MSc – Phase Transition in the Density of States of Quantum Spin Glasses

Summary

In my master thesis I worked on quantum spin glasses. The main novel finding was a phase transition between a semicircular and Gaussian density of states.

Abstract

We prove that the empirical density of states of quantum spin glasses on arbitrary graphs converges to a normal distribution as long as the maximal degree is negligible compared with the total number of edges. This extends the recent results of [10] that were proved for graphs with bounded chromatic number and with symmetric coupling distribution. Furthermore, we generalise the result to arbitrary hypergraphs. We test the optimality of our condition on the maximal degree for p-uniform hypergraphs that correspond to $p$-spin glass Hamiltonians acting on n indistinguishable spin-$1/2$ particles. At the critical threshold $p = n^{1/2}$ we find a sharp classical-quantum phase transition between the normal distribution and the Wigner semicircle law. The former is characteristic to classical systems with commuting variables, while the latter is a signature of noncommutative random matrix theory. The main results of this thesis are also summarised in [5].

Thesis

thesis.pdf