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Sep 22, 2013
09/13

by
S. Bose; V. Vedral

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We consider the apparatus in a quantum measurement process to be in a mixed state. We propose a simple upper bound on the probability of correctly distinguishing any number of mixed states. We use this to derive fundamental bounds on the efficiency of a measurement in terms of the temperature of the apparatus.

Source: http://arxiv.org/abs/quant-ph/0004016v1

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Sep 24, 2013
09/13

by
A. Hutton; S. Bose

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We show that the amount of entanglement needed as an initial resource to set up a certain final amount of entanglement between two ends of a noisy channel can be reduced in certain cases by using quantum repeaters. Our investigation (for various channels) considers cases when a large number of entangled pairs are transmitted through the channel using known asymptotic results and conjectured bounds on distillable entanglement.

Source: http://arxiv.org/abs/quant-ph/0103023v1

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Sep 23, 2013
09/13

by
A. Hutton; S. Bose

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We compare a star and a ring network of interacting spins in terms of the entanglement they can provide between the nearest and the next to nearest neighbor spins in the ground state. We then investigate whether this entanglement can be optimized by allowing the system to interact through a weighted combination of the star and the ring geometries. We find that such a weighted combination is indeed optimal in certain circumstances for providing the highest entanglement between two chosen spins....

Source: http://arxiv.org/abs/quant-ph/0408077v1

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Sep 19, 2013
09/13

by
A. Hutton; S. Bose

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We investigate analytically a star network of spins, in which all spins interact exclusively with a central spin through Heisenberg XX couplings of equal strength. We find that the central spin correlates and entangles the other spins at zero temperature to a degree that depends on the total number of spins. Surprisingly, the entanglement depends on the evenness or oddness of this number and some correlations are substantial even for an infinite collection of spins. We show how symmetric...

Source: http://arxiv.org/abs/quant-ph/0208114v1

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Jul 20, 2013
07/13

by
S. Bose; D. Home

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We point out an earlier unnoticed implication of quantum indistinguishability, namely, a property which we call `dualism' that characterizes the entanglement of two identical particles (say, two ions of the same species) -- a feature which is absent in the entanglement of two non-identical particles (say, two ions of different species). A crucial application of this property is that it can be used to test quantum indistinguishability without bringing the relevant particles together, thereby...

Source: http://arxiv.org/abs/1304.1435v1

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Sep 18, 2013
09/13

by
S. Bose; D. Home

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We show a hitherto unexplored consequence of the property of identicity in quantum mechanics. If two identical objects, distinguished by a dynamical variable A, are in certain entangled states of another dynamical variable B, then, for such states, they are also entangled in variable A when distinguished from each other by variable B. This dualism is independent of quantum statistics. Departures from identicity of the objects due to arbitrarily small differences in their innate attributes...

Source: http://arxiv.org/abs/quant-ph/0505217v1

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Sep 18, 2013
09/13

by
A. Hutton; S. Bose

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We investigate the differences between distributing entanglement using star and ring type network topologies. Assuming symmetrically distributed users, we asses the relative merits of the two network topologies as a function of the number of users when the amount of resources and the type of the quantum channel are kept fixed. For limited resources, we find that the topology better suited for entanglement distribution could differ from that which is more suitable for classical communications.

Source: http://arxiv.org/abs/quant-ph/0202116v1

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Sep 18, 2013
09/13

by
S. Bose; D. Home

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A general and an arbitrarily efficient scheme for entangling the spins (or any spin-like degree of freedom) of two independent uncorrelated identical particles by a combination of two particle interferometry and which way detection is formulated. It is shown that the same setup could be used to identify the quantum statistics of the incident particles from either the sign or the magnitude of measured spin correlations. Our setup also exhibits a curious complementarity between particle...

Source: http://arxiv.org/abs/quant-ph/0101093v2

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Sep 19, 2013
09/13

by
S. Bose; V. Vedral

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We show that on exceeding a certain degree of mixedness (as quantified by the von Neumann entropy), entangled states become useless for teleporatation. By increasing the dimension of the entangled systems, this entropy threshold can be made arbitrarily close to maximal. This entropy is found to exceed the entropy threshold sufficient to ensure the failure of dense coding.

