1
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Dogra S, McCord JJ, Paraoanu GS. Coherent interaction-free detection of microwave pulses with a superconducting circuit. Nat Commun 2022; 13:7528. [PMID: 36476574 PMCID: PMC9729670 DOI: 10.1038/s41467-022-35049-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2022] [Accepted: 11/16/2022] [Indexed: 12/12/2022] Open
Abstract
The interaction-free measurement is a fundamental quantum effect whereby the presence of a photosensitive object is determined without irreversible photon absorption. Here we propose the concept of coherent interaction-free detection and demonstrate it experimentally using a three-level superconducting transmon circuit. In contrast to standard interaction-free measurement setups, where the dynamics involves a series of projection operations, our protocol employs a fully coherent evolution that results, surprisingly, in a higher probability of success. We show that it is possible to ascertain the presence of a microwave pulse resonant with the second transition of the transmon, while at the same time avoid exciting the device onto the third level. Experimentally, this is done by using a series of Ramsey microwave pulses coupled into the first transition and monitoring the ground-state population.
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Affiliation(s)
- Shruti Dogra
- grid.5373.20000000108389418QTF Centre of Excellence, Department of Applied Physics, Aalto University, FI-00076 Aalto, Finland
| | - John J. McCord
- grid.5373.20000000108389418QTF Centre of Excellence, Department of Applied Physics, Aalto University, FI-00076 Aalto, Finland
| | - Gheorghe Sorin Paraoanu
- grid.5373.20000000108389418QTF Centre of Excellence, Department of Applied Physics, Aalto University, FI-00076 Aalto, Finland
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2
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Song M, Steinmetz J, Zhang Y, Nauriyal J, Lyons K, Jordan AN, Cardenas J. Enhanced on-chip phase measurement by inverse weak value amplification. Nat Commun 2021; 12:6247. [PMID: 34716353 PMCID: PMC8556267 DOI: 10.1038/s41467-021-26522-2] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2021] [Accepted: 10/05/2021] [Indexed: 12/01/2022] Open
Abstract
Optical interferometry plays an essential role in precision metrology such as in gravitational wave detection, gyroscopes, and environmental sensing. Weak value amplification enables reaching the shot-noise-limit of sensitivity, which is difficult for most optical sensors, by amplifying the interferometric signal without amplifying certain technical noises. We implement a generalized form of weak value amplification on an integrated photonic platform with a multi-mode interferometer. Our results pave the way for a more sensitive, robust, and compact platform for measuring phase, which can be adapted to fields such as coherent communications and the quantum domain. In this work, we show a 7 dB signal enhancement in our weak value device over a standard Mach-Zehnder interferometer with equal detected optical power, as well as frequency measurements with 2 kHz sensitivity by adding a ring resonator.
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Affiliation(s)
- Meiting Song
- The Institute of Optics, University of Rochester, Rochester, NY, 14627, USA
| | - John Steinmetz
- Department of Physics and Astronomy, University of Rochester, Rochester, NY, 14627, USA
| | - Yi Zhang
- The Institute of Optics, University of Rochester, Rochester, NY, 14627, USA
| | - Juniyali Nauriyal
- The Institute of Optics, University of Rochester, Rochester, NY, 14627, USA
- Department of Electrical and Computer Engineering, University of Rochester, Rochester, NY, 14627, USA
| | - Kevin Lyons
- Hoplite AI, 2 Fox Glen Ct., Clifton Park, NY, 12065, USA
| | - Andrew N Jordan
- Department of Physics and Astronomy, University of Rochester, Rochester, NY, 14627, USA
- Institute for Quantum Studies, Chapman University, Orange, CA, 92866, USA
| | - Jaime Cardenas
- The Institute of Optics, University of Rochester, Rochester, NY, 14627, USA.
- Department of Physics and Astronomy, University of Rochester, Rochester, NY, 14627, USA.
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3
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Fang SZ, Tan HT, Li GX, Wu QL. Weak value amplification for angular velocity measurements. APPLIED OPTICS 2021; 60:4335-4339. [PMID: 34143122 DOI: 10.1364/ao.420231] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/20/2021] [Accepted: 04/23/2021] [Indexed: 06/12/2023]
Abstract
The weak-value-amplification technique has shown great importance in the measurement of tiny physical effects. Here we introduce a polarization-dependent angular velocity measurement system consisting of two Glan prisms and a true zero-order half-wave plate, where a non-Fourier-limited Gaussian pulse acts as the meter. The angular velocities measurements results agree well with theoretical predictions, and its uncertainties are bounded by the Cramér-Rao bound. We also investigate uncertainties of angular velocities for different numbers of detected photons and the smallest reliable postselection probability, which can reach ${3.42*10^{- 6}}$.
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4
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Monroe JT, Yunger Halpern N, Lee T, Murch KW. Weak Measurement of a Superconducting Qubit Reconciles Incompatible Operators. PHYSICAL REVIEW LETTERS 2021; 126:100403. [PMID: 33784149 DOI: 10.1103/physrevlett.126.100403] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/25/2020] [Revised: 11/19/2020] [Accepted: 01/29/2021] [Indexed: 06/12/2023]
Abstract
Traditional uncertainty relations dictate a minimal amount of noise in incompatible projective quantum measurements. However, not all measurements are projective. Weak measurements are minimally invasive methods for obtaining partial state information without projection. Recently, weak measurements were shown to obey an uncertainty relation cast in terms of entropies. We experimentally test this entropic uncertainty relation with strong and weak measurements of a superconducting transmon qubit. A weak measurement, we find, can reconcile two strong measurements' incompatibility, via backaction on the state. Mathematically, a weak value-a preselected and postselected expectation value-lowers the uncertainty bound. Hence we provide experimental support for the physical interpretation of the weak value as a determinant of a weak measurement's ability to reconcile incompatible operations.
