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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Harrington PM, Tan D, Naghiloo M, Murch KW. Characterizing a Statistical Arrow of Time in Quantum Measurement Dynamics. PHYSICAL REVIEW LETTERS 2019; 123:020502. [PMID: 31386500 DOI: 10.1103/physrevlett.123.020502] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/16/2018] [Revised: 04/02/2019] [Indexed: 06/10/2023]
Abstract
In both thermodynamics and quantum mechanics, the arrow of time is characterized by the statistical likelihood of physical processes. We characterize this arrow of time for the continuous quantum measurement dynamics of a superconducting qubit. By experimentally tracking individual weak measurement trajectories, we compare the path probabilities of forward and backward-in-time evolution to develop an arrow of time statistic associated with measurement dynamics. We compare the statistics of individual trajectories to ensemble properties showing that the measurement dynamics obeys both detailed and integral fluctuation theorems, thus establishing the consistency between microscopic and macroscopic measurement dynamics.
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Affiliation(s)
- P M Harrington
- 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
| | - M Naghiloo
- Department of Physics, Washington University, St. Louis, Missouri 63130, USA
| | - 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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3
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Atalaya J, Hacohen-Gourgy S, Siddiqi I, Korotkov AN. Correlators Exceeding One in Continuous Measurements of Superconducting Qubits. PHYSICAL REVIEW LETTERS 2019; 122:223603. [PMID: 31283299 DOI: 10.1103/physrevlett.122.223603] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/12/2018] [Indexed: 06/09/2023]
Abstract
We consider the effect of phase backaction on the correlator ⟨I(t)I(t+τ)⟩ for the output signal I(t) from continuous measurement of a qubit. We demonstrate that the interplay between informational and phase backactions in the presence of Rabi oscillations can lead to the correlator becoming larger than 1, even though |⟨I⟩|≤1. The correlators can be calculated using the generalized "collapse recipe," which we validate using the quantum Bayesian formalism. The recipe can be further generalized to the case of multitime correlators and arbitrary number of detectors, measuring non-commuting qubit observables. The theory agrees well with experimental results for continuous measurement of a transmon qubit. The experimental correlator exceeds the bound of 1 for a sufficiently large angle between the amplified and informational quadratures, causing the phase backaction. The demonstrated effect can be used to calibrate the quadrature misalignment.
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Affiliation(s)
- Juan Atalaya
- Department of Electrical and Computer Engineering, University of California, Riverside, California 92521, USA
| | - Shay Hacohen-Gourgy
- Quantum Nanoelectronics Laboratory, Department of Physics, University of California, Berkeley, California 94720, USA
- Center for Quantum Coherent Science, University of California, Berkeley, California 94720, USA
- Department of Physics, Technion, Haifa 3200003, Israel
| | - Irfan Siddiqi
- Quantum Nanoelectronics Laboratory, Department of Physics, University of California, Berkeley, California 94720, USA
- Center for Quantum Coherent Science, University of California, Berkeley, California 94720, USA
| | - Alexander N Korotkov
- Department of Electrical and Computer Engineering, University of California, Riverside, California 92521, USA
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4
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To catch and reverse a quantum jump mid-flight. Nature 2019; 570:200-204. [DOI: 10.1038/s41586-019-1287-z] [Citation(s) in RCA: 132] [Impact Index Per Article: 26.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2018] [Accepted: 04/04/2019] [Indexed: 11/08/2022]
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5
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Troiani F, Godfrin C, Thiele S, Balestro F, Wernsdorfer W, Klyatskaya S, Ruben M, Affronte M. Landau-Zener Transition in a Continuously Measured Single-Molecule Spin Transistor. PHYSICAL REVIEW LETTERS 2017; 118:257701. [PMID: 28696767 DOI: 10.1103/physrevlett.118.257701] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/11/2017] [Indexed: 06/07/2023]
Abstract
We monitor the Landau-Zener dynamics of a single-ion magnet inserted into a spin-transistor geometry. For increasing field-sweep rates, the spin reversal probability shows increasing deviations from that of a closed system. In the low-conductance limit, such deviations are shown to result from a dephasing process. In particular, the observed behaviors are successfully simulated by means of an adiabatic master equation, with time averaged dephasing (Lindblad) operators. The time average is tentatively interpreted in terms of the finite time resolution of the continuous measurement.
