Atomic-optical interferometry in fractured loops: A general solution for Rydberg radio-frequency receivers

The development of novel radio-frequency atomic receivers has brought attention to the theoretical description of atom-light interactions in sophisticated multilevel schemes. Of special interest are schemes where several interaction paths interfere with each other, bringing about the phase-sensitive measurement of detected radio fields. In the theoretical modeling of those cases, the common assumptions are often insufficient to determine the boundary detection parameters, such as the receiving bandwidth or saturation point, critical for practical considerations of atomic sensing technology. This evokes the resurfacing of the long-standing problem on how to describe an atom-light interaction in a fractured loop. In such a case, the quantum steady state is not achieved even with constant, continuous interactions. Here we propose a method for modeling such a system, basing our approach on the Fourier expansion of a nonequilibrium steady state. The proposed solution is both numerically effective and able to predict edge cases, such as saturation. Furthermore, as an example, we employ this method to provide a complete description of a Rydberg superheterodyne receiver, obtaining the boundary parameters describing the operation of this atomic detector.