Entanglement in Macroscopic Systems

J. Sperling, I. A. Walmsley

Published 2016-11-18Version 1

In the macroscopic reality of our daily live, quantum phenomena such as entanglement are not observable. However, the constituent parts of this classical realm, e.g., atoms or photons, are almost completely determined by the laws of quantum physics. Yet, theory and experiments cannot predict a sharp borderline between the classical and the quantum domain. So, at which point does one lose the information of the quantum correlations in many-particle systems? For addressing this question, we explore the theory of entangled quantum systems of harmonic oscillators consisting of an arbitrary number of interacting particles. We introduce the operational measure of the entanglement visibility to access the measurable entanglement, which will be applied especially to energy measurements. Moreover, the properties of the energy spectrum of entangled and separable states are compared. Our analytical analysis suggest that the entanglement visibility decays with the number of particles without the need of any decoherence process. To strengthen this claim, we also derive and apply a method to detect entanglement in systems without a fixed, but a fluctuating number of particles. In this context, we further study the thermal states of the given correlated system together with the temperature dependence of entanglement.