Optically-biased Rydberg microwave receiver enabled by hybrid nonlinear interferometry

Coupling a Rydberg vapour medium to both microwave and optical fields enables the benefits of all-optical detection, such as minimal disturbance of the measured field and resilience to very strong signals, since no conventional antenna is required. However, peak sensitivity typically relies on adding a microwave local oscillator, which compromises the all-optical nature of the measurement. Here we introduce an alternative, optical-bias detection, that maintains fully optical operation while achieving high sensitivity. To address laser phase noise, which is critical in this approach, we perform a simultaneous measurement of the noise using a nonlinear process and correct it in real time via data processing. This yields a 35 dB improvement in signal-to-noise ratio compared with the basic method. We demonstrate a sensitivity of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mn>176</mml:mn> <mml:mspace></mml:mspace> <mml:mi>nV</mml:mi> <mml:mo>/</mml:mo> <mml:mi>cm</mml:mi> <mml:mo>/</mml:mo> <mml:msqrt><mml:mrow><mml:mi>Hz</mml:mi></mml:mrow> </mml:msqrt> </mml:math> , reliable operation up to 3.5 mV/cm at 13.9 GHz, and quadrature-amplitude modulated data transmission, underlining the ability to detect microwave field quadratures while preserving the unique advantages of all-optical detection.