Arxiv:1705.01108V3 [Cond-Mat.Mes-Hall] 10 Oct 2019 Environment 11 D
Towards understanding two-level-systems in amorphous solids - Insights from quantum circuits Clemens M¨uller,1, 2, 3, ∗ Jared H. Cole,4, y and J¨urgenLisenfeld5, z 1IBM Research Zurich, 8803 R¨uschlikon,Switzerland 2Institute for Theoretical Physics, ETH Z¨urich,8093 Z¨urich,Switzerland 3ARC Centre of Excellence for Engineered Quantum Systems, School of Mathematics and Physics, The University of Queensland, Brisbane, Queensland 4072, Australia 4Chemical and Quantum Physics, School of Science, RMIT University, Melbourne, Victoria 3001, Australia 5Physikalisches Institut, Karlsruhe Institute of Technology, 76131 Karlsruhe, Germany (Dated: October 11, 2019) Amorphous solids show surprisingly universal behaviour at low temperatures. The prevailing wisdom is that this can be explained by the existence of two-state defects within the material. The so-called standard tunneling model has become the established framework to explain these results, yet it still leaves the central question essentially unanswered - what are these two-level defects? This question has recently taken on a new urgency with the rise of superconducting circuits in quantum computing, circuit quantum electrodynamics, magnetometry, electrometry and metrology. Superconducting circuits made from aluminium or niobium are fundamentally limited by losses due to two-level defects within the amorphous oxide layers encasing them. On the other hand, these circuits also provide a novel and effective method for studying the very defects which limit their operation. We can now go beyond ensemble measurements and probe individual defects - observing the quantum nature of their dynamics and studying their formation, their behaviour as a function of applied field, strain, temperature and other properties. This article reviews the plethora of recent experimental results in this area and discusses the various theoretical models which have been used to describe the observations.
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