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Affiliation(s)
- F Troiani
- Centro S3, Istituto Nanoscienze-CNR, via G. Campi 213/A, I-41125 Modena, Italy
| | - C Godfrin
- Institut L. Néel, CNRS, Av des Martyrs 25, F-38000 Grenoble, France
| | - S Thiele
- Institut L. Néel, CNRS, Av des Martyrs 25, F-38000 Grenoble, France
| | - F Balestro
- Institut L. Néel, CNRS, Av des Martyrs 25, F-38000 Grenoble, France
| | - W Wernsdorfer
- Institut L. Néel, CNRS, Av des Martyrs 25, F-38000 Grenoble, France
- Institute of Nanotechnology, Karlsruhe Institute of Technology (KIT), D-76344 Eggenstein Leopoldshafen, Germany
| | - S Klyatskaya
- Institute of Nanotechnology, Karlsruhe Institute of Technology (KIT), D-76344 Eggenstein Leopoldshafen, Germany
| | - M Ruben
- Institute of Nanotechnology, Karlsruhe Institute of Technology (KIT), D-76344 Eggenstein Leopoldshafen, Germany
| | - M Affronte
- Centro S3, Istituto Nanoscienze-CNR, via G. Campi 213/A, I-41125 Modena, Italy
- Dipartimento di Scienze Fisiche, Informatiche e Matematiche, Università di Modena e Reggio Emilia, via G. Campi 213/a, I-41125 Modena, Italy
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6
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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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7
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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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8
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Sherman JA, Curtis MJ, Szwer DJ, Allcock DTC, Imreh G, Lucas DM, Steane AM. Experimental recovery of a qubit from partial collapse. PHYSICAL REVIEW LETTERS 2013; 111:180501. [PMID: 24237494 DOI: 10.1103/physrevlett.111.180501] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/15/2013] [Indexed: 06/02/2023]
Abstract
We describe and implement a method to restore the state of a single qubit, in principle perfectly, after it has partially collapsed. The method resembles the classical Hahn spin echo but works on a wider class of relaxation processes, in which the quantum state partially leaves the computational Hilbert space. It is not guaranteed to work every time, but successful outcomes are heralded. We demonstrate, using a single trapped ion, a better performance from this recovery method than can be obtained employing projection and postselection alone. The demonstration features a novel qubit implementation that permits both partial collapse and coherent manipulations with high fidelity.
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Affiliation(s)
- J A Sherman
- Clarendon Laboratory, Department of Physics, University of Oxford, Parks Road, Oxford OX1 3PU, United Kingdom
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9
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Groen JP, Ristè D, Tornberg L, Cramer J, de Groot PC, Picot T, Johansson G, DiCarlo L. Partial-measurement backaction and nonclassical weak values in a superconducting circuit. PHYSICAL REVIEW LETTERS 2013; 111:090506. [PMID: 24033014 DOI: 10.1103/physrevlett.111.090506] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/21/2013] [Revised: 06/29/2013] [Indexed: 06/02/2023]
Abstract
We realize indirect partial measurement of a transmon qubit in circuit quantum electrodynamics by interaction with an ancilla qubit and projective ancilla measurement with a dedicated readout resonator. Accurate control of the interaction and ancilla measurement basis allows tailoring the measurement strength and operator. The tradeoff between measurement strength and qubit backaction is characterized through the distortion of a qubit Rabi oscillation imposed by ancilla measurement in different bases. Combining partial and projective qubit measurements, we provide the solid-state demonstration of the correspondence between a nonclassical weak value and the violation of a Leggett-Garg inequality.
