Observation of the Rydberg resonance in surface electrons on superfluid helium confined in a 4-$\mu$m deep channel

TL;DR

This study reports the first observation of Rydberg resonance in surface electrons on superfluid helium confined in a microchannel, demonstrating microwave-induced transitions and their dependence on electrostatic conditions, relevant for quantum computing.

Contribution

First experimental detection of microwave-induced Rydberg resonance in confined surface electrons on superfluid helium within a microchannel, with theoretical and finite-element modeling support.

Findings

Resonance observed at 0.4-0.5 THz range

Resonance broadening of about 10 GHz explained by electric field inhomogeneity

Good agreement between experimental data and theoretical calculations

Abstract

We report the first observation of the microwave-induced intersubband (Rydberg) resonance in the surface-bound electrons on superfluid helium confined in a single 4-$\mu$m deep channel. The resonance signal from a few thousand of surface electrons comprising the Wigner Solid (WS) is detected by observing WS melting due to the microwave absorption. The observed transition frequency for the two lowest Rydberg states, in the range of 0.4-0.5 THz, is determined by the image charges induced by the surface electrons in conducting electrodes of the microchannel and the potentials due to applied voltages, and is in a good agreement with our calculations. The observed large broadening of the resonance on the order of 10 GHz, which is due to inhomegeneous distribution of the pressing electric field in the microchannel, is also in a reasonable agreement with our finite-element modeling calculations. This study of the confined electrons is motivated by their potential use for charge and spin qubits.