5,089 research outputs found
Quantum Capacities for Entanglement Networks
We discuss quantum capacities for two types of entanglement networks:
for the quantum repeater network with free classical
communication, and for the tensor network as the rank of the
linear operation represented by the tensor network. We find that
always equals in the regularized case for the samenetwork graph.
However, the relationships between the corresponding one-shot capacities
and are more complicated, and the min-cut upper
bound is in general not achievable. We show that the tensor network can be
viewed as a stochastic protocol with the quantum repeater network, such that
is a natural upper bound of . We analyze the
possible gap between and for certain networks,
and compare them with the one-shot classical capacity of the corresponding
classical network
Channel Capacities versus Entanglement Measures in Multiparty Quantum States
For quantum states of two subsystems, entanglement measures are related to
capacities of communication tasks -- highly entangled states give higher
capacity of transmitting classical as well as quantum information. However, we
show that this is no more the case in general: quantum capacities of
multi-access channels, motivated by communication in quantum networks, do not
have any relation with genuine multiparty entanglement measures. Along with
revealing the structural richness of multi-access channel capacities, this
gives us a tool to classify multiparty quantum states from the perspective of
its usefulness in quantum networks, which cannot be visualized by known
multiparty entanglement measures.Comment: 6 pages, 2 figures, RevTeX4; v2: minor changes, some implications
strengthene
Controllable Entanglement Distribution Network Based on Silicon Quantum Photonics
The entanglement distribution network connects remote users through sharing
entanglement resources, which is essential for realizing quantum internet. We
proposed a controllable entanglement distribution network (c-EDN) based on a
silicon quantum photonic chip. The entanglement resources were generated by a
quantum light source array based on spontaneous four-wave mixing (SFWM) in
silicon waveguides and distributed to different users through time-reversed
Hong-Ou-Mandel interferences in on-chip Mach-Zehnder interferometers with
thermal phase shifters. A chip sample was designed and fabricated, supporting a
c-EDN with 3 subnets and 24 users. The network topology of entanglement
distributions could be reconfigured in three network states by controlling the
quantum interferences through the phase shifters, which was demonstrated
experimentally. Furthermore, a reconfigurable entanglement-based QKD network
was realized as an application of the c-EDN. The reconfigurable network
topology makes the c-EDN suitable for future quantum networks requiring
complicated network control and management. Moreover, it is also shows that
silicon quantum photonic chips have great potential for large-scale c-EDN,
thanks to their capacities on generating and manipulating plenty of
entanglement resources
Quantum network communication -- the butterfly and beyond
We study the k-pair communication problem for quantum information in networks
of quantum channels. We consider the asymptotic rates of high fidelity quantum
communication between specific sender-receiver pairs. Four scenarios of
classical communication assistance (none, forward, backward, and two-way) are
considered. (i) We obtain outer and inner bounds of the achievable rate regions
in the most general directed networks. (ii) For two particular networks
(including the butterfly network) routing is proved optimal, and the free
assisting classical communication can at best be used to modify the directions
of quantum channels in the network. Consequently, the achievable rate regions
are given by counting edge avoiding paths, and precise achievable rate regions
in all four assisting scenarios can be obtained. (iii) Optimality of routing
can also be proved in classes of networks. The first class consists of directed
unassisted networks in which (1) the receivers are information sinks, (2) the
maximum distance from senders to receivers is small, and (3) a certain type of
4-cycles are absent, but without further constraints (such as on the number of
communicating and intermediate parties). The second class consists of arbitrary
backward-assisted networks with 2 sender-receiver pairs. (iv) Beyond the k-pair
communication problem, observations are made on quantum multicasting and a
static version of network communication related to the entanglement of
assistance.Comment: 15 pages, 17 figures. Final versio
Quantum Communication Network Utilizing Quadripartite Entangled States of Optical Field
We propose two types of quantum dense coding communication networks with
optical continuous variables, in which a quadripartite entangled state of the
optical field with totally three-party correlations of quadrature amplitudes is
utilized. In the networks, the exchange of information between any two
participants can be manipulated by one or two of the remaining participants.
The channel capacities for a variety of communication protocols are numerically
calculated. Due to the fact that the quadripartite entangled states applied in
the communication systems have been successfully prepared already in the
laboratory, the proposed schemes are experimentally accessible at present
Directed percolation effects emerging from superadditivity of quantum networks
Entanglement indcued non--additivity of classical communication capacity in
networks consisting of quantum channels is considered. Communication lattices
consisiting of butterfly-type entanglement breaking channels augmented, with
some probability, by identity channels are analyzed. The capacity
superadditivity in the network is manifested in directed correlated bond
percolation which we consider in two flavours: simply directed and randomly
oriented. The obtained percolation properties show that high capacity
information transfer sets in much faster in the regime of superadditive
communication capacity than otherwise possible. As a byproduct, this sheds
light on a new type of entanglement based quantum capacity percolation
phenomenon.Comment: 6 pages, 4 figure
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