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Affiliation(s)
- Jonathan T Monroe
- Department of Physics, Washington University, St. Louis, Missouri 63130, USA
| | - Nicole Yunger Halpern
- ITAMP, Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts 02138, USA
- Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
- Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
- Center for Theoretical Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
- Joint Center for Quantum Information and Computer Science, NIST and University of Maryland, College Park, Maryland 20742, USA
- Institute for Physical Science and Technology, University of Maryland, College Park, Maryland 20742, USA
- Institute for Quantum Information and Matter, California Institute of Technology, Pasadena, California 91125, USA
| | - Taeho Lee
- Department of Physics, Washington University, St. Louis, Missouri 63130, USA
| | - Kater W Murch
- Department of Physics, Washington University, St. Louis, Missouri 63130, USA
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5
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Naghiloo M, Tan D, Harrington PM, Alonso JJ, Lutz E, Romito A, Murch KW. Heat and Work Along Individual Trajectories of a Quantum Bit. PHYSICAL REVIEW LETTERS 2020; 124:110604. [PMID: 32242716 DOI: 10.1103/physrevlett.124.110604] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/28/2019] [Accepted: 02/07/2020] [Indexed: 06/11/2023]
Abstract
We use a near quantum limited detector to experimentally track individual quantum state trajectories of a driven qubit formed by the hybridization of a waveguide cavity and a transmon circuit. For each measured quantum coherent trajectory, we separately identify energy changes of the qubit as heat and work, and verify the first law of thermodynamics for an open quantum system. We further establish the consistency of these results by comparison with the master equation approach and the two-projective-measurement scheme, both for open and closed dynamics, with the help of a quantum feedback loop that compensates for the exchanged heat and effectively isolates the qubit.
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Affiliation(s)
- M Naghiloo
- Department of Physics, Washington University, St. Louis, Missouri 63130, USA
| | - D Tan
- Department of Physics, Washington University, St. Louis, Missouri 63130, USA
- Shenzhen Institute for Quantum Science and Engineering and Department of Physics, Southern University of Science and Technology, Shenzhen 518055, People's Republic of China
| | - P M Harrington
- Department of Physics, Washington University, St. Louis, Missouri 63130, USA
| | - J J Alonso
- Department of Physics, Friedrich-Alexander-Universität Erlangen-Nürnberg, D-91058 Erlangen, Germany
| | - E Lutz
- Institute for Theoretical Physics I, University of Stuttgart, D-70550 Stuttgart, Germany
| | - A Romito
- Department of Physics, Lancaster University, Lancaster LA1 4YB, United Kingdom
| | - K W Murch
- Department of Physics, Washington University, St. Louis, Missouri 63130, USA
- Institute for Materials Science and Engineering, St. Louis, Missouri 63130, USA
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6
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High-resolution spectroscopy of single nuclear spins via sequential weak measurements. Nat Commun 2019; 10:594. [PMID: 30723212 PMCID: PMC6363762 DOI: 10.1038/s41467-019-08544-z] [Citation(s) in RCA: 43] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2018] [Accepted: 01/16/2019] [Indexed: 12/04/2022] Open
Abstract
Nuclear magnetic resonance (NMR) of single spins have recently been detected by quantum sensors. However, the spectral resolution has been limited by the sensor’s relaxation to a few kHz at room temperature. This can be improved by using quantum memories, at the expense of sensitivity. In contrast, classical signals can be measured with exceptional spectral resolution by using continuous measurement techniques, without compromising sensitivity. When applied to single-spin NMR, it is critical to overcome the impact of back action inherent of quantum measurement. Here we report sequential weak measurements on a single 13C nuclear spin. The back-action causes the spin to undergo a quantum dynamics phase transition from coherent trapping to coherent oscillation. Single-spin NMR at room-temperature with a spectral resolution of 3.8 Hz is achieved. These results enable the use of measurement-correlation schemes for the detection of very weakly coupled single spins. Quantum sensors can have exceptional properties but the limits on their performance involve nonclassical effects such as quantum backaction. Here the authors show how to mitigate the effects of backaction on the spectral resolution of an NV centre nuclear spin sensor by controlling the measurement strength.
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7
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Abstract
Conditional expectation values of quantum mechanical observables reflect unique non-classical correlations, and are generally sensitive to decoherence. We consider the circumstances under which such sensitivity to decoherence is removed, namely, when the measurement process is subjected to conservation laws. Specifically, we address systems with additive conserved quantities and identify sufficient conditions for the system state such that its coherence plays no role in the conditional expectation values of observables that commute with the conserved quantity. We discuss our findings for a specific model where the system-detector coupling is given by the Jaynes-Cummings interaction, which is relevant to experiments tracking trajectories of qubits in cavities. Our results clarify, among others, the role of coherence in thermal measurements in current architectures for quantum thermodynamics experiments.
