1
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Libersky M, McKenzie RD, Silevitch DM, Stamp PCE, Rosenbaum TF. Direct Observation of Collective Electronuclear Modes about a Quantum Critical Point. PHYSICAL REVIEW LETTERS 2021; 127:207202. [PMID: 34860035 DOI: 10.1103/physrevlett.127.207202] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/12/2021] [Revised: 07/12/2021] [Accepted: 10/13/2021] [Indexed: 06/13/2023]
Abstract
We directly measure the low energy excitation modes of the quantum Ising magnet LiHoF_{4} using microwave spectroscopy. Instead of a single electronic mode, we find a set of collective electronuclear modes, in which the spin-1/2 Ising electronic spins hybridize with the bath of spin-7/2 Ho nuclear spins. The lowest-lying electronuclear mode softens at the approach to the quantum critical point, even in the presence of disorder. This softening is rapidly quenched by a longitudinal magnetic field. Similar electronuclear structures should exist in other spin-based quantum Ising systems.
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Affiliation(s)
- M Libersky
- Division of Physics, Mathematics, and Astronomy, California Institute of Technology, Pasadena, California 91125, USA
| | - R D McKenzie
- Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada
| | - D M Silevitch
- Division of Physics, Mathematics, and Astronomy, California Institute of Technology, Pasadena, California 91125, USA
| | - P C E Stamp
- Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada
- Pacific Institute of Theoretical Physics, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada
| | - T F Rosenbaum
- Division of Physics, Mathematics, and Astronomy, California Institute of Technology, Pasadena, California 91125, USA
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2
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The Rayleigh-Lorentz invariant for superconducting resonators and optimal adiabatic qubit-information detection. Sci Rep 2021; 11:13722. [PMID: 34215762 PMCID: PMC8253750 DOI: 10.1038/s41598-021-92555-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2020] [Accepted: 06/07/2021] [Indexed: 11/14/2022] Open
Abstract
Dynamical properties of a resonator can be analyzed using the Rayleigh–Lorentz invariant which is not an exact constant but varies more or less over time depending on variations of parameters. We investigate the time behavior of this invariant for a superconducting nano-resonator in order for better understanding of qubit-information detection with the resonator. Superconducting resonators which uses parametric resonance in a Josephson junction circuit can be utilized in implementing diverse next generation nano-optic and nano-electronic devices such as quantum computing systems. Through the analyses of the temporal evolution of the invariant, we derive a condition for optimal adiabatic qubit-information detection with the resonator. This condition is helpful for controlling the dynamics of the resonators over long periods of time. It is necessary to consider it when designing a nano-resonator used for quantum nondemolition readouts of qubit states, crucial in quantum computation.
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3
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Bilmes A, Megrant A, Klimov P, Weiss G, Martinis JM, Ustinov AV, Lisenfeld J. Resolving the positions of defects in superconducting quantum bits. Sci Rep 2020; 10:3090. [PMID: 32080272 PMCID: PMC7033136 DOI: 10.1038/s41598-020-59749-y] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2019] [Accepted: 01/31/2020] [Indexed: 11/22/2022] Open
Abstract
Solid-state quantum coherent devices are quickly progressing. Superconducting circuits, for instance, have already been used to demonstrate prototype quantum processors comprising a few tens of quantum bits. This development also revealed that a major part of decoherence and energy loss in such devices originates from a bath of parasitic material defects. However, neither the microscopic structure of defects nor the mechanisms by which they emerge during sample fabrication are understood. Here, we present a technique to obtain information on locations of defects relative to the thin film edge of the qubit circuit. Resonance frequencies of defects are tuned by exposing the qubit sample to electric fields generated by electrodes surrounding the chip. By determining the defect's coupling strength to each electrode and comparing it to a simulation of the field distribution, we obtain the probability at which location and at which interface the defect resides. This method is applicable to already existing samples of various qubit types, without further on-chip design changes. It provides a valuable tool for improving the material quality and nano-fabrication procedures towards more coherent quantum circuits.
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Affiliation(s)
- Alexander Bilmes
- Physikalisches Institut, Karlsruhe Institute of Technology, Karlsruhe, 76131, Germany.
| | | | - Paul Klimov
- Google, Santa Barbara, California, 93117, USA
| | - Georg Weiss
- Physikalisches Institut, Karlsruhe Institute of Technology, Karlsruhe, 76131, Germany
| | | | - Alexey V Ustinov
- Physikalisches Institut, Karlsruhe Institute of Technology, Karlsruhe, 76131, Germany
- National University of Science and Technology MISiS, Moscow, 119049, Russia
- Russian Quantum Center, Skolkovo, Moscow, 143025, Russia
| | - Jürgen Lisenfeld
- Physikalisches Institut, Karlsruhe Institute of Technology, Karlsruhe, 76131, Germany
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4
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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: 35] [Impact Index Per Article: 7.0] [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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5
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Lee KH, Chakram S, Kim SE, Mujid F, Ray A, Gao H, Park C, Zhong Y, Muller DA, Schuster DI, Park J. Two-Dimensional Material Tunnel Barrier for Josephson Junctions and Superconducting Qubits. NANO LETTERS 2019; 19:8287-8293. [PMID: 31661615 DOI: 10.1021/acs.nanolett.9b03886] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Quantum computing based on superconducting qubits requires the understanding and control of the materials, device architecture, and operation. However, the materials for the central circuit element, the Josephson junction, have mostly been focused on using the AlOx tunnel barrier. Here, we demonstrate Josephson junctions and superconducting qubits employing two-dimensional materials as the tunnel barrier. We batch-fabricate and design the critical Josephson current of these devices via layer-by-layer stacking N layers of MoS2 on the large scale. Based on such junctions, MoS2 transmon qubits are engineered and characterized in a bulk superconducting microwave resonator for the first time. Our work allows Josephson junctions to access the diverse material properties of two-dimensional materials that include a wide range of electrical and magnetic properties, which can be used to study the effects of different material properties in superconducting qubits and to engineer novel quantum circuit elements in the future.
