89,468 research outputs found
Entanglement detection beyond the CCNR criterion for infinite-dimensions
In this paper, in terms of the relation between the state and the reduced
states of it, we obtain two inequalities which are valid for all separable
states in infinite-dimensional bipartite quantum systems. One of them provides
an entanglement criterion which is strictly stronger than the computable
cross-norm or realignment (CCNR) criterion.Comment: 11 page
Optimal nonlocal multipartite entanglement concentration based on projection measurements
We propose an optimal nonlocal entanglement concentration protocol (ECP) for
multi-photon systems in a partially entangled pure state, resorting to the
projection measurement on an additional photon. One party in quantum
communication first performs a parity-check measurement on her photon in an
N-photon system and an additional photon, and then she projects the additional
photon into an orthogonal Hilbert space for dividing the original -photon
systems into two groups. In the first group, the N parties will obtain a subset
of -photon systems in a maximally entangled state. In the second group, they
will obtain some less-entangled N-photon systems which are the resource for the
entanglement concentration in the next round. By iterating the entanglement
concentration process several times, the present ECP has the maximal success
probability which is just equivalent to the entanglement of the partially
entangled state. That is, this ECP is an optimal one.Comment: 5 pages, 4 figure
Hilbert Expansion from the Boltzmann equation to relativistic Fluids
We study the local-in-time hydrodynamic limit of the relativistic Boltzmann
equation using a Hilbert expansion. More specifically, we prove the existence
of local solutions to the relativistic Boltzmann equation that are nearby the
local relativistic Maxwellian constructed from a class of solutions to the
relativistic Euler equations that includes a large subclass of near-constant,
non-vacuum fluid states. In particular, for small Knudsen number, these
solutions to the relativistic Boltzmann equation have dynamics that are
effectively captured by corresponding solutions to the relativistic Euler
equations.Comment: 50 page
Entanglement changing power of two-qubit unitary operations
We consider a two-qubit unitary operation along with arbitrary local unitary
operations acts on a two-qubit pure state, whose entanglement is C_0. We give
the conditions that the final state can be maximally entangled and be
non-entangled. When the final state can not be maximally entangled, we give the
maximal entanglement C_max it can reach. When the final state can not be
non-entangled, we give the minimal entanglement C_min it can reach. We think
C_max and C_min represent the entanglement changing power of two-qubit unitary
operations. According to this power we define an order of gates.Comment: 11 page
Magnetic anisotropy and spin-spiral wave in V, Cr and Mn atomic chains on Cu(001) surface: First principles calculations
Recent ab intio studies of the magnetic properties of all 3d transition
metal(TM) freestanding atomic chains predicted that these nanowires could have
a giant magnetic anisotropy energy (MAE) and might support a spin-spiral
structure, thereby suggesting that these nanowires would have technological
applicationsin, e.g., high density magnetic data storages. In order to
investigate how the substrates may affect the magnetic properties of the
nanowires, here we systematically study the V, Cr and Mn linear atomic chains
on the Cu(001) surface based on the density functional theory with the
generalized gradient approximation. We find that V, Cr, and Mn linear chains on
the Cu(001) surface still have a stable or metastable ferromagnetic state.
However, the ferromagnetic state is unstable against formation of a
noncollinear spin-spiral structure in the Mn linear chains and also the V
linear chain on the atop sites on the Cu(001) surface, due to the frustrated
magnetic interactions in these systems. Nonetheless, the presence of the
Cu(001) substrate does destabilize the spin-spiral state already present in the
freestanding V linear chain and stabilizes the ferromagnetic state in the V
linear chain on the hollow sites on Cu(001). When spin-orbit coupling (SOC) is
included, the spin magnetic moments remain almost unchanged, due to the
weakness of SOC in 3d TM chains. Furthermore, both the orbital magnetic moments
and MAEs for the V, Cr and Mn are small, in comparison with both the
corresponding freestanding nanowires and also the Fe, Co and Ni linear chains
on the Cu (001) surface.Comment: Accepted for publication in J. Phys. D: Applied Physic
Efficient multipartite entanglement purification with the entanglement link from a subspace
We present an efficient multipartite entanglement purification protocol
(MEPP) for N-photon systems in a Greenberger-Horne-Zeilinger state with
parity-check detectors. It contains two parts. One is the conventional MEPP
with which the parties can obtain a high-fidelity N-photon ensemble directly,
similar to the MEPP with controlled-not gates. The other is our recycling MEPP
in which the entanglement link is used to produce some -photon entangled
systems from entangled N'-photon subsystems (2 \leq N'<N) coming from the
instances which are just discarded in all existing conventional MEPPs. The
entangled N'-photon subsystems are obtained efficiently by measuring the
photons with potential bit-flip errors. With these two parts, the present MEPP
has a higher efficiency than all other conventional MEPPs.Comment: 17 pages, 9 figures, 2 tables. We correct the error in the address of
the author in the published version (Phys. Rev. A 84, 052312 (2011)
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