210 research outputs found
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
Uhlmann's geometric phase in presence of isotropic decoherence
Uhlmann's mixed state geometric phase [Rep. Math. Phys. {\bf 24}, 229 (1986)]
is analyzed in the case of a qubit affected by isotropic decoherence treated in
the Markovian approximation. It is demonstrated that this phase decreases
rapidly with increasing decoherence rate and that it is most fragile to weak
decoherence for pure or nearly pure initial states. In the unitary case, we
compare Uhlmann's geometric phase for mixed states with that occurring in
standard Mach-Zehnder interferometry [Phys. Rev. Lett. {\bf 85}, 2845 (2000)]
and show that the latter is more robust to reduction in the length of the Bloch
vector. We also describe how Uhlmann's geometric phase in the present case
could in principle be realized experimentally.Comment: New ref added, refs updated, journal ref adde
Adiabatic Approximation for weakly open systems
We generalize the adiabatic approximation to the case of open quantum
systems, in the joint limit of slow change and weak open system disturbances.
We show that the approximation is ``physically reasonable'' as under wide
conditions it leads to a completely positive evolution, if the original master
equation can be written on a time-dependent Lindblad form. We demonstrate the
approximation for a non-Abelian holonomic implementation of the Hadamard gate,
disturbed by a decoherence process. We compare the resulting approximate
evolution with numerical simulations of the exact equation.Comment: New material added, references added and updated, journal reference
adde
Geometric phases for non-degenerate and degenerate mixed states
This paper focuses on the geometric phase of general mixed states under
unitary evolution. Here we analyze both non-degenerate as well as degenerate
states. Starting with the non-degenerate case, we show that the usual procedure
of subtracting the dynamical phase from the total phase to yield the geometric
phase for pure states, does not hold for mixed states. To this end, we furnish
an expression for the geometric phase that is gauge invariant. The parallelity
conditions are shown to be easily derivable from this expression. We also
extend our formalism to states that exhibit degeneracies. Here with the
holonomy taking on a non-abelian character, we provide an expression for the
geometric phase that is manifestly gauge invariant. As in the case of the
non-degenerate case, the form also displays the parallelity conditions clearly.
Finally, we furnish explicit examples of the geometric phases for both the
non-degenerate as well as degenerate mixed states.Comment: 23 page
Phases of quantum states in completely positive non-unitary evolution
We define an operational notion of phases in interferometry for a quantum
system undergoing a completely positive non-unitary evolution. This definition
is based on the concepts of quantum measurement theory. The suitable
generalization of the Pancharatnan connection allows us to determine the
dynamical and geometrical parts of the total phase between two states linked by
a completely positive map. These results reduce to the knonw expressions of
total, dynamical and geometrical phases for pure and mixed states evolving
unitarily.Comment: 2 figure
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