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Affiliation(s)
- J P Groen
- Kavli Institute of Nanoscience, Delft University of Technology, P.O. Box 5046, 2600 GA Delft, The Netherlands
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10
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Schindler P, Monz T, Nigg D, Barreiro JT, Martinez EA, Brandl MF, Chwalla M, Hennrich M, Blatt R. Undoing a quantum measurement. PHYSICAL REVIEW LETTERS 2013; 110:070403. [PMID: 25166354 DOI: 10.1103/physrevlett.110.070403] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/05/2012] [Indexed: 06/03/2023]
Abstract
In general, a quantum measurement yields an undetermined answer and alters the system to be consistent with the measurement result. This process maps multiple initial states into a single state and thus cannot be reversed. This has important implications in quantum information processing, where errors can be interpreted as measurements. Therefore, it seems that it is impossible to correct errors in a quantum information processor, but protocols exist that are capable of eliminating them if they affect only part of the system. In this work we present the deterministic reversal of a fully projective measurement on a single particle, enabled by a quantum error-correction protocol in a trapped ion quantum information processor. We further introduce an in-sequence, single-species recooling procedure to counteract the motional heating of the ion string due to the measurement.
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Affiliation(s)
- Philipp Schindler
- Institut für Experimentalphysik, Universität Innsbruck, Technikerstrasse 25, A-6020 Innsbruck, Austria
| | - Thomas Monz
- Institut für Experimentalphysik, Universität Innsbruck, Technikerstrasse 25, A-6020 Innsbruck, Austria
| | - Daniel Nigg
- Institut für Experimentalphysik, Universität Innsbruck, Technikerstrasse 25, A-6020 Innsbruck, Austria
| | - Julio T Barreiro
- Institut für Experimentalphysik, Universität Innsbruck, Technikerstrasse 25, A-6020 Innsbruck, Austria
| | - Esteban A Martinez
- Institut für Experimentalphysik, Universität Innsbruck, Technikerstrasse 25, A-6020 Innsbruck, Austria
| | - Matthias F Brandl
- Institut für Experimentalphysik, Universität Innsbruck, Technikerstrasse 25, A-6020 Innsbruck, Austria
| | - Michael Chwalla
- Institut für Experimentalphysik, Universität Innsbruck, Technikerstrasse 25, A-6020 Innsbruck, Austria and Institut für Quantenoptik und Quanteninformation der Österreichischen Akademie der Wissenschaften, Technikerstrasse 21a, A-6020 Innsbruck, Austria
| | - Markus Hennrich
- Institut für Experimentalphysik, Universität Innsbruck, Technikerstrasse 25, A-6020 Innsbruck, Austria
| | - Rainer Blatt
- Institut für Experimentalphysik, Universität Innsbruck, Technikerstrasse 25, A-6020 Innsbruck, Austria and Institut für Quantenoptik und Quanteninformation der Österreichischen Akademie der Wissenschaften, Technikerstrasse 21a, A-6020 Innsbruck, Austria
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11
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Hatridge M, Shankar S, Mirrahimi M, Schackert F, Geerlings K, Brecht T, Sliwa KM, Abdo B, Frunzio L, Girvin SM, Schoelkopf RJ, Devoret MH. Quantum back-action of an individual variable-strength measurement. Science 2013; 339:178-81. [PMID: 23307736 DOI: 10.1126/science.1226897] [Citation(s) in RCA: 191] [Impact Index Per Article: 17.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Measuring a quantum system can randomly perturb its state. The strength and nature of this back-action depend on the quantity that is measured. In a partial measurement performed by an ideal apparatus, quantum physics predicts that the system remains in a pure state whose evolution can be tracked perfectly from the measurement record. We demonstrated this property using a superconducting qubit dispersively coupled to a cavity traversed by a microwave signal. The back-action on the qubit state of a single measurement of both signal quadratures was observed and shown to produce a stochastic operation whose action is determined by the measurement result. This accurate monitoring of a qubit state is an essential prerequisite for measurement-based feedback control of quantum systems.
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Affiliation(s)
- M Hatridge
- Department of Applied Physics and Physics, Yale University, New Haven, CT 06520, USA.
