861 research outputs found
Quantum thermodynamics in strong coupling: heat transport and refrigeration
The performance characteristics of a heat rectifier and a heat pump are
studied in a non Markovian framework. The device is constructed from a molecule
connected to a hot and cold reservoir. The heat baths are modelled using the
stochastic surrogate Hamiltonian method. The molecule is modelled by an
asymmetric double-well potential. Each well is semi-locally connected to a heat
bath composed of spins. The dynamics is driven by a combined system-bath
Hamiltonian. The temperature of the baths is regulated by a secondary spin bath
composed of identical spins in thermal equilibrium. A random swap operation
exchange spins between the primary and secondary baths. The combined system is
studied in various system-bath coupling strengths. In all cases the average
heat current always flows from the hot towards the cold bath in accordance to
the second law of thermodynamics. The asymmetry of the double well generates a
rectifying effect meaning that when the left and right baths are exchanged the
heat current follows the hot to cold direction. The heat current is larger when
the high frequency is coupled to the hot bath. Adding an external driving field
can reverse the transport direction. Such a refrigeration effect is modelled by
a periodic driving field in resonance with the frequency difference of the two
potential wells. A minimal driving amplitude is required to overcome the heat
leak effect. In the strong driving regime the cooling power is non-monotonic
with the system-bath coupling
Distributed Binary Detection with Lossy Data Compression
Consider the problem where a statistician in a two-node system receives
rate-limited information from a transmitter about marginal observations of a
memoryless process generated from two possible distributions. Using its own
observations, this receiver is required to first identify the legitimacy of its
sender by declaring the joint distribution of the process, and then depending
on such authentication it generates the adequate reconstruction of the
observations satisfying an average per-letter distortion. The performance of
this setup is investigated through the corresponding rate-error-distortion
region describing the trade-off between: the communication rate, the error
exponent induced by the detection and the distortion incurred by the source
reconstruction. In the special case of testing against independence, where the
alternative hypothesis implies that the sources are independent, the optimal
rate-error-distortion region is characterized. An application example to binary
symmetric sources is given subsequently and the explicit expression for the
rate-error-distortion region is provided as well. The case of "general
hypotheses" is also investigated. A new achievable rate-error-distortion region
is derived based on the use of non-asymptotic binning, improving the quality of
communicated descriptions. Further improvement of performance in the general
case is shown to be possible when the requirement of source reconstruction is
relaxed, which stands in contrast to the case of general hypotheses.Comment: to appear on IEEE Trans. Information Theor
Image scanning lensless fiber-bundle endomicroscopy
Fiber-based confocal endomicroscopy has shown great promise for
minimally-invasive deep-tissue imaging. Despite its advantages, confocal
fiber-bundle endoscopy inherently suffers from undersampling due to the spacing
between fiber cores, and low collection efficiency when the target is not in
proximity to the distal fiber facet. Here, we demonstrate an adaptation of
image-scanning microscopy (ISM) to lensless fiber bundle endoscopy, doubling
the spatial sampling frequency and significantly improving collection
efficiency. Our approach only requires replacing the confocal detector with a
camera. It improves the spatial resolution for targets placed at a distance
from the fiber tip, and addresses the fundamental challenge of
aliasing/pixelization artifacts
Estimation of gloss from rough surface parameters
Gloss is a quantity used in the optical industry to quantify and categorize
materials according to how well they scatter light specularly. With the aid of
phase perturbation theory, we derive an approximate expression for this
quantity for a one-dimensional randomly rough surface. It is demonstrated that
gloss depends in an exponential way on two dimensionless quantities that are
associated with the surface randomness: the root-mean-square roughness times
the perpendicular momentum transfer for the specular direction, and a
correlation function dependent factor times a lateral momentum variable
associated with the collection angle. Rigorous Monte Carlo simulations are used
to access the quality of this approximation, and good agreement is observed
over large regions of parameter space.Comment: 5 page
Optically induced flat bands in twisted bilayer graphene
Twisted bilayer graphene at the magic twist angle features flat energy bands, which lead to superconductivity and strong correlation physics. These unique properties are typically limited to a narrow range of twist angles around the magic angle with a small allowed tolerance. Here, we report on a mechanism that enables flattening of the band structure using coherent optical illumination, leading to emergence of flat isolated Floquet-Bloch bands. We show that the effect can be realized with relatively weak optical beams at the visible-infrared range (below the material bandwidth) and persist for a wide range of small twist angles, increasing the allowed twist tolerance by an order of magnitude. We discuss the conditions under which these bands exhibit a nonzero Chern number. These optically induced flat bands could potentially host strongly correlated nonequilibrium electronic states of matter
K-space interpretation of image-scanning-microscopy
In recent years, image-scanning microscopy (ISM, also termed
pixel-reassignment microscopy) has emerged as a technique that improves the
resolution and signal-to-noise compared to confocal and widefield microscopy by
employing a detector array at the image plane of a confocal laser scanning
microscope. Here, we present a k-space analysis of coherent ISM, showing that
ISM is equivalent to spotlight synthetic-aperture radar (SAR) and analogous to
oblique-illumination microscopy. This insight indicates that ISM can be
performed with a single detector placed in the k-space of the sample, which we
numerically demonstrate
Application of quantum coherence and decoherence
Coherent phenomena in molecular chromophores interacting with a dissipative environment is addressed. We defined coherence by the phenomena of decoherence which collapses the system to pointer states. Coherent irreducible phenomena takes place in a time window before the system collapses. We describe a computational model: The Stochastic Surrogate Hamiltonian that can deal with such complex quantum systems. The conditions for coherent control are analyzed. A prerequisite for coherent phenomena is the ability to perform coherent control using shaped light sources. We show that weak field coherent control is enabled by interaction with the environment.Israel Science Foundatio
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