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Shahpoor Moradi

Publications and source records attributed to Shahpoor Moradi.

15 recordsLinked to original sources
arXiv2018

Entanglement in anisotropic expanding spacetime

We study the effect of space anisotropy in the entanglement generated by expanding universe on spin 0 and 1/2 fields. For massive scalar field we find revivals of entanglement entropy vs momentum after decreasing from the maximum at k = 0. In massive Dirac field the effect is a slight distortion of the non-monotonic profile giving rise to the maximum of entanglement entropy at k > 0. More interestingly, massless field of both type can only get entangled through anisotropy, with a maximum of entanglement entropy occurring at k > 0.

gr-qc↗
arXiv2016

Spacetime anisotropy affects cosmological entanglement

Most existing cosmological entanglement studies are focused on the isotropic Robertson-Walker (RW) spacetime. Here we go beyond this limitation and study the influence of anisotropy on entanglement generated by dynamical spacetime. Since the isotropic spacetime is viewed as a background medium and the anisotropy is incorporated as perturbation, we decompose entanglement entropy into isotropic and anisotropic contributions. The latter is shown to be non-negligible by analyzing two cosmological models with weak and conformal coupling. We also show the possibility of using entanglement to infer about universe features.

gr-qc↗
arXiv2016

The role of spin in entanglement generated by expanding spacetime

We investigate the effects of spin on entanglement arising in Dirac field in an expanding spacetime characterized by the Robertson-Walker metric. We present a general approach that allows us to treat the case where only charge conservation is required, as well as the case where also angular momentum conservation is required. We fiend that in both situations entanglement, quantified by subsystem entropy, behaves the same and does not qualitatively deviates from the spinless case. Differences only arise when particles and/or antiparticles are present in the input state.

quant-ph↗
arXiv2013

Spin-Particles Entanglement in Robertson-Walker Spacetime

We study the entanglement between two modes of Dirac field in an expanding spacetime characterized by the Robertson-Walker metric. This spacetime model turns out to be asymptotically (in the remote past and far future regions) Minkowskian. Then, on the one hand we show entanglement creation between particles and anti-particles when passing from remote past to far future. On the other hand we show that particles entanglement in the remote past degrades into the far future. These effects are traced back to particles creation. In our analysis we highlight the role of spin (polarization) of particles and compare the results with those obtainable without accounting for it.

gr-qc↗
arXiv2012

Testing quantum nonlocality for three coupled quantum dots within optical microcavity QED

Bell's inequality in three coupled quantum dots (QDs) within cavity QED, including Forster and exciton-phonon interactions, is investigated theoretically. For an initially entangled state, Bell's inequality is valid for certain times and violated for some other times. It is shown that the system moves from a product state to a entangled state and back again during it's time evolution.

quant-ph↗
arXiv2012

Frame independent nonlocality for three qubit state

Bell's inequality is investigated for the three qubit GHZ state in relativistic regime. Two different relativistic spin operator are considered. One of them is defined by Lee, and the other is the Pauli-Lubanski pseudovector used by Kim \textit{et al}. It is shown that for both spin operator Bell's inequality is still maximally violated in a Lorentz-boosted frame.

quant-ph↗
arXiv2012

Relativity of mixed entangled states

We obtain the necessary and sufficient separability and distillability conditions of mixtures of a maximally entangled state and the completely separable state in relativistic setting. In an inertial frame we study the entanglement under Wigner rotations induced by Lorentz transformations. We also investigate the mixed state entanglement of scalar and Dirac fields as seen by two relatively accelerated observers. For scalar field we show that in infinite acceleration limit the state has no longer distillable entanglement. For dirac field the entanglement in the infinite acceleration limit is finite. In both cases we show that there are states that will change from entangled into separable for a certain value of velocity or acceleration. We conclude that distillability is a relative concept, depending on the frame in which it is observed.

quant-ph↗
arXiv2012

Cosmological Entanglement

We investigate the connection between the entanglement generated by expanding universe and the cosmological parameters. We show that the faster the universe expands and the larger the total volume results the higher degree of entanglement.

quant-ph↗
arXiv2012

Distillability of entanglement in accelerated frames

We study the entanglement distillability of bipartite mixed states of two modes of a free Dirac field as seen by two relatively accelerated parties. It is shown that there are states that will change from distillable into separable for a certain value of acceleration. We exemplify these criteria in the context of Werner states.

quant-ph↗
arXiv2012

Entanglement Generation by Time Varying Refractive Index: Analogy with Cosmological Model

Generation of entanglement between modes of a electromagnetic fields by sudden change of the refractive index of a medium is considered. We use the analogy between the Fock-space formulation of pair creation caused by the contraction and expansion of the universe on one hand and the pair creation in time-dependent electric fields on the other hand. It is shown that entanglement between photons encodes information concerning the underlying refractive index of a medium.

quant-ph↗
arXiv2012

Maximally entangled states and Bell's inequality in relativistic regime

In this Letter we show that in relativistic regime maximally entangled state of two spin-1/2 particles not only gives maximal violation of the Bell-CHSH inequality but also gives the largest violation attainable for any pairs of four spin observables that are noncommuting for both systems. Also we extend our results to three spin-1/2 particles. We obtain the largest eigenvalue of Bell operator and show that this value is equal to expectation value of Bell operator on GHZ state.

quant-ph↗
arXiv2012

Degradation of entanglement in moving frames

The distillability of bipartite entangled state as seen by moving observers has been investigated. It is found that the same initial entanglement for a state parameter $α$ and its "normalized partner" $\sqrt{1-α^2}$ will be degraded as seen by moving observer. It is shown that in the ultra relativistic limit, the state does not have distillable entanglement for any $α$.

quant-ph↗
arXiv2012

Relativistic quantum nonlocality for the three-qubit Greenberger-Horne-Zeilinger state

Lorentz transformation of three-qubit Greenberger-Horne-Zeilinger (GHZ) state is studied. Also we obtain the relativistic spin joint measurement for the transformed state. Using these results it is shown that Bell's inequality is maximally violated for three-qubit GHZ state in relativistic regime. For ultrarelativistic particles we obtain the critical value for boost speed which Bell's inequality is not violated for velocities smaller than this value. We also show that in ultrarelativistic limit Bell's inequality is maximally violated for GHZ state.

quant-ph↗
arXiv2012

Bell's inequality with Dirac particles

We study Bell's inequality using the Bell states constructed from four component Dirac spinors. Spin operator is related to the Pauli-Lubanski pseudo vector which is relativistic invariant operator. By using Lorentz transformation, in both Bell states and spin operator, we obtain an observer independent Bell's inequality, so that it is maximally violated as long as it is violated maximally in the rest frame.

quant-ph↗