1,175 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.
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
Zeno and anti-Zeno effects for photon polarization dephasing
We discuss a simple, experimentally feasible scheme, which elucidates the
principles of controlling ("engineering") the reservoir spectrum and the
spectral broadening incurred by repeated measurements. This control can yield
either the inhibition (Zeno effect) or the acceleration (anti-Zeno effect) of
the quasi-exponential decay of the observed state by means of frequent
measurements. In the discussed scheme, a photon is bouncing back and forth
between two perfect mirrors, each time passing a polarization rotator. The
horizontal and vertical polarizations can be viewed as analogs of an excited
and a ground state of a two level system (TLS). A polarization beam splitter
and an absorber for the vertically polarized photon are inserted between the
mirrors, and effect measurements of the polarization. The polarization angle
acquired in the electrooptic polarization rotator can fluctuate randomly, e.g.,
via noisy modulation. In the absence of an absorber the polarization
randomization corresponds to TLS decay into an infinite-temperature reservoir.
The non-Markovian nature of the decay stems from the many round-trips required
for the randomization. We consider the influence of the polarization
measurements by the absorber on this non-Markovian decay, and develop a theory
of the Zeno and anti-Zeno effects in this system.Comment: 11 pages, 4 figure
Superluminal Optical Phase Conjugation: Pulse Reshaping and Instability
We theoretically investigate the response of optical phase conjugators to
incident probe pulses. In the stable (sub-threshold) operating regime of an
optical phase conjugator it is possible to transmit probe pulses with a
superluminally advanced peak, whereas conjugate reflection is always
subluminal. In the unstable (above-threshold) regime, superluminal response
occurs both in reflection and in transmission, at times preceding the onset of
exponential growth due to the instability.Comment: 9 pages, 6 figures, RevTex, to appear in Phys. Rev.
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.
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
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