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8
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Direct quantum process tomography via measuring sequential weak values of incompatible observables. Nat Commun 2018; 9:192. [PMID: 29335489 PMCID: PMC5768737 DOI: 10.1038/s41467-017-02511-2] [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: 08/20/2017] [Accepted: 12/06/2017] [Indexed: 11/09/2022] Open
Abstract
The weak value concept has enabled fundamental studies of quantum measurement and, recently, found potential applications in quantum and classical metrology. However, most weak value experiments reported to date do not require quantum mechanical descriptions, as they only exploit the classical wave nature of the physical systems. In this work, we demonstrate measurement of the sequential weak value of two incompatible observables by making use of two-photon quantum interference so that the results can only be explained quantum physically. We then demonstrate that the sequential weak value measurement can be used to perform direct quantum process tomography of a qubit channel. Our work not only demonstrates the quantum nature of weak values but also presents potential new applications of weak values in analyzing quantum channels and operations.
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9
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Wang K, Emary C, Zhan X, Bian Z, Li J, Xue P. Enhanced violations of Leggett-Garg inequalities in an experimental three-level system. OPTICS EXPRESS 2017; 25:31462-31470. [PMID: 29245821 DOI: 10.1364/oe.25.031462] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/17/2017] [Accepted: 11/22/2017] [Indexed: 06/07/2023]
Abstract
Leggett-Garg inequalities are tests of macroscopic realism that can be violated by quantum mechanics. In this letter, we realise photonic Leggett-Garg tests on a three-level system and implement measurements that admit three distinct measurement outcomes, rather than the usual two. In this way we obtain violations of three- and four-time Leggett-Garg inequalities that are significantly in excess of those obtainable in standard Leggett-Garg tests. We also report violations the quantum-witness equality up to the maximum permitted for a three-outcome measurement. Our results highlight differences between spatial and temporal correlations in quantum mechanics.
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10
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Wendin G. Quantum information processing with superconducting circuits: a review. REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2017; 80:106001. [PMID: 28682303 DOI: 10.1088/1361-6633/aa7e1a] [Citation(s) in RCA: 107] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
During the last ten years, superconducting circuits have passed from being interesting physical devices to becoming contenders for near-future useful and scalable quantum information processing (QIP). Advanced quantum simulation experiments have been shown with up to nine qubits, while a demonstration of quantum supremacy with fifty qubits is anticipated in just a few years. Quantum supremacy means that the quantum system can no longer be simulated by the most powerful classical supercomputers. Integrated classical-quantum computing systems are already emerging that can be used for software development and experimentation, even via web interfaces. Therefore, the time is ripe for describing some of the recent development of superconducting devices, systems and applications. As such, the discussion of superconducting qubits and circuits is limited to devices that are proven useful for current or near future applications. Consequently, the centre of interest is the practical applications of QIP, such as computation and simulation in Physics and Chemistry.
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Affiliation(s)
- G Wendin
- Department of Microtechnology and Nanoscience-MC2, Chalmers University of Technology, SE-41296 Gothenburg, Sweden
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11
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George RE, Senior J, Saira OP, Pekola JP, de Graaf SE, Lindström T, Pashkin YA. Multiplexing Superconducting Qubit Circuit for Single Microwave Photon Generation. JOURNAL OF LOW TEMPERATURE PHYSICS 2017; 189:60-75. [PMID: 32025044 PMCID: PMC6979489 DOI: 10.1007/s10909-017-1787-x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/14/2016] [Accepted: 06/20/2017] [Indexed: 06/10/2023]
Abstract
We report on a device that integrates eight superconducting transmon qubits in λ / 4 superconducting coplanar waveguide resonators fed from a common feedline. Using this multiplexing architecture, each resonator and qubit can be addressed individually, thus reducing the required hardware resources and allowing their individual characterisation by spectroscopic methods. The measured device parameters agree with the designed values, and the resonators and qubits exhibit excellent coherence properties and strong coupling, with the qubit relaxation rate dominated by the Purcell effect when brought in resonance with the resonator. Our analysis shows that the circuit is suitable for generation of single microwave photons on demand with an efficiency exceeding 80%.
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Affiliation(s)
- R. E. George
- Physics Department, Lancaster University, Lancaster, LA1 4YB UK
| | - J. Senior
- Low Temperature Laboratory, Department of Applied Physics, Aalto University School of Science, P.O. Box 13500, 00076 AALTO, Finland
| | - O.-P. Saira
- Low Temperature Laboratory, Department of Applied Physics, Aalto University School of Science, P.O. Box 13500, 00076 AALTO, Finland
| | - J. P. Pekola
- Low Temperature Laboratory, Department of Applied Physics, Aalto University School of Science, P.O. Box 13500, 00076 AALTO, Finland
| | - S. E. de Graaf
- National Physical Laboratory, Hampton Road, Teddington, TW11 0LW UK
| | - T. Lindström
- National Physical Laboratory, Hampton Road, Teddington, TW11 0LW UK
| | - Yu A. Pashkin
- Physics Department, Lancaster University, Lancaster, LA1 4YB UK
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12
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Knee GC, Kakuyanagi K, Yeh MC, Matsuzaki Y, Toida H, Yamaguchi H, Saito S, Leggett AJ, Munro WJ. A strict experimental test of macroscopic realism in a superconducting flux qubit. Nat Commun 2016; 7:13253. [PMID: 27811844 PMCID: PMC5097155 DOI: 10.1038/ncomms13253] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2016] [Accepted: 09/15/2016] [Indexed: 11/15/2022] Open
Abstract
Macroscopic realism is the name for a class of modifications to quantum theory that allow macroscopic objects to be described in a measurement-independent manner, while largely preserving a fully quantum mechanical description of the microscopic world. Objective collapse theories are examples which aim to solve the quantum measurement problem through modified dynamical laws. Whether such theories describe nature, however, is not known. Here we describe and implement an experimental protocol capable of constraining theories of this class, that is more noise tolerant and conceptually transparent than the original Leggett–Garg test. We implement the protocol in a superconducting flux qubit, and rule out (by ∼84 s.d.) those theories which would deny coherent superpositions of 170 nA currents over a ∼10 ns timescale. Further, we address the ‘clumsiness loophole' by determining classical disturbance with control experiments. Our results constitute strong evidence for the superposition of states of nontrivial macroscopic distinctness. Objective collapse theories are formulations of quantum physics that attempt to solve the measurement problem through modified dynamical laws. Here, the authors constrain such theories by testing a generalization of the Leggett-Garg inequality in a superconducting flux qubit experiment.
