Impact of time-ordered measurements of the two states in a niobium superconducting qubit structure

TL;DR

This paper investigates thermal activation in a niobium superconducting qubit by time-ordered measurements, estimating a high quality factor indicative of potential for long quantum coherence times.

Contribution

It introduces a method to measure thermal activation rates in a superconducting qubit using time-ordered magnetization measurements, providing insights into device quality.

Findings

Estimated quality factor of 10^6 for the devices

Thermal activation rates depend on temperature and ramp time

Potential for observing long quantum coherence times

Abstract

Measurements of thermal activation are made in a superconducting, niobium Persistent-Current (PC) qubit structure, which has two stable classical states of equal and opposite circulating current. The magnetization signal is read out by ramping the bias current of a DC SQUID. This ramping causes time-ordered measurements of the two states, where measurement of one state occurs before the other. This time-ordering results in an effective measurement time, which can be used to probe the thermal activation rate between the two states. Fitting the magnetization signal as a function of temperature and ramp time allows one to estimate a quality factor of 10^6 for our devices, a value favorable for the observation of long quantum coherence times at lower temperatures.