Radio-Frequency Methods for Majorana-Based Quantum Devices: Fast Charge Sensing and Phase-Diagram Mapping

Radio-frequency (rf) reflectometry is implemented in hybrid semiconductor-superconductor nanowire systems designed to probe Majorana zero modes. Two approaches are presented. In the first, hybrid nanowire-based devices are part of a resonant circuit, allowing conductance to be measured as a function of several gate voltages approximately 40 times faster than using conventional low-frequency lock-in methods. In the second, nanowire devices are capacitively coupled to a nearby rf single-electron transistor made from a separate nanowire, allowing rf detection of charge, including charge-only measurement of the crossover from 2 e interisland charge transitions at zero magnetic field to 1 e transitions at axial magnetic fields above 0.6 T, where a topological state is expected. Single-electron sensing yields a signal-to-noise ratio exceeding 3 and a visibility of 99.8% for a measurement time of 1 μ s .