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Affiliation(s)
- George C Knee
- NTT Basic Research Laboratories, NTT Corporation, 3-1 Morinosato-Wakamiya, Atsugi, Kanagawa 243-0198, Japan
| | - Kosuke Kakuyanagi
- NTT Basic Research Laboratories, NTT Corporation, 3-1 Morinosato-Wakamiya, Atsugi, Kanagawa 243-0198, Japan
| | - Mao-Chuang Yeh
- Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
| | - Yuichiro Matsuzaki
- NTT Basic Research Laboratories, NTT Corporation, 3-1 Morinosato-Wakamiya, Atsugi, Kanagawa 243-0198, Japan
| | - Hiraku Toida
- NTT Basic Research Laboratories, NTT Corporation, 3-1 Morinosato-Wakamiya, Atsugi, Kanagawa 243-0198, Japan
| | - Hiroshi Yamaguchi
- NTT Basic Research Laboratories, NTT Corporation, 3-1 Morinosato-Wakamiya, Atsugi, Kanagawa 243-0198, Japan
| | - Shiro Saito
- NTT Basic Research Laboratories, NTT Corporation, 3-1 Morinosato-Wakamiya, Atsugi, Kanagawa 243-0198, Japan
| | - Anthony J Leggett
- Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
| | - William J Munro
- NTT Basic Research Laboratories, NTT Corporation, 3-1 Morinosato-Wakamiya, Atsugi, Kanagawa 243-0198, Japan
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13
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Mapping quantum state dynamics in spontaneous emission. Nat Commun 2016; 7:11527. [PMID: 27167893 PMCID: PMC4865872 DOI: 10.1038/ncomms11527] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2016] [Accepted: 04/05/2016] [Indexed: 11/08/2022] Open
Abstract
The evolution of a quantum state undergoing radiative decay depends on how its emission is detected. If the emission is detected in the form of energy quanta, the evolution is characterized by a quantum jump to a lower energy state. In contrast, detection of the wave nature of the emitted radiation leads to different dynamics. Here, we investigate the diffusive dynamics of a superconducting artificial atom under continuous homodyne detection of its spontaneous emission. Using quantum state tomography, we characterize the correlation between the detected homodyne signal and the emitter's state, and map out the conditional back-action of homodyne measurement. By tracking the diffusive quantum trajectories of the state as it decays, we characterize selective stochastic excitation induced by the choice of measurement basis. Our results demonstrate dramatic differences from the quantum jump evolution associated with photodetection and highlight how continuous field detection can be harnessed to control quantum evolution.
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14
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Piacentini F, Avella A, Levi MP, Lussana R, Villa F, Tosi A, Zappa F, Gramegna M, Brida G, Degiovanni IP, Genovese M. Experiment Investigating the Connection between Weak Values and Contextuality. PHYSICAL REVIEW LETTERS 2016; 116:180401. [PMID: 27203309 DOI: 10.1103/physrevlett.116.180401] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/05/2016] [Indexed: 06/05/2023]
Abstract
Weak value measurements have recently given rise to a great amount of interest in both the possibility of measurement amplification and the chance for further quantum mechanics foundations investigation. In particular, a question emerged about weak values being proof of the incompatibility between quantum mechanics and noncontextual hidden variables theories (NCHVTs). A test to provide a conclusive answer to this question was given by Pusey [Phys. Rev. Lett. 113, 200401 (2014)], where a theorem was derived showing the NCHVT incompatibility with the observation of anomalous weak values under specific conditions. In this Letter we realize this proposal, clearly pointing out the connection between weak values and the contextual nature of quantum mechanics.
