52 research outputs found
Incommensurate structure factor in a hole-doped spin-1 system
The nickelate compound Y_{2}BaNiO_{5} is a spin-1 Haldane-gap
antiferromagnet. The compound is doped with holes on replacing the off-chain
Y^{3+} ions by Ca^{2+} ions. Inelastic neutron scattering (INS) experiments
reveal the existence of sub-gap states on doping. A recent INS experiment
provides evidence for an incommensurate double-peaked structure factor S(q)
corresponding to the sub-gap states. In this paper, we formulate a microscopic
theory for the origin of the incommensurate peak.Comment: 14 Pages, Latex, 3 Figure
Character of Locally Inequivalent Classes of States and Entropy of Entanglement
In this letter we have established the physical character of pure bipartite
states with the same amount of entanglement in the same Schmidt rank that
either they are local unitarily connected or they are incomparable. There exist
infinite number of deterministically locally inequivalent classes of pure
bipartite states in the same Schmidt rank (starting from three) having same
amount of entanglement. Further, if there exists incomparable states with same
entanglement in higher Schmidt ranks (greater than three), then they should
differ in at least three Schmidt coefficients.Comment: 4 pages, revtex4, no figure, accepted in Physical Review A (rapid
communications
Bell-Correlated Activable Bound Entanglement in Multiqubit Systems
We show that the Hilbert space of even number () of qubits can always
be decomposed as a direct sum of four orthogonal subspaces such that the
normalized projectors onto the subspaces are activable bound entangled (ABE)
states. These states also show a surprising recursive relation in the sense
that the states belonging to qubits are Bell correlated to the states of
qubits; hence, we refer to these states as Bell-Correlated ABE (BCABE)
states. We also study the properties of noisy BCABE states and show that they
are very similar to that of two qubit Bell-diagonal states
More assistance of entanglement, less rounds of classical communication
Classical communication plays a crucial role to distinguish locally a class
of quantum states. Despite considerable advances, we have very little knowledge
about the number of measurement and communication rounds needed to implement a
discrimination task by local quantum operations and classical communications
(in short, LOCC). In this letter, we are able to show the relation between
round numbers with the local discrimination of a set of pure bipartite
orthogonal quantum states. To demonstrate the possible strong dependence on the
round numbers, we consider a class of orthogonal product states in , which require at least round of classical communications. Curiously
the round number can be reduced to by the assistance of one-ebit of
entanglement as resource and can be reduced further by assistance of more
entanglement. We are also able to show that the number of LOCC rounds needed
for a discrimination task may depend on the amount of entanglement assistances.Comment: 11 pages, 3 figures, revtex, comments welcom
Tight upper bound of genuine four party Svetlichny type nonlocality with and without local filtering
Identifying the nonlocality of a multiparty quantum state is an important
task in quantum mechanics. Seevinck and Svetlichny [Phys. Rev. Lett. 89, 060401
(2002)], and independently, Collins and co-workers [Phys. Rev. Lett. 88, 170405
(2002)] have generalized the tripartite notion of Svetlichny nonlocality to
n-parties. Here we have developed a tight upper bound for genuine four party
Svetlichny type nonlocality. The constraints on the quantum states for the
tightness of the bound are also presented. The method enables us to provide
necessary and sufficient conditions for violating the four qubit Svetlichny
type inequality for several quantum states. The relations between the genuine
multipartite entanglement and the maximal quantum value of the Seevinck and
Svetlichny operators for pure four qubit states are also discussed.
Consequently, we have exhibited genuine four qubit hidden nonlocality under
local filtering. Our result provides an effective and operational method for
further study of multipartite quantum nonlocality.Comment: 10 pages, 2 figures, revtex, comments welcome. arXiv admin note: text
overlap with arXiv:quant-ph/0602143, arXiv:1710.01601 by other author
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