Entanglement Content Research Articles

Entanglement sharing in one-particle states

Entanglement sharing among sites of one-particle states is considered using the measure of concurrence. These are the simplest in an hierarchy of number-specific states of many qubits and corresponds to ``one-magnon'' states of spins. We study the effects of onsite potentials that are both integrable and nonintegrable. In the integrable case we point to a metal-insulator transition that reflects on the way entanglement is shared. In the nonintegrable case the average entanglement content increases and saturates along with a transition to classical chaos. Such quantum chaotic states are shown to have universal concurrence distributions that are modified Bessel functions derivable within random matrix theory. Time-reversal breaking and time evolving states are shown to possess significantly higher entanglement sharing capacity that eigenstates of time-reversal symmetric systems. We use the ordinary Harper and kicked Harper Hamiltonians as model systems.

L-S decomposition for 2x2 density matrix by using Wootters's basis

An analytical expression for optimal Lewenstein-Sanpera (L-S) decomposition of a generic two qubit density matrix is given. By evaluating the L-S decomposition of Bell decomposable states, the optimal decomposition for arbitrary full rank state of two qubit system is obtained via local quantum operations and classical communications (LQCC). In Bell decomposable case the separable state optimizing L-S decomposition, minimize the von Neumann relative entropy as a measure of entanglement. The L-S decomposition for a generic two-qubit density matrix is only obtained by using Wootters's basis. It is shown that the average concurrence of the decomposition is equal to the concurrence of the state. It is also shown that all the entanglement content of the state is concentrated in the Wootters's state |x_1> associated with the largest eigenvalue \lambda_1 of the Hermitian matrix \sqrt{\sqrt{rho}\tilde{rho}\sqrt{rho}} . It is shown that a given density matrix rho with corresponding set of positive numbers \lambda_i and Wootters's basis can transforms under SO(4,c) into a generic 2x2 matrix with the same set of positive numbers but with new Wootters's basis, where the local unitary transformations correspond to SO(4,r) transformations, hence, \rho can be represented as coset space SO(4,c)/SO(4,r) together with positive numbers lambda_i.

Quantum Teleportation in Noisy Environments

Teleportation of an unknown quantum state is an interesting issue in quantum information processing. Unit fidelity is achieved if sender and receiver share a maximally entangled state corresponding to the Hilbert space of the quantum state to be teleported. Realistic experiments necessarily make use of passive optical devices such as beam splitters and optical fibers which show losses. Losses however, are known to degrade the entanglement content, and hence the teleportation fidelity, of any given quantum state. This is due to the interaction with a noisy environment, say, an optical fiber. We combine two methods, multiparticle entanglement and appropriate filtering, to ‘restore’ some of the entanglement lost during the transmission process. The filtering parameter and the basis used in the projective measurement of the multiparticle-entangled state can be optimized for given material properties (refractive index, fiber length).

Effect of Diluent Content during Polymerization on Equilibrium Deformational Behavior and Structural Parameters of Polymer Network

AbstractThe deformational behavior of poly(ethylene glycol monomethacrylate) which was crosslinked by ethylene glycol dimethacrylate in a concentration range c = 0.05–1.0 × 10−4 mole/cm.3 and polymerized in the presence of 0.05–0.75 volume parts of water was studied. The deformational behavior of these systems may be described by a two‐parameter equation. We found that the value of the constant C2 and the content of permanent entanglements increased linearly with increasing content of polymer in the polymerizing mixture v0. The efficiency of crosslinking also increased and approached the theoretical value at v0 = 1. The measured data can be expressed by the relation v = Kv + Q, where v is the number of effective network chains, and K and Q are the constants depending on the crosslinking agent content, the crosslinking efficiency, and the entanglement content. On the basis of experimental data obtained it is assumed that the entanglements show partly a permanent effect and partly a labile one, the latter influencing the value of the constant C2.