Source: http://arxiv.org/abs/quant-ph/9912033v1

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Jul 20, 2013
07/13

by
G. Bowen; S. Bose

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We show that standard teleportation with an arbitrary mixed state resource is equivalent to a generalized depolarizing channel with probabilities given by the maximally entangled components of the resource. This enables the usage of any quantum channel as a generalized depolarizing channel without additional twirling operations. It also provides a nontrivial upper bound on the entanglement of a class of mixed states. Our result allows a consistent and statistically motivated quantification of...

Source: http://arxiv.org/abs/quant-ph/0107132v2

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Sep 18, 2013
09/13

by
S. C. Benjamin; S. Bose

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It has recently been shown that one can perform quantum computation in a Heisenberg chain in which the interactions are 'always on', provided that one can abruptly tune the Zeeman energies of the individual (pseudo-)spins. Here we provide a more complete analysis of this scheme, including several generalizations. We generalize the interaction to an anisotropic form (incorporating the XY, or Forster, interaction as a limit), providing a proof that a chain coupled in this fashion tends to an...

Source: http://arxiv.org/abs/quant-ph/0401071v1

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Sep 23, 2013
09/13

by
H. T. Ng; S. Bose

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We study the dynamical stability of the entanglement between the two spin ensembles in the presence of an environment. For a comparative study, we consider the two cases: a single spin ensemble, and two ensembles linearly coupled to a bath, respectively. In both circumstances, we assume the validity of the Markovian approximation for the bath. We examine the robustness of the state by means of the growth of the linear entropy which gives a measure of the purity of the system. We find out...

Source: http://arxiv.org/abs/0903.0639v1

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Sep 22, 2013
09/13

by
H. T. Ng; S. Bose

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We study two trapped ions coupled to the axial phonon modes of a one-dimensional Coulomb crystal. This system is formally equivalent to the "two spin-boson" model. We propose a scheme to dynamically generate a maximally entangled state of two ions within a decoherence-free subspace. Here the phononic environment of the trapped ions, whatever its temperature and number of modes, serves as the entangling bus. The efficient production of the pure singlet state can be exploited to perform...

Source: http://arxiv.org/abs/0805.3711v1

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Sep 18, 2013
09/13

by
H. T. Ng; S. Bose

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We propose a method to generate entangled light with a Bose-Einstein condensate trapped in a cavity, a system realized in recent experiments. The atoms of the condensate are trapped in a periodic potential generated by a cavity mode. The condensate is continuously pumped by a laser and spontaneously emits a pair of photons of different frequencies in two distinct cavity modes. In this way, the condensate mediates entanglement between two cavity modes which leak out and can be separated and...

Source: http://arxiv.org/abs/0809.5222v1

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Sep 23, 2013
09/13

by
S. Bose; G. S. Agarwal

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We propose two schemes to establish entanglement between two mesoscopic quantum systems through a third mesoscopic quantum system. The first scheme entangles two nano-mechanical oscillators in a non-Gaussian entangled state through a Cooper pair box. Entanglement detection of the nano-mechanical oscillators is equivalent to a teleportation experiment in a mesoscopic setting. The second scheme can entangle two Cooper pair box qubits through a nano-mechanical oscillator in a thermal state without...

Source: http://arxiv.org/abs/cond-mat/0510676v1

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Sep 20, 2013
09/13

by
H. T. Ng; S. Bose

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We study a two-level atom coupled to a Bose-Einstein condensate. We show that the rules governing the decoherence of mesoscopic superpositions involving different classical-like states of the condensate can be probed using this system. This scheme is applicable irrespective of whether the condensate is initially in a coherent, thermal or more generally in any mixture of coherent states. The effects of atom loss and finite temperature to the decoherence can therefore be studied. We also discuss...

Source: http://arxiv.org/abs/0802.3392v1

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Sep 23, 2013
09/13

by
A. T. Costa Jr; S. Bose

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We show how entanglement between two conduction electrons is generated in the presence of a localized magnetic impurity embedded in an otherwise ballistic conductor of special geometry. This process is a generalization of beam-splitter mediated entanglement generation schemes with a localized spin placed at the site of the beam splitter. Our entangling scheme is unconditional and robust to randomness of the initial state of the impurity. The entangled state generated manifests itself in noise...

