105 research outputs found
Towards a corpuscular model of optical phenomena
This thesis presents a collection of event-by-event models that simulate fundamental optical experiments.
The simulation approach is completely based on the experimental facts.
Each component in the model corresponds to one kind of optical device, such as a beam splitter, a wave plate, a detector and so on.
Networks of such components build computational experiments which are one-to-one copies of real experiments.
As all components share the same mechanism (leaning machine) as in the previous work, our event-by-event simulation models are systematic and consistent with each other.
As the model provides a description of interference and other wave phenomena on the level of individual event,
it goes beyond the description of quantum theory. All the results presented in this thesis demonstrate that it is possible to simulate quantum phenomena by classical, non-Hamiltonian, local, causal and dynamical models.
Screening and plasmons in pure and disordered single- and bilayer black phosphorus
We study collective plasmon excitations and screening of disordered single-
and bilayer black phosphorus beyond the low energy continuum approximation. The
dynamical polarizability of phosphorene is computed using a tight-binding model
that properly accounts for the band structure in a wide energy range.
Electron-electron interaction is considered within the Random Phase
Approximation. Damping of the plasmon modes due to different kinds of disorder,
such as resonant scatterers and long-range disorder potentials, is analyzed. We
further show that an electric field applied perpendicular to bilayer
phosphorene can be used to tune the dispersion of the plasmon modes. For
sufficiently large electric field, the bilayer BP enters in a topological phase
with a characteristic plasmon spectrum, which is gaped in the armchair
direction.Comment: 9 pages, 9 figure
Relaxation, thermalization and Markovian dynamics of two spins coupled to a spin bath
It is shown that by fitting a Markovian quantum master equation to the
numerical solution of the time-dependent Schr\"odinger equation of a system of
two spin-1/2 particles interacting with a bath of up to 34 spin-1/2 particles,
the former can describe the dynamics of the two-spin system rather well. The
fitting procedure that yields this Markovian quantum master equation accounts
for all non-Markovian effects in as much the general structure of this equation
allows and yields a description that is incompatible with the Lindblad
equation.Comment: arXiv admin note: text overlap with arXiv:1605.0660
Real-Time Dynamics of Typical and Untypical States in Non-Integrable Systems
For a class of typical states, the real-time and real-space dynamics of
non-equilibrium density profiles has been recently studied for integrable
models, i.e. the spin-1/2 XXZ chain [PRB 95, 035155 (2017)] and the
Fermi-Hubbard chain [PRE 96, 020105 (2017)]. It has been found that the
non-equilibrium dynamics agrees with linear response theory. Moreover, in the
regime of strong interactions, clear signatures of diffusion have been
observed. However, this diffusive behavior strongly depends on the choice of
the initial state and disappears for untypical states without internal
randomness. In the present work, we address the question whether or not the
above findings persist for non-integrable models. As a first step, we study the
spin-1/2 XXZ chain, where integrability can be broken due to an additional
next-nearest neighbor interaction. Furthermore, we analyze the differences of
typical and untypical initial states on the basis of their entanglement and
their local density of states.Comment: 15 pages, 15 figure
Benchmarking gate-based quantum computers
With the advent of public access to small gate-based quantum processors, it
becomes necessary to develop a benchmarking methodology such that independent
researchers can validate the operation of these processors. We explore the
usefulness of a number of simple quantum circuits as benchmarks for gate-based
quantum computing devices and show that circuits performing identity operations
are very simple, scalable and sensitive to gate errors and are therefore very
well suited for this task. We illustrate the procedure by presenting benchmark
results for the IBM Quantum Experience, a cloud-based platform for gate-based
quantum computing.Comment: Accepted for publication in Computer Physics Communication
Event-based simulation of neutron interferometry experiments
A discrete-event approach, which has already been shown to give a
cause-and-effect explanation of many quantum optics experiments, is applied to
single-neutron interferometry experiments. The simulation algorithm yields a
logically consistent description in terms of individual neutrons and does not
require the knowledge of the solution of a wave equation. It is shown that the
simulation method reproduces the results of several single-neutron
interferometry experiments, including experiments which, in quantum theoretical
language, involve entanglement. Our results demonstrate that classical
(non-Hamiltonian) systems can exhibit correlations which in quantum theory are
associated with interference and entanglement, also when all particles emitted
by the source are accounted for.Comment: Accepted for publication in Quantum Matte
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