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Affiliation(s)
- Kan-Heng Lee
- School of Applied and Engineering Physics , Cornell University , Ithaca , New York 14853 , United States
- Pritzker School of Molecular Engineering , University of Chicago , Chicago , Illinois 60637 , United States
| | - Srivatsan Chakram
- James Franck Institute , University of Chicago , Chicago , Illinois 60637 , United States
- Department of Physics , University of Chicago , Chicago , Illinois 60637 , United States
| | - Shi En Kim
- Pritzker School of Molecular Engineering , University of Chicago , Chicago , Illinois 60637 , United States
| | - Fauzia Mujid
- Department of Chemistry , University of Chicago , Chicago , Illinois 60637 , United States
| | - Ariana Ray
- School of Applied and Engineering Physics , Cornell University , Ithaca , New York 14853 , United States
| | - Hui Gao
- Department of Chemistry , University of Chicago , Chicago , Illinois 60637 , United States
- Department of Chemistry and Chemical Biology , Cornell University , Ithaca , New York 14853 , United States
| | - Chibeom Park
- James Franck Institute , University of Chicago , Chicago , Illinois 60637 , United States
- Department of Chemistry , University of Chicago , Chicago , Illinois 60637 , United States
| | - Yu Zhong
- Department of Chemistry , University of Chicago , Chicago , Illinois 60637 , United States
| | - David A Muller
- School of Applied and Engineering Physics , Cornell University , Ithaca , New York 14853 , United States
| | - David I Schuster
- Pritzker School of Molecular Engineering , University of Chicago , Chicago , Illinois 60637 , United States
- James Franck Institute , University of Chicago , Chicago , Illinois 60637 , United States
- Department of Physics , University of Chicago , Chicago , Illinois 60637 , United States
| | - Jiwoong Park
- Pritzker School of Molecular Engineering , University of Chicago , Chicago , Illinois 60637 , United States
- James Franck Institute , University of Chicago , Chicago , Illinois 60637 , United States
- Department of Chemistry , University of Chicago , Chicago , Illinois 60637 , United States
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6
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Opremcak A, Pechenezhskiy IV, Howington C, Christensen BG, Beck MA, Leonard E, Suttle J, Wilen C, Nesterov KN, Ribeill GJ, Thorbeck T, Schlenker F, Vavilov MG, Plourde BLT, McDermott R. Measurement of a superconducting qubit with a microwave photon counter. Science 2018; 361:1239-1242. [DOI: 10.1126/science.aat4625] [Citation(s) in RCA: 44] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2018] [Accepted: 07/17/2018] [Indexed: 11/02/2022]
Affiliation(s)
- A. Opremcak
- Department of Physics, University of Wisconsin–Madison, Madison, WI 53706, USA
| | - I. V. Pechenezhskiy
- Department of Physics, University of Wisconsin–Madison, Madison, WI 53706, USA
| | - C. Howington
- Department of Physics, Syracuse University, Syracuse, NY 13244, USA
| | - B. G. Christensen
- Department of Physics, University of Wisconsin–Madison, Madison, WI 53706, USA
| | - M. A. Beck
- Department of Physics, University of Wisconsin–Madison, Madison, WI 53706, USA
| | - E. Leonard
- Department of Physics, University of Wisconsin–Madison, Madison, WI 53706, USA
| | - J. Suttle
- Department of Physics, University of Wisconsin–Madison, Madison, WI 53706, USA
| | - C. Wilen
- Department of Physics, University of Wisconsin–Madison, Madison, WI 53706, USA
| | - K. N. Nesterov
- Department of Physics, University of Wisconsin–Madison, Madison, WI 53706, USA
| | - G. J. Ribeill
- Department of Physics, University of Wisconsin–Madison, Madison, WI 53706, USA
| | - T. Thorbeck
- Department of Physics, University of Wisconsin–Madison, Madison, WI 53706, USA
| | - F. Schlenker
- Department of Physics, University of Wisconsin–Madison, Madison, WI 53706, USA
| | - M. G. Vavilov
- Department of Physics, University of Wisconsin–Madison, Madison, WI 53706, USA
| | - B. L. T. Plourde
- Department of Physics, Syracuse University, Syracuse, NY 13244, USA
| | - R. McDermott
- Department of Physics, University of Wisconsin–Madison, Madison, WI 53706, USA
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7
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Ockeloen-Korppi CF, Damskägg E, Pirkkalainen JM, Clerk AA, Woolley MJ, Sillanpää MA. Quantum Backaction Evading Measurement of Collective Mechanical Modes. PHYSICAL REVIEW LETTERS 2016; 117:140401. [PMID: 27740800 DOI: 10.1103/physrevlett.117.140401] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/08/2016] [Indexed: 06/06/2023]
Abstract
The standard quantum limit constrains the precision of an oscillator position measurement. It arises from a balance between the imprecision and the quantum backaction of the measurement. However, a measurement of only a single quadrature of the oscillator can evade the backaction and be made with arbitrary precision. Here we demonstrate quantum backaction evading measurements of a collective quadrature of two mechanical oscillators, both coupled to a common microwave cavity. The work allows for quantum state tomography of two mechanical oscillators, and provides a foundation for macroscopic mechanical entanglement and force sensing beyond conventional quantum limits.
