Enhancing Sensitivity of Atomic Microwave Receivers Based on Optimal Laser Arrays

Rydberg atom, which exhibits a strong response to weak electric fields, is regarded as a promising atomic receiver to surpass the sensitivity of conventional receivers. However, its sensitivity is strongly limited by the noise coming from both classical and quantum levels, and how to enhance it significantly remains challenging. In theory, we aim to optimize the laser array, highlighting the importance of coherence among microwave signals and the uniformity of laser beam power within the array, to enhance the signal-to-noise ratio (SNR) and elevate sensitivity to a new standard. To enhance practical application mobility and integration, we propose two optimization schemes: a six-port fiber-coupled vapor cell probe array and cascaded diffraction gratings. We maintain steady MW signal coherence in the laser array by using identical vapor cells and positioning the probe lasers on the incident wave’s equal phase plane. Our findings reveal that the wavefront phase difference for the six-port fiber-coupled vapor cell array is 10°, while the cascaded diffraction gratings show a 16° difference, with laser intensity uniformity reaching 90.4%. In our experiment, a 4.6-dB SNR enhancement was achieved by utilizing the cascaded diffraction gratings to generate $2 \times 2$ probe laser arrays compared to the performance of a laser beam, which can be enhanced further just by adding more laser beams. In particular, a $2 \times 2$ laser array experimental verification yielded $19~\text {nv/cm}/\sqrt {\textrm {Hz}}$ @8.57 GHz. More importantly, the intermediate signals of the laser array maintain coherence. Therefore, SNR improvement is allowed even in detecting weak target signals amid strong noise and clutter. The results could offer an avenue for the design and optimization of ultrahigh-sensitivity Rydberg atomic receivers and promote applications in cosmology, meteorology, communication, and MW quantum technology.