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.
Optical tomography can reveal the intrinsic structure of complex objects with high accuracy. Cold atoms are an excellent model physical system for designing new protocols. By combining the gradient echo memory protocol with spatial homodyne detection, our experiment achieved micron-level resolution and excellent shot-noise limited sensitivity for interrogating atomic coherence. We also demonstrated three-dimensional imaging of an external magnetic field, and plan to extend the scheme to ultra-sensitive three-dimensional imaging of microwave fields using Rydberg atoms. Our work pushes the boundaries of quantum sensing for weak fields and unexplored three-dimensional tomographic imaging. The method may also be applied to hot atoms or solid-state probes, such as color centers, or ions, embedded in an interrogated medium.
The concept of temporal imaging draws from the analogy between paraxial propagation of light in space and in dispersive media. So far, temporal imaging has been demonstrated with ultrafast light, corresponding to spectral precision in the THz range. In our quantum memory, we have implemented full spectral and temporal processing capabilities for ultra narrowband photons, which allow us to perform temporal imaging with MHz bandwidth and kHz precision. Implementation of this concept leads to many implications, which give rise to two distinct super-resolved spectroscopy schemes, inspired by recent developments in spatial super-resolved imaging. One scheme takes advantage of elaborate interference in the quantum memory, while the other uses optimized analysis of a homodyne detector traces. Overall, our approach not only brings temporal imaging to the previously untackled regime but also points to a variety of new schemes useful in quantum sensing.
High performance quantum networks require extensive utilization of multiplexing techniques, relaying on photonic spatial and temporal structure. Multimode quantum memories for light, where photons are stored in the form of collective atomic excitations, may constitute building blocks of such networks; however, a requirement arises to implement complex linear operations on the stored excitations. In our photonic processor we experimentally demonstrate how the off-resonant ac-Stark shift (ACS) may be employed to manipulate the spatial and temporal structure of photons stored in a highly multimode quantum memory as the collective atomic excitations – spin waves.
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