PRIX DES TROIS PHYSICIENS 2024 - YVES POMEAU - Statistical Physics and Quantum Mechanics

Yves POMEAU

Wednesday, January 24, 2024
1:30 p.m. — ConfIV (E244)

Quantum Mechanics is understood as a statistical/probabilistic  theory describing a non-deterministic evolution of physical objects. This seems to be formally opposite to the formulation of the theory with explicit first order in time equations, Schrodinger or Dirac. This apparent contradiction disappears if one takes into account that there are infinitely many degrees of freedom in the dynamics as for instance in the case of an atom interacting with the EM field in an unbounded medium. This causes a non deterministic evolution, as for instance in the case of an atom initially in an excited state and decaying later by emitting a photon. I'll show how to describe this non deterministic dynamics in the case of an atom kept more or less permanently in an exited state by irradiation with a classical resonant field. This evolution is precisely described by a Kolmogorov equation relying on the widely different time scales involved. This gives a method allowing to show precisely the irreversible character of the emission process (or quantum jump).