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Enhanced Diffusion and the Spontaneous Collapse Model of the Wave Function

Lucas F. Santos, Carlos O. Escobar

Published Dec 16, 1998• 0 citations
OpenAlex

Abstract

After finding analogies between turbulence and the beable interpretation of the spontaneous collapse model of the wave function, we unravel the underlying Lévy dynamics in such model. Using an affine noise in the collapse process, we obtain the intermittency corrections to Richardson’s t 3 law for the turbulent diffusion. PACS: 05.40.Fb, 03.65.Bz, 02.50.Ey Typeset using REVTEX 1 In studying the phenomenon of enhanced diffusion, Shlesinger et al [1] were led to introduce the concept of a Lévy walk as an extension of the more familiar Lévy flight [2]. The basic difference between a Lévy flight and a Lévy walk is that for the latter, although the walker visits all sites visited by the flight, the jumps do not occur instantaneously, but there may be a time delay before the next jump. Shlesinger et al obtained an integral transport equation involving a scaled memory which is nonlocal in space and time. Contrary to the infinite mean square displacement obtained in a Lévy flight, the solution of such transport

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Enhanced diffusion and the continuous spontaneous localization model

Léa Ferreira dos Santos, Carlos O. Escobar

We find an analogy between turbulence and the dynamics of the continuous spontaneous localization model (CSL) of the wave function. The use of a standard white noise in the localization process gives Richardson's ${t}^{3}$ law for the turbulent diffusion, while the introduction of an affine noise in the CSL allows us to obtain the intermittency corrections to this law.

arXiv:quant-ph/9812040•Physical Review A•Oct 1, 1999•5 citations

The quantum Lévy walk

Manuel O Cáceres, Marco Nizama

We introduce the quantum Lévy walk to study transport and decoherence in a quantum random model. We have derived from second-order perturbation theory the quantum master equation for a Lévy-like particle that moves along a lattice through scale-free hopping while interacting with a thermal bath of oscillators. The general evolution of the quantum Lévy particle has been solved for different preparations of the system. We examine the evolution of the quantum purity, the localized correlation and the probability to be in a lattice site, all of them leading to important conclusions concerning quantum irreversibility and decoherence features. We prove that the quantum thermal mean-square displacement is finite under a constraint that is different when compared to the classical Weierstrass random walk. We prove that when the mean-square displacement is infinite the density of state has a complex null-set inside the Brillouin zone. We show the existence of a critical behavior in the continuous eigenenergy which is related to its non-differentiability and self-affine characteristics. In general, our approach allows us to study analytically quantum fluctuations and decoherence in a long-range hopping model.

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The quantum Lévy walk

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We introduce the quantum Levy walk to study transport and decoherence in a quantum random model. We have derived from second order perturbation theory the quantum master equation for a extit{Levy-like particle }that moves along a lattice through hopping scale-free while interacting with a thermal bath of oscillators. The general evolution of the quantum Levy particle has been solved for different preparations of the system. We examine the evolution of the quantum purity, the localized correlation, and the probability to be in a lattice site, all them leading to important conclusions concerning quantum irreversibility and decoherence features. We prove that the quantum thermal mean-square displacement is finite under a constraint that is different when compared to the classical Weierstrass random walk. We prove that when the mean-square displacement is infinite the density of state has a complex null-set inside the Brillouin zone. We show the existence of a critical behavior in the continuous eigenenergy which is related to its non-differentiability and self-affine characteristics. In general our approach allows to study analytically quantum fluctuations and decoherence in a long-range hopping model.

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Lévy models for collapse of the wave function

Dorje C. Brody, Lane P. Hughston

Abstract Recently there has been much progress in the development of stochastic models for state reduction in quantum mechanics. In such models, the collapse of the wave function is a physical process, governed by a nonlinear stochastic differential equation that generalizes the Schrödinger equation. The present paper considers energy-based stochastic extensions of the Schrödinger equation. Most of the work carried out hitherto in this area has been concerned with models where the process driving the stochastic dynamics of the quantum state is Brownian motion. Here, the Brownian framework is broadened to a wider class of models where the noise process is of the Lévy type, admitting stationary and independent increments. The properties of such models are different from those of Brownian reduction models. In particular, for Lévy models the decoherence rate depends on the overall scale of the energy. Thus, in Lévy reduction models, a macroscopic quantum system will spontaneously collapse to an eigenstate even if the energy level gaps are small.

