Microwave Sensing of Andreev Bound States in a Gate-Defined Superconducting Quantum Point Contact

Abstract

We use a superconducting microresonator as a cavity to sense absorption of microwaves by a superconducting quantum point contact defined by surface gates over a proximitized two-dimensional electron gas. Renormalization of the cavity frequency with phase difference across the point contact is consistent with adiabatic coupling to Andreev bound states. Near $\pi$ phase difference, we observe random fluctuations in absorption with gate voltage, related to quantum interference-induced modulations in the electron transmission. We identify features consistent with the presence of single Andreev bound states and describe the Andreev-cavity interaction using a dispersive Jaynes-Cummings model. By fitting the weak Andreev-cavity coupling, we extract ~GHz decoherence consistent with charge noise and the transmission dispersion associated with a localized state.

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• Detection of Majorana zero modes bound to Josephson vortices in planar superconductor-topological insulator-superconductor junctions
• Microwave Andreev bound state spectroscopy in a semiconductor-based Planar Josephson junction
• Finite Length Effects and Coulomb Interaction in Ge Quantum Well-Based Josephson Junctions Probed with Microwave Spectroscopy
• Determination of the current-phase relation of an InAs 2DEG Josephson junction with a microwave resonator