15,334 research outputs found
Mixedness and teleportation
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.Comment: 6 pages, no figure
Distillable entanglement in dimension
Distillable entanglement () is one of the acceptable measures of
entanglement of mixed states. Based on discrimination through local operation
and classical communication, this paper gives for two classes of
orthogonal multipartite maximally entangled states.Comment: 6 page
Entangled webs: Tight bound for symmetric sharing of entanglement
Quantum entanglement cannot be unlimitedly shared among arbitrary number of
qubits. Larger the number of entangled pairs in an N-qubit system, smaller the
degree of bi-partite entanglement is. We analyze a system of N qubits in which
an arbitrary pair of particles is entangled. We show that the maximum degree of
entanglement (measured in the concurrence) between any pair of qubits is 2/N.
This tight bound can be achieved when the qubits are prepared in a pure
symmetric (with respect to permutations) state with just one qubit in the basis
state |0> and the others in the basis state |1>.Comment: 4 pages, 1 figur
Entangled Rings
Consider a ring of N qubits in a translationally invariant quantum state. We
ask to what extent each pair of nearest neighbors can be entangled. Under
certain assumptions about the form of the state, we find a formula for the
maximum possible nearest-neighbor entanglement. We then compare this maximum
with the entanglement achieved by the ground state of an antiferromagnetic ring
consisting of an even number of spin-1/2 particles. We find that, though the
antiferromagnetic ground state does not maximize the nearest-neighbor
entanglement relative to all other states, it does so relative to other states
having zero z-component of spin.Comment: 19 pages, no figures; v2 includes new results; v3 corrects a
numerical error for the case N=
Multipartite pure-state entanglement and the generalized GHZ states
We show that not all 4-party pure states are GHZ reducible (i.e., can be
generated reversibly from a combination of 2-, 3- and 4-party maximally
entangled states by local quantum operations and classical communication
asymptotically) through an example, we also present some properties of the
relative entropy of entanglement for those 3-party pure states that are GHZ
reducible, and then we relate these properties to the additivity of the
relative entropy of entanglement.Comment: 7 pages, Revtex, type error correcte
Entanglement Degree of Parasupersymmetric Coherent States of Harmonic Oscillator
We study the boson-parafermion entanglement of the parasupersymmetric
coherent states of the harmonic oscillator and derive the degree of
entanglement in terms of the concurrence. The conditions for obtaining the
maximal entanglement is also examined, and it is shown that in the usual
supersymmetry situation we can obtain maximally entangled Bell states.Comment: 8 pages, 1 figur
Classical, quantum and total correlations
We discuss the problem of separating consistently the total correlations in a
bipartite quantum state into a quantum and a purely classical part. A measure
of classical correlations is proposed and its properties are explored.Comment: 10 pages, 3 figure
Limits for entanglement measures
We show that {\it any} entanglement measure suitable for the regime of
high number of entangled pairs satisfies where and
are entanglement of distillation and formation respectively. We also
exhibit a general theorem on bounds for distillable entanglement. The results
are obtained by use of a very transparent reasoning based on the fundamental
principle of entanglement theory saying that entanglement cannot increase under
local operations and classical communication.Comment: 4 pages, Revtex, typos correcte
Measurement of the 6S-7S transition polarizablility in atomic cesium and an improved test of the standard model
The ratio of the off-diagonal hyperfine amplitude to the tensor transition
polarizability (Mhf/beta) for the 6S-7S transition in cesium has been measured.
The value of beta=27.024(43)(expt)(67)(theory)a_0^3 is then obtained using an
accurate semi-empirical value of Mhf. This is combined with a previous
measurement of parity nonconservation in atomic cesium and previous atomic
structure calculations to determine the value of the weak charge. The
uncertainties in the atomic structure calculations are updated (and reduced) in
light of new experimental tests. The result Q_W=-72.06(28)(expt) (34)(theory)
differs from the prediction of the standard model of elementary particle
physics by 2.5 sigma.Comment: 12 pages, 1 figur
Natural Thermal and Magnetic Entanglement in 1D Heisenberg Model
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.Comment: 4 pages, 5 figure
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