
Books
Next20090604T04:02:35Z  Hierarchical quantum information splitting  We present a scheme for asymmetric quantum information splitting, where a
sender distributes asymmetrically a qubit to distant agents in a network. The
asymmetric distribution leads to that the agents have different powers to
reconstruct the sender's qubit. In other words, the authorities of the agents
for getting the quantum secret are hierarchized. The scheme does not need the
agents to get together and make nonlocal operations. Our scheme can also be
modified to implement controlled teleportation against uncooperation of part of
supervisors.
 
20110119T14:48:03Z  Multiparty hierarchical quantuminformation splitting  We propose a scheme for multiparty hierarchical quantuminformation splitting
(QIS) with a multipartite entangled state, where a boss distributes a secret
quantum state to two grades of agents asymmetrically. The agents who belong to
different grades have different authorities for recovering boss's secret.
Except for boss's Bellstate measurement, no nonlocal operation is involved.
The presented scheme is also shown to be secure against eavesdropping. Such a
hierarchical QIS is expected to find useful applications in the field of modern
multipartite quantum cryptography.
 
20110925T07:50:54Z  Optimal ancillafree phasecovariant telecloning of qudits via
nonmaximally entangled states  We study the onetotwo phasecovariant telecloning of a qudit without
ancilla. We show that the fidelity of the two clones can reach that of the
clones in the optimal ancillabased onetotwo phasecovariant cloning and
telecloning, i.e., the limitation of quantum mechanics. More interestingly, it
is a nonmaximally entangled state rather than the maximally entangled state
that can be used to realize such a telecloning task.
 
20090801T14:50:01Z  Genuine (k, m)threshold controlled teleportation and its security  We propose genuine ($k$, $m$)threshold controlling schemes for controlled
teleportation via multiparticle entangled states, where the teleportation of a
quantum state from a sender (Alice) to a receiver (Bob) is under the control of
$m$ supervisors such that $k$ ($k\leq m$) or more of these supervisors can help
Bob recover the transferred state. By construction, anyone of our quantum
channels is a genuine multipartite entangled state of which any two parts are
inseparable. Their properties are compared and contrasted with those of the
wellknown GreenbergerHorneZeilinger, W, and linear cluster states, and also
several other genuine multipartite entangled states recently introduced in
literature. We show that our schemes are secure against both Bob's dishonesty
and supervisors' treacheries. For the latter case, the game theory is utilized
to prove that supervisors' cheats can be well prevented. In addition to their
practical importance, our schemes are also useful in seeking and exploring
genuine multipartite entangled states and opening another perspective for the
applications of the game theory in quantum information science.
 
20110604T07:25:25Z  Remote information concentration and multipartite entanglement in
multilevel systems  Remote information concentration (RIC) in $d$level systems (qudits) is
studied. It is shown that the quantum information initially distributed in
three spatially separated qudits can be remotely and deterministically
concentrated to a single qudit via an entangled channel without performing any
global operations. The entangled channel can be different types of genuine
multipartite pure entangled states which are inequivalent under local
operations and classical communication. The entangled channel can also be a
mixed entangled state, even a bound entangled state which has a similar form to
the Smolin state, but has different features from the Smolin state. A common
feature of all these pure and mixed entangled states is found, i.e., they have
$d^2$ common commuting stabilizers. The differences of quditRIC and qubitRIC
($d=2$) are also analyzed.
 
20130204T09:30:26Z  Manytoone remote information concentration for qudits and multipartite
entanglement  Telecloning and its reverse process, referred to as remote information
concentration(RIC), have attracted considerable interest because of their
potential applications in quantuminformation processing. We here present a
general scheme for RIC in dlevel systems (qudits), in which the quantum
information initially distributed in many spatially separated qudits can be
remotely and deterministically concentrated to a single qudit via an entangled
channel without performing any global operations. We show that the entangled
channel of RIC can be different types of entangled states, including mixed
states as well as pure ones. More interestingly, these mixed states include a
bound entangled state which has a similar form to the generalized Smolin state
but has different characteristics from it. We also show that there exists a
multipartite entangled state which can be used to implement both telecloning
and RIC in the twolevel system. Our manytoone RIC protocol could be slightly
modified to perform some types of manytomany RIC tasks.
 