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Affiliation(s)
- C F Ockeloen-Korppi
- Department of Applied Physics, Aalto University, P.O. Box 15100, FI-00076 AALTO, Finland
| | - E Damskägg
- Department of Applied Physics, Aalto University, P.O. Box 15100, FI-00076 AALTO, Finland
| | - J-M Pirkkalainen
- Department of Applied Physics, Aalto University, P.O. Box 15100, FI-00076 AALTO, Finland
| | - A A Clerk
- Department of Physics, McGill University, 3600 rue University, Montréal, Quebec H3A 2T8, Canada
| | - M J Woolley
- School of Engineering and Information Technology, UNSW Canberra, Australian Capital Territory 2600, Australia
| | - M A Sillanpää
- Department of Applied Physics, Aalto University, P.O. Box 15100, FI-00076 AALTO, Finland
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8
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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: 46] [Impact Index Per Article: 5.8] [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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9
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Barends R, Kelly J, Megrant A, Sank D, Jeffrey E, Chen Y, Yin Y, Chiaro B, Mutus J, Neill C, O'Malley P, Roushan P, Wenner J, White TC, Cleland AN, Martinis JM. Coherent Josephson qubit suitable for scalable quantum integrated circuits. PHYSICAL REVIEW LETTERS 2013; 111:080502. [PMID: 24010421 DOI: 10.1103/physrevlett.111.080502] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/05/2013] [Indexed: 06/02/2023]
Abstract
We demonstrate a planar, tunable superconducting qubit with energy relaxation times up to 44 μs. This is achieved by using a geometry designed to both minimize radiative loss and reduce coupling to materials-related defects. At these levels of coherence, we find a fine structure in the qubit energy lifetime as a function of frequency, indicating the presence of a sparse population of incoherent, weakly coupled two-level defects. We elucidate this defect physics by experimentally varying the geometry and by a model analysis. Our "Xmon" qubit combines facile fabrication, straightforward connectivity, fast control, and long coherence, opening a viable route to constructing a chip-based quantum computer.
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Affiliation(s)
- R Barends
- Department of Physics, University of California, Santa Barbara, California 93106, USA
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10
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Sete EA, Galiautdinov A, Mlinar E, Martinis JM, Korotkov AN. Catch-disperse-release readout for superconducting qubits. PHYSICAL REVIEW LETTERS 2013; 110:210501. [PMID: 23745846 DOI: 10.1103/physrevlett.110.210501] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/26/2013] [Indexed: 06/02/2023]
Abstract
We analyze a single-shot readout for superconducting qubits via the controlled catch, dispersion, and release of a microwave field. A tunable coupler is used to decouple the microwave resonator from the transmission line during the dispersive qubit-resonator interaction, thus circumventing damping from the Purcell effect. We show that, if the qubit frequency tuning is sufficiently adiabatic, a fast high-fidelity qubit readout is possible, even in the strongly nonlinear dispersive regime. Interestingly, the Jaynes-Cummings nonlinearity leads to the quadrature squeezing of the resonator field below the standard quantum limit, resulting in a significant decrease of the measurement error.
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Affiliation(s)
- Eyob A Sete
- Department of Electrical Engineering, University of California, Riverside, California 92521, USA.
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11
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Li J, Paraoanu GS, Cicak K, Altomare F, Park JI, Simmonds RW, Sillanpää MA, Hakonen PJ. Dynamical Autler-Townes control of a phase qubit. Sci Rep 2012; 2:645. [PMID: 22966420 PMCID: PMC3437518 DOI: 10.1038/srep00645] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2012] [Accepted: 08/22/2012] [Indexed: 11/23/2022] Open
Abstract
Routers, switches, and repeaters are essential components of modern information-processing systems. Similar devices will be needed in future superconducting quantum computers. In this work we investigate experimentally the time evolution of Autler-Townes splitting in a superconducting phase qubit under the application of a control tone resonantly coupled to the second transition. A three-level model that includes independently determined parameters for relaxation and dephasing gives excellent agreement with the experiment. The results demonstrate that the qubit can be used as a ON/OFF switch with 100 ns operating time-scale for the reflection/transmission of photons coming from an applied probe microwave tone. The ON state is realized when the control tone is sufficiently strong to generate an Autler-Townes doublet, suppressing the absorption of the probe tone photons and resulting in a maximum of transmission.
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Affiliation(s)
- Jian Li
- O.V. Lounasmaa Laboratory, Aalto University, PO Box 15100, FI-00076 AALTO, Finland.
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12
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Lecocq F, Pop IM, Peng Z, Matei I, Crozes T, Fournier T, Naud C, Guichard W, Buisson O. Junction fabrication by shadow evaporation without a suspended bridge. NANOTECHNOLOGY 2011; 22:315302. [PMID: 21737875 DOI: 10.1088/0957-4484/22/31/315302] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
We present a novel shadow evaporation technique for the realization of junctions and capacitors. The design by e-beam lithography of strongly asymmetric undercuts on a bilayer resist enables in situ fabrication of junctions and capacitors without the use of the well-known suspended bridge (Dolan 1977 Appl. Phys. Lett. 31 337-9). The absence of bridges increases the mechanical robustness of the resist mask as well as the accessible range of the junction size, from 10(-2) µm(2) to more than 10(4) µm(2). We have fabricated Al/AlO(x)/Al Josephson junctions, phase qubit and capacitors using a 100 kV e-beam writer. Although this high voltage enables a precise control of the undercut, implementation using a conventional 20 kV e-beam is also discussed. The phase qubit coherence times, extracted from spectroscopy resonance width, Rabi and Ramsey oscillation decays and energy relaxation measurements, are longer than the ones obtained in our previous samples realized by standard techniques. These results demonstrate the high quality of the junction obtained by this bridge-free technique.
