2,081 research outputs found
Kinetics and thermodynamics of first-order Markov chain copolymerization
We report a theoretical study of stochastic processes modeling the growth of
first-order Markov copolymers, as well as the reversed reaction of
depolymerization. These processes are ruled by kinetic equations describing
both the attachment and detachment of monomers. Exact solutions are obtained
for these kinetic equations in the steady regimes of multicomponent
copolymerization and depolymerization. Thermodynamic equilibrium is identified
as the state at which the growth velocity is vanishing on average and where
detailed balance is satisfied. Away from equilibrium, the analytical expression
of the thermodynamic entropy production is deduced in terms of the Shannon
disorder per monomer in the copolymer sequence. The Mayo-Lewis equation is
recovered in the fully irreversible growth regime. The theory also applies to
Bernoullian chains in the case where the attachment and detachment rates only
depend on the reacting monomer
Redundancy of classical and quantum correlations during decoherence
We analyze the time dependence of entanglement and total correlations between
a system and fractions of its environment in the course of decoherence. For the
quantum Brownian motion model we show that the entanglement and total
correlations have rather different dependence on the size of the environmental
fraction. Redundancy manifests differently in both types of correlations and
can be related with induced--classicality. To study this we introduce a new
measure of redundancy and compare it with the existing one.Comment: 6 pages, 4 figure
Statistical Complexity of Simple 1D Spin Systems
We present exact results for two complementary measures of spatial structure
generated by 1D spin systems with finite-range interactions. The first, excess
entropy, measures the apparent spatial memory stored in configurations. The
second, statistical complexity, measures the amount of memory needed to
optimally predict the chain of spin values. These statistics capture distinct
properties and are different from existing thermodynamic quantities.Comment: 4 pages with 2 eps Figures. Uses RevTeX macros. Also available at
http://www.santafe.edu/projects/CompMech/papers/CompMechCommun.htm
Nonlocal resources in the presence of Superselection Rules
Superselection rules severely alter the possible operations that can be
implemented on a distributed quantum system. Whereas the restriction to local
operations imposed by a bipartite setting gives rise to the notion of
entanglement as a nonlocal resource, the superselection rule associated with
particle number conservation leads to a new resource, the \emph{superselection
induced variance} of local particle number. We show that, in the case of pure
quantum states, one can quantify the nonlocal properties by only two additive
measures, and that all states with the same measures can be asymptotically
interconverted into each other by local operations and classical communication.
Furthermore we discuss how superselection rules affect the concepts of
majorization, teleportation and mixed state entanglement.Comment: 4 page
Natural Metric for Quantum Information Theory
We study in detail a very natural metric for quantum states. This new
proposal has two basic ingredients: entropy and purification. The metric for
two mixed states is defined as the square root of the entropy of the average of
representative purifications of those states. Some basic properties are
analyzed and its relation with other distances is investigated. As an
illustrative application, the proposed metric is evaluated for 1-qubit mixed
states.Comment: v2: enlarged; presented at ISIT 2008 (Toronto
Quantum superadditivity in linear optics networks: sending bits via multiple access Gaussian channels
We study classical capacity regions of quantum Gaussian multiple access
channels (MAC). In classical variants of such channels, whilst some capacity
superadditivity-type effects such as the so called {\it water filling effect}
may be achieved, a fundamental classical additivity law can still be
identified, {\it viz.} adding resources to one sender is never advantageous to
other senders in sending their respective information to the receiver. Here, we
show that quantum resources allows violation of this law, by providing two
illustrative schemes of experimentally feasible Gaussian MACs.Comment: 4 pages, 2 figure
The classical capacity of quantum thermal noise channels to within 1.45 bits
We find a tight upper bound for the classical capacity of quantum thermal
noise channels that is within bits of Holevo's lower bound. This
lower bound is achievable using unentangled, classical signal states, namely
displaced coherent states. Thus, we find that while quantum tricks might offer
benefits, when it comes to classical communication they can only help a bit.Comment: Two pages plus a bi
Using mutual information to measure order in model glass-formers
Whether or not there is growing static order accompanying the dynamical
heterogeneity and increasing relaxation times seen in glassy systems is a
matter of dispute. An obstacle to resolving this issue is that the order is
expected to be amorphous and so not amenable to simple order parameters. We use
mutual information to provide a general measurement of order that is sensitive
to multi-particle correlations. We apply this to two glass-forming systems (2D
binary mixtures of hard disks with different size ratios to give varying
amounts of hexatic order) and show that there is little growth of amorphous
order in the system without crystalline order. In both cases we measure the
dynamical length with a four-point correlation function and find that it
increases significantly faster than the static lengths in the system as density
is increased. We further show that we can recover the known scaling of the
dynamic correlation length in a kinetically constrained model, the 2-TLG.Comment: 10 pages, 12 Figure
Experimental Observation of Quantum Correlations in Modular Variables
We experimentally detect entanglement in modular position and momentum
variables of photon pairs which have passed through -slit apertures. We
first employ an entanglement criteria recently proposed in [Phys. Rev. Lett.
{\bf 106}, 210501 (2011)], using variances of the modular variables. We then
propose an entanglement witness for modular variables based on the Shannon
entropy, and test it experimentally. Finally, we derive criteria for
Einstein-Podolsky-Rosen-Steering correlations using variances and entropy
functions. In both cases, the entropic criteria are more successful at
identifying quantum correlations in our data.Comment: 7 pages, 4 figures, comments welcom
Modeling Maxwell's demon with a microcanonical Szilard engine
Following recent work by Marathe and Parrondo [PRL, 104, 245704 (2010)], we
construct a classical Hamiltonian system whose energy is reduced during the
adiabatic cycling of external parameters, when initial conditions are sampled
microcanonically. Combining our system with a device that measures its energy,
we propose a cyclic procedure during which energy is extracted from a heat bath
and converted to work, in apparent violation of the second law of
thermodynamics. This paradox is resolved by deriving an explicit relationship
between the average work delivered during one cycle of operation, and the
average information gained when measuring the system's energy
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