598 research outputs found
The emission of electromagnetic radiation from a quantum system interacting with an external noise: A general result
No full textWe compute the spectrum of radiation emitted by a generic quantum system interacting with an external classic noise. Our motivation is a wish to understand this phenomenon within the framework of collapse models. However, the computation is general and applies to practically any situation in which a quantum system interacts with a noise. The computation is carried out at a perturbative level. This poses problems as regards the correct way of performing the analysis, as repeatedly discussed in the literature. We will also clarify this issue
Seven non-standard models coupling quantum matter and gravity
No full textWe review seven models, which consistently couple quantum matter and
(Newtonian) gravity in a non standard way. For each of them we present the
underlying motivations, the main equations and, when available, a comparison
with experimental data.Comment: 15 pages. Article prepared for the Special Topic Collection
"Celebrating Sir Roger Penrose's Nobel Prize
Spontaneous photon emission from a non-relativistic free charged particle in collapse models: A case study
No full textWe study the photon emission rate of a non relativistic charged particle interacting with an external classical noise through its position. Both the particle and the electromagnetic field are quantized. Under only the dipole approximation, the equations of motion can be solved exactly for a free particle, or a particle bounded by an harmonic pot
ential. The physical quantity we will be interested in is the spectrum of the radiation emitt ed by the particle,
due to the interaction with the noise. We will highlight several properties of the spectrum and clarify some issues appeared in the literature, regarding the exact mathematical formula of a spectrum for a free particle
Collapse Models: Main Properties and the State of Art of the Experimental Tests
No full textCollapse models represent one of the possible solutions to the measurement problem. These models modify the Schrödinger dynamics with nonlinear and stochastic terms, which guarantee the localization in space of the wave function avoiding macroscopic superpositions, like that described in Schrödinger’s cat paradox. The Ghirardi–Rimini–Weber (GRW) and the Continuous Spontaneous Localization (CSL) models are the most studied among the collapse models. Here, we briefly summarize the main features of these models and the advances in their experimental investigation
On spontaneous photon emission in collapse models
No full textWe reanalyze the problem of spontaneous photon emission in collapse models. We show that the extra term found by Bassi and Duerr is present for non-white (colored) noise, but its coefficient is proportional to the zero frequency Fourier component of the noise. This leads one to suspect that the extra term is an artifact. When the calculation is repeated with the final electron in a wave packet and with the noise confined to a bounded region, the extra term vanishes in the limit of continuum state normalization. The result obtained by Fu and by Adler and Ramazanoglu from application of the Golden Rule is then recovered
Bohmian mechanics, collapse models and the emergence of classicality
No full textWe discuss the emergence of classical trajectories in Bohmian mechanics, when a macroscopic object interacts with an external environment. We show that in such a case the conditional wave function of the system follows a dynamics which, under reasonable assumptions, corresponds to that of the Ghirardi–Rimini–Weber (GRW) collapse model. As a consequence, Bohmian trajectories evolve classically. Our analysis also shows how the GRW (istantaneous) collapse process can be derived by an underlying continuous interaction of a quantum system with an external agent, thus throwing a light on how collapses can emerge from a deeper level theory
On the testability of the K\'arolyh\'azy model
No full textK\'arolyh\'azy's original proposal, suggesting that space-time fluctuations
could be a source of decoherence in space, faced a significant challenge due to
an unexpectedly high emission of radiation (13 orders of magnitude more than
what was observed in the latest experiment). To address this issue, we
reevaluated K\'arolyh\'azy's assumption that the stochastic metric fluctuation
must adhere to a wave equation. By considering more general correlation
functions of space-time fluctuations, we resolve the problem and consequently
revive the aforementioned proposal.Comment: 16 page
On the spontaneous emission of electromagnetic radiation in the CSL model
No full textSpontaneous photon emission in the Continuous Spontaneous Localization (CSL) model is studied one more time. In the CSL model each particle interacts with a noise field that induces the collapse of its wave function. As a consequence of this interaction, when the particle is electrically charged, it radiates. As discussed in Adler (2013) the formula for the emission rate, to first perturbative order, contains two terms: one is proportional to the Fourier component of the noise field at the same frequency as that of the emitted photon and one is proportional to the zero Fourier component of the noise field. As discussed in previous works, this second term seems unphysical. In Adler (2013) it was shown that the unphysical term disappears when the noise is confined to a bounded region and the final particle’s state is a wave packet. Here we investigate the origin of this unphysical term and why it vanishes according to the previous prescription. We will see that perturbation theory is formally not valid in the large time limit since the effect of the noise accumulates continuously in time. Therefore either one performs an exact calculation (or at least in some way includes higher order terms) as we do here, or one finds a way to make a perturbative calculation meaningful, e.g., by confining the system as in Adler (2013)
Collapse dynamics are diffusive
No full textNon-interferometric experiments have been successfully employed to constrain
models of spontaneous wave function collapse, which predict a violation of the
quantum superposition principle for large systems. These experiments are
grounded on the fact that, according to these models, the dynamics is driven by
a noise that, besides collapsing the wave function in space, generates a
diffusive motion with characteristic signatures, which, though small, can be
tested. The non-interferometric approach might seem applicable only to those
models which implement the collapse through a noisy dynamics, not to any model,
which collapses the wave function in space. Here we show that this is not the
case: under reasonable assumptions, any collapse dynamics (in space) is
diffusive. Specifically, we prove that any space-translation invariant dynamics
which complies with the no-signaling constraint, if collapsing the wave
function in space, must change the average momentum of the system, and/or its
spread.Comment: 20 page
Coherent scattering in non relativistic quantum mechanics
No full textIn this paper we give a pedagogical explanation of coherence effects in non relativistic scattering processes. Coherent scattering is important not only because it is a clear manifestation of the wave character of the interaction in these regimes, but also because it helps in increasing the cross section and thus the observable effects. We show under which conditions a particle scatters coherently on a multi-particle system. In a nutshell, in order to have coherent scattering, the incident particle has not to resolve the internal structure of the composite system. We show that the above condition is satisfied when the de Broglie length of the incident particle is much larger than the size of the system
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