Laboratoire de Physique Théorique de la Matière Condensée

LPTMC Seminars

7.4.2024 - 5.5.2024

  • Séminaire TQM: Dganit Meidan (BGU, Beer-Sheva, Israël)

    Date 02.05.2024 14:00 - 15:00
    Séminaires TQM

    Theory of free fermion dynamics – from monitored to post selected evolution

    Monitored quantum systems undergo Measurement-induced Phase Transitions (MiPTs) stemming from the interplay between measurements and unitary dynamics. When the detector readout is post- selected to match a given value, the dynamics is generated by a Non-Hermitian Hamiltonian with MiPTs characterized by different universal features. Here, we derive a partial post-selected stochastic Schrodinger equation based on a microscopic description of continuous weak measurement. This formalism connects the monitored and post-selected dynamics to a broader family of stochastic evolution. We apply the formalism to a chain of free fermions subject to partial post-selected monitoring of local fermion parities. Within a 2-replica approach, we obtained an effective bosonized Hamiltonian in the strong post-selected limit. Using a renormalization group analysis, we find that the universality of the non-Hermitian MiPT is stable against a finite (weak) amount of stochasticity. We further show that the passage to the monitored universality occurs abruptly at finite partial post-selection, which we confirm from the numerical finite size scaling of the MiPT. Our approach establishes a way to study MiPTs for arbitrary subsets of quantum trajectories and provides a potential route to tackle the experimental post-selected problem.

  • Alessio Lerose (University of Oxford)

    24.04.2024 10:45 - 11:45
    Séminaires

    Synthetic quantum matter out of equilibrium: A few recent advances from theory to simulation

    "Synthetic matter" has emerged as a new paradigm of quantum many-body physics, characterized by unprecedented degree of spatiotemporal control and programmability of Hamiltonian interactions. If on the one hand these experimental developments bring us closer to Feynman's vision of a universal quantum simulator for challenging open questions in many-body physics, on the other hand new fundamental theory questions on the behavior of quantum matter far from thermal equilibrium become accessible. Thermalization dynamics of isolated quantum systems and non-thermal states of matter are now at the center of multiple research efforts in theoretical physics. In this talk I will describe recent advances in understanding the mechanism of thermalization as well as long-lived non-equilibrium states of matter. Specifically, I will introduce an influence-functional approach to quantum many-body dynamics and describe preliminary evidence that it helps classifying non-equilibrium universal behavior. Furthermore, I will discuss the synthetic-matter version of the celebrated Coleman's false-vacuum decay scenario, and show that unique dynamical features appear, including emergent quasi-many-body-localized dynamics of interfaces and metastable long-range order. In parallel, I will describe how such theoretical advances led to unforeseen developments in applications, from a numerical method for strongly correlated electrons to a strategy for quantum simulation of real-time phenomena in lattice gauge theories.