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

K. Segall·D. Crankshaw·D. Nakada·T. P. Orlando·L. S. Levitov·S. Lloyd·N. Markovic·S. O. Valenzuela·M. Tinkham·K. K. Berggren
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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.

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K. Segall, D. Crankshaw, D. Nakada, T. P. Orlando, L. S. Levitov, S. Lloyd, N. Markovic, S. O. Valenzuela, M. Tinkham, K. K. Berggren. 2003-02-26. Impact of time-ordered measurements of the two states in a niobium superconducting qubit structure. https://doi.org/10.1103/physrevb.67.220506

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