138 research outputs found
Reexamination of entanglement of superpositions
We find tight lower and upper bounds on the entanglement of a superposition
of two bipartite states in terms of the entanglement of the two states
constituting the superposition. Our upper bound is dramatically tighter than
the one presented in Phys. Rev. Lett 97, 100502 (2006) and our lower bound can
be used to provide lower bounds on different measures of entanglement such as
the entanglement of formation and the entanglement of subspaces. We also find
that in the case in which the two states are one-sided orthogonal, the
entanglement of the superposition state can be expressed explicitly in terms of
the entanglement of the two states in the superposition.Comment: 5 pages, Published versio
Faithful Teleportation with Partially Entangled States
We write explicitly a general protocol for faithful teleportation of a
d-state particle (qudit) via a partially entangled pair of (pure) -state
particles. The classical communication cost (CCC) of the protocol is
bits, and it is implemented by a {\em projective} measurement
performed by Alice, and a unitary operator performed by Bob (after receiving
from Alice the measurement result). We prove the optimality of our protocol by
a comparison with the concentrate and teleport strategy. We also show that if
or if there is no residual entanglement left after the faithful
teleportation, the CCC of {\em any} protocol is at least bits.
Furthermore, we find a lower bound on the CCC in the process transforming one
bipartite state to another by means of local operation and classical
communication (LOCC).Comment: 5 pages, RevTex4, This significantly modified version accepted for
publication in Phys. Rev.
How many ebits can be unlocked with one classical bit?
We find an upper bound on the rate at which entanglement can be unlocked by
classical bits. In particular, we show that for quantum information sources
that are specified by ensambles of pure bipartite states, one classical bit can
unlock at most one ebit.Comment: 3 pages, Brief Report, Comments are Welcom
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