Macroscopic properties of interacting bosons: a unified approach to the Thermodynamic Challenge

Introduction

Interacting bosons are unique quantum systems, whose low temperature phases exhibit fascinating quantum mechanics effects at a macroscopic scale. In the past two decades, the mathematical understanding of these systems improved tremendously. However, their behavior in the thermodynamic limit is still poorly understood, although this is the appropriate large scale limit to prove the emergence of scaling laws and universality, as well as to investigate the occurrence of phase transitions.

Objectives

MaTCh aims at investigating the low energy properties of interacting bosons in the thermodynamic limit, and at gaining a mathematical understanding of the emergence of correlated phases, in the form of:

• Bose-Einstein condensation
• Quasi-long range order

Additionally, it seeks to understand their instabilities due to:

1. Thermal fluctuations
2. Three-body recombination effects of Efimov type

Methodology

Our plan is to exploit scaling limits as a framework to identify and overcome, one at a time, the mathematical obstructions that currently prevent us from controlling the system at finite density in the thermodynamic limit.

In order to make progress on this program, MaTCh will introduce novel mathematical methods, inspired by renormalization group approaches and grounded in the second quantization techniques developed by the P.I. and collaborators, valid on an increasing sequence of scales.

Impact

Ultimately, the research led by MaTCh will lay the foundation for the rigorous description of several phenomena which are at the frontiers of present theoretical and experimental research. This includes areas where collective excitations of quantum systems are described in terms of emergent Bose gases, such as:

• The BCS theory for superconductivity
• The molecular description of strongly interacting Fermi gases
• The spin-wave theory for quantum magnetism