Next seminar

Title Emergence of
 semilocal Gibbs ensembles
Speaker Maurizio Fagotti (LPTMS)
Date&time 📅 May 31
🕓 11:00 AM Rome
Location Room 128 + virtual
Abstract I consider nonequilibrium time evolution in quantum spin chains after a global quench. I show that global symmetries can invalidate the standard picture of local relaxation to maximum-entropy statistical ensembles and provide a solution to the problem. The issue arises when the Hamiltonian possesses conservation laws that are not (pseudo)local but act as such in the symmetry-restricted space where time evolution occurs. I focus on a specific example with a spin-flip symmetry and establish a connection with symmetry-protected topological order in equilibrium at zero temperature. In the second part of the talk I discuss some exceptional features of the infinite-time limit. In particular, the excess of entropy of a spin block triggered by a local perturbation in the initial state grows logarithmically with the subsystem’s length. Finally, I discuss the melting of the order induced either by a (symmetry-breaking) rotation of the initial state or by an increase of the temperature.

References: [1] M. Fagotti, Phys. Rev. Lett. 128, 110602 (2022) [arXiv:2110.11322] [2] M. Fagotti, V. Marić, and L. Zadnik, arXiv:2205.02221.

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Next journal club meeting

Title Adiabatic eigenstate deformations: A probe for quantum chaos
Speaker Rajat Kumar Panda
Date&time 📅 July 8
🕓 14.30
Abstract Quantum chaos is essential for the emergence of statistical mechanics and thermodynamics. It manifests itself in the effective description of the eigenstates of chaotic Hamiltonians through random matrix ensembles and the eigenstate thermalization hypothesis. Standard measures of chaos in quantum many-body systems are level statistics and the spectral form factor. In this seminar, following the paper [PhysRevX.10.041017], we will see how the norm of the adiabatic gauge potential, the generator of adiabatic deformations between eigenstates, serves as a measure of quantum chaos. Using two generic classes of spin chains, I will compare the sensitivity of different probing methods.
🔗 Past journal club meetings

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