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Müller C, Cole JH, Lisenfeld J. Towards understanding two-level-systems in amorphous solids: insights from quantum circuits. REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2019; 82:124501. [PMID: 31404914 DOI: 10.1088/1361-6633/ab3a7e] [Citation(s) in RCA: 46] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
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 (TLS)? 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 TLS 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. In doing so, it summarises the current approaches to solving this fundamentally important problem in solid-state physics.
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Affiliation(s)
- Clemens Müller
- IBM Research Zurich, 8803 Rüschlikon, Switzerland. Institute for Theoretical Physics, ETH Zürich, 8093 Zürich, Switzerland. ARC Centre of Excellence for Engineered Quantum Systems, School of Mathematics and Physics, The University of Queensland, Brisbane, Queensland 4072, Australia
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Suppression of low-frequency charge noise in superconducting resonators by surface spin desorption. Nat Commun 2018; 9:1143. [PMID: 29559633 PMCID: PMC5861058 DOI: 10.1038/s41467-018-03577-2] [Citation(s) in RCA: 45] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2017] [Accepted: 02/22/2018] [Indexed: 11/09/2022] Open
Abstract
Noise and decoherence due to spurious two-level systems located at material interfaces are long-standing issues for solid-state quantum devices. Efforts to mitigate the effects of two-level systems have been hampered by a lack of knowledge about their chemical and physical nature. Here, by combining dielectric loss, frequency noise and on-chip electron spin resonance measurements in superconducting resonators, we demonstrate that desorption of surface spins is accompanied by an almost tenfold reduction in the charge-induced frequency noise in the resonators. These measurements provide experimental evidence that simultaneously reveals the chemical signatures of adsorbed magnetic moments and highlights their role in generating charge noise in solid-state quantum devices.
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Lisenfeld J, Bilmes A, Matityahu S, Zanker S, Marthaler M, Schechter M, Schön G, Shnirman A, Weiss G, Ustinov AV. Decoherence spectroscopy with individual two-level tunneling defects. Sci Rep 2016; 6:23786. [PMID: 27030167 PMCID: PMC4815015 DOI: 10.1038/srep23786] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2016] [Accepted: 03/14/2016] [Indexed: 12/01/2022] Open
Abstract
Recent progress with microfabricated quantum devices has revealed that an ubiquitous source of noise originates in tunneling material defects that give rise to a sparse bath of parasitic two-level systems (TLSs). For superconducting qubits, TLSs residing on electrode surfaces and in tunnel junctions account for a major part of decoherence and thus pose a serious roadblock to the realization of solid-state quantum processors. Here, we utilize a superconducting qubit to explore the quantum state evolution of coherently operated TLSs in order to shed new light on their individual properties and environmental interactions. We identify a frequency-dependence of TLS energy relaxation rates that can be explained by a coupling to phononic modes rather than by anticipated mutual TLS interactions. Most investigated TLSs are found to be free of pure dephasing at their energy degeneracy points, around which their Ramsey and spin-echo dephasing rates scale linearly and quadratically with asymmetry energy, respectively. We provide an explanation based on the standard tunneling model, and identify interaction with incoherent low-frequency (thermal) TLSs as the major mechanism of the pure dephasing in coherent high-frequency TLS.
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Affiliation(s)
- Jürgen Lisenfeld
- Physikalisches Institut, Karlsruhe Institute of Technology (KIT), 76131 Karlsruhe, Germany
| | - Alexander Bilmes
- Physikalisches Institut, Karlsruhe Institute of Technology (KIT), 76131 Karlsruhe, Germany
| | - Shlomi Matityahu
- Department of Physics, Ben-Gurion University of the Negev, Beer Sheva 84105, Israel
| | - Sebastian Zanker
- Institut für Theoretische Festkörperphysik, KIT, 76131 Karlsruhe, Germany
| | - Michael Marthaler
- Institut für Theoretische Festkörperphysik, KIT, 76131 Karlsruhe, Germany
| | - Moshe Schechter
- Department of Physics, Ben-Gurion University of the Negev, Beer Sheva 84105, Israel
| | - Gerd Schön
- Institut für Theoretische Festkörperphysik, KIT, 76131 Karlsruhe, Germany
| | - Alexander Shnirman
- Institut für Theorie der Kondensierten Materie, KIT, 76131 Karlsruhe, Germany
- L. D. Landau Institute for Theoretical Physics RAS, Kosygina street 2, 119334 Moscow, Russia
| | - Georg Weiss
- Physikalisches Institut, Karlsruhe Institute of Technology (KIT), 76131 Karlsruhe, Germany
| | - Alexey V. Ustinov
- Physikalisches Institut, Karlsruhe Institute of Technology (KIT), 76131 Karlsruhe, Germany
- National University of Science and Technology MISIS, Leninsky prosp. 4, Moscow, 119049, Russia
- Russian Quantum Center, 100 Novaya St., Skolkovo, 143025 Moscow region, Russia
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