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Affiliation(s)
- Florent Lecocq
- Institut Néel, CNRS and Université Joseph Fourier, Grenoble, France
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13
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Kataoka M, Fletcher JD, See P, Giblin SP, Janssen TJBM, Griffiths JP, Jones GAC, Farrer I, Ritchie DA. Tunable nonadiabatic excitation in a single-electron quantum dot. PHYSICAL REVIEW LETTERS 2011; 106:126801. [PMID: 21517337 DOI: 10.1103/physrevlett.106.126801] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/14/2010] [Indexed: 05/30/2023]
Abstract
We report the observation of nonadiabatic excitations of single electrons in a quantum dot. Using a tunable-barrier single-electron pump, we have developed a way of reading out the excitation spectrum and level population of the dot by using the pump current as a probe. When the potential well is deformed at subnanosecond time scales, electrons are excited to higher levels. In the presence of a perpendicular magnetic field, the excited states follow a Fock-Darwin spectrum. Our experiments provide a simple model system to study nonadiabatic processes of quantum particles.
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Affiliation(s)
- M Kataoka
- National Physical Laboratory, Hampton Road, Teddington, Middlesex TW11 0LW, United Kingdom
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14
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Lisenfeld J, Müller C, Cole JH, Bushev P, Lukashenko A, Shnirman A, Ustinov AV. Measuring the temperature dependence of individual two-level systems by direct coherent control. PHYSICAL REVIEW LETTERS 2010; 105:230504. [PMID: 21231441 DOI: 10.1103/physrevlett.105.230504] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/02/2010] [Indexed: 05/30/2023]
Abstract
We demonstrate a new method to directly manipulate the state of individual two-level systems (TLSs) in phase qubits. It allows one to characterize the coherence properties of TLSs using standard microwave pulse sequences, while the qubit is used only for state readout. We apply this method to measure the temperature dependence of TLS coherence for the first time. The energy relaxation time T1 is found to decrease quadratically with temperature for the two TLSs studied in this work, while their dephasing time measured in Ramsey and spin-echo experiments is found to be T1 limited at all temperatures.
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Affiliation(s)
- J Lisenfeld
- Physikalisches Institut, Karlsruhe Institute of Technology, D-76128 Karlsruhe, Germany
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15
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Bianchetti R, Filipp S, Baur M, Fink JM, Lang C, Steffen L, Boissonneault M, Blais A, Wallraff A. Control and tomography of a three level superconducting artificial atom. PHYSICAL REVIEW LETTERS 2010; 105:223601. [PMID: 21231385 DOI: 10.1103/physrevlett.105.223601] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/29/2010] [Indexed: 05/30/2023]
Abstract
A number of superconducting qubits, such as the transmon or the phase qubit, have an energy level structure with small anharmonicity. This allows for convenient access of higher excited states with similar frequencies. However, special care has to be taken to avoid unwanted higher-level populations when using short control pulses. Here we demonstrate the preparation of arbitrary three level superposition states using optimal control techniques in a transmon. Performing dispersive readout, we extract the populations of all three levels of the qutrit and study the coherence of its excited states. Finally we demonstrate full quantum state tomography of the prepared qutrit states and evaluate the fidelities of a set of states, finding on average 95%.
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Affiliation(s)
- R Bianchetti
- Department of Physics, ETH Zurich, CH-8093 Zürich, Switzerland
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16
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Shalibo Y, Rofe Y, Shwa D, Zeides F, Neeley M, Martinis JM, Katz N. Lifetime and coherence of two-level defects in a Josephson junction. PHYSICAL REVIEW LETTERS 2010; 105:177001. [PMID: 21231072 DOI: 10.1103/physrevlett.105.177001] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/14/2010] [Indexed: 05/30/2023]
Abstract
We measure the lifetime (T₁) and coherence (T₂) of two-level defect states (TLSs) in the insulating barrier of a Josephson phase qubit and compare to the interaction strength between the two systems. We find for the average decay times a power-law dependence on the corresponding interaction strengths, whereas for the average coherence times we find an optimum at intermediate coupling strengths. We explain both the lifetime and the coherence results using the standard TLS model, including dipole radiation by phonons and anticorrelated dependence of the energy parameters on environmental fluctuations.
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Affiliation(s)
- Yoni Shalibo
- Racah Institute of Physics, The Hebrew University of Jerusalem, Israel
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17
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Allman MS, Altomare F, Whittaker JD, Cicak K, Li D, Sirois A, Strong J, Teufel JD, Simmonds RW. rf-SQUID-mediated coherent tunable coupling between a superconducting phase qubit and a lumped-element resonator. PHYSICAL REVIEW LETTERS 2010; 104:177004. [PMID: 20482130 DOI: 10.1103/physrevlett.104.177004] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/06/2010] [Indexed: 05/29/2023]
Abstract
We demonstrate coherent tunable coupling between a superconducting phase qubit and a lumped-element resonator. The coupling strength is mediated by a flux-biased rf SQUID operated in the nonhysteretic regime. By tuning the applied flux bias to the rf SQUID we change the effective mutual inductance, and thus the coupling energy, between the phase qubit and resonator. We verify the modulation of coupling strength from 0 to 100 MHz by observing modulation in the size of the splitting in the phase qubit's spectroscopy, as well as coherently by observing modulation in the vacuum Rabi oscillation frequency when on resonance. The measured spectroscopic splittings and vacuum Rabi oscillations agree well with theoretical predictions.
