title: Observation of directly interacting coherent two-level systems in an amorphous material.
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.
authors: Physikalisches Institut, Karlsruhe Institute of Technology, 76131 Karlsruhe, Germany.
authors: Jürgen
authors: J
authors: Lisenfeld
authors: Physikalisches Institut, Karlsruhe Institute of Technology, 76131 Karlsruhe, Germany.
authors: Grigorij J
authors: GJ
authors: Grabovskij
authors: 1] Département de Physique, Université de Sherbrooke, Sherbrooke, Québec, Canada J1K 2R1 [2] ARC Centre of Excellence for Engineered Quantum Systems, School of Mathematics and Physics, University of Queensland, Brisbane, Queensland 4072, Australia.
authors: Clemens
authors: C
authors: Müller
authors: Chemical and Quantum Physics, School of Applied Sciences, RMIT University, Melbourne 3001, Australia.
authors: Jared H
authors: JH
authors: Cole
authors: Physikalisches Institut, Karlsruhe Institute of Technology, 76131 Karlsruhe, Germany.
authors: Georg
authors: G
authors: Weiss
authors: 1] Physikalisches Institut, Karlsruhe Institute of Technology, 76131 Karlsruhe, Germany [2] National University of Science and Technology MISIS, Leninsky prosp. 4, Moscow, 119049, Russia.
authors: Alexey V
authors: AV
authors: Ustinov
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