23,610 research outputs found
Entanglement generation with a quantum channel and a shared state
We introduce a new protocol, the channel-state coding protocol, to quantum
Shannon theory. This protocol generates entanglement between a sender and
receiver by coding for a noisy quantum channel with the aid of a noisy shared
state. The mother and father protocols arise as special cases of the
channel-state coding protocol, where the channel is noiseless or the state is a
noiseless maximally entangled state, respectively. The channel-state coding
protocol paves the way for formulating entanglement-assisted quantum
error-correcting codes that are robust to noise in shared entanglement.
Finally, the channel-state coding protocol leads to a Smith-Yard
superactivation, where we can generate entanglement using a zero-capacity
erasure channel and a non-distillable bound entangled state.Comment: 5 pages, 3 figure
Entanglement-assisted communication of classical and quantum information
We consider the problem of transmitting classical and quantum information
reliably over an entanglement-assisted quantum channel. Our main result is a
capacity theorem that gives a three-dimensional achievable rate region. Points
in the region are rate triples, consisting of the classical communication rate,
the quantum communication rate, and the entanglement consumption rate of a
particular coding scheme. The crucial protocol in achieving the boundary points
of the capacity region is a protocol that we name the classically-enhanced
father protocol. The classically-enhanced father protocol is more general than
other protocols in the family tree of quantum Shannon theoretic protocols, in
the sense that several previously known quantum protocols are now child
protocols of it. The classically-enhanced father protocol also shows an
improvement over a time-sharing strategy for the case of a qubit dephasing
channel--this result justifies the need for simultaneous coding of classical
and quantum information over an entanglement-assisted quantum channel. Our
capacity theorem is of a multi-letter nature (requiring a limit over many uses
of the channel), but it reduces to a single-letter characterization for at
least three channels: the completely depolarizing channel, the quantum erasure
channel, and the qubit dephasing channel.Comment: 23 pages, 5 figures, 1 table, simplification of capacity region--it
now has the simple interpretation as the unit resource capacity region
translated along the classically-enhanced father trade-off curv
Transmission Pricing of Distributed Multilateral Energy Transactions to Ensure System Security and Guide Economic Dispatch
Entanglement-assisted quantum turbo codes
An unexpected breakdown in the existing theory of quantum serial turbo coding
is that a quantum convolutional encoder cannot simultaneously be recursive and
non-catastrophic. These properties are essential for quantum turbo code
families to have a minimum distance growing with blocklength and for their
iterative decoding algorithm to converge, respectively. Here, we show that the
entanglement-assisted paradigm simplifies the theory of quantum turbo codes, in
the sense that an entanglement-assisted quantum (EAQ) convolutional encoder can
possess both of the aforementioned desirable properties. We give several
examples of EAQ convolutional encoders that are both recursive and
non-catastrophic and detail their relevant parameters. We then modify the
quantum turbo decoding algorithm of Poulin et al., in order to have the
constituent decoders pass along only "extrinsic information" to each other
rather than a posteriori probabilities as in the decoder of Poulin et al., and
this leads to a significant improvement in the performance of unassisted
quantum turbo codes. Other simulation results indicate that
entanglement-assisted turbo codes can operate reliably in a noise regime 4.73
dB beyond that of standard quantum turbo codes, when used on a memoryless
depolarizing channel. Furthermore, several of our quantum turbo codes are
within 1 dB or less of their hashing limits, so that the performance of quantum
turbo codes is now on par with that of classical turbo codes. Finally, we prove
that entanglement is the resource that enables a convolutional encoder to be
both non-catastrophic and recursive because an encoder acting on only
information qubits, classical bits, gauge qubits, and ancilla qubits cannot
simultaneously satisfy them.Comment: 31 pages, software for simulating EA turbo codes is available at
http://code.google.com/p/ea-turbo/ and a presentation is available at
http://markwilde.com/publications/10-10-EA-Turbo.ppt ; v2, revisions based on
feedback from journal; v3, modification of the quantum turbo decoding
algorithm that leads to improved performance over results in v2 and the