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Radiation trapping and Lévy flights in atomic vapours: an introductory review

Martine Chevrollier

Multiple scattering is a process in which a particle is repeatedly deflected by other particles. In an overwhelming majority of cases, the ensuing random walk can successfully be described through Gaussian, or normal, statistics. However, like a (growing) number of other apparently inoffensive systems, diffusion of light in dilute atomic vapours eludes this familiar interpretation, exhibiting a superdiffusive behaviour. As opposed to normal diffusion, whereby the particle executes steps in random directions but with lengths slightly varying around an average value (like a drunkard whose next move is unpredictable but certain to within a few tens of centimetres), superdiffusion is characterised by sudden abnormally long steps (Lévy flights) interrupting sequences of apparently regular jumps which, although very rare, determine the whole dynamics of the system. The formal statistics tools to describe superdiffusion already exist and rely on stable, well understood distributions. As scientists become aware of, and more familiar with, this non-orthodox possibility of interpretation of random phenomena, new systems are discovered or re-interpreted as following Lévy statistics. Propagation of light in resonant atomic vapours is one of these systems which have been studied for decades and have only recently been shown to be the scene of Lévy flights.

arXiv:1311.0253•Contemporary Physics•May 1, 2012•22 citations

Quantum Spontaneous Stochasticity

Gregory L. Eyink, Theodore D. Drivas

The quantum wave-function of a massive particle with small initial uncertainties (consistent with the uncertainty relation) is believed to spread very slowly, so that the dynamics is deterministic. This assumes that the classical motions for given initial data are unique. In fluid turbulence non-uniqueness due to "roughness" of the advecting velocity field is known to lead to stochastic motion of classical particles. Vanishingly small random perturbations are magnified by Richardson diffusion in a "nearly rough" velocity field so that motion remains stochastic as the noise disappears, or classical spontaneous stochasticity, . Analogies between stochastic particle motion in turbulence and quantum evolution suggest that there should be quantum spontaneous stochasticity (QSS). We show this for 1D models of a particle in a repulsive potential that is "nearly rough" with $V(x) \sim C|x|^{1+α}$ at distances $|x|\gg \ell$ , for some UV cut-off $\ell$, and for initial Gaussian wave-packet centered at 0. We consider the WKB limit with $\hbar/m \to 0$, then position-spread $σ\to 0$. The limit of the position density is non-deterministic, with equal probabilities of the particle following either of two, non-unique classical solutions and with "Richardson-like" spreading of the wave-packet. The splitting of the wave-packet occurs in a very short time $t\sim(\ell^{1+α}/C)^{1/2}$ for small $\ell$. QSS also occurs in the scattering of a wave-packet off the rough potential, for careful fine-tuning. We also consider other semi-classical limits by a numerical solution of the Schrödinger equation, observing QSS both in position- and momentum-space. Although the wave-function remains split into two widely separated branches in the classical limit, rapid phase oscillations within each branch prevent any coherent superposition. These effects should be observable in laboratory experiments.

