Sensitive detection of the Rydberg transition in trapped electrons on liquid helium using radio-frequency reflectometry
Phys. Rev. Applied 26, 024010 – Published 6 August, 2026
DOI: https://doi.org/10.1103/4fx7-fk1z
Abstract
Radio-frequency (rf) reflectometry provides a useful method for sensitive and fast detection of dynamic processes in quantum systems. We use this method to detect excitation of the quantized (Rydberg) states of the vertical motion in a system of surface-bound electrons on liquid helium. The Rydberg transition is detected as a change in the rf reflection from a resonant circuit coupled to microwave-excited electrons. It is found that the observed reflection response drastically differs from an expected state-dependent dispersive shift of the resonant frequency. To elucidate the origin of the observed response, the result is compared with an independent reflection measurement on the same electron system modulated by an electrostatic potential and with a numerical simulation using the Green’s function method. The findings suggest that the observed response to the Rydberg resonance must be attributed to the in-plane motion of the photoexcited many-electron system rather than to the Rydberg transitions of independent electrons. Our work demonstrates that rf reflectometry could be a useful tool to study dynamic processes, such as quantum ac transport and collective excitations, in this system.
