773 research outputs found
Reflections on the “gesture-first” hypothesis of language origins
The main lines of evidence taken as support for the “gesture-first” hypothesis of language origins are briefly evaluated, and the problem that speech poses for this hypothesis is discussed. I conclude that language must have evolved in the oral–aural and kinesic modalities together, with neither modality taking precedence over the other
Quantum walks on general graphs
Quantum walks, both discrete (coined) and continuous time, on a general graph
of N vertices with undirected edges are reviewed in some detail. The resource
requirements for implementing a quantum walk as a program on a quantum computer
are compared and found to be very similar for both discrete and continuous time
walks. The role of the oracle, and how it changes if more prior information
about the graph is available, is also discussed.Comment: 8 pages, v2: substantial rewrite improves clarity, corrects errors
and omissions; v3: removes major error in final section and integrates
remainder into other sections, figures remove
Interface Width and Bulk Stability: requirements for the simulation of Deeply Quenched Liquid-Gas Systems
Simulations of liquid-gas systems with extended interfaces are observed to
fail to give accurate results for two reasons: the interface can get ``stuck''
on the lattice or a density overshoot develops around the interface. In the
first case the bulk densities can take a range of values, dependent on the
initial conditions. In the second case inaccurate bulk densities are found. In
this communication we derive the minimum interface width required for the
accurate simulation of liquid gas systems with a diffuse interface. We
demonstrate this criterion for lattice Boltzmann simulations of a van der Waals
gas. When combining this criterion with predictions for the bulk stability we
can predict the parameter range that leads to stable and accurate simulation
results. This allows us to identify parameter ranges leading to high density
ratios of over 1000. This is despite the fact that lattice Boltzmann
simulations of liquid-gas systems were believed to be restricted to modest
density ratios of less than 20.Comment: 5 pages, 3 figure
Binary fluids under steady shear in three dimensions
We simulate by lattice Boltzmann the steady shearing of a binary fluid
mixture with full hydrodynamics in three dimensions. Contrary to some
theoretical scenarios, a dynamical steady state is attained with finite
correlation lengths in all three spatial directions. Using large simulations we
obtain at moderately high Reynolds numbers apparent scaling expon ents
comparable to those found by us previously in 2D. However, in 3D there may be a
crossover to different behavior at low Reynolds number: accessing this regime
requires even larger computational resource than used here.Comment: 4 pages, 3 figure
Generic quantum walk using a coin-embedded shift operator
The study of quantum walk processes has been widely divided into two standard
variants, the discrete-time quantum walk (DTQW) and the continuous-time quantum
walk (CTQW). The connection between the two variants has been established by
considering the limiting value of the coin operation parameter in the DTQW, and
the coin degree of freedom was shown to be unnecessary [26]. But the coin
degree of freedom is an additional resource which can be exploited to control
the dynamics of the QW process. In this paper we present a generic quantum walk
model using a quantum coin-embedded unitary shift operation . The
standard version of the DTQW and the CTQW can be conveniently retrieved from
this generic model, retaining the features of the coin degree of freedom in
both variants.Comment: 5 pages, 1 figure, Publishe
Complementarity and quantum walks
We show that quantum walks interpolate between a coherent `wave walk' and a
random walk depending on how strongly the walker's coin state is measured;
i.e., the quantum walk exhibits the quintessentially quantum property of
complementarity, which is manifested as a trade-off between knowledge of which
path the walker takes vs the sharpness of the interference pattern. A physical
implementation of a quantum walk (the quantum quincunx) should thus have an
identifiable walker and the capacity to demonstrate the interpolation between
wave walk and random walk depending on the strength of measurement.Comment: 7 pages, RevTex, 2 figures; v2 adds references; v3 updated to
incorporate feedback and updated references; v4 substantially expanded to
clarify presentatio
Classical Diffusion of a quantum particle in a noisy environment
We study the spreading of a quantum-mechanical wavepacket in a
one-dimensional tight-binding model with a noisy potential, and analyze the
emergence of classical diffusion from the quantum dynamics due to decoherence.
We consider a finite correlation time of the noisy environment, and treat the
system by utilizing the separation of fast (dephasing) and slow (diffusion)
processes. We show that classical diffusive behavior emerges at long times, and
we calculate analytically the dependence of the classical diffusion coefficient
on the noise magnitude and correlation time. This method provides a general
solution to this problem for arbitrary conditions of the noisy environment. The
results are relevant to a large variety of physical systems, from electronic
transport in solid state physics, to light transmission in optical devices,
diffusion of excitons, and quantum computation
Entanglement, discord and the power of quantum computation
We show that the ability to create entanglement is necessary for execution of
bipartite quantum gates even when they are applied to unentangled states and
create no entanglement. Starting with a simple example we demonstrate that to
execute such a gate bi-locally the local operations and classical
communications (LOCC) should be supplemented by shared entanglement. Our
results point to the changes in quantum discord, which is a measure of
quantumness of correlations even in the absence of entanglement, as the
indicator of failure of a LOCC implementation of the gates.Comment: Published version. More results are adde
Quantumness of noisy quantum walks: a comparison between measurement-induced disturbance and quantum discord
Noisy quantum walks are studied from the perspective of comparing their
quantumness as defined by two popular measures, measurement-induced disturbance
(MID) and quantum discord (QD). While the former has an operational definition,
unlike the latter, it also tends to overestimate non-classicality because of a
lack of optimization over local measurements. Applied to quantum walks, we find
that MID, while acting as a loose upper bound on QD, still tends to reflect
correctly the trends in the behavior of the latter. However, there are regimes
where its behavior is not indicative of non-classicality: in particular, we
find an instance where MID increases with the application of noise, where we
expect a reduction of quantumness.Comment: 5 pages with 4 figures, Published Versio
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