832 research outputs found
Remote information concentration and multipartite entanglement in multilevel systems
Remote information concentration (RIC) in -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
common commuting stabilizers. The differences of qudit-RIC and qubit-RIC
() are also analyzed.Comment: 10 pages, 3 figure
Multipartite maximally entangled states in symmetric scenarios
We consider the class of (N+1)-partite states suitable for protocols where
there is a powerful party, the authority, and the other N parties play the same
role, namely the state of their system live in the symmetric Hilbert space. We
show that, within this scenario, there is a "maximally entangled state" that
can be transform by a LOCC protocol into any other state. In addition, we show
how to make the protocol efficiently including the construction of the state
and discuss security issues for possible applications to cryptographic
protocols. As an immediate consequence we recover a sequential protocol that
implements the one to N symmetric cloning.Comment: 6 pages, 4 figure
Multipartite entanglement via the Mayer-Vietoris theorem
The connection between entanglement and topology manifests itself in the form
of the ER-EPR duality. This statement however refers to the maximally entangled
states only. In this article I study the multipartite entanglement and the way
in which it relates to the topological interpretation of the ER-EPR duality.
The dimensional genus torus will be generalised to a -dimensional
general torus, where the information about the multipartite entanglement will
be encoded in the higher inclusion maps of the Mayer-Vietorist sequence.Comment: 2 figure
Optical state engineering, quantum communication, and robustness of entanglement promiscuity in three-mode Gaussian states
We present a novel, detailed study on the usefulness of three-mode Gaussian
states states for realistic processing of continuous-variable quantum
information, with a particular emphasis on the possibilities opened up by their
genuine tripartite entanglement. We describe practical schemes to engineer
several classes of pure and mixed three-mode states that stand out for their
informational and/or entanglement properties. In particular, we introduce a
simple procedure -- based on passive optical elements -- to produce pure
three-mode Gaussian states with {\em arbitrary} entanglement structure (upon
availability of an initial two-mode squeezed state). We analyze in depth the
properties of distributed entanglement and the origin of its sharing structure,
showing that the promiscuity of entanglement sharing is a feature peculiar to
symmetric Gaussian states that survives even in the presence of significant
degrees of mixedness and decoherence. Next, we discuss the suitability of the
considered tripartite entangled states to the implementation of quantum
information and communication protocols with continuous variables. This will
lead to a feasible experimental proposal to test the promiscuous sharing of
continuous-variable tripartite entanglement, in terms of the optimal fidelity
of teleportation networks with Gaussian resources. We finally focus on the
application of three-mode states to symmetric and asymmetric telecloning, and
single out the structural properties of the optimal Gaussian resources for the
latter protocol in different settings. Our analysis aims to lay the basis for a
practical quantum communication with continuous variables beyond the bipartite
scenario.Comment: 33 pages, 10 figures (some low-res due to size constraints), IOP
style; (v2) improved and reorganized, accepted for publication in New Journal
of Physic
Monogamy relation in multipartite continuous-variable quantum teleportation
Quantum teleportation (QT) is a fundamentally remarkable communication
protocol that also finds many important applications for quantum informatics.
Given a quantum entangled resource, it is crucial to know to what extent one
can accomplish the QT. This is usually assessed in terms of output fidelity,
which can also be regarded as an operational measure of entanglement. In the
case of multipartite communication when each communicator possesses a part of
-partite entangled state, not all pairs of communicators can achieve a high
fidelity due to monogamy property of quantum entanglement. We here investigate
how such a monogamy relation arises in multipartite continuous-variable (CV)
teleportation particularly using a Gaussian entangled state. We show a strict
monogamy relation, i.e. a sender cannot achieve a fidelity higher than optimal
cloning limit with more than one receiver. While this seems rather natural
owing to the no-cloning theorem, a strict monogamy relation still holds even if
the sender is allowed to individually manipulate the reduced state in
collaboration with each receiver to improve fidelity. The local operations are
further extended to non-Gaussian operations such as photon subtraction and
addition, and we demonstrate that the Gaussian cloning bound cannot be beaten
by more than one pair of communicators. Furthermore we investigate a
quantitative form of monogamy relation in terms of teleportation capability,
for which we show that a faithful monogamy inequality does not exist.Comment: 10 pages, 6 figures, published versio
Four-photon orbital angular momentum entanglement
Quantum entanglement shared between more than two particles is essential to
foundational questions in quantum mechanics, and upcoming quantum information
technologies. So far, up to 14 two-dimensional qubits have been entangled, and
an open question remains if one can also demonstrate entanglement of
higher-dimensional discrete properties of more than two particles. A promising
route is the use of the photon orbital angular momentum (OAM), which enables
implementation of novel quantum information protocols, and the study of
fundamentally new quantum states. To date, only two of such multidimensional
particles have been entangled albeit with ever increasing dimensionality. Here
we use pulsed spontaneous parametric downconversion (SPDC) to produce photon
quadruplets that are entangled in their OAM, or transverse-mode degrees of
freedom; and witness genuine multipartite Dicke-type entanglement. Apart from
addressing foundational questions, this could find applications in quantum
metrology, imaging, and secret sharing.Comment: 5 pages, 4 figure
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