49 research outputs found
Heralded W state preparation using laser-designed super-atoms
We propose a scheme for preparing an ensemble of atoms in a maximally
entangled W state by exploiting the Rydberg blockade effect. The success of our
protocol is indicated by the detection of an ion, which thus serves as a herald
for successful entangled state preparation. The fidelity of the preparation
scheme is independent of the number of atoms in the ensemble. Therefore, a
small cloud of atoms in a dipole trap randomly loaded from a background gas can
be reliably prepared in a maximally entangled state despite of atom number
fluctuations.Comment: 7 pages, 3 figure
Coherent versus incoherent excitation dynamics in dissipative many-body Rydberg systems
We study the impact of dephasing on the excitation dynamics of a cloud of
ultracold two-level Rydberg atoms for both resonant and off-resonant laser
excitation, using the wave function Monte Carlo (MCWF) technique. We find that
while for resonant laser driving, dephasing mainly leads to an increase of the
Rydberg population and a decrease of the Mandel Q parameter, at off-resonant
driving strong dephasing toggles between direct excitation of pairs of atoms
and subsequent excitation of single atoms, respectively. These two excitation
mechanisms can be directly quantified via the pair correlation function, which
shows strong suppression of the two-photon resonance peak for strong dephasing.
Consequently, qualitatively different dynamics arise in the excitation
statistics for weak and strong dephasing in off-resonant excitation. Our
findings show that time-resolved excitation number measurements can serve as a
powerful tool to identify the dominating process in the system's excitation
dynamics.Comment: 10 pages, 10 figure
Variational Monte Carlo Approach to Partial Differential Equations with Neural Networks
The accurate numerical solution of partial differential equations is a
central task in numerical analysis allowing to model a wide range of natural
phenomena by employing specialized solvers depending on the scenario of
application. Here, we develop a variational approach for solving partial
differential equations governing the evolution of high dimensional probability
distributions. Our approach naturally works on the unbounded continuous domain
and encodes the full probability density function through its variational
parameters, which are adapted dynamically during the evolution to optimally
reflect the dynamics of the density. For the considered benchmark cases we
observe excellent agreement with numerical solutions as well as analytical
solutions in regimes inaccessible to traditional computational approaches.Comment: 6 + 3 pages, 4 figure
Many-Body Effects in Rydberg Gases : Coherent Dynamics of Strongly Interacting Two-Level Atoms and Nonlinear Optical Response of a Rydberg Gas in EIT Configuration
Subject of this thesis is the theoretical investigation of ensembles of atoms that are coherently laser-excited to a Rydberg state. Rydberg excited atoms interact with each other over large distances, which leads to strongly correlated many-body dynamics, demanding powerful numerical tools for their modeling. The first part of the thesis deals with effective two-level atoms consisting of a ground and a Rydberg state only. For resonant laser excitation a modified scaling behavior of the excitation number is observed, which is caused by effects of finite system size and coarse graining of the medium due to the finite atomic density. For off-resonant excitation, ordered structures arise out of an initially homogeneous gas, which are reflected in strongly peaked spatial correlations and modified excitation statistics. In the second part a fast decaying intermediate level is additionally taken into account. In this situation the phenomenon of electromagnetically induced transparency (EIT) is encountered. This effect is suppressed in the presence of strong interactions between the Rydberg atoms leading to an optical nonlinearity. A model predicting the properties of a cloud of Rydberg atoms in EIT configuration is developed. In both parts the models are validated by comparing their predictions to recent experimental observations
Non-linear absorption and density dependent dephasing in Rydberg EIT-media
Light propagation through an ensemble of ultra-cold Rydberg atoms in
electromagnetically induced transparency (EIT) configuration is studied. In
strongly interacting Rydberg EIT media, non-linear optical effects lead to a
non-trivial dependence of the degree of probe beam attenuation on the medium
density and on its initial intensity. We develop a Monte Carlo rate equation
model that self-consistently includes the effect of the probe beam attenuation
to investigate the steady state of the Rydberg medium driven by two laser
fields. We compare our results to recent experimental data and to results of
other state-of-the-art models for light propagation in Rydberg EIT-media. We
find that for low probe field intensities, our results match the experimental
data best if a density-dependent dephasing rate is included in the model. At
higher probe intensities, our model deviates from other theoretical approaches,
as it predicts a spectral asymmetry together with line broadening. These are
likely due to off-resonant excitation channels, which however have not been
observed in recent experiments. Atomic motion and coupling to additional
Rydberg levels are discussed as possible origins for these deviations.Comment: 10 pages, 8 figure