Magnetic field fluctuations are a dominant source of dephasing in Zeeman-encoded trapped-ion qubits, limiting coherence time and the fidelity of quantum operations, particularly in modular quantum networks where phase stability must be maintained across spatially separated nodes. In this work, we design and characterize an active magnetic field stabilization system based on real-time feedback using a high-resolution magnetometer, a digitally controlled Red Pitaya platform, and a coil actuator with a measured gain of ∼ −5.37 G/V. Spectral measurements of the laboratory environment reveal dominant 60 Hz magnetic noise with amplitudes on the order of 400 µG and significant harmonic content. The system operates at a sampling rate of ∼ 605 Hz with an actuator bandwidth of ∼ 85 Hz, enabling targeted suppression of these low-frequency components. Given a Zeeman sensitivity of ∼ 2.8 MHz/G, such fluctuations correspond to kilohertz-scale frequency noise, which rapidly dephases qubit superpositions. Suppression of these fluctuations is therefore expected to reduce phase noise and extend coherence times, with first-order estimates suggesting improvement from the submillisecond regime into the few-millisecond regime for Zeeman-sensitive qubits. These results demonstrate that active magnetic-field stabilization is a practical approach to reducing environmental dephasing and improving the performance of trapped-ion quantum network experiments.
Saketha Male (Fri,) studied this question.