1,222 research outputs found
Three-party qutrit-state sharing
A three-party scheme for securely sharing an arbitrary unknown single-qutrit
state is presented. Using a general Greenberger-Horne-Zeilinger (GHZ) state as
the quantum channel among the three parties, the quantum information (i.e., the
qutrit state) from the sender can be split in such a way that the information
can be recovered if and only if both receivers collaborate. Moreover, the
generation of the scheme to multi-party case is also sketched.Comment: 7 page
Trade-offs in multi-party Bell inequality violations in qubit networks
Two overlapping bipartite binary input Bell inequalities cannot be
simultaneously violated as this would contradict the usual no-signalling
principle. This property is known as monogamy of Bell inequality violations and
generally Bell monogamy relations refer to trade-offs between simultaneous
violations of multiple inequalities. It turns out that multipartite Bell
inequalities admit weaker forms of monogamies that allow for violations of a
few inequalities at once. Here we systematically study monogamy relations
between correlation Bell inequalities both within quantum theory and under the
sole assumption of no signalling. We first investigate the trade-offs in Bell
violations arising from the uncertainty relation for complementary binary
observables, and exhibit several network configurations in which a tight
trade-off arises in this fashion. We then derive a tight trade-off relation
which cannot be obtained from the uncertainty relation showing that it does not
capture monogamy entirely. The results are extended to Bell inequalities
involving different number of parties and find applications in
device-independent secret sharing and device-independent randomness extraction.
Although two multipartite Bell inequalities may be violated simultaneously, we
show that genuine multi-party non-locality, as evidenced by a generalised
Svetlichny inequality, does exhibit monogamy property. Finally, using the
relations derived we reveal the existence of flat regions in the set of quantum
correlations.Comment: 15 pages, 5 figure
Single-photon-assisted entanglement concentration of a multi-photon system in a partially entangled W state with weak cross-Kerr nonlinearity
We propose a nonlocal entanglement concentration protocol (ECP) for
-photon systems in a partially entangled W state, resorting to some
ancillary single photons and the parity-check measurement based on cross-Kerr
nonlinearity. One party in quantum communication first performs a parity-check
measurement on her photon in an -photon system and an ancillary photon, and
then she picks up the even-parity instance for obtaining the standard W state.
When she obtains an odd-parity instance, the system is in a less-entanglement
state and it is the resource in the next round of entanglement concentration.
By iterating the entanglement concentration process several times, the present
ECP has the total success probability approaching to the limit in theory. The
present ECP has the advantage of a high success probability. Moreover, the
present ECP requires only the -photon system itself and some ancillary
single photons, not two copies of the systems, which decreases the difficulty
of its implementation largely in experiment. It maybe have good applications in
quantum communication in future.Comment: 7 pages, 3 figure
Multiparty Quantum Secret Sharing
Based on a quantum secure direct communication (QSDC) protocol [Phys. Rev.
A69(04)052319], we propose a -threshold scheme of multiparty quantum
secret sharing of classical messages (QSSCM) using only single photons. We take
advantage of this multiparty QSSCM scheme to establish a scheme of multiparty
secret sharing of quantum information (SSQI), in which only all quantum
information receivers collaborate can the original qubit be reconstructed. A
general idea is also proposed for constructing multiparty SSQI schemes from any
QSSCM scheme
Hierarchical quantum communication
A general approach to study the hierarchical quantum information splitting
(HQIS) is proposed and the same is used to systematically investigate the
possibility of realizing HQIS using different classes of 4-qubit entangled
states that are not connected by SLOCC. Explicit examples of HQIS using 4-qubit
cluster state and 4-qubit |\Omega> state are provided. Further, the proposed
HQIS scheme is generalized to introduce two new aspects of hierarchical quantum
communication. To be precise, schemes of probabilistic hierarchical quantum
information splitting and hierarchical quantum secret sharing are obtained by
modifying the proposed HQIS scheme. A number of practical situations where
hierarchical quantum communication would be of use are also presented.Comment: 14 pages, 6 tables, no figur
Bell inequalities and distillability in N-quantum-bit systems
The relation between Bell inequalities with two two-outcome measurements per
site and distillability is analyzed in systems of an arbitrary number of
quantum bits. We observe that the violation of any of these inequalities by a
quantum state implies that pure-state entanglement can be distilled from it.
The corresponding distillation protocol may require that some of the parties
join into several groups. We show that there exists a link between the amount
of the Bell inequality violation and the size of the groups they have to form
for distillation. Thus, a strong violation is always sufficient for full
N-partite distillability. This result also allows for a security proof of
multi-partite quantum key distribution (QKD) protocols.Comment: REVTEX, 12 pages, two figure
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