18,018 research outputs found
Computation of the asymptotic states of modulated open quantum systems with a numerically exact realization of the quantum trajectory method
Quantum systems out of equilibrium are presently a subject of active
research, both in theoretical and experimental domains. In this work we
consider time-periodically modulated quantum systems which are in contact with
a stationary environment. Within the framework of a quantum master equation,
the asymptotic states of such systems are described by time-periodic density
operators. Resolution of these operators constitutes a non-trivial
computational task. To go beyond the current size limits, we use the quantum
trajectory method which unravels master equation for the density operator into
a set of stochastic processes for wave functions. The asymptotic density matrix
is calculated by performing a statistical sampling over the ensemble of quantum
trajectories, preceded by a long transient propagation. We follow the ideology
of event-driven programming and construct a new algorithmic realization of the
method. The algorithm is computationally efficient, allowing for long 'leaps'
forward in time, and is numerically exact in the sense that, being given the
list of uniformly distributed (on the unit interval) random numbers, , one could propagate a quantum trajectory (with 's
as norm thresholds) in a numerically exact way. %Since the quantum trajectory
method falls into the class of standard sampling problems, performance of the
algorithm %can be substantially improved by implementing it on a computer
cluster. By using a scalable -particle quantum model, we demonstrate that
the algorithm allows us to resolve the asymptotic density operator of the model
system with states on a regular-size computer cluster, thus reaching
the scale on which numerical studies of modulated Hamiltonian systems are
currently performed
Glass Ceiling Commission - The Impact of the Glass Ceiling and Structural Change on Minorities and Women
Glass Ceiling ReportGlassCeilingBackground12StructuralChange.pdf: 9391 downloads, before Oct. 1, 2020
A system of relational syllogistic incorporating full Boolean reasoning
We present a system of relational syllogistic, based on classical
propositional logic, having primitives of the following form:
Some A are R-related to some B;
Some A are R-related to all B;
All A are R-related to some B;
All A are R-related to all B.
Such primitives formalize sentences from natural language like `All students
read some textbooks'. Here A and B denote arbitrary sets (of objects), and R
denotes an arbitrary binary relation between objects. The language of the logic
contains only variables denoting sets, determining the class of set terms, and
variables denoting binary relations between objects, determining the class of
relational terms. Both classes of terms are closed under the standard Boolean
operations. The set of relational terms is also closed under taking the
converse of a relation. The results of the paper are the completeness theorem
with respect to the intended semantics and the computational complexity of the
satisfiability problem.Comment: Available at
http://link.springer.com/article/10.1007/s10849-012-9165-
Nonlinear nanomechanical resonators for quantum optoelectromechanics
We present a scheme for tuning and controlling nano mechanical resonators by
subjecting them to electrostatic gradient fields, provided by nearby tip
electrodes. We show that this approach enables access to a novel regime of
optomechanics, where the intrinsic nonlinearity of the nanoresonator can be
explored. In this regime, one or several laser driven cavity modes coupled to
the nanoresonator and suitably adjusted gradient fields allow to control the
motional state of the nanoresonator at the single phonon level. Some
applications of this platform have been presented previously [New J. Phys. 14,
023042 (2012), Phys. Rev. Lett. 110, 120503 (2013)]. Here, we provide a
detailed description of the corresponding setup and its optomechanical coupling
mechanisms, together with an in-depth analysis of possible sources of damping
or decoherence and a discussion of the readout of the nanoresonator state.Comment: 15 pages, 6 figure
Measurable Consequences of the Local Breakdown of the Concept of Temperature
Local temperature defined by a local canonical state of the respective
subsystem, does not always exist in quantum many body systems. Here, we give
some examples of how this breakdown of the temperature concept on small length
scales might be observed in experiments: Measurements of magnetic properties of
an anti-ferromagnetic spin-1 chain. We show that those magnetic properties are
in fact strictly local. As a consequence their measurement reveals whether the
local (reduced) state can be thermal. If it is, a temperature may be associated
to the measurement results, while this would lead to inconsistencies otherwise.Comment: some comments added, results remain unchange
Magnetic Field Generation in Core-Sheath Jets via the Kinetic Kelvin-Helmholtz Instability
We have investigated magnetic field generation in velocity shears via the
kinetic Kelvin-Helmholtz instability (kKHI) using a relativistic plasma jet
core and stationary plasma sheath. Our three-dimensional particle-in-cell
simulations consider plasma jet cores with Lorentz factors of 1.5, 5, and 15
for both electron-proton and electron-positron plasmas. For electron-proton
plasmas we find generation of strong large-scale DC currents and magnetic
fields which extend over the entire shear-surface and reach thicknesses of a
few tens of electron skin depths. For electron-positron plasmas we find
generation of alternating currents and magnetic fields. Jet and sheath plasmas
are accelerated across the shear surface in the strong magnetic fields
generated by the kKHI. The mixing of jet and sheath plasmas generates
transverse structure similar to that produced by the Weibel instability.Comment: 28 pages, 12 figures, in press, ApJ, September 10, 201
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