Séminaires du LPTMC
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Weitao Chen
16.05.2024 14:00 - 15:00SéminairesTitre TBA
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Denis Ullmo (LPTMS)
13.05.2024 10:45 - 11:45SéminairesPedestrians in static crowds are not grains, but game players.
The short-term (‘operational’) dynamics of pedestrian crowds are generally thought to involve no anticipation, except perhaps the avoidance of the most imminent
collisions. I will show that current models rooted in this belief fail to reproduce essential features observed experimentally by Nicolas et al. [Sci. Rep. 9, 105 (2019).] when a static crowd is crossed by an intruder.The missing ingredient can be identified as the pedestrians’ ability to plan ahead far enough beyond the next interaction. On this basis, I will introduce a minimal model based on mean-field game theory which proves remarkably successful in capturing the experimental observations associated with this setting, but also other daily-life situations such as partial metro boarding. These findings are clear evidence that a long term game theoretical approach is key to capturing essential elements of the dynamics of crowds.
[refs : Phys. Rev. E 107, 024612 (2023), SciPost Phys. 16, 104 (2024)]
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Séminaire TQM: Dganit Meidan (BGU, Beer-Sheva, Israël)
02.05.2024 14:00 - 15:00Séminaires TQMTheory 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.
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Alessio Lerose (University of Oxford)
24.04.2024 10:45 - 11:45SéminairesSynthetic quantum matter out of equilibrium: A few recent advances from theory to simulation
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Manuel Pino (Nanotechnology Group, Universidad de Salamanca)
25.03.2024 10:45 - 11:45SéminairesCorrelated volumes for metallic wavefunctions on a random-regular graph
We study the metallic phase of the Anderson model in a random-regular graph, specifically the
degree of ergodicity of the high-energy wavefunctions. We use the multifractal formalism to analyze numerical data for unprecedented large system sizes, obtaining a set of correlated volumes which control finite-size effects. Those volumes grow very fast with disorder strength but show no tendency to diverge, at least in an intermediate metallic regime. Close to the Anderson transitions, we characterize the crossover to system sizes much smaller than the first correlated volume. Once this crossover has taken place, we obtain evidence of a scaling in which the derivative of the first fractal dimension behaves critically with an exponent ν = 1.The talk is based on the following works:
- Correlated volumes for extended wavefunctions on a random-regular graph.
M Pino, JE Roman arXiv preprint. ArXiv:2311.07690 (2023)
- Scaling up the Anderson transition in random-regular graphs.
M Pino. Physical Review Research 2 (4), 042031 (2020)
- From ergodic to non-ergodic chaos in Rosenzweig–Porter model.
M Pino, J Tabanera, P Serna Journal of Physics A: Mathematical and Theoretical 52 (47), 475101 (2019)