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12
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13
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Ruskov R, Korotkov AN, Mølmer K. Qubit state monitoring by measurement of three complementary observables. PHYSICAL REVIEW LETTERS 2010; 105:100506. [PMID: 20867502 DOI: 10.1103/physrevlett.105.100506] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/10/2010] [Indexed: 05/29/2023]
Abstract
We consider the evolution of a qubit (spin 1/2) under the simultaneous continuous measurement of three noncommuting qubit operators σ(x), σ(y), and σ(z). For identical ideal detectors, the qubit state evolves by approaching a pure state with a random direction in the Bloch vector space and by undergoing locally isotropic diffusion in the perpendicular directions. The quantum state conditioned on the complete detector record is used to assess the fidelity of classically inspired estimates based on running time averages and discrete time bin detector outputs.
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Affiliation(s)
- Rusko Ruskov
- Lundbeck Foundation Theoretical Center for Quantum System Research, Department of Physics and Astronomy, University of Aarhus, DK-8000 Aarhus C, Denmark
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14
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Asano Y, Suemune I, Takayanagi H, Hanamura E. Luminescence of a cooper pair. PHYSICAL REVIEW LETTERS 2009; 103:187001. [PMID: 19905825 DOI: 10.1103/physrevlett.103.187001] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/06/2009] [Indexed: 05/28/2023]
Abstract
This Letter theoretically discusses the photon emission spectra of a superconducting p-n junction. On the basis of the second order perturbation theory for electron-photon interaction, we show that the recombination of a Cooper pair with two p-type carriers causes enhancement of the luminescence intensity. The calculated results of photon emission spectra explain characteristic features of observed signal in an recent experiment. Our results indicate high functionalities of superconducting light-emitting devices.
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Affiliation(s)
- Yasuhiro Asano
- Department of Applied Physics, Hokkaido University, Sapporo 060-8628, Japan
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15
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Li J, Chalapat K, Paraoanu GS. Measurement-induced entanglement of two superconducting qubits. ACTA ACUST UNITED AC 2009. [DOI: 10.1088/1742-6596/150/2/022051] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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16
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Shikerman F, Barkai E. Probing dynamics of single molecules: Nonlinear spectroscopy approach. J Chem Phys 2008; 129:244702. [PMID: 19123521 DOI: 10.1063/1.3037221] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
A two level model of a single molecule undergoing spectral diffusion dynamics and interacting with a sequence of two short laser pulses is investigated. Analytical solution for the probability of n=0,1,2 photon emission events for the telegraph and Gaussian processes is obtained. We examine under what circumstances the photon statistics emerging from such pump-probe setup provides new information on the stochastic process parameters and what are the measurement limitations of this technique. The impulsive and selective limits, the semiclassical approximation, and the fast modulation limit exhibit general behaviors of this new type of spectroscopy. We show that in the fast modulation limit, where one has to use impulsive pulses in order to obtain meaningful results, the information on the photon statistics is contained in the molecule's dipole correlation function, equivalently to continuous wave experiments. In contrast, the photon statistics obtained within the selective limit depends on the both spectral shifts and rates and exhibits oscillations, which are not found in the corresponding line shape.
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Affiliation(s)
- F Shikerman
- Department of Physics, Bar Ilan University, Ramat-Gan 52900, Israel
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17
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Lee MT, Zhang WM. Non-Markovian suppression of charge qubit decoherence in the quantum point contact measurement. J Chem Phys 2008; 129:224106. [DOI: 10.1063/1.3036114] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
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18
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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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19
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20
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Rudner MS, Shytov AV, Levitov LS, Berns DM, Oliver WD, Valenzuela SO, Orlando TP. Quantum phase tomography of a strongly driven qubit. PHYSICAL REVIEW LETTERS 2008; 101:190502. [PMID: 19113251 DOI: 10.1103/physrevlett.101.190502] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/11/2008] [Indexed: 05/27/2023]
Abstract
The interference between repeated Landau-Zener transitions in a qubit swept through an avoided level crossing results in Stückelberg oscillations in qubit magnetization, a hallmark of the coherent strongly driven regime in two-level systems. The two-dimensional Fourier transforms of the resulting oscillatory patterns are found to exhibit a family of one-dimensional curves in Fourier space, in agreement with recent observations in a superconducting qubit. We interpret these images in terms of time evolution of the quantum phase of the qubit state and show that they can be used to probe dephasing mechanisms.