results of Poulin et al. in arXiv:0712.288
An upper limit for the water outgassing rate of the main-belt comet 176P/LINEAR observed with Herschel/HIFI
176P/LINEAR is a member of the new cometary class known as main-belt comets
(MBCs). It displayed cometary activity shortly during its 2005 perihelion
passage that may be driven by the sublimation of sub-surface ices. We have
therefore searched for emission of the H2O 110-101 ground state rotational line
at 557 GHz toward 176P/LINEAR with the Heterodyne Instrument for the Far
Infrared (HIFI) on board the Herschel Space Observatory on UT 8.78 August 2011,
about 40 days after its most recent perihelion passage, when the object was at
a heliocentric distance of 2.58 AU. No H2O line emission was detected in our
observations, from which we derive sensitive 3-sigma upper limits for the water
production rate and column density of < 4e25 molec/s and of < 3e10 cm^{-2},
respectively. From the peak brightness measured during the object's active
period in 2005, this upper limit is lower than predicted by the relation
between production rates and visual magnitudes observed for a sample of comets
by Jorda et al. (2008) at this heliocentric distance. Thus, 176P/LINEAR was
likely less active at the time of our observation than during its previous
perihelion passage. The retrieved upper limit is lower than most values derived
for the H2O production rate from the spectroscopic search for CN emission in
MBCs.Comment: 5 pages, 2 figures. Minor changes to match published versio
Analytical technique for simplification of the encoder-decoder circuit for a perfect five-qubit error correction
Simpler encoding and decoding networks are necessary for more reliable
quantum error correcting codes (QECCs). The simplification of the
encoder-decoder circuit for a perfect five-qubit QECC can be derived
analytically if the QECC is converted from its equivalent one-way entanglement
purification protocol (1-EPP). In this work, the analytical method to simplify
the encoder-decoder circuit is introduced and a circuit that is as simple as
the existent simplest circuits is presented as an example. The encoder-decoder
circuit presented here involves nine single- and two-qubit unitary operations,
only six of which are controlled-NOT (CNOT) gates
Modeling of combustion processes of stick propellants via combined Eulerian-Lagrangian approach
This research is motivated by the improved ballistic performance of large-caliber guns using stick propellant charges. A comprehensive theoretical model for predicting the flame spreading, combustion, and grain deformation phenomena of long, unslotted stick propellants is presented. The formulation is based upon a combined Eulerian-Lagrangian approach to simulate special characteristics of the two phase combustion process in a cartridge loaded with a bundle of sticks. The model considers five separate regions consisting of the internal perforation, the solid phase, the external interstitial gas phase, and two lumped parameter regions at either end of the stick bundle. For the external gas phase region, a set of transient one-dimensional fluid-dynamic equations using the Eulerian approach is obtained; governing equations for the stick propellants are formulated using the Lagrangian approach. The motion of a representative stick is derived by considering the forces acting on the entire propellant stick. The instantaneous temperature and stress fields in the stick propellant are modeled by considering the transient axisymmetric heat conduction equation and dynamic structural analysis
Distributed allocation of mobile sensing swarms in gyre flows
We address the synthesis of distributed control policies to enable a swarm of
homogeneous mobile sensors to maintain a desired spatial distribution in a
geophysical flow environment, or workspace. In this article, we assume the
mobile sensors (or robots) have a "map" of the environment denoting the
locations of the Lagrangian coherent structures or LCS boundaries. Based on
this information, we design agent-level hybrid control policies that leverage
the surrounding fluid dynamics and inherent environmental noise to enable the
team to maintain a desired distribution in the workspace. We establish the
stability properties of the ensemble dynamics of the distributed control
policies. Since realistic quasi-geostrophic ocean models predict double-gyre
flow solutions, we use a wind-driven multi-gyre flow model to verify the
feasibility of the proposed distributed control strategy and compare the
proposed control strategy with a baseline deterministic allocation strategy.
Lastly, we validate the control strategy using actual flow data obtained by our
coherent structure experimental testbed.Comment: 10 pages, 14 Figures, added reference
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