4,769 research outputs found
Correlations in Free Fermionic States
We study correlations in a bipartite, Fermionic, free state in terms of
perturbations induced by one party on the other. In particular, we show that
all so conditioned free states can be modelled by an auxiliary Fermionic system
and a suitable completely positive map.Comment: 17 pages, no figure
Energy-weighted density matrix embedding of open correlated chemical fragments
We present a multi-scale approach to efficiently embed an ab initio
correlated chemical fragment described by its energy-weighted density matrices,
and entangled with a wider mean-field many-electron system. This approach,
first presented in Phys. Rev. B, 98, 235132 (2018), is here extended to account
for realistic long-range interactions and broken symmetry states. The scheme
allows for a systematically improvable description in the range of correlated
fluctuations out of the fragment into the system, via a self-consistent
optimization of a coupled auxiliary mean-field system. It is discussed that the
method has rigorous limits equivalent to existing quantum embedding approaches
of both dynamical mean-field theory, as well as density matrix embedding
theory, to which this method is compared, and the importance of these
correlated fluctuations is demonstrated. We derive a self-consistent local
energy functional within the scheme, and demonstrate the approach for Hydrogen
rings, where quantitative accuracy is achieved despite only a single atom being
explicitly treated.Comment: 14 pages, 8 figure
Coherent Oscillations in an Exciton-Polariton Josephson Junction
We report on the observation of spontaneous coherent oscillations in a
microcavity polariton bosonic Josephson junction. The condensation of exciton
polaritons takes place under incoherent excitation in a disordered environment,
where double potential wells tend to appear in the disordered landscape.
Coherent oscillations set on at an excitation power well above the condensation
threshold. The time resolved population and phase dynamics reveal the analogy
with the AC Josephson effect. We have introduced a theoretical two-mode model
to describe the observed effects, which allows us to explain how the different
realizations of the pulsed experiment have a similar phase relation
The Air-temperature Response to Green/blue-infrastructure Evaluation Tool (TARGET v1.0) : an efficient and user-friendly model of city cooling
The adverse impacts of urban heat and global climate change are leading policymakers to consider green and blue infrastructure (GBI) for heat mitigation benefits. Though many models exist to evaluate the cooling impacts of GBI, their complexity and computational demand leaves most of them largely inaccessible to those without specialist expertise and computing facilities. Here a new model called The Air-temperature Response to Green/blue-infrastructure Evaluation Tool (TARGET) is presented. TARGET is designed to be efficient and easy to use, with fewer user-defined parameters and less model input data required than other urban climate models. TARGET can be used to model average street-level air temperature at canyon-to-block scales (e.g. 100 m resolution), meaning it can be used to assess temperature impacts of suburb-to-city-scale GBI proposals. The model aims to balance realistic representation of physical processes and computation efficiency. An evaluation against two different datasets shows that TARGET can reproduce the magnitude and patterns of both air temperature and surface temperature within suburban environments. To demonstrate the utility of the model for planners and policymakers, the results from two precinct-scale heat mitigation scenarios are presented. TARGET is available to the public, and ongoing development, including a graphical user interface, is planned for future work
Penrose-Onsager Criterion Validation in a One-Dimensional Polariton Condensate
We perform quantum tomography on one-dimensional polariton condensates,
spontaneously occurring in linear disorder valleys in a CdTe planar microcavity
sample. By the use of optical interferometric techniques, we determine the
first-order coherence function and the amplitude and phase of the order
parameter of the condensate, providing a full reconstruction of the single
particle density matrix for the polariton system. The experimental data are
used as input to theoretically test the consistency of Penrose-Onsager
criterion for Bose-Einstein condensation in the framework of nonequilibrium
polariton condensates. The results confirm the pertinence and validity of the
criterion for a non equilibrium condensed gas.Comment: 5 pages, 4 figure
Observation of long-lived polariton states in semiconductor microcavities across the parametric threshold
The excitation spectrum around the pump-only stationary state of a polariton
optical parametric oscillator (OPO) in semiconductor microcavities is
investigated by time-resolved photoluminescence. The response to a weak pulsed
perturbation in the vicinity of the idler mode is directly related to the
lifetime of the elementary excitations. A dramatic increase of the lifetime is
observed for a pump intensity approaching and exceeding the OPO threshold. The
observations can be explained in terms of a critical slowing down of the
dynamics upon approaching the threshold and the following onset of the soft
Goldstone mode
Laser application to measure vertical sea temperature and turbidity, design phase
An experiment to test a new method was designed, using backscattered radiation from a laser beam to measure oceanographic parameters in a fraction of a second. Tyndall, Rayleigh, Brillouin, and Raman scattering all are utilized to evaluate the parameters. A beam from a continuous argon ion laser is used together with an interferometer and interference filters to gather the information. The results are checked by direct measurements. Future shipboard and airborne experiments are described
A practical guide to density matrix embedding theory in quantum chemistry
Density matrix embedding theory (DMET) provides a theoretical framework to
treat finite fragments in the presence of a surrounding molecular or bulk
environment, even when there is significant correlation or entanglement between
the two. In this work, we give a practically oriented and explicit description
of the numerical and theoretical formulation of DMET. We also describe in
detail how to perform self-consistent DMET optimizations. We explore different
embedding strategies with and without a self-consistency condition in hydrogen
rings, beryllium rings, and a sample S2 reaction. The source code
for the calculations in this work can be obtained from
\url{https://github.com/sebwouters/qc-dmet}.Comment: 41 pages, 10 figure
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