# Mercredi 24 mai 2017

11h00 – 12h00, Amphi 5 du CPT

### Résumé

Quantum trajectories are Markov chains on the space of quantum states that arise as models of repeated measurements of quantum systems. These Markov chains can be defined through non i.i.d. random products of matrices. One of the fundamental questions regarding Markov chains is the characterisation of their invariant measures. Particularly if the Markov chain accepts a unique invariant probability measure, the law of the system state becomes asymptotically independent of the specific initial state. With M. Fraas, Y. Pautrat and C. Pellegrini we recently proved the uniqueness and convergence towards an invariant probability measure over quantum states for quantum trajectories. In this talk, I will present our result and the new state estimation technique we use in the proof. I will also describe what new possibilities in the study of quantum trajectories our new approach opens.

14h00 – 15h00, Amphi 5 du CPT

### Résumé

In this talk I will describe a research
program devoted to the characterization of the
absolutely continuous spectrum of a self-adjoint operator H in terms of the transport
properties of a suitable class of open quantum systems canonically associated to H.
The talk is based on joint works with L. Bruneau, Y. Last and C-A. Pillet.

14h00 – 15h00, Amphi of CPPM

### Axion Phenomenology from Unquenched Lattice QCD

#### Guido Martinelli (Università Roma “La Sapienza”)

The properties of the QCD axion can be studied from the dependence of strong interactions on the $\theta$-parameter. We present a study of the moments of the topological charge for temperatures up to around 600 MeV, obtained by lattice QCD simulations with 2+1 flavors at the physical quark masses. Our numerical results for the topological susceptibility, when compared to the instanton gas calculation, differ both in size and in the temperature dependence. We discuss the implications of these results for axion phenomenology, a comparison with other more recent studies and the prospects for future investigations. We also present some new results recently obtained at finer lattice spacing using metadynamics to reduce the systematic error due to the topological freezing.

15h30 – 16h30, Amphi 5 du CPT

### The Hamiltonian Description of Matter

#### P. J. Morrison* (Department of Physics, University of Texas at Austin)

Conventional field theories, classical versions of quantum field theories, possess a canonical structure in both their action functional and Hamiltonian descriptions. Alternatively, field theories that are typically used to describe the dynamics of matter, classical models developed for classical purposes, such as fluids, magnetofluids, plasma kinetic theories etc., possess structure with special properties. Loosely speaking, matter models correspond to flows on Poisson manifolds as opposed to more conventional symplectic manifolds, and this is manifested in the Poisson bracket having noncanonical form. In this talk I will survey this noncanonical structure and describe how it has been and continues to be used in applications.

*morrison chez physics.utexas.edu

mai 2017 :