Abstract

The Nobel Prize in Physics 2021 (Part I)

Zoom meeting Link

After a very concise account of the many motivations for this year Nobel prize in physics for “FOR GROUNDBREAKING CONTRIBUTIONS TO OUR UNDERSTANDING OF COMPLEX PHYSICAL SYSTEMS” to Syukuro Manabe, Klaus Hasselmann and Giorgio Parisi, we will focus on the theory for complex disordered systems known as Replica Symmetry Breaking (RSB) theory. This is the approach that allows to understand and predict the behaviors of systems displaying a phase characterized by infinitely many states. Not just two, as in a magnet, but an infinite number. We will make a short historical survey on the theory of spin-glasses, beginning with Edwards and Anderson in 1975 and having a fundamental breakthrough with Parisi in 1979, trying to show how new concepts and mathematical tools were introduced. We will show how, apart from spin-glasses, different complex phenomena can be described by different kinds of RSB. We will eventually dedicate the final part of the talk to the quest for the experimental demonstration of the theory, that we formalized and performed in the framework of random lasers (2015). The measure of the Parisi order parameter is a complicated problem because large disordered systems take a very long time to thermalize and because microscopic spin configurations have to be measured to evaluate overlap values. We tackle the problem in which the role of spins is played by light modes, established and coupled in an optically random medium because of multiple light scattering. In presence of external power pumping this model reproduces the behavior of a particular kind of so-called random lasers. We termed them glassy random lasers. The statistical mechanical theory of the stationary lasing regime, a theory of multimode light amplification in random media, is nothing else than a spin-glass theory, displaying a variety of RSB regimes as the pumping increases.

Bibliography:

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