20130916T03:02:47Z  Nonmaximally entangled states can be better for quantum correlation
distribution and storage  For carrying out many quantum information protocols entanglement must be
established in advance between two distant parties. Practically, inevitable
interaction of entangled subsystems with their environments during distribution
and storage will result in degradation of entanglement. Here we investigate the
decoherence of twoqubit entangled states in the local amplitude noise. We show
that there exists a set of partially entangled states that are more robust than
maximally entangled states in terms of the residual quantum correlation
measured by concurrence, fully entangled fraction, and quantum discord. This
result indicates that nonmaximally entangled states can outperform maximally
entangled states for quantum correlation distribution and storage under the
amplitude damping. It also educes a notable consequence that the ordering of
states under quantum correlation monotones can be reversed even by local
tracepreserving and completely positive maps.
 
20140209T04:08:24Z  Manipulation of tripartitetobipartite entanglement localization under
quantum noises and its application to entanglement distribution  This paper is to investigate the effects of quantum noises on entanglement
localization by taking an example of reducing a threequbit
GreenbergerHorneZeilinger (GHZ) state to a twoqubit entangled state. We
consider, respectively, two types of quantum decoherence, i.e.,
amplitudedamping and depolarizing decoherence, and explore the best von
Neumann measurements on one of three qubits of the triple GHZ state for making
the amount of entanglement of the collapsed bipartite state be as large as
possible. The results indicate that different noises have different impacts on
entanglement localization, and that the optimal strategy for reducing a
threequbit GHZ state to a twoqubit one via local measurements and classical
communications in the amplitudedamping case is different from that in the
noisefree case. We also show that the idea of entanglement localization could
be utilized to improve the quality of bipartite entanglement distributing
through amplitudedamping channels. These findings might shed a new light on
entanglement manipulations and transformations.
 
20130928T02:51:17Z  Impurityinduced Dicke quantum phase transition in an impuritydoped
cavityBoseEinstein condensate  We present a new generalized Dicke model, an impuritydoped Dicke model
(IDDM), by the use of an impuritydoped cavityBoseEinstein condensate. It is
shown that the impurity atom can induce Dicke quantum phase transition (QPT)
from the normal phase to superradiant phase at a critic value of the impurity
population. It is found that the IDDM exhibits continuous Dicke QPT with an
infinite number of critical points, which is significantly different from that
observed in the standard Dicke model with only one critical point. It is
revealed that the impurityinduced Dicke QPT can happen in an arbitrary
coupling regime of the cavity field and atoms while the Dicke QPT in the
standard Dicke model occurs only in the strong coupling regime of the cavity
field and atoms. This opens a way to observe the Dicke QPT in the intermediate
and even weak coupling regime of the cavity field and atoms.
 
20111228T15:36:00Z  Photonic twoqubit parity gate with tiny crossKerr nonlinearity  The crossKerr nonlinearity (XKNL) effect can induce efficient photon
interactions in principle with which photonic multiqubit gates can be performed
using far fewer physical resources than linear optical schemes. Unfortunately,
it is extremely challenging to generate giant crossKerr nonlinearities. In
recent years, much effort has been made to perform multiqubit gates via weak
XKNLs. However, the required nonlinearity strengths are still difficult to
achieve in the experiment. We here propose an XKNLbased scheme for realizing a
twophoton polarizationparity gate, a universal twoqubit gate, in which the
required strength of the nonlinearity could be orders of magnitude weaker than
those required for previous schemes. The scheme utilizes a ring cavity fed by a
coherent state as a quantum information bus which interacts with a path mode of
the two polarized photons (qubits). The XKNL effect makes the bus pick up a
phase shift dependent on the photon number of the path mode. Even when the
potential phase shifts are very small they can be effectively measured using
photonnumber resolving detectors, which accounts for the fact that our scheme
can work in the regime of tiny XKNL. The measurement outcome reveals the parity
(even parity or odd parity) of the two polarization qubits.
 

