Informal Quantum Seminar: Giacomo Bracci Testasecca (SISSA)

In this seminar, I will present recent results on the two-dimensional quantum Heisenberg model with bond disorder, focusing on the emergence and nature of spin-glass order in the quantum regime. Combining large-scale quantum simulations with a semiclassical expansion around classical states, we identify an extended region of the zero temperature quantum phase diagram where conventional long-range magnetic order disappears in the thermodynamic limit, while the overlap order parameter remains finite, signalling a stable quantum spin-glass phase. The semiclassical analysis provides a microscopic characterization of this regime: at leading order, the  quadratic spin-wave Hamiltonian reveals that the character of low-energy excitations is controlled by the correlations inherited from the underlying classical states. We find that the spin waves are weakly localized and discuss how the addition of interactions leads to ergodicity restoring.

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