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Affiliation(s)
- M S Allman
- National Institute of Standards and Technology, 325 Broadway, Boulder, Colorado 80305-3328, USA
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18
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Tsai JS. Toward a superconducting quantum computer. Harnessing macroscopic quantum coherence. PROCEEDINGS OF THE JAPAN ACADEMY. SERIES B, PHYSICAL AND BIOLOGICAL SCIENCES 2010; 86:275-292. [PMID: 20431256 PMCID: PMC3417795 DOI: 10.2183/pjab.86.275] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/16/2009] [Accepted: 02/09/2010] [Indexed: 05/29/2023]
Abstract
Intensive research on the construction of superconducting quantum computers has produced numerous important achievements. The quantum bit (qubit), based on the Josephson junction, is at the heart of this research. This macroscopic system has the ability to control quantum coherence. This article reviews the current state of quantum computing as well as its history, and discusses its future. Although progress has been rapid, the field remains beset with unsolved issues, and there are still many new research opportunities open to physicists and engineers.
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Affiliation(s)
- Jaw-Shen Tsai
- Nano Electronics Research Laboratories, NEC and Advanced Science Institute, RIKEN, 34 Miyukigaoka, Ibaraki, Japan.
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19
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Sillanpää MA, Li J, Cicak K, Altomare F, Park JI, Simmonds RW, Paraoanu GS, Hakonen PJ. Autler-Townes effect in a superconducting three-level system. PHYSICAL REVIEW LETTERS 2009; 103:193601. [PMID: 20365921 DOI: 10.1103/physrevlett.103.193601] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/16/2009] [Indexed: 05/29/2023]
Abstract
When a three-level quantum system is irradiated by an intense coupling field resonant with one of the three possible transitions, the absorption peak of an additional probe field involving the remaining level is split. This process is known in quantum optics as the Autler-Townes effect. We observe these phenomena in a superconducting Josephson phase qubit, which can be considered an "artificial atom" with a multilevel quantum structure. The spectroscopy peaks can be explained reasonably well by a simple three-level Hamiltonian model. Simulation of a more complete model (including dissipation, higher levels, and cross coupling) provides excellent agreement with all of the experimental data.
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Affiliation(s)
- Mika A Sillanpää
- Helsinki University of Technology, Low Temperature Laboratory, Puumiehenkuja 2B, Espoo, FIN-02015 HUT Finland.
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20
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Violation of Bell's inequality in Josephson phase qubits. Nature 2009; 461:504-6. [PMID: 19779447 DOI: 10.1038/nature08363] [Citation(s) in RCA: 85] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2009] [Accepted: 08/04/2009] [Indexed: 11/08/2022]
Abstract
The measurement process plays an awkward role in quantum mechanics, because measurement forces a system to 'choose' between possible outcomes in a fundamentally unpredictable manner. Therefore, hidden classical processes have been considered as possibly predetermining measurement outcomes while preserving their statistical distributions. However, a quantitative measure that can distinguish classically determined correlations from stronger quantum correlations exists in the form of the Bell inequalities, measurements of which provide strong experimental evidence that quantum mechanics provides a complete description. Here we demonstrate the violation of a Bell inequality in a solid-state system. We use a pair of Josephson phase qubits acting as spin-1/2 particles, and show that the qubits can be entangled and measured so as to violate the Clauser-Horne-Shimony-Holt (CHSH) version of the Bell inequality. We measure a Bell signal of 2.0732 +/- 0.0003, exceeding the maximum amplitude of 2 for a classical system by 244 standard deviations. In the experiment, we deterministically generate the entangled state, and measure both qubits in a single-shot manner, closing the detection loophole. Because the Bell inequality was designed to test for non-classical behaviour without assuming the applicability of quantum mechanics to the system in question, this experiment provides further strong evidence that a macroscopic electrical circuit is really a quantum system.
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21
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Romero G, García-Ripoll JJ, Solano E. Microwave photon detector in circuit QED. PHYSICAL REVIEW LETTERS 2009; 102:173602. [PMID: 19518782 DOI: 10.1103/physrevlett.102.173602] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/23/2008] [Indexed: 05/27/2023]
Abstract
In this Letter we design a metamaterial composed of discrete superconducting elements that implements a high-efficiency microwave photon detector. Our design consists of a microwave guide coupled to an array of metastable quantum circuits, whose internal states are irreversibly changed due to the absorption of photons. This proposal can be widely applied to different physical systems and can be generalized to implement a microwave photon counter.
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Affiliation(s)
- G Romero
- Departamento de Física, Universidad de Santiago de Chile, USACH, Casilla 307, Santiago 2, Chile
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22
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Hoskinson E, Lecocq F, Didier N, Fay A, Hekking FWJ, Guichard W, Buisson O, Dolata R, Mackrodt B, Zorin AB. Quantum dynamics in a camelback potential of a dc SQUID. PHYSICAL REVIEW LETTERS 2009; 102:097004. [PMID: 19392556 DOI: 10.1103/physrevlett.102.097004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/13/2008] [Indexed: 05/27/2023]
Abstract
We investigate a quadratic-quartic anharmonic oscillator formed by a potential well between two potential barriers. We realize this novel potential with a dc SQUID at near-zero current bias and flux bias near half a flux quantum. Escape out of the central well can occur via tunneling through either of the two barriers. We find good agreement with a generalized double-path macroscopic quantum tunneling theory. We also demonstrate an "optimal line" in current and flux bias along which the oscillator, which can be operated as a phase qubit, is insensitive to decoherence due to low-frequency current fluctuations.
