabi frequency lies within the servo-bump bandwidth. This technique can be readily adapted to other optical qubits with minimal modifications.

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Jia-Yang Gao, Jianwei Lee, Morteza Ahmadi, Manas Mukherjee. 2026-07-27. Pound-Drever-Hall Feedforward for Trapped-Ion Optical Qubits. https://arxiv.org/abs/2607.24050

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