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Szombati D, Gomez Frieiro A, Müller C, Jones T, Jerger M, Fedorov A. Quantum Rifling: Protecting a Qubit from Measurement Back Action. PHYSICAL REVIEW LETTERS 2020; 124:070401. [PMID: 32142306 DOI: 10.1103/physrevlett.124.070401] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/20/2019] [Accepted: 01/27/2020] [Indexed: 06/10/2023]
Abstract
Quantum mechanics postulates that measuring the qubit's wave function results in its collapse, with the recorded discrete outcome designating the particular eigenstate that the qubit collapsed into. We show that this picture breaks down when the qubit is strongly driven during measurement. More specifically, for a fast evolving qubit the measurement returns the time-averaged expectation value of the measurement operator, erasing information about the initial state of the qubit while completely suppressing the measurement backaction. We call this regime quantum rifling, as the fast spinning of the Bloch vector protects it from deflection into either of its eigenstates. We study this phenomenon with two superconducting qubits coupled to the same probe field and demonstrate that quantum rifling allows us to measure either one of the qubits on demand while protecting the state of the other from measurement backaction. Our results allow for the implementation of selective readout multiplexing of several qubits, contributing to the efficient scaling up of quantum processors for future quantum technologies.
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Affiliation(s)
- Daniel Szombati
- ARC Centre of Excellence for Engineered Quantum Systems, St Lucia, Queensland 4072, Australia
- School of Mathematics and Physics, University of Queensland, St Lucia, Queensland 4072, Australia
| | - Alejandro Gomez Frieiro
- ARC Centre of Excellence for Engineered Quantum Systems, St Lucia, Queensland 4072, Australia
- School of Mathematics and Physics, University of Queensland, St Lucia, Queensland 4072, Australia
| | | | - Tyler Jones
- ARC Centre of Excellence for Engineered Quantum Systems, St Lucia, Queensland 4072, Australia
- School of Mathematics and Physics, University of Queensland, St Lucia, Queensland 4072, Australia
| | - Markus Jerger
- ARC Centre of Excellence for Engineered Quantum Systems, St Lucia, Queensland 4072, Australia
- School of Mathematics and Physics, University of Queensland, St Lucia, Queensland 4072, Australia
| | - Arkady Fedorov
- ARC Centre of Excellence for Engineered Quantum Systems, St Lucia, Queensland 4072, Australia
- School of Mathematics and Physics, University of Queensland, St Lucia, Queensland 4072, Australia
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Stace TM, Doherty AC, Reilly DJ. Dynamical steady States in driven quantum systems. PHYSICAL REVIEW LETTERS 2013; 111:180602. [PMID: 24237499 DOI: 10.1103/physrevlett.111.180602] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/04/2013] [Indexed: 06/02/2023]
Abstract
We derive dynamical equations for a driven, dissipative quantum system in which the environment-induced relaxation rate is comparable to the Rabi frequency, avoiding assumptions on the frequency dependence of the environmental coupling. When the environmental coupling varies significantly on the scale of the Rabi frequency, secular or rotating wave approximations break down. We avoid these approximations, yielding dynamical steady states which account for the interaction between driven quantum dots and their phonon environment. The theory, which is motivated by recent experimental observations, qualitatively and quantitatively describes the transition from asymmetric unsaturated resonances at weak driving to population inversion at strong driving.
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Affiliation(s)
- T M Stace
- ARC Centre for Engineered Quantum Systems, University of Queensland, Brisbane 4072, Australia
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Li ZZ, Lam CH, Yu T, You JQ. Detector-induced backaction on the counting statistics of a double quantum dot. Sci Rep 2013; 3:3026. [PMID: 24149587 PMCID: PMC3805975 DOI: 10.1038/srep03026] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2013] [Accepted: 10/04/2013] [Indexed: 12/02/2022] Open
Abstract
Full counting statistics of electron transport is of fundamental importance for a deeper understanding of the underlying physical processes in quantum transport in nanoscale devices. The backaction effect from a detector on the nanoscale devices is also essential due to its inevitable presence in experiments. Here we investigate the backaction of a charge detector in the form of a quantum point contact (QPC) on the counting statistics of a biased double quantum dot (DQD). We show that this inevitable QPC-induced backaction can have profound effects on the counting statistics under certain conditions, e.g., changing the shot noise from being sub-Poissonian to super-Poissonian, and changing the skewness from being positive to negative. Also, we show that both Fano factor and skewness can be either enhanced or suppressed by increasing the energy difference between two single-dot levels of the DQD under the detector-induced backaction.
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Affiliation(s)
- Zeng-Zhao Li
- Beijing Computational Science Research Center, Beijing 100084, China
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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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Jin J, Welack S, Luo J, Li XQ, Cui P, Xu RX, Yan Y. Dynamics of quantum dissipation systems interacting with fermion and boson grand canonical bath ensembles: Hierarchical equations of motion approach. J Chem Phys 2007; 126:134113. [PMID: 17430022 DOI: 10.1063/1.2713104] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
A hierarchical equations of motion formalism for a quantum dissipation system in a grand canonical bath ensemble surrounding is constructed on the basis of the calculus-on-path-integral algorithm, together with the parametrization of arbitrary non-Markovian bath that satisfies fluctuation-dissipation theorem. The influence functionals for both the fermion or boson bath interaction are found to be of the same path integral expression as the canonical bath, assuming they all satisfy the Gaussian statistics. However, the equation of motion formalism is different due to the fluctuation-dissipation theories that are distinct and used explicitly. The implications of the present work to quantum transport through molecular wires and electron transfer in complex molecular systems are discussed.