Source: http://arxiv.org/abs/quant-ph/0109045v2

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Jul 20, 2013
07/13

by
S. Parker; S. Bose; M. B. Plenio

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We develop theoretical and numerical tools for the quantification of entanglement in systems with continuous degrees of freedom. Continuous variable entanglement swapping is introduced and based on this idea we develop methods of entanglement purification for continuous variable systems. The success of these entanglement purification methods is then assessed using these tools.

Source: http://arxiv.org/abs/quant-ph/9906098v1

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Sep 22, 2013
09/13

by
S. Bose; K. Jacobs; P. L. Knight

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We describe how a quantum system composed of a cavity field interacting with a movable mirror can be utilized to generate a large variety of nonclassical states of both the cavity field and the mirror. First we consider state preparation of the cavity field. The system dynamics will prepare a single mode of the cavity field in a multicomponent Schr\"{o}dinger cat state, in a similar manner to that in a Kerr medium. In addition, when two or more cavity modes interact with the mirror, they...

Source: http://arxiv.org/abs/quant-ph/9708002v1

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Sep 17, 2013
09/13

by
M. Avellino; S. Bose; A. J. Fisher

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This letter details a simple scheme to entangle two neutrons by successive scattering from a macroscopic sample. In zero magnetic field the entanglement falls as the sample size increases. However, by applying a field and tuning the momentum of the neutrons, one can achieve a substantial degree of entanglement irrespective of the size of the sample.

Source: http://arxiv.org/abs/0807.1637v2

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Sep 21, 2013
09/13

by
M. Paternostro; S. Bose; M. S. Kim

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We study the conditions for the probing of an environment affecting one party of a bipartite system of interacting objects by measurements operated only on the other element. We show that entanglement plays no crucial role in such an environment-characterization. On the other hand, if an interaction is established between the two parties, information can be reliably gathered. This result holds for both discrete and continuous variables and helps in the interpretation of recent experiments...

Source: http://arxiv.org/abs/0706.0492v1

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Jul 20, 2013
07/13

by
S. Bose; K. Jacobs; P. L. Knight

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We propose a quantum optical version of Schr\"{o}dinger's famous gedanken experiment in which the state of a microscopic system (a cavity field) becomes entangled with and disentangled from the state of a massive object (a movable mirror). Despite the fact that a mixture of Schr\"{o}dinger cat states is produced during the evolution (due to the fact that the macroscopic mirror starts off in a thermal state), this setup allows us to systematically probe the rules by which a...

Source: http://arxiv.org/abs/quant-ph/9712017v2

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Sep 18, 2013
09/13

by
I. Fuentes-Guridi; S. Bose; V. Vedral

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We propose a scheme for measuring the Berry phase in the vibrational degree of freedom of a trapped ion. Starting from the ion in a vibrational coherent state we show how to reverse the sign of the coherent state amplitude by using a purely geometric phase. This can then be detected through the internal degrees of freedom of the ion. Our method can be applied to preparation of Schr\"odinger cat states.

Source: http://arxiv.org/abs/quant-ph/0006112v3

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Sep 21, 2013
09/13

by
T. Boness; S. Bose; T. S. Monteiro

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We study the dynamics of a single excitation in a Heisenberg spin-chain subjected to a sequence of periodic pulses from an external, parabolic, magnetic field. We show that, for experimentally reasonable parameters, a pair of counter-propagating coherent states are ejected from the centre of the chain. We find an illuminating correspondence with the quantum time evolution of the well-known paradigm of quantum chaos, the Quantum Kicked Rotor (QKR). From this we can analyse the entanglement...

Source: http://arxiv.org/abs/quant-ph/0602106v2

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Sep 22, 2013
09/13

by
H. Wichterich; J. Molina-Vilaplana; S. Bose

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We compute the entanglement between separated blocks in certain spin models showing that at criticality this entanglement is a function of the ratio of the separation to the length of the blocks and can be written as a product of a power law and an exponential decay. It thereby interpolates between the entanglement of individual spins and blocks of spins. It captures features of correlation functions at criticality as well as the monogamous nature of entanglement. We exemplify invariant...

