Flip-chip-based microwave spectroscopy of Andreev bound states in a planar Josephson junction

TL;DR

This paper introduces a flip-chip microwave measurement technique for Andreev bound states in a planar Josephson junction, demonstrating control via gating and phase biasing, with potential for advanced superconductor-semiconductor device applications.

Contribution

It presents a novel flip-chip approach for microwave spectroscopy of Andreev bound states, enabling independent control and phase biasing in planar Josephson junctions.

Findings

Controlled Andreev bound states with high transmission (~0.98).

Demonstrated phase biasing effects on resonator frequency.

Achieved gate-tunable superconducting gap of 184 μeV.

Abstract

We demonstrate a flip-chip-based approach to microwave measurements of Andreev bound states in a gate-tunable planar Josephson junction using inductively-coupled superconducting low-loss resonators. By means of electrostatic gating, we present control of both the density and transmission of Andreev bound states. Phase biasing of the device shifted the resonator frequency, consistent with the modulation of supercurrent in the junction. Two-tone spectroscopy measurements revealed an isolated Andreev bound state consistent with an average induced superconducting gap of $184~\mathrm{\mu eV}$ and a gate-tunable transmission approaching $0.98$. Our results represent the feasibility of using the flip-chip technique to address and study Andreev bound states in planar Josephson junctions, and they give a promising path towards microwave applications with superconductor-semiconductor two-dimensional materials.