Quantum Fluctuations in Mesoscopic Systems

TL;DR

This paper develops a comprehensive theory of quantum fluctuations in mesoscopic systems, highlighting their persistence despite decoherence and exploring how environmental noise can induce entanglement among collective observables.

Contribution

It introduces a general framework for understanding quantum fluctuations in open mesoscopic systems, including their dynamics and potential for entanglement generation.

Findings

Quantum fluctuations remain quantum in the thermodynamic limit.

Certain environments can entangle collective fluctuations through noise.

Decoherence is not the sole factor affecting mesoscopic quantum behavior.

Abstract

Recent experimental results point to the existence of coherent quantum phenomena in systems made of a large number of particles, despite the fact that for many-body systems the presence of decoherence is hardly negligible and emerging classicality is expected. This behaviour hinges on collective observables, named quantum fluctuations, that retain a quantum character even in the thermodynamic limit: they provide useful tools for studying properties of many-body systems at the mesoscopic level, in between the quantum microscopic scale and the classical macroscopic one. We hereby present the general theory of quantum fluctuations in mesoscopic systems and study their dynamics in a quantum open system setting, taking into account the unavoidable effects of dissipation and noise induced by the external environment. As in the case of microscopic systems, decoherence is not always the only dominating effect at the mesoscopic scale: certain type of environments can provide means for entangling collective fluctuations through a purely noisy mechanism.