7,231 research outputs found
A Quantum Optical Spring
We study the dynamics of the quantum optical spring, i.e., a spring whose
spring constant undergoes discreet jumps depending on the quantum state of
another system. We show the existence of revivals and fractional revivals in
the quantum dynamics reminiscent of similar dynamical features in cavity QED.
We recover in the semi classical limit the results for an oscillator whose
frequency undergoes a sudden change. The quantum optical spring is conceivable
for example by a micromirror under the influence of radiation pressure by a
field which is strictly quantum. Our work suggests that driven systems would in
general exhibit a very different dynamics if the drive is replaced by a quantum
source.Comment: 5 figure
Comparing Nonparametric Bayesian Tree Priors for Clonal Reconstruction of Tumors
Statistical machine learning methods, especially nonparametric Bayesian
methods, have become increasingly popular to infer clonal population structure
of tumors. Here we describe the treeCRP, an extension of the Chinese restaurant
process (CRP), a popular construction used in nonparametric mixture models, to
infer the phylogeny and genotype of major subclonal lineages represented in the
population of cancer cells. We also propose new split-merge updates tailored to
the subclonal reconstruction problem that improve the mixing time of Markov
chains. In comparisons with the tree-structured stick breaking prior used in
PhyloSub, we demonstrate superior mixing and running time using the treeCRP
with our new split-merge procedures. We also show that given the same number of
samples, TSSB and treeCRP have similar ability to recover the subclonal
structure of a tumor.Comment: Preprint of an article submitted for consideration in the Pacific
Symposium on Biocomputing \c{opyright} 2015; World Scientific Publishing Co.,
Singapore, 2015; http://psb.stanford.edu
Persistent spin oscillations in a spin-orbit-coupled superconductor
Quasi-two-dimensional superconductors with tunable spin-orbit coupling are
very interesting systems with properties that are also potentially useful for
applications. In this manuscript we demonstrate that these systems exhibit
undamped collective spin oscillations that can be excited by the application of
a supercurrent. We propose to use these collective excitations to realize
persistent spin oscillators operating in the frequency range of 10 GHz - 1 THz.Comment: 10 pages, 4 figures, published versio
Quantum Critical Point and Entanglement in a Matrix Product Ground State
In this paper, we study the entanglement properties of a spin-1 model the
exact ground state of which is given by a Matrix Product state. The model
exhibits a critical point transition at a parameter value a=0. The longitudinal
and transverse correlation lengths are known to diverge as a tends to zero. We
use three different entanglement measures S(i) (the one-site von Neumann
entropy), S(i,j) (the two-body entanglement) and G(2,n) (the generalized global
entanglement) to determine the entanglement content of the MP ground state as
the parameter a is varied. The entanglement length, associated with S(i,j), is
found to diverge in the vicinity of the quantum critical point a=0. The first
derivative of the entanglement measure E (=S(i), S(i,j)) w.r.t. the parameter a
also diverges. The first derivative of G(2,n) w.r.t. a does not diverge as a
tends to zero but attains a maximum value at a=0. At the QCP itself all the
three entanglement measures become zero. We further show that multipartite
correlations are involved in the QPT at a=0.Comment: 14 pages, 6 figure
A van Hemmen-Kondo model for disordered strongly correlated electron systems
We present here a theoretical model in order to describe the competition
between the Kondo effect and the spin glass behavior. The spin glass part of
the starting Hamiltonian contains Ising spins with an intersite exchange
interaction given by the local van Hemmen model, while the Kondo effect is
described as usual by the intrasite exchange . We obtain, for large
values, a Kondo phase and, for smaller values, a succession, with
decreasingComment: 14 pages, 4 figures, accepted for publication in Phys. Rev.
Waveguide microgripper for identification, sensing and manipulation
A Waveguide Microgripper utilizes flexible optical waveguides as gripping arms, which provide the physical means for grasping a microobject, while simultaneously enabling light to be delivered and collected. This unique capability allows extensive optical characterization of the structure being held such as transmission, reflection or fluorescence. One of the simplest capabilities of the waveguide microgripper is to be able to detect the presence of a microobject between the microgripper facets by monitoring the transmitted intensity of light coupled through the facets. The intensity of coupled light is expected to drop when there is an object obstructing the path of light. The optical sensing and characterization function of the microgripper is a strong function of the optical power incident on the structure of interest. Hence it is important to understand the factors affecting the power distribution across the facet. The microgripper is also capable of detecting the fluorescence. This capability of microgripper is expected to have applications in medical, bio-medical and related fields
Mechanism of margination in confined flows of blood and other multicomponent suspensions
Flowing blood displays a phenomenon called margination, in which leukocytes
and platelets are preferentially found near blood vessel walls, while
erythrocytes are depleted from these regions. Here margination is investigated
using direct hydrodynamic simulations of a binary suspension of stiff (s) and
floppy (f) capsules, as well as a stochastic model that incorporates the key
particle transport mechanisms in suspensions -- wall-induced hydrodynamic
migration and shear-induced pair collisions. The stochastic model allows the
relative importance of these two mechanisms to be directly evaluated and
thereby indicates that margination, at least in the dilute case, is largely due
to the differential dynamics of homogeneous (e.g. s-s) and heterogeneous (s-f)
collisionsComment: 5 Pages, 4 figure
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