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Affiliation(s)
- Jinshuang Jin
- Department of Chemistry, Hong Kong University of Science and Technology, Kowloon, Hong Kong.
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Alvarez GA, Danieli EP, Levstein PR, Pastawski HM. Environmentally induced quantum dynamical phase transition in the spin swapping operation. J Chem Phys 2006; 124:194507. [PMID: 16729825 DOI: 10.1063/1.2193518] [Citation(s) in RCA: 74] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Quantum information processing relies on coherent quantum dynamics for a precise control of its basic operations. A swapping gate in a two-spin system exchanges the degenerate states |(up arrow, down arrow)> and |(down arrow, up arrow)>. In NMR, this is achieved turning on and off the spin-spin interaction b=DeltaE that splits the energy levels and induces an oscillation with a natural frequency DeltaE/Planck's. Interaction of strength Planck's/tau(SE), with an environment of neighboring spins, degrades this oscillation within a decoherence time scale tau(phi). While the experimental frequency omega and decoherence time tau(phi) were expected to be roughly proportional to b/Planck's and tau(SE), respectively, we present here experiments that show drastic deviations in both omega and tau(phi). By solving the many spin dynamics, we prove that the swapping regime is restricted to DeltaEtau(SE) similar or greater than Planck's. Beyond a critical interaction with the environment the swapping freezes and the decoherence rate drops as 1/tau(phi) proportional to (b/Planck's)2tau(SE). The transition between quantum dynamical phases occurs when omega proportional to sqrt (b/Planck's)2-(k/tau(SE)2 becomes imaginary, resembling an overdamped classical oscillator. Here, 0< or =k2< or =1 depends only on the anisotropy of the system-environment interaction, being 0 for isotropic and 1 for XY interactions. This critical onset of a phase dominated by the quantum Zeno effect opens up new opportunities for controlling quantum dynamics.
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Affiliation(s)
- Gonzalo A Alvarez
- Facultad de Matemática, Astronomía y Física, Universidad Nacional de Córdoba, Ciudad Universitaria, 5000 Córdoba, Argentina
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Barrett SD, Stace TM. Continuous measurement of a microwave-driven solid state qubit. PHYSICAL REVIEW LETTERS 2006; 96:017405. [PMID: 16486516 DOI: 10.1103/physrevlett.96.017405] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/09/2004] [Indexed: 05/06/2023]
Abstract
We analyze the dynamics of a continuously observed, damped, microwave-driven solid state charge qubit, consisting of a single electron in a double well potential. The microwave field induces transitions between the qubit eigenstates, which have a profound effect on the detector output current. Useful information about the qubit dynamics, such as dephasing and relaxation rates, and the Rabi frequency, can be extracted from the detector conductance and output noise power spectrum. We also propose a technique for single-shot electron spin readout, for spin based quantum information processing, which has a number of practical advantages over existing schemes.
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Affiliation(s)
- S D Barrett
- Hewlett-Packard Laboratories, Filton Road, Stoke Gifford, Bristol BS34 8QZ, United Kingdom.
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Stace TM, Doherty AC, Barrett SD. Population inversion of a driven two-level system in a structureless bath. PHYSICAL REVIEW LETTERS 2005; 95:106801. [PMID: 16196950 DOI: 10.1103/physrevlett.95.106801] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/03/2004] [Indexed: 05/04/2023]
Abstract
We derive a master equation for a driven double quantum dot damped by an unstructured phonon bath, and calculate the spectral density. We find that bath-mediated photon absorption is important at relatively strong driving, and may even dominate the dynamics, inducing population inversion of the double-dot system. This phenomenon is consistent with recent experimental observations.
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Averin DV, Korotkov AN. Comment on "continuous quantum measurement: inelastic tunneling and lack of current oscillations". PHYSICAL REVIEW LETTERS 2005; 94:069701. [PMID: 15783788 DOI: 10.1103/physrevlett.94.069701] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/15/2004] [Indexed: 05/24/2023]
Affiliation(s)
- Dmitri V Averin
- Department of Physics and Astronomy, USB, SUNY Stony Brook, New York 11794-3800, USA
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Li XQ, Cui P, Yan Y. Spontaneous relaxation of a charge qubit under electrical measurement. PHYSICAL REVIEW LETTERS 2005; 94:066803. [PMID: 15783765 DOI: 10.1103/physrevlett.94.066803] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/11/2004] [Indexed: 05/24/2023]
Abstract
In this work we first derive a generalized conditional master equation for quantum measurement by a mesoscopic detector, then study the readout characteristics of qubit measurement where a number of remarkable new features are found. The work would, in particular, highlight the qubit spontaneous relaxation effect induced by the measurement itself rather than an external thermal bath.
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Affiliation(s)
- Xin-Qi Li
- State Key Laboratory for Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, P.O. Box 912, Beijing 100083, China
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