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Affiliation(s)
- E Hoskinson
- Institut Néel, C.N.R.S.-Université Joseph Fourier, BP 166, 38042 Grenoble-cedex 9, France
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23
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Katz N, Neeley M, Ansmann M, Bialczak RC, Hofheinz M, Lucero E, O'Connell A, Wang H, Cleland AN, Martinis JM, Korotkov AN. Reversal of the weak measurement of a quantum state in a superconducting phase qubit. PHYSICAL REVIEW LETTERS 2008; 101:200401. [PMID: 19113317 DOI: 10.1103/physrevlett.101.200401] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/11/2008] [Indexed: 05/27/2023]
Abstract
We demonstrate in a superconducting qubit the conditional recovery (uncollapsing) of a quantum state after a partial-collapse measurement. A weak measurement extracts information and results in a nonunitary transformation of the qubit state. However, by adding a rotation and a second partial measurement with the same strength, we erase the extracted information, canceling the effect of both measurements. The fidelity of the state recovery is measured using quantum process tomography and found to be above 70% for partial-collapse strength less than 0.6.
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Affiliation(s)
- Nadav Katz
- Department of Physics, University of California, Santa Barbara, California 93106, USA
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24
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Abstract
Superconducting circuits are macroscopic in size but have generic quantum properties such as quantized energy levels, superposition of states, and entanglement, all of which are more commonly associated with atoms. Superconducting quantum bits (qubits) form the key component of these circuits. Their quantum state is manipulated by using electromagnetic pulses to control the magnetic flux, the electric charge or the phase difference across a Josephson junction (a device with nonlinear inductance and no energy dissipation). As such, superconducting qubits are not only of considerable fundamental interest but also might ultimately form the primitive building blocks of quantum computers.
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Affiliation(s)
- John Clarke
- Department of Physics,366 LeConte Hall, University of California, Berkeley, California 94720, USA.
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25
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Lucero E, Hofheinz M, Ansmann M, Bialczak RC, Katz N, Neeley M, O'Connell AD, Wang H, Cleland AN, Martinis JM. High-fidelity gates in a single josephson qubit. PHYSICAL REVIEW LETTERS 2008; 100:247001. [PMID: 18643615 DOI: 10.1103/physrevlett.100.247001] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/07/2008] [Indexed: 05/26/2023]
Abstract
We demonstrate new experimental procedures for measuring small errors in a superconducting quantum bit (qubit). By carefully separating out gate and measurement errors, we construct a complete error budget and demonstrate single qubit gate fidelities of 0.98, limited by energy relaxation. We also introduce a new metrology tool-- Ramsey interference error filter-that can measure the occupation probability of the state |2> which is outside the computational basis, down to 10{-4}, thereby confirming that our quantum system stays within the qubit manifold during single qubit logic operations.
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Affiliation(s)
- Erik Lucero
- Department of Physics, University of California at Santa Barbara, Broida Hall, Santa Barbara, California 93106, USA
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26
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Fay A, Hoskinson E, Lecocq F, Lévy LP, Hekking FWJ, Guichard W, Buisson O. Strong tunable coupling between a superconducting charge and phase qubit. PHYSICAL REVIEW LETTERS 2008; 100:187003. [PMID: 18518410 DOI: 10.1103/physrevlett.100.187003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/21/2007] [Indexed: 05/26/2023]
Abstract
We have realized a tunable coupling over a large frequency range between an asymmetric Cooper pair transistor (charge qubit) and a dc SQUID (phase qubit). Our circuit enables the independent manipulation of the quantum states of each qubit as well as their entanglement. The measurement of the charge qubit's quantum states is performed by an adiabatic quantum transfer from the charge to the phase qubit. The measured coupling strength is in agreement with an analytic theory including a capacitive and a tunable Josephson coupling between the two qubits.
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Affiliation(s)
- A Fay
- Institut Néel, C.N.R.S.-Université Joseph Fourier, BP 166, 38042 Grenoble-cedex 9, France
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27
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Bialczak RC, McDermott R, Ansmann M, Hofheinz M, Katz N, Lucero E, Neeley M, O'Connell AD, Wang H, Cleland AN, Martinis JM. 1/f Flux noise in Josephson phase qubits. PHYSICAL REVIEW LETTERS 2007; 99:187006. [PMID: 17995432 DOI: 10.1103/physrevlett.99.187006] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/11/2007] [Indexed: 05/25/2023]
Abstract
We present a new method to measure 1/f noise in Josephson quantum bits (qubits) that yields low-frequency spectra below 1 Hz. A comparison of the noise taken at positive and negative bias of a phase qubit shows the dominant noise source to be flux noise and not junction critical-current noise, with a magnitude similar to that measured previously in other systems. Theoretical calculations show that the level of flux noise is not compatible with the standard model of noise from two-level state defects in the surface oxides of the films.
