403 research outputs found
Local Detection of Entanglement
We construct an explicit model where it can be established if a two mode pure
Gaussian system is entangled or not by acting only on one of the parts that
constitute the system. Measuring the dispersion in momentum and the time
evolution of the dispersion in position of one particle we can tell if
entanglement is present as well as the degree of entanglement of the system.Comment: 6 pages, 4 figures, title changed, published version: to appear in
European Physical Journal
Generalized Quantum Telecloning
We present a generalized telecloning (GTC) protocol where the quantum channel
is non-optimally entangled and we study how the fidelity of the telecloned
states depends on the entanglement of the channel. We show that one can
increase the fidelity of the telecloned states, achieving the optimal value in
some situations, by properly choosing the measurement basis at Alice's, albeit
turning the protocol to a probabilistic one. We also show how one can convert
the GTC protocol to the teleportation protocol via proper unitary operations.Comment: 6 pages, 1 figure, RevTex4; v2: published version, 8 pages, 4
figures, RevTex4, to appear at Eur. Phys. J.
Fermion Virtual Effects in Cross Section
We analyse the contribution of new heavy virtual fermions to the cross section. We find that there exists a relevant
interplay between trilinear and bilinear oblique corrections. The result
strongly depends on the chiral or vector--like nature of the new fermions. As
for the chiral case we consider sequential fermions: one obtains substantial
deviation from the Standard model prediction, making the effect possibly
detectable at or GeV linear colliders. As an example for
the vector--like case we take a SUSY extension with heavy charginos and
neutralinos: due to cancellation, the final effect turns out to be negligible.Comment: uuencoded, gz-compressed, tar-ed file. 8 pages, 4 EPS figures, uses
EPSFIG.ST
Detecting quantum critical points at finite temperature via quantum teleportation
We show that the quantum teleportation protocol is a powerful tool to study
quantum phase transitions (QPTs) at finite temperatures. We consider a pair of
spins from an infinite spin-1/2 chain (XXZ model) in equilibrium with a
reservoir at temperature T as the resource used by Alice and Bob to implement
the teleportation protocol. We show that the efficiency of this pair of spins
to teleport a qubit is drastically affected after we cross a quantum critical
point (QCP), even for high values of T. Also, we show that the present tool is
as sharp as quantum discord (QD) to spotlight a QCP, where QD is the best
finite T QCP detector known to date. Contrary to QD, however, we show that the
present tool is easier to compute theoretically and has a direct experimental
and operational meaning.Comment: 10 pages, 14 figures, two columns, RevTex
Quantum teleportation of an arbitrary two-qubit state and its relation to multipartite entanglement
We explicitly show a protocol in which an arbitrary two qubit state vertical bar phi >=a vertical bar 00 >+b vertical bar 01 >+c vertical bar 10 >+d vertical bar 11 > is faithfully and deterministically teleported from Alice to Bob. We construct the 16 orthogonal generalized Bell states that can be used to teleport the two qubits. The local operations Bob must perform on his qubits in order to recover the teleported state are also constructed. They are restricted only to single-qubit gates. This means that a controlled-NOT gate is not necessary to complete the protocol. A generalization where N qubits are teleported is also shown. We define a generalized magic basis, which possesses interesting properties. These properties help us to suggest a generalized concurrence from which we construct a measure of entanglement that has a clear physical interpretation: A multipartite state has maximum entanglement if it is a genuine quantum teleportation channel.713
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