Andreev Probe of Persistent Current States in Superconducting Quantum Circuits

TL;DR

This paper demonstrates a highly sensitive Andreev interferometer technique for real-time, precise measurement of persistent current quantum states in superconducting circuits, enabling detailed energy spectrum analysis.

Contribution

It introduces a novel, fast, and precise method using Andreev interferometers to measure local phase differences in superconducting quantum circuits.

Findings

Continuous read-out of quantum states achieved

Energy spectrum of circuits successfully constructed

Probe outperforms previous measurement methods

Abstract

Using the extraordinary sensitivity of Andreev interferometers to the superconducting phase difference associated with currents, we measure the persistent current quantum states in superconducting loops interrupted by Josephson junctions. Straightforward electrical resistance measurements of the interferometers give continuous read-out of the states, allowing us to construct the energy spectrum of the quantum circuit. The probe is estimated to be more precise and faster than previous methods, and can measure the local phase difference in a wide range of superconducting circuits.