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Affiliation(s)
- M S Rudner
- Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
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21
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Amplitude spectroscopy of a solid-state artificial atom. Nature 2008; 455:51-7. [PMID: 18769433 DOI: 10.1038/nature07262] [Citation(s) in RCA: 122] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2008] [Accepted: 07/11/2008] [Indexed: 11/08/2022]
Abstract
The energy-level structure of a quantum system, which has a fundamental role in its behaviour, can be observed as discrete lines and features in absorption and emission spectra. Conventionally, spectra are measured using frequency spectroscopy, whereby the frequency of a harmonic electromagnetic driving field is tuned into resonance with a particular separation between energy levels. Although this technique has been successfully employed in a variety of physical systems, including natural and artificial atoms and molecules, its application is not universally straightforward and becomes extremely challenging for frequencies in the range of tens to hundreds of gigahertz. Here we introduce a complementary approach, amplitude spectroscopy, whereby a harmonic driving field sweeps an artificial atom through the avoided crossings between energy levels at a fixed frequency. Spectroscopic information is obtained from the amplitude dependence of the system's response, thereby overcoming many of the limitations of a broadband-frequency-based approach. The resulting 'spectroscopy diamonds', the regions in parameter space where transitions between specific pairs of levels can occur, exhibit interference patterns and population inversion that serve to distinguish the atom's spectrum. Amplitude spectroscopy provides a means of manipulating and characterizing systems over an extremely broad bandwidth, using only a single driving frequency that may be orders of magnitude smaller than the energy scales being probed.
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22
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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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23
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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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24
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Li SX, Qiu W, Han S, Wei YF, Zhu XB, Gu CZ, Zhao SP, Wang HB. Observation of macroscopic quantum tunneling in a single Bi2Sr2CaCu2O8+delta surface intrinsic Josephson junction. PHYSICAL REVIEW LETTERS 2007; 99:037002. [PMID: 17678315 DOI: 10.1103/physrevlett.99.037002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/28/2006] [Indexed: 05/16/2023]
Abstract
We report on the first unambiguous observation of macroscopic quantum tunneling (MQT) in a single submicron Bi(2)Sr(2)CaCu(2)O(8+delta) surface intrinsic Josephson junction (IJJ) by measuring its temperature-dependent switching current distribution. All relevant junction parameters were determined in situ in the classical regime and were used to predict the behavior of the IJJ in the quantum regime via MQT theory. Experimental results agree quantitatively with the theoretical predictions, thus confirming the MQT picture. Furthermore, the data also indicate that the surface IJJ, where the current flows along the c axis of the crystal, has the conventional sinphi current-phase relationship.
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Affiliation(s)
- Shao-Xiong Li
- Department of Physics and Astronomy, University of Kansas, Lawrence, Kansas 66045, USA
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Korotkov AN, Jordan AN. Undoing a weak quantum measurement of a solid-state qubit. PHYSICAL REVIEW LETTERS 2006; 97:166805. [PMID: 17155425 DOI: 10.1103/physrevlett.97.166805] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/06/2006] [Indexed: 05/12/2023]
Abstract
We propose an experiment which demonstrates the undoing of a weak continuous measurement of a solid-state qubit, so that any unknown initial state is fully restored. The undoing procedure has only a finite probability of success because of the nonunitary nature of quantum measurement, though it is accompanied by a clear experimental indication of whether or not the undoing has been successful. The probability of success decreases with increasing strength of the measurement, reaching zero for a traditional projective measurement. Measurement undoing ("quantum undemolition") may be interpreted as a kind of quantum eraser, in which the information obtained from the first measurement is erased by the second measurement, which is an essential part of the undoing procedure. The experiment can be realized using quantum dot (charge) or superconducting (phase) qubits.
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Affiliation(s)
- Alexander N Korotkov
- Department of Electrical Engineering, University of California, Riverside, CA 92521-0204, USA
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