Observation of directly interacting coherent two-level systems in an amorphous material.

Jürgen Lisenfeld,Alexey V Ustinov,Grigorij J Grabovskij,Clemens Müller,Georg Weiss,Jared H Cole

doi:10.1038/ncomms7182

Abstract

Parasitic two-level tunnelling systems originating from structural material defects affect the functionality of various microfabricated devices by acting as a source of noise. In particular, superconducting quantum bits may be sensitive to even single defects when these reside in the tunnel barrier of the qubit’s Josephson junctions, and this can be exploited to observe and manipulate the quantum states of individual tunnelling systems. Here, we detect and fully characterize a system of two strongly interacting defects using a novel technique for high-resolution spectroscopy. Mutual defect coupling has been conjectured to explain various anomalies of glasses, and was recently suggested as the origin of low-frequency noise in superconducting devices. Our study provides conclusive evidence of defect interactions with full access to the individual constituents, demonstrating the potential of superconducting qubits for studying material defects. All our observations are consistent with the assumption that defects are generated by atomic tunnelling.

Highlights

Parasitic two-level tunnelling systems originating from structural material defects affect the functionality of various microfabricated devices by acting as a source of noise
First signatures of coherent two-level systems (TLS) in phase qubits were found in spectroscopy data, where observed avoided level crossings manifest the defects’ two-level quantum character[3,4]
We report the first clear experimental evidence of two coherently interacting TLS residing in the tunnel barrier of a Josephson junction (JJ)

Summary

Introduction

Parasitic two-level tunnelling systems originating from structural material defects affect the functionality of various microfabricated devices by acting as a source of noise. Mutual defect coupling has been conjectured to explain various anomalies of glasses, and was recently suggested as the origin of low-frequency noise in superconducting devices. First signatures of coherent TLS in phase qubits were found in spectroscopy data, where observed avoided level crossings manifest the defects’ two-level quantum character[3,4]. Often, these defects show longer coherence times than the qubit itself[5], and might be useful as quantum memories[6] and resources for quantum algorithms[7,8]. Interpretation of the measurement based on atomic tunnelling systems fully accounts for all observations

Methods

Results

Conclusion