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Affiliation(s)
- F Piacentini
- INRIM, Strada delle Cacce 91, I-10135 Torino, Italy
| | - A Avella
- INRIM, Strada delle Cacce 91, I-10135 Torino, Italy
| | - M P Levi
- INRIM, Strada delle Cacce 91, I-10135 Torino, Italy
| | - R Lussana
- Politecnico di Milano, Dipartimento di Elettronica, Informazione e Bioingegneria, Piazza Leonardo da Vinci 32, 20133 Milano, Italy
| | - F Villa
- Politecnico di Milano, Dipartimento di Elettronica, Informazione e Bioingegneria, Piazza Leonardo da Vinci 32, 20133 Milano, Italy
| | - A Tosi
- Politecnico di Milano, Dipartimento di Elettronica, Informazione e Bioingegneria, Piazza Leonardo da Vinci 32, 20133 Milano, Italy
| | - F Zappa
- Politecnico di Milano, Dipartimento di Elettronica, Informazione e Bioingegneria, Piazza Leonardo da Vinci 32, 20133 Milano, Italy
| | - M Gramegna
- INRIM, Strada delle Cacce 91, I-10135 Torino, Italy
| | - G Brida
- INRIM, Strada delle Cacce 91, I-10135 Torino, Italy
| | | | - M Genovese
- INRIM, Strada delle Cacce 91, I-10135 Torino, Italy
- INFN, Via P. Giuria 1, I-10125 Torino, Italy
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15
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Foroozani N, Naghiloo M, Tan D, Mølmer K, Murch KW. Correlations of the Time Dependent Signal and the State of a Continuously Monitored Quantum System. PHYSICAL REVIEW LETTERS 2016; 116:110401. [PMID: 27035288 DOI: 10.1103/physrevlett.116.110401] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/05/2015] [Indexed: 06/05/2023]
Abstract
In quantum physics, measurements give random results and yield a corresponding random backaction on the state of the system subject to measurement. If a quantum system is probed continuously over time, its state evolves along a stochastic quantum trajectory. To investigate the characteristic properties of such dynamics, we perform weak continuous measurements on a superconducting qubit that is driven to undergo Rabi oscillations. From the data we observe a number of striking temporal correlations within the time dependent signals and the quantum trajectories of the qubit, and we discuss their explanation in terms of quantum measurement and photodetection theory.
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Affiliation(s)
- N Foroozani
- Department of Physics, Washington University, St. Louis, Missouri 63130, USA
| | - M Naghiloo
- Department of Physics, Washington University, St. Louis, Missouri 63130, USA
| | - D Tan
- Department of Physics, Washington University, St. Louis, Missouri 63130, USA
| | - K Mølmer
- Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C, Denmark
| | - K W Murch
- Department of Physics, Washington University, St. Louis, Missouri 63130, USA
- Institute for Materials Science and Engineering, St. Louis, Missouri 63130, USA
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16
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Feng W, Liang P, Qin L, Li XQ. Exact quantum Bayesian rule for qubit measurements in circuit QED. Sci Rep 2016; 6:20492. [PMID: 26841968 PMCID: PMC4740905 DOI: 10.1038/srep20492] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2015] [Accepted: 01/05/2016] [Indexed: 11/10/2022] Open
Abstract
Developing efficient framework for quantum measurements is of essential importance to quantum science and technology. In this work, for the important superconducting circuit-QED setup, we present a rigorous and analytic solution for the effective quantum trajectory equation (QTE) after polaron transformation and converted to the form of Stratonovich calculus. We find that the solution is a generalization of the elegant quantum Bayesian approach developed in arXiv:1111.4016 by Korotokov and currently applied to circuit-QED measurements. The new result improves both the diagonal and off-diagonal elements of the qubit density matrix, via amending the distribution probabilities of the output currents and several important phase factors. Compared to numerical integration of the QTE, the resultant quantum Bayesian rule promises higher efficiency to update the measured state, and allows more efficient and analytical studies for some interesting problems such as quantum weak values, past quantum state, and quantum state smoothing. The method of this work opens also a new way to obtain quantum Bayesian formulas for other systems and in more complicated cases.
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Affiliation(s)
- Wei Feng
- Department of Physics, Tianjin University, Tianjin 300072, China
- Center for Advanced Quantum Studies and Department of Physics, Beijing Normal University, Beijing 100875, China
| | - Pengfei Liang
- Center for Advanced Quantum Studies and Department of Physics, Beijing Normal University, Beijing 100875, China
| | - Lupei Qin
- Center for Advanced Quantum Studies and Department of Physics, Beijing Normal University, Beijing 100875, China
| | - Xin-Qi Li
- Center for Advanced Quantum Studies and Department of Physics, Beijing Normal University, Beijing 100875, China
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17
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Budroni C, Vitagliano G, Colangelo G, Sewell RJ, Gühne O, Tóth G, Mitchell MW. Quantum Nondemolition Measurement Enables Macroscopic Leggett-Garg Tests. PHYSICAL REVIEW LETTERS 2015; 115:200403. [PMID: 26613423 DOI: 10.1103/physrevlett.115.200403] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/27/2015] [Indexed: 06/05/2023]
Abstract
We show how a test of macroscopic realism based on Leggett-Garg inequalities (LGIs) can be performed in a macroscopic system. Using a continuous-variable approach, we consider quantum nondemolition (QND) measurements applied to atomic ensembles undergoing magnetically driven coherent oscillation. We identify measurement schemes requiring only Gaussian states as inputs and giving a significant LGI violation with realistic experimental parameters and imperfections. The predicted violation is shown to be due to true quantum effects rather than to a classical invasivity of the measurement. Using QND measurements to tighten the "clumsiness loophole" forces the stubborn macrorealist to recreate quantum backaction in his or her account of measurement.
