Research On The Counter Rotating Wave Effects

Recently,the researches on the atom-photon interaction have been pushed into the ultrastrong coupling regime,where the coupling is so strong that the rotating wave approximation(RWA)is no longer valid.In this regime,the counter rotating wave(CRW)interaction cannot be ignored and it will lead to new phenomena.In this thesis,the counter rotating wave effects in the ultra-strong coupling regime are investigated The main achievements include:1.We design a circuit quantum electronic dynamics(QED)system with a tunable coupling between an artificial atom and a superconducting resonator while keeping the cavity frequency and the atomic frequency invariant.By controlling the time dependence of the external magnetic flux,we show that it is possible to tune the interaction from the extremely weak coupling regime to the ultrastrong coupling one.Using the quantum perturbation theory,we obtain the coupling strength as a function of the external magnetic flux.We also find that our system is remarkably insensitive to the main noises,which shows its reliability in the fields of quantum simulation and quantum computing.In particular,it is worthy to point out that the best performance of our qubit both in terms of tunable coupling and coherence is achieved when the penetrating fluxes through two SQUIDs are in a restricted range near?0/2.2.We study the single-photon scattering on a system composed by a coupling cavity array with a two-level atom in the center cavity,which,by varying two outside coupling parameters,corresponds to a model from a supercavity QED to a waveguide QED with counter-rotating wave(CRW)interaction.By applying a time-independent scattering theory based on the bound states in the scattering region,we find that the CRW interaction obviously changes the transmission valley even in the weak atom-cavity coupling regime;In particular,the CRW interaction leads to an inelastic scattering process and a Fano-type resonance,which is directly observed in the crossover from the supercavity QED case to the waveguide QED case.3.We propose a scheme to enhance the photon generation from the vacuum by a bang-bang(switching on/off)control of the CRW interaction.By developing a pruning greedy algorithm to search the optimal control sequence,we find that the maximum photon number obtained for a given time period in our scheme can be dramatically increased up to several orders than that from switching on the CRW interaction.