1,148 research outputs found
A robust boson dispenser: Quantum state preparation in interacting many-particle systems
We present a technique to control the spatial state of a small cloud of
interacting particles at low temperatures with almost perfect fidelity using
spatial adiabatic passage. To achieve this, the resonant trap energies of the
system are engineered in such a way that a single, well-defined eigenstate
connects the initial and desired states and is isolated from the rest of the
spectrum. We apply this procedure to the task of separating a well-defined
number of particles from an initial cloud and show that it can be implemented
in radio-frequency traps using experimentally realistic parameters.Comment: 10 pages, 9 figure
Twonniers: Interaction-induced effects on Bose-Hubbard parameters
We study the effects of the repulsive on-site interactions on the broadening
of the localized Wannier functions used for calculating the parameters to
describe ultracold atoms in optical lattices. For this, we replace the common
single-particle Wannier functions, which do not contain any information about
the interactions, by two-particle Wannier functions ("Twonniers") obtained from
an exact solution which takes the interactions into account. We then use these
interaction-dependent basis functions to calculate the Bose--Hubbard model
parameters, showing that they are substantially different both at low and high
lattice depths, from the ones calculated using single-particle Wannier
functions. Our results suggest that density effects are not negligible for many
parameter ranges and need to be taken into account in metrology experiments.Comment: 6 pages, 3 figure
Shaken not stirred: Creating exotic angular momentum states by shaking an optical lattice
We propose a method to create higher orbital states of ultracold atoms in the
Mott regime of an optical lattice. This is done by periodically modulating the
position of the trap minima (known as shaking) and controlling the interference
term of the lasers creating the lattice. These methods are combined with
techniques of shortcuts to adiabaticity. As an example of this, we show
specifically how to create an anti-ferromagnetic type ordering of angular
momentum states of atoms. The specific pulse sequences are designed using
Lewis-Riesenfeld invariants and a four-level model for each well. The results
are compared with numerical simulations of the full Schroedinger equation.Comment: 20 pages, 8 figure
Transport of ultracold atoms between concentric traps via spatial adiabatic passage
Spatial adiabatic passage processes for ultracold atoms trapped in
tunnel-coupled cylindrically symmetric concentric potentials are investigated.
Specifically, we discuss the matter-wave analogue of the rapid adiabatic
passage (RAP) technique for a high fidelity and robust loading of a single atom
into a harmonic ring potential from a harmonic trap, and for its transport
between two concentric rings. We also consider a system of three concentric
rings and investigate the transport of a single atom between the innermost and
the outermost rings making use of the matter-wave analogue of the stimulated
Raman adiabatic passage (STIRAP) technique. We describe the RAP-like and
STIRAP-like dynamics by means of a two- and a three-state models, respectively,
obtaining good agreement with the numerical simulations of the corresponding
two-dimensional Schr\"odinger equation.Comment: 13 pages, 6 figure
Efficient construction of maximally localized photonic Wannier functions: locality criterion and initial conditions
Wannier function expansions are well suited for the description of photonic-
crystal-based defect structures, but constructing maximally localized Wannier
functions by optimizing the phase degree of freedom of the Bloch modes is
crucial for the efficiency of the approach. We systematically analyze different
locality criteria for maximally localized Wannier functions in two- dimensional
square and triangular lattice photonic crystals, employing (local)
conjugate-gradient as well as (global) genetic-algorithm-based, stochastic
methods. Besides the commonly used second moment (SM) locality measure, we
introduce a new locality measure, namely the integrated modulus (IM) of the
Wannier function. We show numerically that, in contrast to the SM criterion,
the IM criterion leads to an optimization problem with a single extremum, thus
allowing for fast and efficient construction of maximally localized Wannier
functions using local optimization techniques. We also present an analytical
formula for the initial choice of Bloch phases, which under certain conditions
represents the global maximum of the IM criterion and, thus, further increases
the optimization efficiency in the general case
Entanglement in spatial adiabatic processes for interacting atoms
We study the dynamics of the non-classical correlations for few atom systems
in the presence of strong interactions for a number of recently developed
adiabatic state preparation protocols. We show that entanglement can be created
in a controlled fashion and can be attributed to two distinct sources, the
atom-atom interaction and the distribution of atoms among different traps.Comment: 9 pages, 3 figure
Promoting the psychological well-being of healthcare providers facing the burden of adverse events: a systematic review of second victim support resources
Given the negative impact of adverse events on the wellbeing of healthcare providers, easy access to psychological support is crucial. We aimed to describe the types of support resources available in healthcare organizations, their benefits for second victims, peer supporters' experiences, and implementation challenges. We also explored how these resources incorporate aspects of Safety I and Safety II. We searched six databases up to 19 December 2019 and additional literature, including weekly search alerts until 21 January 2021. Two reviewers independently performed all methodological steps (search, selection, quality assessment, data extraction, formal narrative synthesis). The 16 included studies described 12 second victim support resources, implemented between 2006 and 2017. Preliminary data indicated beneficial effects not only for the affected staff but also for the peer responders who considered their role to be challenging but gratifying. Challenges during program implementation included persistent blame culture, limited awareness of program availability, and lack of financial resources. Common goals of the support programs (e.g., fostering coping strategies, promoting individual resilience) are consistent with Safety II and may promote system resilience. Investing in second victim support structures should be a top priority for healthcare institutions adopting a systemic approach to safety and striving for just culture
Classical Vs Quantum Probability in Sequential Measurements
We demonstrate in this paper that the probabilities for sequential
measurements have features very different from those of single-time
measurements. First, they cannot be modelled by a classical stochastic process.
Second, they are contextual, namely they depend strongly on the specific
measurement scheme through which they are determined. We construct
Positive-Operator-Valued measures (POVM) that provide such probabilities. For
observables with continuous spectrum, the constructed POVMs depend strongly on
the resolution of the measurement device, a conclusion that persists even if we
consider a quantum mechanical measurement device or the presence of an
environment. We then examine the same issues in alternative interpretations of
quantum theory. We first show that multi-time probabilities cannot be naturally
defined in terms of a frequency operator. We next prove that local hidden
variable theories cannot reproduce the predictions of quantum theory for
sequential measurements, even when the degrees of freedom of the measuring
apparatus are taken into account. Bohmian mechanics, however, does not fall in
this category. We finally examine an alternative proposal that sequential
measurements can be modelled by a process that does not satisfy the Kolmogorov
axioms of probability. This removes contextuality without introducing
non-locality, but implies that the empirical probabilities cannot be always
defined (the event frequencies do not converge). We argue that the predictions
of this hypothesis are not ruled out by existing experimental results
(examining in particular the "which way" experiments); they are, however,
distinguishable in principle.Comment: 56 pages, latex; revised and restructured. Version to appear in
Found. Phy
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