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Affiliation(s)
- C Budroni
- Naturwissenschaftlich-Technische Fakultät, Universität Siegen, Walter-Flex-Str. 3, D-57068 Siegen, Germany
| | - G Vitagliano
- Department of Theoretical Physics, University of the Basque Country UPV/EHU, P.O. Box 644, E-48080 Bilbao, Spain
| | - G Colangelo
- ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, 08860 Castelldefels, Barcelona, Spain
| | - R J Sewell
- ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, 08860 Castelldefels, Barcelona, Spain
| | - O Gühne
- Naturwissenschaftlich-Technische Fakultät, Universität Siegen, Walter-Flex-Str. 3, D-57068 Siegen, Germany
| | - G Tóth
- Department of Theoretical Physics, University of the Basque Country UPV/EHU, P.O. Box 644, E-48080 Bilbao, Spain
- IKERBASQUE, Basque Foundation for Science, E-48013 Bilbao, Spain
- Wigner Research Centre for Physics, Hungarian Academy of Sciences, P.O. Box 49, H-1525 Budapest, Hungary
| | - M W Mitchell
- ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, 08860 Castelldefels, Barcelona, Spain
- ICREA-Institució Catalana de Recerca i Estudis Avançats, 08015 Barcelona, Spain
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18
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Pang S, Brun TA. Improving the Precision of Weak Measurements by Postselection Measurement. PHYSICAL REVIEW LETTERS 2015; 115:120401. [PMID: 26430972 DOI: 10.1103/physrevlett.115.120401] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/08/2014] [Indexed: 06/05/2023]
Abstract
Postselected weak measurement is a useful protocol for amplifying weak physical effects. However, there has recently been controversy over whether it gives any advantage in precision. While it is now clear that retaining failed postselections can yield more Fisher information than discarding them, the advantage of postselection measurement itself still remains to be clarified. In this Letter, we address this problem by studying two widely used estimation strategies: averaging measurement results, and maximum likelihood estimation, respectively. For the first strategy, we find a surprising result that squeezed coherent states of the pointer can give postselected weak measurements a higher signal-to-noise ratio than standard ones while all standard coherent states cannot, which suggests that raising the precision of weak measurements by postselection calls for the presence of "nonclassicality" in the pointer states. For the second strategy, we show that the quantum Fisher information of postselected weak measurements is generally larger than that of standard weak measurements, even without using the failed postselection events, but the gap can be closed with a proper choice of system state.
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Affiliation(s)
- Shengshi Pang
- Department of Electrical Engineering, University of Southern California, Los Angeles, California 90089, USA
| | - Todd A Brun
- Department of Electrical Engineering, University of Southern California, Los Angeles, California 90089, USA
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19
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Tan D, Weber SJ, Siddiqi I, Mølmer K, Murch KW. Prediction and retrodiction for a continuously monitored superconducting qubit. PHYSICAL REVIEW LETTERS 2015; 114:090403. [PMID: 25793786 DOI: 10.1103/physrevlett.114.090403] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/01/2014] [Indexed: 06/04/2023]
Abstract
The quantum state of a superconducting transmon qubit inside a three-dimensional cavity is monitored by transmission of a microwave field through the cavity. The information inferred from the measurement record is incorporated in a density matrix ρ_{t}, which is conditioned on probe results until t, and in an auxiliary matrix E_{t}, which is conditioned on probe results obtained after t. Here, we obtain these matrices from experimental data and we illustrate their application to predict and retrodict the outcome of weak and strong qubit measurements.
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Affiliation(s)
- D Tan
- Department of Physics, Washington University, St. Louis, Missouri 63130, USA
| | - S J Weber
- Quantum Nanoelectronics Laboratory, Department of Physics, University of California, Berkeley, California 94720, USA
| | - I Siddiqi
- Quantum Nanoelectronics Laboratory, Department of Physics, University of California, Berkeley, California 94720, USA
| | - K Mølmer
- Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C, Denmark
| | - K W Murch
- Department of Physics, Washington University, St. Louis, Missouri 63130, USA
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20
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Lim HT, Lee JC, Hong KH, Kim YH. Avoiding entanglement sudden death using single-qubit quantum measurement reversal. OPTICS EXPRESS 2014; 22:19055-19068. [PMID: 25320992 DOI: 10.1364/oe.22.019055] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
When two entangled qubits, each owned by Alice and Bob, undergo separate decoherence, the amount of entanglement is reduced, and often, weak decoherence causes complete loss of entanglement, known as entanglement sudden death. Here we show that it is possible to apply quantum measurement reversal on a single-qubit to avoid entanglement sudden death, rather than on both qubits. Our scheme has important applications in quantum information processing protocols based on distributed or stored entangled qubits as they are subject to decoherence.
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21
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Weber SJ, Chantasri A, Dressel J, Jordan AN, Murch KW, Siddiqi I. Mapping the optimal route between two quantum states. Nature 2014; 511:570-3. [DOI: 10.1038/nature13559] [Citation(s) in RCA: 146] [Impact Index Per Article: 14.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2014] [Accepted: 05/30/2014] [Indexed: 12/27/2022]
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22
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Pang S, Dressel J, Brun TA. Entanglement-assisted weak value amplification. PHYSICAL REVIEW LETTERS 2014; 113:030401. [PMID: 25083620 DOI: 10.1103/physrevlett.113.030401] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/23/2014] [Indexed: 06/03/2023]
Abstract
Large weak values have been used to amplify the sensitivity of a linear response signal for detecting changes in a small parameter, which has also enabled a simple method for precise parameter estimation. However, producing a large weak value requires a low postselection probability for an ancilla degree of freedom, which limits the utility of the technique. We propose an improvement to this method that uses entanglement to increase the efficiency. We show that by entangling and postselecting n ancillas, the postselection probability can be increased by a factor of n while keeping the weak value fixed (compared to n uncorrelated attempts with one ancilla), which is the optimal scaling with n that is expected from quantum metrology. Furthermore, we show the surprising result that the quantum Fisher information about the detected parameter can be almost entirely preserved in the postselected state, which allows the sensitive estimation to approximately saturate the relevant quantum Cramér-Rao bound. To illustrate this protocol we provide simple quantum circuits that can be implemented using current experimental realizations of three entangled qubits.