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Affiliation(s)
- Radoslaw C Bialczak
- Department of Physics, University of California, Santa Barbara, California 93106, USA
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28
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Sillanpää MA, Park JI, Simmonds RW. Coherent quantum state storage and transfer between two phase qubits via a resonant cavity. Nature 2007; 449:438-42. [PMID: 17898762 DOI: 10.1038/nature06124] [Citation(s) in RCA: 113] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2007] [Accepted: 07/25/2007] [Indexed: 11/09/2022]
Abstract
As with classical information processing, a quantum information processor requires bits (qubits) that can be independently addressed and read out, long-term memory elements to store arbitrary quantum states, and the ability to transfer quantum information through a coherent communication bus accessible to a large number of qubits. Superconducting qubits made with scalable microfabrication techniques are a promising candidate for the realization of a large-scale quantum information processor. Although these systems have successfully passed tests of coherent coupling for up to four qubits, communication of individual quantum states between superconducting qubits via a quantum bus has not yet been realized. Here, we perform an experiment demonstrating the ability to coherently transfer quantum states between two superconducting Josephson phase qubits through a quantum bus. This quantum bus is a resonant cavity formed by an open-ended superconducting transmission line of length 7 mm. After preparing an initial quantum state with the first qubit, this quantum information is transferred and stored as a nonclassical photon state of the resonant cavity, then retrieved later by the second qubit connected to the opposite end of the cavity. Beyond simple state transfer, these results suggest that a high-quality-factor superconducting cavity could also function as a useful short-term memory element. The basic architecture presented here can be expanded, offering the possibility for the coherent interaction of a large number of superconducting qubits.
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Affiliation(s)
- Mika A Sillanpää
- National Institute of Standards and Technology, 325 Broadway, Boulder, Colorado 80305, USA
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29
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Lisenfeld J, Lukashenko A, Ansmann M, Martinis JM, Ustinov AV. Temperature dependence of coherent oscillations in Josephson phase qubits. PHYSICAL REVIEW LETTERS 2007; 99:170504. [PMID: 17995313 DOI: 10.1103/physrevlett.99.170504] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/23/2007] [Indexed: 05/25/2023]
Abstract
We experimentally investigate the temperature dependence of Rabi oscillations and Ramsey fringes in superconducting phase qubits. In a wide range of temperatures, we find that both the decay time and the amplitude of these coherent oscillations remain nearly unaffected by thermal fluctuations. In the two-level limit, coherent qubit response rapidly vanishes as soon as the energy of thermal fluctuations k(B)T becomes larger than the energy level spacing variant Planck's over h omega of the qubit. In contrast, a sample of much shorter coherence times displayed semiclassical oscillations very similar to Rabi oscillation, but showing a qualitatively different temperature dependence. Our observations shed new light on the origin of decoherence in superconducting qubits. The experimental data suggest that, without degrading already achieved coherence times, phase qubits can be operated at temperatures much higher than those reported till now.
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Affiliation(s)
- J Lisenfeld
- Physikalisches Institut III, Universität Erlangen-Nürnberg, D-91058 Erlangen, Germany
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30
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Yoshihara F, Harrabi K, Niskanen AO, Nakamura Y, Tsai JS. Decoherence of flux qubits due to 1/f flux noise. PHYSICAL REVIEW LETTERS 2006; 97:167001. [PMID: 17155426 DOI: 10.1103/physrevlett.97.167001] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/16/2006] [Indexed: 05/12/2023]
Abstract
We have investigated decoherence in Josephson-junction flux qubits. Based on the measurements of decoherence at various bias conditions, we discriminate contributions of different noise sources. We present a Gaussian decay function extracted from the echo signal as evidence of dephasing due to 1/f flux noise whose spectral density is evaluated to be about (10(-6)Phi0)2/Hz at 1 Hz. We also demonstrate that, at an optimal bias condition where the noise sources are well decoupled, the coherence observed in the echo measurement is limited mainly by energy relaxation of the qubit.
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Affiliation(s)
- F Yoshihara
- The Institute of Physical and Chemical Research (RIKEN), Wako, Saitama, Japan
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31
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Zagoskin AM, Ashhab S, Johansson JR, Nori F. Quantum two-level systems in Josephson junctions as naturally formed qubits. PHYSICAL REVIEW LETTERS 2006; 97:077001. [PMID: 17026265 DOI: 10.1103/physrevlett.97.077001] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/31/2006] [Indexed: 05/12/2023]
Abstract
The two-level systems (TLSs) naturally occurring in Josephson junctions constitute a major obstacle for the operation of superconducting phase qubits. Since these TLSs can possess remarkably long decoherence times, we show that such TLSs can themselves be used as qubits, allowing for a well controlled initialization, universal sets of quantum gates, and readout. Thus, a single current-biased Josephson junction can be considered as a multiqubit register. It can be coupled to other junctions to allow the application of quantum gates to an arbitrary pair of qubits in the system. Our results indicate an alternative way to realize superconducting quantum information processing.
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Affiliation(s)
- A M Zagoskin
- Frontier Research System, The Institute of Physical and Chemical Research (RIKEN), Wako-shi, Saitama, Japan
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32
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Steffen M, Ansmann M, McDermott R, Katz N, Bialczak RC, Lucero E, Neeley M, Weig EM, Cleland AN, Martinis JM. State tomography of capacitively shunted phase qubits with high fidelity. PHYSICAL REVIEW LETTERS 2006; 97:050502. [PMID: 17026085 DOI: 10.1103/physrevlett.97.050502] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/17/2006] [Indexed: 05/12/2023]
Abstract
We introduce a new design concept for superconducting phase quantum bits (qubits) in which we explicitly separate the capacitive element from the Josephson tunnel junction for improved qubit performance. The number of two-level systems that couple to the qubit is thereby reduced by an order of magnitude and the measurement fidelity improves to 90%. This improved design enables the first demonstration of quantum state tomography with superconducting qubits using single-shot measurements.