Source: http://arxiv.org/abs/0811.1285v2

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Sep 22, 2013
09/13

by
S. Bose; V. Vedral; P. L. Knight

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We generalize the procedure of entanglement swapping to obtain a scheme for manipulating entanglement in multiparticle systems. We describe how this scheme allows to establish multiparticle entanglement between particles belonging to distant users in a communication network through a prior distribution of singlets followed by only local measurements. We show that this scheme can be regarded as a method of generating entangled states of many particles and compare it with existing schemes using...

Source: http://arxiv.org/abs/quant-ph/9708004v1

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Sep 19, 2013
09/13

by
H. Azuma; S. Bose; V. Vedral

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We investigate the creation of entanglement by the application of phases whose value depends on the state of a collection of qubits. First we give the necessary and sufficient conditions for a given set of phases to result in the creation of entanglement in a state comprising of an arbitrary number of qubits. Then we analyze the creation of entanglement between any two qubits in three qubit pure and mixed states. We use our result to prove that entanglement is necessary for Deutsch-Jozsa...

Source: http://arxiv.org/abs/quant-ph/0102029v3

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Sep 22, 2013
09/13

by
M. Avellino; A. J. Fisher; S. Bose

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We calculate the fidelity of transmission of a single qubit between distant sites on semi-infinite and finite chains of spins coupled via the magnetic dipole interaction. We show that such systems often perform better than their Heisenberg nearest-neighbour coupled counterparts, and that fidelities closely approaching unity can be attained between the ends of finite chains without any special engineering of the system, although state transfer becomes slow in long chains. We discuss possible...

Source: http://arxiv.org/abs/quant-ph/0603148v6

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Sep 19, 2013
09/13

by
S. Bose; V. Vedral; P. L. Knight

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We investigate the purification of entangled states by local actions using a variant of entanglement swapping. We show that there exists a measure of entanglement which is conserved in this type of purification procedure.

Source: http://arxiv.org/abs/quant-ph/9812013v2

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Sep 22, 2013
09/13

by
S. Bose; L. Rallan; V. Vedral

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By considering quantum computation as a communication process, we relate its efficiency to a communication capacity. This formalism allows us to rederive lower bounds on the complexity of search algorithms. It also enables us to link the mixedness of a quantum computer to its efficiency. We discuss the implications of our results for quantum measurement.

Source: http://arxiv.org/abs/quant-ph/0003072v1

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Sep 20, 2013
09/13

by
S. Bose; M. B. Plenio; V. Vedral

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Ideal dense coding protocols allow one to use prior maximal entanglement to send two bits of classical information by the physical transfer of a single encoded qubit. We investigate the case when the prior entanglement is not maximal and the initial state of the entangled pair of qubits being used for the dense coding is a mixed state. We find upper and lower bounds on the capability to do dense coding in terms of the various measures of entanglement and in terms of the average mutual...

Source: http://arxiv.org/abs/quant-ph/9810025v2

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Sep 19, 2013
09/13

by
D. Burgarth; V. Giovannetti; S. Bose

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The scalability of solid state quantum computation relies on the ability of connecting the qubits to the macroscopic world. Quantum chains can be used as quantum wires to keep regions of external control at a distance. However even in the absence of external noise their transfer fidelity is too low to assure reliable connections. We propose a method of optimizing the fidelity by minimal usage of the available resources, consisting of applying a suitable sequence of two-qubit gates at the end of...

Source: http://arxiv.org/abs/quant-ph/0610018v3

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Sep 19, 2013
09/13

by
H. Wichterich; J. Vidal; S. Bose

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The entanglement between noncomplementary blocks of a many-body system, where a part of the system forms an ignored environment, is a largely untouched problem without analytic results. We rectify this gap by studying the logarithmic negativity between two macroscopic sets of spins in an arbitrary tripartition of a collection of mutually interacting spins described by the Lipkin-Meshkov-Glick Hamiltonian. This entanglement measure is found to be finite and universal at the critical point for...

Source: http://arxiv.org/abs/0910.1011v2

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Jun 28, 2018
06/18

by
S. Bose; D. Home; S. Mal

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The Leggett-Garg inequality (LGI), based on the notions of realism and noninvasive measurability, is applied in the context of a linear harmonic oscillator. It is found that merely through observing at various instants which region of the potential well, the oscillating quantum object is in, the LGI can be violated without taking recourse to any ancillary quantum system. Strikingly, this violation reveals an unexplored nonclassicality of the state which is considered the most...

