Limitation of entanglement due to spatial qubit separation

Doll, Roland; Wubs, Martijn; Hänggi, Peter; Kohler, Sigmund

doi:10.1209/epl/i2006-10326-y

Cited by 44 publications

(58 citation statements)

References 29 publications

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“…We elaborate more on this relation in appendix E. This relation of the theorem to the robustness of DFSs, which we make clear by the elementary considerations above, was not noticed before. It is opposite to previous suggestions that continue to proliferate in the literature [20,21,27,28,[32][33][34][35].…”

Section: Expansion Of the Dynamical Fidelitycontrasting

confidence: 92%

Dynamical fidelity susceptibility of decoherence-free subspaces

Kattemölle

Wezel

2019

Phys. Rev. A

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In idealized models of a quantum register and its environment, quantum information can be stored indefinitely by encoding it into a decoherence-free subspace (DFS). Nevertheless, perturbations to the idealized register-environment coupling will cause decoherence in any realistic setting. Expanding a measure for state preservation, the dynamical fidelity, in powers of the strength of the perturbations, we prove stability to linear order is a generic property of quantum state evolution. The effect of noise perturbation is quantified by a concise expression for the strength of the quadratic, leading order, which we define as the dynamical fidelity susceptibility of DFSs. Under the physical restriction that noise acts on the register k-locally, this susceptibility is bounded from above by a polynomial in the system size. These general results are illustrated by two physically relevant examples. Knowledge of the susceptibility can be used to increase coherence times of future quantum computers.

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Section: Expansion Of the Dynamical Fidelitycontrasting

confidence: 92%

Dynamical fidelity susceptibility of decoherence-free subspaces

Kattemölle

Wezel

2019

Phys. Rev. A

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“…Except some few exactly solvable models [38,40,41] it is not clear how to relate the reduced dynamics to the microscopically first principles dynamics based upon the Hamiltonian structure of quantum dynamics [38,42]. The exactly solvable model of pure dephasing has been applied for studying quantum channels [43] or in exploring the dynamics of quantum entanglement [44][45][46][47][48]. Despite its simplicity the highly non-trivial properties of geometric phase of qubits has also been discussed [49][50][51][52].…”

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confidence: 99%

Geometric phase as a determinant of a qubit– environment coupling

Dajka

Łuczka

Hänggi

2010

Quantum Inf Process

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We investigate the qubit geometric phase and its properties in dependence on the mechanism for decoherence of a qubit weakly coupled to its environment. We consider two sources of decoherence: dephasing coupling (without exchange of energy with environment) and dissipative coupling (with exchange of energy). Reduced dynamics of the qubit is studied in terms of the rigorous Davies Markovian quantum master equation, both at zero and non-zero temperature. For pure dephasing coupling, the geometric phase varies monotonically with respect to the polar angle (in the Bloch sphere representation) parameterizing an initial state of the qubit. Moreover, it is antisymmetric about some points on the geometric phase-polar angle plane. This is in distinct contrast to the case of dissipative coupling for which the variation of the geometric phase with respect to the polar angle typically is non-monotonic, displaying local extrema and is not antisymmetric. Sensitivity of the geometric phase to details of the decoherence source can make it a tool for testing the nature of the qubit-environment interaction.

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“…An intermediate case is obtained if the coupling depends on the position r j of the qubits. A reasonable model, corresponding to point scatterings of fields with wave vector k, is given by g (j) k = g k exp (ik · r j ), and its implications are studied in [20].…”

Section: Qubits See Different Reservoirsmentioning

confidence: 99%

Introduction to Decoherence Theory

Hornberger

Entanglement and Decoherence

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143

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This introduction to the theory of decoherence is aimed at readers with an interest in the science of quantum information. In that field, one is usually content with simple, abstract descriptions of non-unitary "quantum channels" to account for imperfections in quantum processing tasks. However, in order to justify such models of non-unitary evolution and to understand their limits of applicability it is important to know their physical basis. I will therefore emphasize the dynamic and microscopic origins of the phenomenon of decoherence, and will relate it to concepts from quantum information where applicable, in particular to the theory of quantum measurement.The study of decoherence, though based at the heart of quantum theory, is a relatively young subject. It was initiated in the 1970's and 1980's with the work of H. D. Zeh and W. Zurek on the emergence of classicality in the quantum framework. Until that time the orthodox interpretation of quantum mechanics dominated, with its strict distinction between the classical macroscopic world and the microscopic quantum realm. The mainstream attitude concerning the boundary between the quantum and the classical was that this was a purely philosophical problem, intangible by any physical analysis. This changed with the understanding that there is no need for denying quantum mechanics to hold even macroscopically, if one is only able to understand within the framework of quantum mechanics why the macro-world appears to be classical. For instance, macroscopic objects are found in approximate position eigenstates of their center-of-mass, but never in superpositions of macroscopically distinct positions. The original motivation for the study of decoherence was to explain these effective super-selection rules and the apparent emergence of classicality within quantum theory by appreciating the crucial role played by the environment of a quantum system. Hence, the relevant theoretical framework for the study of decoherence is the theory of open quantum systems, which treats the effects of an unThis text corresponds to a chapter in: A. Buchleitner, C. Viviescas, and M. Tiersch (Eds.), Entanglement and Decoherence.

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Limitation of entanglement due to spatial qubit separation

Cited by 44 publications

References 29 publications

Dynamical fidelity susceptibility of decoherence-free subspaces

Dynamical fidelity susceptibility of decoherence-free subspaces

Geometric phase as a determinant of a qubit– environment coupling

Introduction to Decoherence Theory

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