Rydberg Transitions
Quantum capacitance induced by Rydberg transitions
Electrons on liquid helium offer a clean platform for quantum computing, with spin states expected to have long coherence times. However, spin-state detection remains challenging. A promising approach maps the spin state onto a Rydberg state, detectable via an LC tank circuit with high sensitivity and small footprint. As a proof of concept, we detect Rydberg transitions of an electron ensemble using frequency-modulated microwaves. Adiabatic transitions induce measurable quantum capacitance. The achieved sensitivity allows resolving the Rydberg transition of a single electron, paving the way for scalable spin-state readout and helium-based quantum technologies.
Reflected RF power measured with a spectrum analyzer as a function of the microwave (MW) carrier frequency fMW. The frequency modulation (FM) parameters are fmf = 1 kHz and fma = 768 MHz. Sideband signals appear at f = fRF ± fmf around fMW = 165 GHz, corresponding to the Rydberg transition.