2,110 research outputs found
Frequent observations accelerate decay: The anti-Zeno effect
The quantum Zeno effect (QZE) is the striking prediction that the decay of
any unstable quantum state can be inhibited by sufficiently frequent
observations (measurements). The consensus opinion has upheld the QZE as a
general feature of quantum mechanics, which should lead to the inhibition of
any decay. The claim of QZE generality hinges on the assumption that successive
observations can in principle be made at time intervals too short for the
system to change appreciably. However, this assumption and the generality of
the QZE have scarcely been investigated thus far. We have addressed these
issues by showing that (i) the QZE is principally unattainable in radiative or
radioactive decay, because the required measurement rates would cause the
system to disintegrate; (ii) decay acceleration by frequent measurements (the
anti-Zeno effect -- AZE) is much more ubiquitous than its inhibition. The AZE
is shown to be observable as the enhancement of tunneling rates (e.g., for
atoms trapped in ramped-up potentials or in current-swept Josephson junctions),
fluorescence rates (e.g., for Rydberg atoms perturbed by noisy optical fields)
and photon depolarization rates (in randomly modulated Pockels cells).Comment: 8 pages, 13 figures, 1 table; revised version. Submitted to Z.
Naturforsch.
Some Remarks on Oscillating Inflation
In a recent paper Damour and Mukhanov describe a scenario where inflation may
continue during the oscillatory phase. This effect is possible because the
scalar field spends a significant fraction of each period of oscillation on the
upper part of the potential. Such additional period of inflation could push
perturbations after the slow roll regime to observable scales. Although in this
work we show that the small region of the Damour-Mukhanov parameter q gives the
main contribution to oscillating inflation, it was not satisfactory understood
until now. Furthermore, it gives an expression for the energy density spectrum
of perturbations, which is well behaved in the whole physical range of q .Comment: 4 pages including figures caption, 3 ps-figures. To appear in Phys.
Rev.
Universal dynamical control of quantum mechanical decay: Modulation of the coupling to the continuum
We derive and investigate an expression for the dynamically modified decay of
states coupled to an arbitrary continuum. This expression is universally valid
for weak temporal perturbations. The resulting insights can serve as useful
recipes for optimized control of decay and decoherence.Comment: 4 pages, 2 figures. Rewritten, changed figures, added reference
Gender and migration: IMISCOE short reader
This open access short reader offers a critical review of the debates on the transformation of migration and gendered mobilities primarily in Europe, though also engaging in wider theoretical insights. Building on empirical case studies and grounded in an analytical framework that incorporates both men and women, masculinities, sexualities and wider intersectional insights, this reader provides an accessible overview of conceptual developments and methodological shifts and their implications for a gendered understanding of migration in the past 30 years. It explores different and emerging approaches in major areas, such as: gendered labour markets across diverse sectors beyond domestic and care work to include skilled sectors of social reproduction; the significance of families in migration and transnational families; displacement, asylum and refugees and the incorporation of gender and sexuality in asylum determination; academic critiques and gendered discourses concerning integration often with the focus on Muslim women. The reader concludes with considerations of the potential impact of three notable developments on gendered migrations and mobilities: Black Lives Matter, Brexit and COVID-19. As such, it is a valuable resource for students, academics, policy makers, and practitioners.
On Metric Preheating
We consider the generation of super-horizon metric fluctuations during an
epoch of preheating in the presence of a scalar field \chi quadratically
coupled to the inflaton. We find that the requirement of efficient broad
resonance is concomitant with a severe damping of super-horizon \delta\chi
quantum fluctuations during inflation. Employing perturbation theory with
backreaction included as spatial averages to second order in the scalar fields
and in the metric, we argue that the usual inflationary prediction for metric
perturbations on scales relevant for structure formation is not strongly
modified.Comment: 5 latex pages, 1 postscript figure included, uses revtex.sty in two
column format and epsf.sty, some typos corrected and references added. Links
and further material at http://astro.uchicago.edu/home/web/sigl/r4.htm
Semiclassical ultraextremal horizons
We examine backreaction of quantum massive fields on multiply-degenerate
(ultraextremal) horizons. It is shown that, under influence of the quantum
backreaction, the horizon of such a kind moves to a new position, near which
the metric does not change its asymptotics, so the ultraextremal black holes
and cosmological spacetimes do exist as self-consistent solutions of the
semiclassical field equations.Comment: References adde
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