Thermal entanglement and teleportation in a three-qubit Heisenberg XXZ model with Dzyaloshinski-Moriya anisotropic antisymmetric interaction

This paper investigates the thermal pairwise entanglement of a three-qubit Heisenberg XXZ chain in the presence of the Dzyaioshinski-Moriya （DM） anisotropic antisymmetric interaction and quantum teleportation when using the Heisenberg chain as a channel. The entanglement dependences on the DM interaction and temperature are given in detail. It obtains the relation between the concurrence and average fidelity, and shows that the same concurrence can lead different average fidelities. Moreover, it finds the thermally entangled states which do not violate the Bell inequalities, and can still be used for quantum teleportation.

The geometry of violation of Bell's inequality

The purpose of this paper is to deduce an analytical expression for the violation of Bell's inequality by quantum theory and plane trigonometry, and expound the violation and maximal violation of the first, second type Bell's inequality in detail. Further, we find out the sufficient conditions for the region in which Bell's inequalities are violated.

Quantum Mysteries for No One

I provide a critical reassessment of David Mermin’s influential and misleading parable, “Quantum Mysteries for Anyone”, identifying its errors and resolving them with a complete analysis of the quantum experiment it is meant to portray. Accessible to popular readership and requiring no knowledge of quantum physics at all, his exposition describes the curious behaviour of a machine that is designed to parody the empirical results of quantum experiments monitoring the spins of a pair of electrons under various conditions. The mysteries are said to unfold from contradictory results produced by a signal process that is proposed to explain them. I find that these results derive from a mathematical error of neglect, coupled with a confusion of two distinct types of experiments under consideration. One of these, a gedankenexperiment, provides the context in which the fabled defiance of Bell’s inequality is thought to emerge. The errors are corrected by the recognition of functional relations embedded within the experimental conditions that have been long unnoticed. A Monte Carlo simulation of results in accord with the actual abstemious claims of quantum theory supports probability values that Mermin decries as unwarranted. However, the distribution it suggests is not definitive, in accord with the expressed agnostic position of quantum theory regarding measurements that cannot be executed. Bounding quantum probabilities are computed for the results of the gedankenexperiment relevant to Bell’s inequality which inspired the parable. The problem is embedded in a 3 × 3 design of Stern-Gerlach magnet orientations at two observation stations. Computational resolution on the basis of Bruno de Finetti’s fundamental theorem of probability requires the evaluation of a battery of three paired linear programming problems. Though technicalities are ornate, the message is clear. There are no mysteries of quantum mechanics that derive from mistaken understandings of Bell’s inequality… for anyone.

Orbital angular momentum based intra- and interparticle entangled states generated via a quantum dot source

Engineering single-photon states endowed with orbital angular momentum (OAM) is a powerful toolfor quantum information photonic implementations. Indeed, due to its unbounded nature, OAM is suitable forencoding qudits, allowing a single carrier to transport a large amount of information. Most of the experimentalplatforms employ spontaneous parametric down-conversion processes to generate single photons, evenif this approach is intrinsically probabilistic, leading to scalability issues for an increasing number of qudits.Semiconductor quantum dots (QDs) have been used to get over these limitations by producing on-demand pure and indistinguishable single-photon states, although only recently they have been exploitedto create OAM modes. Our work employs a bright QD single-photon source to generate a complete set ofquantum states for information processing with OAM-endowed photons. We first study hybrid intraparticleentanglement between OAM and polarization degrees of freedom of a single photon whose preparationwas certified by means of Hong–Ou–Mandel visibility. Then, we investigate hybrid interparticle OAM-based entanglement by exploiting a probabilistic entangling gate. The performance of our approach isassessed by performing quantum state tomography and violating Bell inequalities. Our results pave theway for the use of deterministic sources for the on-demand generation of photonic high-dimensionalquantum states.