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Affiliation(s)
- Matthias Steffen
- Department of Physics and California Nanosystems Institute, University of California, Santa Barbara, CA 93106, USA
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33
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Katz N, Ansmann M, Bialczak RC, Lucero E, McDermott R, Neeley M, Steffen M, Weig EM, Cleland AN, Martinis JM, Korotkov AN. Coherent State Evolution in a Superconducting Qubit from Partial-Collapse Measurement. Science 2006; 312:1498-500. [PMID: 16763142 DOI: 10.1126/science.1126475] [Citation(s) in RCA: 141] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Measurement is one of the fundamental building blocks of quantum-information processing systems. Partial measurement, where full wavefunction collapse is not the only outcome, provides a detailed test of the measurement process. We introduce quantum-state tomography in a superconducting qubit that exhibits high-fidelity single-shot measurement. For the two probabilistic outcomes of partial measurement, we find either a full collapse or a coherent yet nonunitary evolution of the state. This latter behavior explicitly confirms modern quantum-measurement theory and may prove important for error-correction algorithms in quantum computation.
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Affiliation(s)
- N Katz
- Department of Physics and California NanoSystems Institute, University of California, Santa Barbara, CA 93106, USA
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34
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Lupaşcu A, Driessen EFC, Roschier L, Harmans CJPM, Mooij JE. High-contrast dispersive readout of a superconducting flux qubit using a nonlinear resonator. PHYSICAL REVIEW LETTERS 2006; 96:127003. [PMID: 16605947 DOI: 10.1103/physrevlett.96.127003] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/27/2006] [Indexed: 05/08/2023]
Abstract
We demonstrate high-contrast state detection of a superconducting flux qubit. Detection is realized by probing the microwave transmission of a nonlinear resonator, based on a SQUID. Depending on the driving strength of the resonator, the detector can be operated in the monostable or the bistable mode. The bistable operation combines high-sensitivity with intrinsic latching. The measured contrast of Rabi oscillations is as high as 87%; of the missing 13%, only 3% of the loss of contrast is unaccounted for. Experiments involving two consecutive detection pulses are consistent with preparation of the qubit state by the first measurement.
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Affiliation(s)
- A Lupaşcu
- Kavli Institute of Nanoscience, Delft University of Technology, Post Office Box 5046, 2600GA Delft, The Netherlands
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35
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Martinis JM, Cooper KB, McDermott R, Steffen M, Ansmann M, Osborn KD, Cicak K, Oh S, Pappas DP, Simmonds RW, Yu CC. Decoherence in Josephson qubits from dielectric loss. PHYSICAL REVIEW LETTERS 2005; 95:210503. [PMID: 16384123 DOI: 10.1103/physrevlett.95.210503] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/21/2005] [Indexed: 05/05/2023]
Abstract
Dielectric loss from two-level states is shown to be a dominant decoherence source in superconducting quantum bits. Depending on the qubit design, dielectric loss from insulating materials or the tunnel junction can lead to short coherence times. We show that a variety of microwave and qubit measurements are well modeled by loss from resonant absorption of two-level defects. Our results demonstrate that this loss can be significantly reduced by using better dielectrics and fabricating junctions of small area . With a redesigned phase qubit employing low-loss dielectrics, the energy relaxation rate has been improved by a factor of 20, opening up the possibility of multiqubit gates and algorithms.
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Affiliation(s)
- John M Martinis
- Department of Physics, University of California, Santa Barbara, California 93106, USA
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36
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Johnson PR, Parsons WT, Strauch FW, Anderson JR, Dragt AJ, Lobb CJ, Wellstood FC. Macroscopic tunnel splittings in superconducting phase qubits. PHYSICAL REVIEW LETTERS 2005; 94:187004. [PMID: 15904404 DOI: 10.1103/physrevlett.94.187004] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/23/2004] [Indexed: 05/02/2023]
Abstract
Prototype Josephson-junction based qubit coherence times are too short for quantum computing. Recent experiments probing superconducting phase qubits have revealed previously unseen fine splittings in the transition energy spectra. These splittings have been attributed to new microscopic degrees of freedom (microresonators), a previously unknown source of decoherence. We show that macroscopic resonant tunneling in the extremely asymmetric double-well potential of the phase qubit can have observational consequences that are strikingly similar to the observed data.
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Affiliation(s)
- Philip R Johnson
- Department of Physics, University of Maryland, College Park, MD 20850, USA.
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37
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McDermott R, Simmonds RW, Steffen M, Cooper KB, Cicak K, Osborn KD, Oh S, Pappas DP, Martinis JM. Simultaneous State Measurement of Coupled Josephson Phase Qubits. Science 2005; 307:1299-302. [PMID: 15731451 DOI: 10.1126/science.1107572] [Citation(s) in RCA: 247] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
One of the many challenges of building a scalable quantum computer is single-shot measurement of all the quantum bits (qubits). We have used simultaneous single-shot measurement of coupled Josephson phase qubits to directly probe interaction of the qubits in the time domain. The concept of measurement crosstalk is introduced, and we show that its effects are minimized by careful adjustment of the timing of the measurements. We observe the antiphase oscillation of the two-qubit 01 and 10 states, consistent with quantum mechanical entanglement of these states, thereby opening the possibility for full characterization of multiqubit gates and elementary quantum algorithms.
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Affiliation(s)
- R McDermott
- Department of Physics, University of California, Santa Barbara, CA 93106, USA
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