53 research outputs found
Many-body Anderson localization in one dimensional systems
We show, using quasi-exact numerical simulations, that Anderson localization
of one-dimensional particles in a disordered potential survives in the presence
of attractive interaction between particles. The localization length of the
composite particle can be computed analytically for weak disorder and is in
good agreement with the quasi-exact numerical observations using Time Evolving
Block Decimation. Our approach allows for simulation of the entire experiment
including the final measurement of all atom positions.Comment: 12pp, 5 fig, version accepted in NJ
Out of equilibrium dynamics with Matrix Product States
Theoretical understanding of strongly correlated systems in one spatial
dimension (1D) has been greatly advanced by the density-matrix renormalization
group (DMRG) algorithm, which is a variational approach using a class of
entanglement-restricted states called Matrix Product States (MPSs). However,
DRMG suffers from inherent accuracy restrictions when multiple states are
involved due to multi-state targeting and also the approximate representation
of the Hamiltonian and other operators. By formulating the variational approach
of DMRG explicitly for MPSs one can avoid errors inherent in the multi-state
targeting approach. Furthermore, by using the Matrix Product Operator (MPO)
formalism, one can exactly represent the Hamiltonian and other operators. The
MPO approach allows 1D Hamiltonians to be templated using a small set of finite
state automaton rules without reference to the particular microscopic degrees
of freedom. We present two algorithms which take advantage of these properties:
eMPS to find excited states of 1D Hamiltonians and tMPS for the time evolution
of a generic time-dependent 1D Hamiltonian. We properly account for
time-ordering of the propagator such that the error does not depend on the rate
of change of the Hamiltonian. Our algorithms use only the MPO form of the
Hamiltonian, and so are applicable to microscopic degrees of freedom of any
variety, and do not require Hamiltonian-specialized implementation. We
benchmark our algorithms with a case study of the Ising model, where the
critical point is located using entanglement measures. We then study the
dynamics of this model under a time-dependent quench of the transverse field
through the critical point. Finally, we present studies of a dipolar, or
long-range Ising model, again using entanglement measures to find the critical
point and study the dynamics of a time-dependent quench through the critical
point.Comment: 35 pages, 10 figures, submitted to NJP for the focus issue "Out of
equilibrium dynamics in strongly interacting 1D systems
Quantum dynamics of atomic bright solitons under splitting and re-collision, and implications for interferometry
We numerically study the classical and quantum dynamics of an atomic bright
soliton in a highly-elongated one-dimensional harmonic trap with a Gaussian
barrier. In the regime of the recent experiment by Dyke {\it et al.}, the
system realizes a coherent nonlinear soliton beam-splitter and interferometer
whose accuracy we analyze. In the case of tighter radial trap confinement and
enhanced quantum fluctuations, a split soliton can represent a spin-squeezed,
or alternatively, a fragmented condensate with reduced phase-coherence that can
be measured by interfering the split soliton by the barrier. We also find large
quantum mechanical uncertainties in the soliton's position and momentum due to
nonlinear interaction with the barrier.Comment: 30 pages, 9 figures. Modified in response to referees' comments, and
with additional simulation result
Men, Mental Health and Elite Sport: a Narrative Review
Mental health in elite sport is receiving more publicity due to an increase in male athletes sharing their personal experiences. Sports injury is recognised as the major risk factor for psychological distress amongst male athletes, although anecdotally this may be that athletes are more likely to discuss their emotional wellbeing when related to the injury they are experiencing. Stress can be amplified within elite sport and the pressure they experience in relation to competition and performance can be exacerbated by adverse life events. This ongoing stress does not end when their sporting career does, it can follow them into retirement. The physical and psychological demands placed upon them by the sporting environment may predispose athletes to developing depression. As an athlete's symptoms of mental illness intensify, their performance can be negatively affected leaving them vulnerable and exposed to further symptoms of common mental disorders. The pressure of performance can also expose male athletes to overtraining syndrome which can be difficult to distinguish from depression. Male athletes are more vulnerable to eating disorders compared with males in the general population and they do have anxieties, particularly around their bodies, but find it difficult to disclose their concerns. In addition to this, male athletes are more likely to use substances, including opioids to improve both sport and non-sport performance.Despite the prevalence of common mental disorders in male athletes, stigma still exists, and although some athletes discuss their issues publicly after their career has ended, the majority of athletes prefer to remain silent. There remains a view that athletes who seek help for psychological problems may be seen as weak. Although there is an improvement in help-seeking attitudes within elite sport, further research and education is needed to encourage men to talk about their mental health, share their experiences and to enjoy a greater sense of emotional wellbeing
Antenatal and perinatal management of urinary malformations
After the introduction of maternal US in the 1970s, many urinary tract anomalies are found in utero. On one hand this permits early diagnosis and treatment, avoiding debilitating sequelae to little children. On the other hand, there are many anomalies with no clinical significance and destined to disappear that are labeled as dangerous, creating a discomfort to the child and to the mother as well. The goal of the prenatal diagnosis is not only to obtain a differential diagnosis between pathologies that have similar elements on prenatal US but also to define the prognosis. The collaboration between specialists is fundamental for this purpose. In this context, the chapter takes into consideration various aspects of the prenatal diagnosis and perinatal management of urinary malformations
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