488 research outputs found
Suppression of Zeno effect for distant detectors
We describe the influence of continuous measurement in a decaying system and
the role of the distance from the detector to the initial location of the
system. The detector is modeled first by a step absorbing potential. For a
close and strong detector, the decay rate of the system is reduced; weaker
detectors do not modify the exponential decay rate but suppress the long-time
deviations above a coupling threshold. Nevertheless, these perturbing effects
of measurement disappear by increasing the distance between the initial state
and the detector, as well as by improving the efficiency of the detector.Comment: 4 pages, 4 figure
No classical limit of quantum decay for broad states
Though the classical treatment of spontaneous decay leads to an exponential
decay law, it is well known that this is an approximation of the quantum
mechanical result which is a non-exponential at very small and large times for
narrow states. The non exponential nature at large times is however hard to
establish from experiments. A method to recover the time evolution of unstable
states from a parametrization of the amplitude fitted to data is presented. We
apply the method to a realistic example of a very broad state, the sigma meson
and reveal that an exponential decay is not a valid approximation at any time
for this state. This example derived from experiment, shows the unique nature
of broad resonances
Complex Scaled Spectrum Completeness for Coupled Channels
The Complex Scaling Method (CSM) provides scattering wave functions which
regularize resonances and suggest a resolution of the identity in terms of such
resonances, completed by the bound states and a smoothed continuum. But, in the
case of inelastic scattering with many channels, the existence of such a
resolution under complex scaling is still debated. Taking advantage of results
obtained earlier for the two channel case, this paper proposes a representation
in which the convergence of a resolution of the identity can be more easily
tested. The representation is valid for any finite number of coupled channels
for inelastic scattering without rearrangement.Comment: Latex file, 13 pages, 4 eps-figure
The role of initial state reconstruction in short and long time deviations from exponential decay
We consider the role of the reconstruction of the initial state in the
deviation from exponential decay at short and long times. The long time decay
can be attributed to a wave that was, in a classical-like, probabilistic sense,
fully outside the initial state or the inner region at intermediate times,
i.e., to a completely reconstructed state, whereas the decay during the
exponential regime is due instead to a non-reconstructed wave. At short times
quantum interference between regenerated and non-regenerated paths is
responsible for the deviation from the exponential decay. We may thus conclude
that state reconstruction is a ``consistent history'' for long time deviations
but not for short ones.Comment: 4 pages, 6 figure
Photoproduction of the Eta-Prime Mesons as a New Tool to Probe Baryon Resonances
We examine eta prime photoproduction, as a novel tool to study baryon
resonances around 2 GeV, of particular interest to the quark shell model, which
predicts a number of them. We find important roles of the form factors at the
strong vertices, and show that the N^*(2080) can be probed efficiently by this
reaction.Comment: Will be published in Phys. Rev.
The various power decays of the survival probability at long times for free quantum particle
The long time behaviour of the survival probability of initial state and its
dependence on the initial states are considered, for the one dimensional free
quantum particle. We derive the asymptotic expansion of the time evolution
operator at long times, in terms of the integral operators. This enables us to
obtain the asymptotic formula for the survival probability of the initial state
, which is assumed to decrease sufficiently rapidly at large .
We then show that the behaviour of the survival probability at long times is
determined by that of the initial state at zero momentum . Indeed,
it is proved that the survival probability can exhibit the various power-decays
like for an arbitrary non-negative integers as ,
corresponding to the initial states with the condition as .Comment: 15 pages, to appear in J. Phys.
'Sexercise': Working out heterosexuality in Jane Fonda’s fitness books
This is an Author's Accepted Manuscript of an article published in Leisure Studies, 30(2), 237 - 255, 2011, copyright Taylor & Francis, available online at: http://www.tandfonline.com/10.1080/02614367.2010.523837.This paper explores the connection between the promotion of heterosexual norms in women’s fitness books written by or in the name of Jane Fonda during the 1980s and the commodification of women’s fitness space in both the public and private spheres. The paper is set in the absence of overt discussions of normative heterosexuality in leisure studies and draws on critical heterosexual scholarship as well as the growing body of work theorising geographies of corporeality and heterosexuality. Using the principles of media discourse analysis, the paper identifies three overlapping characteristics of heterosexuality represented in Jane Fonda’s fitness books, and embodied through the exercise regimes: respectable heterosexual desire, monogamous procreation and domesticity. The paper concludes that the promotion and prescription of exercise for women in the Jane Fonda workout books centred on the reproduction and embodiment of heterosexual corporeality. Set within an emerging commercial landscape of women’s fitness in the 1980s, such exercise practices were significant in the legitimation and institutionalisation of heteronormativity
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
Effect of the measurement on the decay rate of a quantum system
We investigated the electron tunneling out of a quantum dot in the presence
of a continuous monitoring by a detector. It is shown that the Schr\"odinger
equation for the whole system can be reduced to new Bloch-type rate equations
describing the time-development of the detector and the measured system at
once. Using these equations we find that the continuous measurement of the
unstable system does not affect its exponential decay, ,
contrary to expectations based on the Quantum Zeno effect . However, the width
of the energy distribution of the tunneling electron is no more , but
increases due to the decoherence, generated by the detector.Comment: Additional explanations are added. Accepted for publications in Phys.
Rev. Let
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