Non-Conventional Thermal States of Interacting Bosonic Oligomers

TL;DR

This paper explores non-conventional thermal states in interacting bosonic oligomers, revealing non-monotonic modal occupancies that challenge traditional thermodynamic predictions and demonstrate ensemble inequivalence.

Contribution

It introduces a microcanonical approach to describe non-monotonic thermal states in bosonic oligomers, deviating from classical distributions and highlighting ensemble inequivalence.

Findings

Non-monotonic modal occupancies observed in bosonic oligomers.

Deviations from Rayleigh-Jeans and Bose-Einstein distributions.

Microcanonical treatment explains the non-traditional thermal states.

Abstract

There has recently been a growing effort to understand in a comprehensive manner the physics and intricate dynamics of many-body and many-state (multimode) interacting bosonic systems. For instance, in photonics, nonlinear multimode fibers are nowadays intensely investigated due to their promise for ultra-high-bandwidth and high-power capabilities. Similar prospects are pursued in connection with magnon Bose-Einstein condensates, and ultra-cold atoms in periodic lattices for room-temperature quantum devices and quantum computation respectively. While it is practically impossible to monitor the phase space of such complex systems (classically or quantum mechanically), thermodynamics, has succeeded to predict their thermal state: the Rayleigh-Jeans (RJ) distribution for classical fields and the Bose-Einstein (BE) distribution for quantum systems. These distributions are monotonic and promote either the ground state or the most excited mode. Here, we demonstrate the possibility to advance the participation of other modes in the thermal state of bosonic oligomers. The resulting non-monotonic modal occupancies are described by a microcanonical treatment while they deviate drastically from the RJ/BE predictions of canonical and grand-canonical ensembles. Our results provide a paradigm of ensemble equivalence violation and can be used for designing the shape of thermal states.