1,171 research outputs found
On entanglement evolution across defects in critical chains
We consider a local quench where two free-fermion half-chains are coupled via
a defect. We show that the logarithmic increase of the entanglement entropy is
governed by the same effective central charge which appears in the ground-state
properties and which is known exactly. For unequal initial filling of the
half-chains, we determine the linear increase of the entanglement entropy.Comment: 11 pages, 5 figures, minor changes, reference adde
Integrated control of vector-borne diseases of livestock--pyrethroids: panacea or poison?
Tick- and tsetse-borne diseases cost Africa approximately US$4-5 billion per year in livestock production-associated losses. The use of pyrethroid-treated cattle to control ticks and tsetse promises to be an increasingly important tool to counter this loss. However, uncontrolled use of this technology might lead to environmental damage, acaricide resistance in tick populations and a possible exacerbation of tick-borne diseases. Recent research to identify, quantify and to develop strategies to avoid these effects are highlighted
Work fluctuations in quantum spin chains
We study the work fluctuations of two types of finite quantum spin chains
under the application of a time-dependent magnetic field in the context of the
fluctuation relation and Jarzynski equality. The two types of quantum chains
correspond to the integrable Ising quantum chain and the nonintegrable XX
quantum chain in a longitudinal magnetic field. For several magnetic field
protocols, the quantum Crooks and Jarzynski relations are numerically tested
and fulfilled. As a more interesting situation, we consider the forcing regime
where a periodic magnetic field is applied. In the Ising case we give an exact
solution in terms of double-confluent Heun functions. We show that the
fluctuations of the work performed by the external periodic drift are maximum
at a frequency proportional to the amplitude of the field. In the nonintegrable
case, we show that depending on the field frequency a sharp transition is
observed between a Poisson-limit work distribution at high frequencies toward a
normal work distribution at low frequencies.Comment: 10 pages, 13 figure
Entanglement evolution after connecting finite to infinite quantum chains
We study zero-temperature XX chains and transverse Ising chains and join an
initially separate finite piece on one or on both sides to an infinite
remainder. In both critical and non-critical systems we find a typical increase
of the entanglement entropy after the quench, followed by a slow decay towards
the value of the homogeneous chain. In the critical case, the predictions of
conformal field theory are verified for the first phase of the evolution, while
at late times a step structure can be observed.Comment: 15 pages, 11 figure
Edwards-Wilkinson surface over a spherical substrate: noise in the height fluctuations
We study the steady state fluctuations of an Edwards-Wilkinson type surface
with the substrate taken to be a sphere. We show that the height fluctuations
on circles at a given latitude has the effective action of a perfect Gaussian
noise, just as in the case of fixed radius circles on an infinite planar
substrate. The effective surface tension, which is the overall coefficient of
the action, does not depend on the latitude angle of the circles.Comment: 6 page
Liquidity and the multiscaling properties of the volume traded on the stock market
We investigate the correlation properties of transaction data from the New
York Stock Exchange. The trading activity f(t) of each stock displays a
crossover from weaker to stronger correlations at time scales 60-390 minutes.
In both regimes, the Hurst exponent H depends logarithmically on the liquidity
of the stock, measured by the mean traded value per minute. All multiscaling
exponents tau(q) display a similar liquidity dependence, which clearly
indicates the lack of a universal form assumed by other studies. The origin of
this behavior is both the long memory in the frequency and the size of
consecutive transactions.Comment: 7 pages, 3 figures, submitted to Europhysics Letter
On the relation between entanglement and subsystem Hamiltonians
We show that a proportionality between the entanglement Hamiltonian and the
Hamiltonian of a subsystem exists near the limit of maximal entanglement under
certain conditions. Away from that limit, solvable models show that the
coupling range differs in both quantities and allow to investigate the effect.Comment: 7 pages, 2 figures version2: minor changes, typos correcte
The components of empirical multifractality in financial returns
We perform a systematic investigation on the components of the empirical
multifractality of financial returns using the daily data of Dow Jones
Industrial Average from 26 May 1896 to 27 April 2007 as an example. The
temporal structure and fat-tailed distribution of the returns are considered as
possible influence factors. The multifractal spectrum of the original return
series is compared with those of four kinds of surrogate data: (1) shuffled
data that contain no temporal correlation but have the same distribution, (2)
surrogate data in which any nonlinear correlation is removed but the
distribution and linear correlation are preserved, (3) surrogate data in which
large positive and negative returns are replaced with small values, and (4)
surrogate data generated from alternative fat-tailed distributions with the
temporal correlation preserved. We find that all these factors have influence
on the multifractal spectrum. We also find that the temporal structure (linear
or nonlinear) has minor impact on the singularity width of the
multifractal spectrum while the fat tails have major impact on ,
which confirms the earlier results. In addition, the linear correlation is
found to have only a horizontal translation effect on the multifractal spectrum
in which the distance is approximately equal to the difference between its DFA
scaling exponent and 0.5. Our method can also be applied to other financial or
physical variables and other multifractal formalisms.Comment: 6 epl page
Quantum Quench from a Thermal Initial State
We consider a quantum quench in a system of free bosons, starting from a
thermal initial state. As in the case where the system is initially in the
ground state, any finite subsystem eventually reaches a stationary thermal
state with a momentum-dependent effective temperature. We find that this can,
in some cases, even be lower than the initial temperature. We also study
lattice effects and discuss more general types of quenches.Comment: 6 pages, 2 figures; short published version, added references, minor
change
Entanglement spectra of critical and near-critical systems in one dimension
The entanglement spectrum of a pure state of a bipartite system is the full
set of eigenvalues of the reduced density matrix obtained from tracing out one
part. Such spectra are known in several cases to contain important information
beyond that in the entanglement entropy. This paper studies the entanglement
spectrum for a variety of critical and near-critical quantum lattice models in
one dimension, chiefly by the iTEBD numerical method, which enables both
integrable and non-integrable models to be studied. We find that the
distribution of eigenvalues in the entanglement spectra agrees with an
approximate result derived by Calabrese and Lefevre to an accuracy of a few
percent for all models studied. This result applies whether the correlation
length is intrinsic or generated by the finite matrix size accessible in iTEBD.
For the transverse Ising model, the known exact results for the entanglement
spectrum are used to confirm the validity of the iTEBD approach. For more
general models, no exact result is available but the iTEBD results directly
test the hypothesis that all moments of the reduced density matrix are
determined by a single parameter.Comment: 6 pages, 5 figure
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