Topic: Quantum Physics

Source: http://arxiv.org/abs/1509.00196

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Jul 20, 2013
07/13

by
M. C. Arnesen; S. Bose; V. Vedral

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We investigate the entanglement between any two spins in a one dimensional Heisenberg chain as a function of temperature and the external magnetic field. We find that the entanglement in an antiferromagnetic chain can be increased by increasing the temperature or the external field. Increasing the field can also create entanglement between otherwise disentangled spins. This entanglement can be confirmed by testing Bell's inequalities involving any two spins in the solid.

Source: http://arxiv.org/abs/quant-ph/0009060v2

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Sep 19, 2013
09/13

by
D. Gunlycke; S. Bose; V. M. Kendon; V. Vedral

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We investigate the entanglement arising naturally in a 1D Ising chain in a magnetic field in an arbitrary direction. We find that for different temperatures, different orientations of the magnetic field give maximum entanglement. In the high temperature limit, this optimal orientation corresponds to the magnetic field being perpendicular to the Ising orientation (z direction). In the low temperature limit, we find that varying the angle of the magnetic field very slightly from the z direction...

Source: http://arxiv.org/abs/quant-ph/0102137v2

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Sep 23, 2013
09/13

by
J. Molina-Vilaplana; H. Wichterich; V. E. Korepin; S. Bose

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We study the feasibility of extracting a pure entangled state of non-complementary, and potentially well separated, regions of a quantum many-body system. It is shown that this can indeed be accomplished in non-equilibrium scenarios as well as the ground state of the considered spin chain models when one locally measures observables such as magnetization in separated blocks of spins. A general procedure is presented, which can search for the optimal way to extract a pure entangled state through...

Source: http://arxiv.org/abs/0903.4553v1

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Sep 23, 2013
09/13

by
A. Serafini; M. Paternostro; M. S. Kim; S. Bose

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We present two strategies to enhance the dynamical entanglement transfer from continuous variable (CV) to finite dimensional systems by employing multiple qubits. First, we consider the entanglement transfer to a composite finite dimensional system of many qubits simultaneously interacting with a bipartite CV field. We show that, considering realistic conditions in the generation of CV entanglement, a small number of qubits resonantly coupled to the CV system is sufficient for an almost...

Source: http://arxiv.org/abs/quant-ph/0511115v2

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Sep 22, 2013
09/13

by
S. Bose; B. -Q. Jin; V. E. Korepin

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We investigate quantum communication between the sites of a spin-ring with twisted boundary conditions. Such boundary conditions can be achieved by a flux through the ring. We find that a non-zero twist can improve communication through finite odd numbered rings and enable high fidelity multi-party quantum communication through spin rings (working near perfectly for rings of 5 and 7 spins). We show that in certain cases, the twist results in the complete blockage of quantum information flow to...

Source: http://arxiv.org/abs/quant-ph/0409134v3

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Sep 23, 2013
09/13

by
S. Bose; P. L. Knight; M. B. Plenio; V. Vedral

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We show how the state of an atom trapped in a cavity can be teleported to a second atom trapped in a distant cavity simply by detecting photon decays from the cavities. This is a rare example of a decay mechanism playing a constructive role in quantum information processing. The scheme is comparatively easy to implement, requiring only the ability to trap a single three level atom in a cavity.

Source: http://arxiv.org/abs/quant-ph/9908004v2

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Sep 24, 2013
09/13

by
S. Bose; I. Fuentes-Guridi; P. L. Knight; V. Vedral

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We show that entanglement can always arise in the interaction of an arbitrarily large system in any mixed state with a single qubit in a pure state. This small initial purity is enough to enforce entanglement even when the total entropy is close to maximum. We demonstrate this feature using the Jaynes-Cummings interaction of a two level atom in a pure state with a field in a thermal state at an arbitrarily high temperature. We find the time and temperature variation of a lower bound on the...

Source: http://arxiv.org/abs/quant-ph/0103063v2

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Sep 18, 2013
09/13

by
I. Fuentes-Guridi; A. Carollo; S. Bose; V. Vedral

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We calculate the Berry phase of a spin-1/2 particle in a magnetic field considering the quantum nature of the field. The phase reduces to the standard Berry phase in the semiclassical limit and eigenstate of the particle acquires a phase in the vacuum. We also show how to generate a vacuum induced Berry phase considering two quantized modes of the field which has a interesting physical interpretation.

