DC measurements of macroscopic quantum levels in a superconducting qubit structure with a time-ordered meter

TL;DR

This paper reports DC measurements of macroscopic quantum levels in a superconducting qubit using a time-ordered SQUID magnetometer, revealing quantum tunneling and relaxation times.

Contribution

It introduces a method to measure quantum levels in a superconducting qubit with a time-ordered magnetometer, providing new insights into quantum tunneling and relaxation.

Findings

Observation of macroscopic resonant tunneling at quantum level positions

Intrawell relaxation time of approximately 50 microseconds

Different signatures depending on tunneling direction

Abstract

DC measurements are made in a superconducting, persistent current qubit structure with a time-ordered meter. The persistent-current qubit has a double-well potential, with the two minima corresponding to magnetization states of opposite sign. Macroscopic resonant tunneling between the two wells is observed at values of energy bias that correspond to the positions of the calculated quantum levels. The magnetometer, a Superconducting Quantum Interference Device (SQUID), detects the state of the qubit in a time-ordered fashion, measuring one state before the other. This results in a different meter output depending on the initial state, providing different signatures of the energy levels for each tunneling direction. From these measurements, the intrawell relaxation time is found to be about 50 microseconds.