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Affiliation(s)
- Shengshi Pang
- Department of Electrical Engineering, University of Southern California, Los Angeles, California 90089, USA
| | - Justin Dressel
- Department of Electrical Engineering, University of California, Riverside, California 92521, USA
| | - Todd A Brun
- Department of Electrical Engineering, University of Southern California, Los Angeles, California 90089, USA
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23
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Szigeti SS, Carvalho ARR, Morley JG, Hush MR. Ignorance is bliss: general and robust cancellation of decoherence via no-knowledge quantum feedback. PHYSICAL REVIEW LETTERS 2014; 113:020407. [PMID: 25062148 DOI: 10.1103/physrevlett.113.020407] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/04/2014] [Indexed: 06/03/2023]
Abstract
A "no-knowledge" measurement of an open quantum system yields no information about any system observable; it only returns noise input from the environment. Surprisingly, performing such a no-knowledge measurement can be advantageous. We prove that a system undergoing no-knowledge monitoring has reversible noise, which can be canceled by directly feeding back the measurement signal. We show how no-knowledge feedback control can be used to cancel decoherence in an arbitrary quantum system coupled to a Markovian reservoir that is being monitored. Since no-knowledge feedback does not depend on the system state or Hamiltonian, such decoherence cancellation is guaranteed to be general and robust, and can operate in conjunction with any other quantum control protocol. As an application, we show that no-knowledge feedback could be used to improve the performance of dissipative quantum computers subjected to local loss.
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Affiliation(s)
| | - Andre R R Carvalho
- Department of Quantum Science, Research School of Physics and Engineering, The Australian National University, Canberra, Australian Capital Territory 0200, Australia and ARC Centre for Quantum Computation and Communication Technology, The Australian National University, Canberra, Australian Capital Territory 0200, Australia
| | - James G Morley
- School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, United Kingdom
| | - Michael R Hush
- School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, United Kingdom
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24
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Implementing a strand of a scalable fault-tolerant quantum computing fabric. Nat Commun 2014; 5:4015. [DOI: 10.1038/ncomms5015] [Citation(s) in RCA: 205] [Impact Index Per Article: 20.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2014] [Accepted: 04/30/2014] [Indexed: 11/08/2022] Open
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25
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Asadian A, Brukner C, Rabl P. Probing macroscopic realism via Ramsey correlation measurements. PHYSICAL REVIEW LETTERS 2014; 112:190402. [PMID: 24877918 DOI: 10.1103/physrevlett.112.190402] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/15/2013] [Indexed: 06/03/2023]
Abstract
We describe a new and experimentally feasible protocol for performing fundamental tests of quantum mechanics with massive objects. In our approach, a single two-level system is used to probe the motion of a nanomechanical resonator via multiple Ramsey interference measurements. This scheme enables the measurement of modular variables of macroscopic continuous-variable systems; we show that correlations thereof violate a Leggett-Garg inequality and can be applied for tests of quantum contextuality. Our method can be implemented with a variety of different solid-state or photonic qubit-resonator systems, and it provides a clear experimental signature to distinguish the predictions of quantum mechanics from those of other alternative theories at a macroscopic scale.
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Affiliation(s)
- A Asadian
- Institute of Atomic and Subatomic Physics, TU Wien, Stadionallee 2, 1020 Wien, Austria
| | - C Brukner
- Faculty of Physics, University of Vienna, Boltzmanngasse 5, 1090 Vienna, Austria and Institute for Quantum Optics and Quantum Information, Austrian Academy of Sciences, Boltzmanngasse 3, 1090 Vienna, Austria
| | - P Rabl
- Institute of Atomic and Subatomic Physics, TU Wien, Stadionallee 2, 1020 Wien, Austria
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26
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Campagne-Ibarcq P, Bretheau L, Flurin E, Auffèves A, Mallet F, Huard B. Observing interferences between past and future quantum states in resonance fluorescence. PHYSICAL REVIEW LETTERS 2014; 112:180402. [PMID: 24856677 DOI: 10.1103/physrevlett.112.180402] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/06/2014] [Indexed: 06/03/2023]
Abstract
The fluorescence of a resonantly driven superconducting qubit is measured in the time domain, providing a weak probe of the qubit dynamics. Prior preparation and final, single-shot measurement of the qubit allows us to average fluorescence records conditionally on past and future knowledge. The resulting interferences reveal purely quantum features characteristic of weak values. We demonstrate conditional averages that go beyond classical boundaries and probe directly the jump operator associated with relaxation. The experimental results are remarkably captured by a recent theory, which generalizes quantum mechanics to open quantum systems whose past and future are known.