Source: http://arxiv.org/abs/quant-ph/0202128v2

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Sep 18, 2013
09/13

by
S. Bose; S. F. Huelga; M. B. Plenio

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We present a task which can be faithfully solved with finite resources only when aided by particles prepared in a particular entangled state: the singlet state. The task consists of identifying the mutual parallelity or orthogonality of weak distant magnetic fields whose absolute directions are completely unknown.

Source: http://arxiv.org/abs/quant-ph/0005020v1

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Sep 19, 2013
09/13

by
MGA Paris; M Plenio; D Jonathan; S Bose; GM D'Ariano

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We describe a nonlinear interferometric setup to perform a complete optical Bell measurement, i.e. to unambigously discriminate the four polarization entangled EPR-Bell photon pairs. The scheme is robust against detector inefficiency.

Source: http://arxiv.org/abs/quant-ph/9911036v1

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Sep 23, 2013
09/13

by
A. Bayat; D. Burgarth; S. Mancini; S. Bose

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We investigate the multiple use of a ferromagnetic spin chain for quantum and classical communications without resetting. We find that the memory of the state transmitted during the first use makes the spin chain a qualitatively different quantum channel during the second transmission, for which we find the relevant Kraus operators. We propose a parameter to quantify the amount of memory in the channel and find that it influences the quality of the channel, as reflected through fidelity and...

Source: http://arxiv.org/abs/0710.2348v2

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Sep 21, 2013
09/13

by
J. Eisert; M. B. Plenio; S. Bose; J. Hartley

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We study arrays of mechanical oscillators in the quantum domain and demonstrate how the motions of distant oscillators can be entangled without the need for control of individual oscillators and without a direct interaction between them. These oscillators are thought of as being members of an array of nano-electromechanical resonators with a voltage being applicable between neighboring resonators. Sudden non-adiabatic switching of the interaction results in a squeezing of the states of the...

Source: http://arxiv.org/abs/quant-ph/0311113v3

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Sep 22, 2013
09/13

by
S. Bose; A. Ekert; Y. Omar; N. Paunkovic; V. Vedral

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We present an application of particle statistics to the problem of optimal ambiguous discrimination of quantum states. The states to be discriminated are encoded in the internal degrees of freedom of identical particles, and we use the bunching and antibunching of the external degrees of freedom to discriminate between various internal states. We show that we can achieve the optimal single-shot discrimination probability using only the effects of particle statistics. We discuss interesting...

Source: http://arxiv.org/abs/quant-ph/0309090v1

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Sep 18, 2013
09/13

by
Jinhyoung Lee; M. Paternostro; M. S. Kim; S. Bose

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We investigate how entanglement can be transferred between qubits and continuous variable (CV) systems. We find that one ebit borne in maximally entangled qubits can be fully transferred to two CV systems which are initially prepared in pure separable Gaussian field with high excitation. We show that it is possible, though not straightforward, to retrieve the entanglement back to qubits from the entangled CV systems. The possibility of deposition of multiple ebits from qubits to the initially...

Source: http://arxiv.org/abs/quant-ph/0509095v1

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Sep 18, 2013
09/13

by
Y. Omar; N. Paunkovic; S. Bose; V. Vedral

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Both the topics of entanglement and particle statistics have aroused enormous research interest since the advent of quantum mechanics. Using two pairs of entangled particles we show that indistinguishability enforces a transfer of entanglement from the internal to the spatial degrees of freedom without any interaction between these degrees of freedom. Moreover, sub-ensembles selected by local measurements of the path will in general have different amounts of entanglement in the internal degrees...

Source: http://arxiv.org/abs/quant-ph/0105120v2

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Sep 23, 2013
09/13

by
Y. Omar; N. Paunkovic; L. Sheridan; S. Bose

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We introduce the concept of a quantum walk with two particles and study it for the case of a discrete time walk on a line. A quantum walk with more than one particle may contain entanglement, thus offering a resource unavailable in the classical scenario and which can present interesting advantages. In this work, we show how the entanglement and the relative phase between the states describing the coin degree of freedom of each particle will influence the evolution of the quantum walk. In...

Source: http://arxiv.org/abs/quant-ph/0411065v1