KTH/Nordita/SU seminar in Theoretical Physics

Beyond the rotating wave approximation: effective interactions and quantum phase transitions

by Isabel Sainz (KTH)



We study the distinctive features of quantum dynamics governed by Hamiltonians which do no preserve the total number of excitations. In particular we focus on the physical effects appearing exclusively due to the presence of counter-rotating terms in the Hamiltonians describing interaction of two or more quantum systems. Two interesting in applications limits are analyzed: 1. Weak coupling regime: when the coupling constants is much lower when all the typical system's frequencies. Here we show that a set of effective resonant interactions describes the quantum dynamics. 2. Intermediate regime: when characteristic frequencies of the some interacting subsystems are lower than the coupling constants, but the other are higher. In this case quantum phase transitions naturally arise.