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Affiliation(s)
- P Campagne-Ibarcq
- Laboratoire Pierre Aigrain, Ecole Normale Supérieure, CNRS (UMR 8551), Université Pierre et Marie Curie, Université Denis Diderot 24, rue Lhomond, 75231 Paris Cedex 05, France
| | - L Bretheau
- Laboratoire Pierre Aigrain, Ecole Normale Supérieure, CNRS (UMR 8551), Université Pierre et Marie Curie, Université Denis Diderot 24, rue Lhomond, 75231 Paris Cedex 05, France
| | - E Flurin
- Laboratoire Pierre Aigrain, Ecole Normale Supérieure, CNRS (UMR 8551), Université Pierre et Marie Curie, Université Denis Diderot 24, rue Lhomond, 75231 Paris Cedex 05, France
| | - A Auffèves
- CNRS and Université Grenoble Alpes, Institut Néel, 38042 Grenoble, France
| | - F Mallet
- Laboratoire Pierre Aigrain, Ecole Normale Supérieure, CNRS (UMR 8551), Université Pierre et Marie Curie, Université Denis Diderot 24, rue Lhomond, 75231 Paris Cedex 05, France
| | - B Huard
- Laboratoire Pierre Aigrain, Ecole Normale Supérieure, CNRS (UMR 8551), Université Pierre et Marie Curie, Université Denis Diderot 24, rue Lhomond, 75231 Paris Cedex 05, France
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27
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Saira OP, Groen JP, Cramer J, Meretska M, de Lange G, DiCarlo L. Entanglement genesis by ancilla-based parity measurement in 2D circuit QED. PHYSICAL REVIEW LETTERS 2014; 112:070502. [PMID: 24579578 DOI: 10.1103/physrevlett.112.070502] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/22/2013] [Indexed: 06/03/2023]
Abstract
We present an indirect two-qubit parity meter in planar circuit quantum electrodynamics, realized by discrete interaction with an ancilla and a subsequent projective ancilla measurement with a dedicated, dispersively coupled resonator. Quantum process tomography and successful entanglement by measurement demonstrate that the meter is intrinsically quantum nondemolition. Separate interaction and measurement steps allow the execution of subsequent data-qubit operations in parallel with ancilla measurement, offering time savings over continuous schemes.
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Affiliation(s)
- O-P Saira
- Kavli Institute of Nanoscience, Delft University of Technology, Post Office Box 5046, 2600 GA Delft, The Netherlands
| | - J P Groen
- Kavli Institute of Nanoscience, Delft University of Technology, Post Office Box 5046, 2600 GA Delft, The Netherlands
| | - J Cramer
- Kavli Institute of Nanoscience, Delft University of Technology, Post Office Box 5046, 2600 GA Delft, The Netherlands
| | - M Meretska
- Kavli Institute of Nanoscience, Delft University of Technology, Post Office Box 5046, 2600 GA Delft, The Netherlands
| | - G de Lange
- Kavli Institute of Nanoscience, Delft University of Technology, Post Office Box 5046, 2600 GA Delft, The Netherlands
| | - L DiCarlo
- Kavli Institute of Nanoscience, Delft University of Technology, Post Office Box 5046, 2600 GA Delft, The Netherlands
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28
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Observing single quantum trajectories of a superconducting quantum bit. Nature 2013; 502:211-4. [PMID: 24108052 DOI: 10.1038/nature12539] [Citation(s) in RCA: 258] [Impact Index Per Article: 23.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2013] [Accepted: 08/07/2013] [Indexed: 11/08/2022]
Abstract
The length of time that a quantum system can exist in a superposition state is determined by how strongly it interacts with its environment. This interaction entangles the quantum state with the inherent fluctuations of the environment. If these fluctuations are not measured, the environment can be viewed as a source of noise, causing random evolution of the quantum system from an initially pure state into a statistical mixture--a process known as decoherence. However, by accurately measuring the environment in real time, the quantum system can be maintained in a pure state and its time evolution described by a 'quantum trajectory' determined by the measurement outcome. Here we use weak measurements to monitor a microwave cavity containing a superconducting quantum bit (qubit), and track the individual quantum trajectories of the system. In this set-up, the environment is dominated by the fluctuations of a single electromagnetic mode of the cavity. Using a near-quantum-limited parametric amplifier, we selectively measure either the phase or the amplitude of the cavity field, and thereby confine trajectories to either the equator or a meridian of the Bloch sphere. We perform quantum state tomography at discrete times along the trajectory to verify that we have faithfully tracked the state of the quantum system as it diffuses on the surface of the Bloch sphere. Our results demonstrate that decoherence can be mitigated by environmental monitoring, and validate the foundation of quantum feedback approaches based on Bayesian statistics. Moreover, our experiments suggest a new means of implementing 'quantum steering'--the harnessing of action at a distance to manipulate quantum states through measurement.
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29
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Gammelmark S, Julsgaard B, Mølmer K. Past quantum states of a monitored system. PHYSICAL REVIEW LETTERS 2013; 111:160401. [PMID: 24182235 DOI: 10.1103/physrevlett.111.160401] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/03/2013] [Revised: 08/22/2013] [Indexed: 06/02/2023]
Abstract
A density matrix ρ(t) yields probabilistic information about the outcome of measurements on a quantum system. We introduce here the past quantum state, which, at time T, accounts for the state of a quantum system at earlier times t<T. The past quantum state Ξ(t) is composed of two objects, ρ(t) and E(t), conditioned on the dynamics and the probing of the system until t and in the time interval [t, T], respectively. The past quantum state is characterized by its ability to make better predictions for the unknown outcome of any measurement at t than the conventional quantum state at that time. On the one hand, our formalism shows how smoothing procedures for estimation of past classical signals by a quantum probe [M. Tsang, Phys. Rev. Lett. 102, 250403 (2009)] apply also to describe the past state of the quantum system itself. On the other hand, it generalizes theories of pre- and postselected quantum states [Y. Aharonov and L. Vaidman, J. Phys. A 24, 2315 (1991)] to systems subject to any quantum measurement scenario, any coherent evolution, and any Markovian dissipation processes.
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Affiliation(s)
- Søren Gammelmark
- Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C, Denmark
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