We propose a new optically-biased Rydberg-atoms detection of microwave fields, that allows truly all-optical operation, while retaining most of the sensitivity. We tackle the issue of laser phase noise, emerging in this type of detection, by facilitating separate measurement of this noise in a nonlinear process.
Abstract 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 176nV/cm/Hz 176 nV / cm / Hz , 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.
One of the advantages of Rydberg atom-based detection of microwave and THz fields is weak distortion of the measured field, allowing for precise and stealthy detection. However, recent developments focused on using Rydberg atoms as a RF mixer with a local oscillator field in a superheterodyne-type detection that is no longer all-optical, as the local oscillator antenna has to be a part of the detector. Here we undertake the task of developing an all-optical detection, where the phase reference is provided not in local oscillator, but instead in the polarization of atoms. To realize this feature, we access the 13.9 GHz Rydberg transition in rubidium with two separate optical excitation paths and measure the beating of probe field. We report an overall detection sensitivity of 176 nV/cm/ √Hz and reliable operation up to 3.5 mV/cm of RF field, results that are parallel to superheterodyne detection method demonstrated in the same setup. The results of this work are largely based on an earlier conducted study, published as a preprint.1 The present manuscript is meant to serve as an appendix to this work, focusing on putting this research in the context of all-optical detection schemes.
High-precision phase measurement of microwave fields underpins a wide range of applications, including wireless communications, distributed radar, plasma diagnostics, and antenna metrology. Existing Rydberg-atom-based approaches, however, often face trade-offs among phase resolution, measurement range, and system complexity. Here we demonstrate a Rydberg-atom-based microwave Mach-Zehnder-type interferometer using a dual-local-oscillator configuration. The two local oscillators establish two coherent interferometric pathways in the Rydberg medium. Their coherent mixing with the signal field produces an interferometric intermediate-frequency output governed by a phase-to-intensity transfer characteristic that enables critical-point enhancement. This scheme supports direct phase retrieval with a resolution exceeding 0.1∘ and unambiguous full 360∘ phase coverage with the reconfigurable dual-LO architecture. Moreover, near the critical interference point, the system exhibits a sharply enhanced phase-to-amplitude transduction, where weak amplitude variations are converted into pronounced phase responses, yielding a sensitivity enhancement exceeding 25 dB. Besides, the same interferometric transfer mechanism enables microwave propagation-distance and polarization metrology, achieving a propagation-distance precision below 20 μm at 5.7 GHz together with a polarization-angle resolution exceeding 0.1∘. This approach eliminates the need for complex optical configurations and lock-in detection, providing a simple, scalable, and reconfigurable Mach-Zehnder-type quantum microwave interferometry framework for multifunctional high-precision microwave metrology.
The detection of microwave (MW) fields with room-temperature Rydberg atomic vapors is a novel technique of optical sensing, introducing a range of merits typically not possible to achieve with conventional antennas [1]. Firstly, the atomic response to MW fields is dependent on a given transition dipole moment between Rydberg energy levels - as this value can be precisely derived from the theory of alkali atoms, e.g. rubidium, Rydberg sensors are intrinsically calibrated and there is no dependency on particular device. Secondly, the detector does not contain any metal parts (apart from trace amount of rubidium), introducing very little distortion to the measured field, so the detection is stealthy, and the detector is practically invulnerable even to strong fields. Typically, however, the best state-of-the-art performance is achieved with an additional local oscillator MW field [2], emitted from the antenna, in which case the scheme is no longer all-optical and some advantages are lost.
We propose and investigate a Rydberg atom sensor based on a loop-level structure, which utilizes the eigenfrequencies of the energy levels as a reference. This design eliminates the need for the local oscillator (LO) electric field required in the traditional superheterodyne structure while maintaining a linear relationship between the readout signal and the microwave (MW) electric field to be measured, along with exhibiting significantly lower harmonic distortion. For experimental validation, we implemented a cesium atomic system based on the loop five-level structure. The system achieved a sensitivity of 62 nVcm -1 Hz -1/2 and maintained 30 dB of harmonic suppression even near the nonlinear operational region under the strong electric field, which is approximately 20 dB higher than that of the superheterodyne structure. This work demonstrates that loop-level-based atomic sensors enable high-sensitivity and wide-dynamic-range (including nonlinear region) MW detection, making them particularly suitable for receiving frequency- and phase-modulated signals that are insensitive to power variations.