Fiber-integrated acousto-optic-modulator-based phase-controlled Rydberg atomic electrometer

A Mach–Zehnder interferometer (MZI) provides an effective interferometric readout approach for enhancing the performance of Rydberg-atom-based microwave electric-field sensing. The phase tuning based on a piezoelectric transducer (PZT) relies on mechanical path length modulation, which can limit phase precision, modulation frequency, and the level of system integration. Here, we demonstrate a fiber-integrated MZI architecture in which the interferometric phase is controlled electronically by a pair of double-pass acousto-optic modulators (AOMs). The additional propagation phase accumulated by the frequency-shifted light in an optical fiber enables continuous tuning of the relative phase between the two interferometer arms over a fixed optical path, without using moving components. A frequency adjustment Δf = 9.463 MHz produces a full 2π phase shift, confirming the reproducibility and continuous tunability of the method, with an experimentally measured phase stability at the milliradian level. Based on this interferometric readout, we implement a Rydberg-atom-based microwave electric-field measurement scheme in a room-temperature cesium vapor cell. At the optimized absorption-dominated operating point of Δϕ = π, corresponding to an AOM driving frequency of 93.9 MHz, the interferometric readout improves the measured signal-to-noise ratio by about 4 dB compared with the non-interferometric case. The directly measured electric-field sensitivity at the position of the cesium vapor cell is 4.2×10−6V/m/Hz. Compared with PZT-based schemes, this approach improves interferometric stability and tuning precision, and provides better compatibility with compact and integrated implementations.