September 11 2017

26.09.-27.09.: Visit of Haggai Landa

Haggai Landa (IPhT, CEA Saclay, France) visits us from Tuesday, September 26th to Wednesday, September 27th. On Tuesday, September 26, at 1 pm in room E.04, he will give a talk on "Ultracold active matter".


Ultracold active matter
The "active" aspect of active matter, from the statistical-physics perspective, is the breaking of detailed balance in the microscopic dynamics. Hence, modelling of nonequilibrium microscopic conditions and their implications, in particular on the macroscopic dynamics (such as the appearance of emergent equilibrium), is now active as a field of research. Surprisingly, recent theory studies and experiments with ultracold ions trapped in vacuum, make contact with these questions;
(i) A fundamental model of transport in a noisy environment is that of the Brownian ratchet, or Brownian motor. It models the emergence of nonvanishing currents in a noisy system despite the vanishing of all mean forces. Crucially based on symmetry breaking, it is a basic model for some of the physics underlying, e.g., biological molecular motors. I will discuss self-organized ion crystals featuring transport of ratchet-like discrete solitons. The rate and direction can be described as a Kramer's escape applied to a collective coordinate, with an emergent effective temperature.
(ii) In recent years ion traps are microfabricated with electrode-ion distances down to tens of micrometers, whence ion dynamics are ruled by an interplay of nonlinearity, chaos, stochastic heating and laser cooling. A detailed understanding of these dynamics is interesting for practical and theoretical reasons, and at the same time, the ion trap offers a system with excellent experimental accessibility to nonequilibrium, microscopic stochastic processes. I will present a study of the structure of phase space and a unified analysis of the Hamiltonian and stochastic dynamics in terms of action angle coordinates.

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