Decoherence by Internal Degrees of Freedom

TL;DR

This paper investigates how internal degrees of freedom in a composite quantum system cause decoherence, leading to suppression of interference, and explores the relationship between entanglement and decoherence through numerical simulations.

Contribution

It demonstrates that internal degrees of freedom induce decoherence in coupled particles, models the coupling as parametric driving, and introduces a measure of system compositeness.

Findings

Decoherence occurs due to internal degrees of freedom coupling.

Coupling can be approximated as parametric driving influenced by the external potential.

Suppression of interference correlates with entanglement between degrees of freedom.

Abstract

We consider a composite system consisting of coupled particles, and investigate decoherence due to coupling of the center-of-mass degree of freedom with the internal degrees of freedom. For a simple model of two bound particles, we show that in general such a decoherence effect exists, and leads to suppression of interference between different paths of the center-of-mass. For the special case of two harmonically-bound particles moving in an external potential in one dimension, we show that the coupling between the center-of-mass and internal degrees of freedom can be approximated as parametric driving, and that nontrivial coupling depends on the second derivative of the external potential. We find a partial solution to this parametric driving problem. For a simple interference experiment, consisting of two wave packets scattering off of a square well, we perform numerical simulations and show a close connection between suppression of interference and entanglement between the center-of-mass and internal degrees of freedom. We also propose a measure of compositeness which quantifies the extent to which a composite system cannot be approximated as a single, indivisible particle. We numerically calculate this quantity for our square well example system.