204 research outputs found
Kinematic approach to off-diagonal geometric phases of nondegenerate and degenerate mixed states
Off-diagonal geometric phases have been developed in order to provide
information of the geometry of paths that connect noninterfering quantal
states. We propose a kinematic approach to off-diagonal geometric phases for
pure and mixed states. We further extend the mixed state concept proposed in
[Phys. Rev. Lett. {\bf 90}, 050403 (2003)] to degenerate density operators. The
first and second order off-diagonal geometric phases are analyzed for unitarily
evolving pairs of pseudopure states.Comment: New section IV, new figure, journal ref adde
Optimal Topological Test for Degeneracies of Real Hamiltonians
We consider adiabatic transport of eigenstates of real Hamiltonians around
loops in parameter space. It is demonstrated that loops that map to nontrivial
loops in the space of eigenbases must encircle degeneracies. Examples from
Jahn-Teller theory are presented to illustrate the test. We show furthermore
that the proposed test is optimal.Comment: Minor corrections, accepted in Phys. Rev. Let
Kinematic approach to the mixed state geometric phase in nonunitary evolution
A kinematic approach to the geometric phase for mixed quantal states in
nonunitary evolution is proposed. This phase is manifestly gauge invariant and
can be experimentally tested in interferometry. It leads to well-known results
when the evolution is unitary.Comment: Minor changes; journal reference adde
Locality and topology in the molecular Aharonov-Bohm effect
It is shown that the molecular Aharonov-Bohm effect is neither nonlocal nor
topological in the sense of the standard magnetic Aharonov-Bohm effect. It is
further argued that there is a close relationship between the molecular
Aharonov-Bohm effect and the Aharonov-Casher effect for an electrically neutral
spin particle encircling a line of charge.Comment: 3 pages, no figure
Using telemedicine in the care of newborn infants after discharge from a neonatal intensive care unit reduced the need of hospital visits
Aim: This study examined the use of telemedicine as a means to follow up infants discharged from a Swedish neonatal intensive care unit to home health care. Methods: Families were randomised to either a control group receiving standard home health care (n = 42 families) or a telemedicine group receiving home health care with telemedicine support (n = 47 families) after discharge from the hospital. Both groups had follow-up hospital appointments with the neonatal nurse. In the telemedicine group, appointments were supplemented by the use of a specially designed web page and video calls. Results: The use of the web page and video calls decreased the number of emergency visits to the hospital (p = 0.047). In the telemedicine group, 26% of the families felt they had more scheduled appointments than necessary, whereas only 6% of the families in the control group thought so (p = 0.037). The parents were highly satisfied with the use of telemedicine. Although the nurses were favourable to using telemedicine, the rigid organisation of the home healthcare programme and the nurses' schedules and work routines prevented its optimal use. Conclusion: The use of telemedicine decreased the need of hospital visits. Organisational adaptations would be necessary to make the best use of telemedicine
Effect of intersubsystem coupling on the geometric phase in a bipartite system
The influence of intersubsystem coupling on the cyclic adiabatic geometric
phase in bipartite systems is investigated. We examine the geometric phase
effects for two uniaxially coupled spin particles, both driven by a
slowly rotating magnetic field. It is demonstrated that the relation between
the geometric phase and the solid angle enclosed by the magnetic field is
broken by the spin-spin coupling, in particular leading to a quenching effect
on the geometric phase in the strong coupling limit.Comment: New title, small changes, journal reference adde
Searching for degeneracies of real Hamiltonians using homotopy classification of loops in SO()
Topological tests to detect degeneracies of Hamiltonians have been put
forward in the past. Here, we address the applicability of a recently proposed
test [Phys. Rev. Lett. {\bf 92}, 060406 (2004)] for degeneracies of real
Hamiltonian matrices. This test relies on the existence of nontrivial loops in
the space of eigenbases SO. We develop necessary means to determine the
homotopy class of a given loop in this space. Furthermore, in cases where the
dimension of the relevant Hilbert space is large the application of the
original test may not be immediate. To remedy this deficiency, we put forward a
condition for when the test is applicable to a subspace of Hilbert space.
Finally, we demonstrate that applying the methodology of [Phys. Rev. Lett. {\bf
92}, 060406 (2004)] to the complex Hamiltonian case does not provide any new
information.Comment: Minor changes, journal reference adde
Doxycycline exposure during adolescence and future risk of non-affective psychosis and bipolar disorder: a total population cohort study
Doxycycline has been hypothesized to prevent development of severe mental illness (SMI) through the suppression of microglia, especially if administered during the intense synaptic pruning period of adolescence. However, results from register studies on potential benefits differ considerably. The aim of the present study was to determine whether doxycycline exposure during adolescence is associated with reduced SMI risk, and to investigate if a direct and specific causality is plausible. This is a Swedish national population register-based cohort study of all individuals born from 1993 to 1997, followed from the age of 13 until end of study at the end of 2016. The primary exposure was cumulative doxycycline prescription ≥3000 mg and outcomes were first diagnosis of non-affective psychosis (F20–F29) and first diagnosis of bipolar disorder (F30–F31). Causal effects were explored through Cox regressions with relevant covariates and secondary analyses of multilevel exposure and comparison to other antibiotics. We found no association between doxycycline exposure and risk of subsequent non-affective psychosis (adjusted hazard ratio (HR) 1.15, 95% CI 0.73–1.81, p = 0.541) and an increased risk of subsequent bipolar disorder (adjusted HR 1.95, 95% CI 1.49–2.55, p < 0.001). We do not believe the association between doxycycline and bipolar disorder is causal as similar associations were observed for other common antibiotics
Spin-orbit coupled Bose-Einstein condensate in a tilted optical lattice
Bloch oscillations appear for a particle in a weakly tilted periodic
potential. The intrinsic spin Hall effect is an outcome of a spin-orbit
coupling. We demonstrate that both these phenomena can be realized
simultaneously in a gas of weakly interacting ultracold atoms exposed to a
tilted optical lattice and to a set of spatially dependent light fields
inducing an effective spin-orbit coupling. It is found that both the spin Hall
as well as the Bloch oscillation effects may coexist, showing, however, a
strong correlation between the two. These correlations are manifested as a
transverse spin current oscillating in-phase with the Bloch oscillations.Comment: 12 pages, 7 figure
Relation between geometric phases of entangled bi-partite systems and their subsystems
This paper focuses on the geometric phase of entangled states of bi-partite
systems under bi-local unitary evolution. We investigate the relation between
the geometric phase of the system and those of the subsystems. It is shown that
(1) the geometric phase of cyclic entangled states with non-degenerate
eigenvalues can always be decomposed into a sum of weighted non-modular pure
state phases pertaining to the separable components of the Schmidt
decomposition, though the same cannot be said in the non-cyclic case, and (2)
the geometric phase of the mixed state of one subsystem is generally different
from that of the entangled state even by keeping the other subsystem fixed, but
the two phases are the same when the evolution operator satisfies conditions
where each component in the Schmidt decomposition is parallel transported
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