arXiv subjects

J. Allam

Publications and source records attributed to J. Allam.

4 recordsLinked to original sources

arXiv2023

Making sense of relativistic Wigner friend scenarios: a problem for unitary accounts of quantum measurements ?

Wigner-friend scenarios -- in which external agents describe a closed laboratory containing a friend making a measurement -- highlight the difficulties inherent to quantum theory when accounting for measurements. In non-relativistic scenarios, the difficulty is to accommodate unitary evolution for a closed system with a definite outcome obtained by the friend. In relativistic scenarios the tensions between quantum theory and relativity induce additional constraints. A generic property of relativistic scenarios is the frame-dependence of state update upon a measurement. Based on a definite example, we will show that this property leads to inconsistent accounts for outcomes obtained in different reference frames. We will further argue that these results point to some fundamental inadequacy when attempting to model actions taken by a complex agent as unitary operations made on simple wavefunctions.

quant-ph↗

arXiv2023

From observer-dependent facts to frame-dependent measurement records in Wigner friend scenarios

The description of Wigner-friend scenarios -- in which external agents describe a closed laboratory containing a friend making a measurement -- remains problematic due to the ambiguous nature of quantum measurements. One option is to endorse assumptions leading to observer-dependent facts, given that the friend's measurement outcome is not defined from the point of view of the external observers. We introduce in this work a model in a relativistic context showing that these assumptions can also lead to measurement records that depend on the inertial reference frame in which the agents make their observations. Our model is based on an entangled pair shared by the friend and a distant agent performing space-like separated measurements. An external observer at rest relative to the closed laboratory and observers in a moving frame do not agree on the observed records, which are not Lorentz transforms of one another.

quant-ph↗

arXiv2022

Effect of a moving mirror on the free fall of a quantum particle in a homogeneous gravitational field

We investigate the effect of time-dependent boundary conditions on the dynamics of a quantum bouncer -- a particle falling in a homogeneous gravitational field on a moving mirror. We examine more particularly the way a moving mirror modifies the properties of the entire wavefunction of a falling particle. We find that some effects, such as the fact that a quantum particle hitting a moving mirror may bounce significantly higher than when the mirror is fixed, are in line with classical intuition. Other effects, such as the change in relative phases or in the current density in spatial regions arbitrarily far from the mirror are specifically quantum. We further discuss how the effects produced by a moving mirror could be observed in link with current experiments, in particular with cold neutrons.

quant-ph↗

arXiv2013

Measurement of a reaction-diffusion crossover in exciton-exciton recombination inside carbon nanotubes using femtosecond optical absorption

Exciton-exciton recombination in isolated semiconducting single-walled carbon nanotubes was studied using femtosecond transient absorption. Under sufficient excitation to saturate the optical absorption, we observed an abrupt transition between reaction- and diffusion- limited kinetics, arising from reactions between incoherent localized excitons with a finite probability of ~ 0.2 per encounter. This represents the first experimental observation of a crossover between classical and critical kinetics in a 1D coalescing random walk, which is a paradigm for the study of non- equilibrium systems.

cond-mat.stat-mech↗