Photon exchange and correlation transfer in atom-atom entanglement dynamics

Abstract. The electronic entanglement between two free atoms initially at rest is obtained including the effects of photon recoil, for the case when quantum dispersion can be neglected during the atomic excited-state lifetime. Different from previous treatments using common or statistically independent reservoirs, a continuous transition between these limits is observed, that depends on the inter-atomic distance and degree of localization. The occurrence of entanglement sudden death and birth as predicted here deviates from the case where the interatomic distance is treated classically by a static value. Moreover, the creation of a dark state is predicted, which manifests itself by a stationary entanglement that even may be created from an initially separable state.

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“…[26]. We believe that these phenomena can be well explained within the framework of a dark state, as discussed here.…”

Section: Discussionsupporting

confidence: 60%

Dynamics of entanglement between two free atoms with quantized motion

Lastra¹,

Wallentowitz²

2010

J. Phys. B: At. Mol. Opt. Phys.

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“…As a matter of fact, this comes as a manifestation of the nonsignaling character of the quantum theory [6]. We also show how this is compatible with the existence of nonlocal correlations at times 0 < t < r/v, a fact pointed out in various theoretical proposals to entangle qubits at arbitrarily short times [7][8][9][10]. More precisely, we give a non-perturbative proof of the fact that the probability of B being excited and A in the ground state is finite and rdependent at any time, even for t < r/v.…”

supporting

confidence: 76%

Fermi Problem with Artificial Atoms in Circuit QED

et al. 2011

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We propose a feasible experimental test of a 1-D version of the Fermi problem using superconducting qubits. We give an explicit non-perturbative proof of strict causality in this model, showing that the probability of excitation of a two-level artificial atom with a dipolar coupling to a quantum field is completely independent of the other qubit until signals from it may arrive. We explain why this is in perfect agreement with the existence of nonlocal correlations and previous results which were used to claim apparent causality problems for Fermi's two-atom system. PACS numbers: 03.65. Ta, 03.65.Ud, 42.50.Ct, 42.50.Dv, Information cannot travel faster than light. But in quantum theory, correlations may be established between spacelike separated events. These facts are not contradictory, since correlations need to be assisted with classical communication in order to transmit information.The two physical phenomena above arise in a natural fashion in the following situation, which is the so-called Fermi problem [1], originally proposed by Fermi to check causality at a microscopic level. At t = 0 a two-level neutral atom A is in its excited state and a two-level neutral atom B in its ground state, with no photons present. If A and B are separated by a distance r and v is the speed of light, can A excite B at times t < r/v? Fermi 's answer was negative but his argument had a mathematical flaw. When a proper analysis is carried on, fundamental quantum theory questions arise due to the interplay between causal signaling and quantum non-local phenomena.These issues led to a controversy [2-5] on the causal behavior of the excitation probability of qubit B, whose conclusions were never put to experimental test. A notorious claim on causality problems in Fermi's two-atom system was given in [2]. The reply of [3] was in the abstract language of algebraic field theory and the proof of strict causality of [5] is perturbative, although given to all orders in perturbation theory. The Fermi problem is usually regarded just as a gedanken experiment, and remains untested, essentially because interactions between real atoms cannot be switched on and off.With this work we give a complete description of the problem in a physical framework in which predictions can be verified. This framework will be circuit QED which can be regarded as a 1-D version of Quantum Electrodynamics (QED) with two-level (artificial) atoms, a testbed which makes it possible to control the interaction and tune the physical parameters. We complete previous descriptions made of the problem and explain how there are no real causality issues for Fermi's two-atom system. We give an explicit non-perturbative proof of strict causality in these setups, showing that the probability of excitation of qubit B is completely independent of qubit A for times t < r/v and for arbitrary initial states. As a matter of fact, this comes as a manifestation of the nonsignaling character of the quantum theory [6]. We also show how this is compatible with the existence of nonlocal co...

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“…Apart from the expected smooth half-life (HL) decaying behavior, the sudden disappearance of entanglement has been theoretically predicted and experimentally observed [4,5]. Widely known as entanglement sudden death (ESD), this non-analytic behavior has been shown to be a generic feature of multipartite quantum systems regardless of whether the environment is modeled as quantum or classical [6][7][8][9][10][11][12][13][14][15][16][17][18][19]. While the monotonic decrease of C(t) is usually associated with Markovian evolution, non-Markovian evolution can also lead to entanglement sudden birth (ESB).…”

Section: Introductionmentioning

confidence: 99%

Topology of Entanglement Evolution of Two Qubits

Zhou

Chern

Fei

et al. 2012

Int. J. Mod. Phys. B

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The dynamics of a two-qubit system is considered with the aim of a general categorization of the different ways in which entanglement can disappear in the course of the evolution, e.g., entanglement sudden death. The dynamics is described by the function n(t), where n is the 15-dimensional polarization vector. This representation is particularly useful because the components of n are direct physical observables, there is a meaningful notion of orthogonality, and the concurrence C can be computed for any point in the space. We analyze the topology of the space S of separable states (those having C = 0), and the often lower-dimensional linear dynamical subspace D that is characteristic of a specific physical model. This allows us to give a rigorous characterization of the four possible kinds of entanglement evolution. Which evolution is realized depends on the dimensionality of D and of D ∩ S, the position of the asymptotic point of the evolution, and whether or not the evolution is "distance-Markovian", a notion we define. We give several examples to illustrate the general principles, and to give a method to compute critical points. We construct a model that shows all four behaviors.

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Photon exchange and correlation transfer in atom-atom entanglement dynamics

Cited by 39 publications

References 25 publications

Dynamics of entanglement between two free atoms with quantized motion

Dynamics of entanglement between two free atoms with quantized motion

Fermi Problem with Artificial Atoms in Circuit QED

Topology of Entanglement Evolution of Two Qubits

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