Sensitive detection of the Rydberg transition in trapped electrons on liquid helium using radio-frequency reflectometry

TL;DR

This paper demonstrates sensitive detection of Rydberg transitions in trapped electrons on liquid helium using radio-frequency reflectometry, revealing collective electron motion effects.

Contribution

It introduces a method to detect Rydberg states via impedance changes and clarifies the role of collective electron motion in the response.

Findings

Rydberg transition detected through impedance change

Resonant collective motion enhances RF response

Vertical displacement response is negligible compared to lateral motion

Abstract

Radio-frequency reflectometry, which probes small changes in the electrical impedance of a device, 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 motional (Rydberg) states of trapped electrons on liquid helium. The Rydberg transition in an ensemble of electrons is detected by a change in the impedance of an rf circuit coupled to the microwave-excited electrons. To elucidate the origin of the observed response, the result is compared with an independent impedance measurement on the same electron system modulated by an electrostatic potential and with a numerical simulation using the Green's function method. Additionally, it is found that the rf response to the Rydberg resonance can be strongly enhanced by a resonant mode of the electron collective motion. Our results suggest that the observed response to the Rydberg resonance must be attributed to the lateral motion of the many-electron system rather than the vertical displacement of the individually excited electrons, as was explicate earlier. A theoretical analysis of the expected response due to the vertical displacement is given.