arXiv:1509.04941•Sep 16, 2015•3 citations
After finding analogies between turbulence and the beable interpretation of the spontaneous collapse model of the wave function, we unravel the underlying Lévy dynamics in such model. Using an affine noise in the collapse process, we obtain the intermittency corrections to Richardson’s t 3 law for the turbulent diffusion. PACS: 05.40.Fb, 03.65.Bz, 02.50.Ey Typeset using REVTEX 1 In studying the phenomenon of enhanced diffusion, Shlesinger et al [1] were led to introduce the concept of a Lévy walk as an extension of the more familiar Lévy flight [2]. The basic difference between a Lévy flight and a Lévy walk is that for the latter, although the walker visits all sites visited by the flight, the jumps do not occur instantaneously, but there may be a time delay before the next jump. Shlesinger et al obtained an integral transport equation involving a scaled memory which is nonlocal in space and time. Contrary to the infinite mean square displacement obtained in a Lévy flight, the solution of such transport
We find an analogy between turbulence and the dynamics of the continuous spontaneous localization model (CSL) of the wave function. The use of a standard white noise in the localization process gives Richardson's t3{t}^{3}t3 law for the turbulent diffusion, while the introduction of an affine noise in the CSL allows us to obtain the intermittency corrections to this law.
We introduce the quantum Lévy walk to study transport and decoherence in a quantum random model. We have derived from second-order perturbation theory the quantum master equation for a Lévy-like particle that moves along a lattice through scale-free hopping while interacting with a thermal bath of oscillators. The general evolution of the quantum Lévy particle has been solved for different preparations of the system. We examine the evolution of the quantum purity, the localized correlation and the probability to be in a lattice site, all of them leading to important conclusions concerning quantum irreversibility and decoherence features. We prove that the quantum thermal mean-square displacement is finite under a constraint that is different when compared to the classical Weierstrass random walk. We prove that when the mean-square displacement is infinite the density of state has a complex null-set inside the Brillouin zone. We show the existence of a critical behavior in the continuous eigenenergy which is related to its non-differentiability and self-affine characteristics. In general, our approach allows us to study analytically quantum fluctuations and decoherence in a long-range hopping model.
We introduce the quantum Levy walk to study transport and decoherence in a quantum random model. We have derived from second order perturbation theory the quantum master equation for a extit{Levy-like particle }that moves along a lattice through hopping scale-free while interacting with a thermal bath of oscillators. The general evolution of the quantum Levy particle has been solved for different preparations of the system. We examine the evolution of the quantum purity, the localized correlation, and the probability to be in a lattice site, all them leading to important conclusions concerning quantum irreversibility and decoherence features. We prove that the quantum thermal mean-square displacement is finite under a constraint that is different when compared to the classical Weierstrass random walk. We prove that when the mean-square displacement is infinite the density of state has a complex null-set inside the Brillouin zone. We show the existence of a critical behavior in the continuous eigenenergy which is related to its non-differentiability and self-affine characteristics. In general our approach allows to study analytically quantum fluctuations and decoherence in a long-range hopping model.
Abstract Recently there has been much progress in the development of stochastic models for state reduction in quantum mechanics. In such models, the collapse of the wave function is a physical process, governed by a nonlinear stochastic differential equation that generalizes the Schrödinger equation. The present paper considers energy-based stochastic extensions of the Schrödinger equation. Most of the work carried out hitherto in this area has been concerned with models where the process driving the stochastic dynamics of the quantum state is Brownian motion. Here, the Brownian framework is broadened to a wider class of models where the noise process is of the Lévy type, admitting stationary and independent increments. The properties of such models are different from those of Brownian reduction models. In particular, for Lévy models the decoherence rate depends on the overall scale of the energy. Thus, in Lévy reduction models, a macroscopic quantum system will spontaneously collapse to an eigenstate even if the energy level gaps are small.
Multiple scattering is a process in which a particle is repeatedly deflected by other particles. In an overwhelming majority of cases, the ensuing random walk can successfully be described through Gaussian, or normal, statistics. However, like a (growing) number of other apparently inoffensive systems, diffusion of light in dilute atomic vapours eludes this familiar interpretation, exhibiting a superdiffusive behaviour. As opposed to normal diffusion, whereby the particle executes steps in random directions but with lengths slightly varying around an average value (like a drunkard whose next move is unpredictable but certain to within a few tens of centimetres), superdiffusion is characterised by sudden abnormally long steps (Lévy flights) interrupting sequences of apparently regular jumps which, although very rare, determine the whole dynamics of the system. The formal statistics tools to describe superdiffusion already exist and rely on stable, well understood distributions. As scientists become aware of, and more familiar with, this non-orthodox possibility of interpretation of random phenomena, new systems are discovered or re-interpreted as following Lévy statistics. Propagation of light in resonant atomic vapours is one of these systems which have been studied for decades and have only recently been shown to be the scene of Lévy flights.
The quantum wave-function of a massive particle with small initial uncertainties (consistent with the uncertainty relation) is believed to spread very slowly, so that the dynamics is deterministic. This assumes that the classical motions for given initial data are unique. In fluid turbulence non-uniqueness due to "roughness" of the advecting velocity field is known to lead to stochastic motion of classical particles. Vanishingly small random perturbations are magnified by Richardson diffusion in a "nearly rough" velocity field so that motion remains stochastic as the noise disappears, or classical spontaneous stochasticity, . Analogies between stochastic particle motion in turbulence and quantum evolution suggest that there should be quantum spontaneous stochasticity (QSS). We show this for 1D models of a particle in a repulsive potential that is "nearly rough" with V(x)∼C∣x∣1+αV(x) \sim C|x|^{1+α}V(x)∼C∣x∣1+α at distances ∣x∣≫ℓ|x|\gg \ell∣x∣≫ℓ , for some UV cut-off ℓ\ellℓ, and for initial Gaussian wave-packet centered at 0. We consider the WKB limit with ℏ/m→0\hbar/m \to 0ℏ/m→0, then position-spread σ→0σ\to 0σ→0. The limit of the position density is non-deterministic, with equal probabilities of the particle following either of two, non-unique classical solutions and with "Richardson-like" spreading of the wave-packet. The splitting of the wave-packet occurs in a very short time t∼(ℓ1+α/C)1/2t\sim(\ell^{1+α}/C)^{1/2}t∼(ℓ1+α/C)1/2 for small ℓ\ellℓ. QSS also occurs in the scattering of a wave-packet off the rough potential, for careful fine-tuning. We also consider other semi-classical limits by a numerical solution of the Schrödinger equation, observing QSS both in position- and momentum-space. Although the wave-function remains split into two widely separated branches in the classical limit, rapid phase oscillations within each branch prevent any coherent superposition. These effects should be observable in laboratory experiments.