Study Of Two-photon Blockade Based On The Dressed States Method

For the single atom-cavity QED system which couples with a classical light field,the detuning caused by the (?) nonlinearity of the J-C model suppresses the absorption of additional photons when the external field resonates with the dressed states,thereby forming a photon blockade effect.One obvious result of photon blockade is the anti-bunching effect.However,in the process of two-photon resonance transition,both bunching and anti-bunching effects could occur,depending on the coupling strength between the atom and the cavity field,and the driving strength of the classical field.In this paper,the J-C model coupling with an external classical light field is described with the dressed state theory,and the two-photon transition process is studied by truncating part of Hilbert space and effectively intercepting six states.In order to describe the effective dynamics of the system,the specific expression of the main equation of the system is obtained.Then,the frequency shift of the dressed states energy level caused by two-photon resonance transition is analyzed by using the main equation method.Using Fr?hlich transformation,the effective Hamiltonian of the system is given.From the obtained main equation,the first-order correlation functions are calculated separately from different transition paths under steady-state conditions.Then the images are drawn,and the different processes are compared and analyzed.Next,the photon second-order correlation function is calculated,and the images are drawn under different parameters,and the bunching and anti-bunching effects are analyzed as well.The results show that the occurrence of photon blockade effect,or the apparent degree of anti-bunching effect in the process of two-photon transition,is determined by multiple parameters.When the dipole coupling strength g of the atom-cavity field is constant,the driving strength? of the external light field increases gradually,and the system will evolve from bunching to anti-bunching behavior,and the anti-bunching effect becomes more and more obvious with the increase of the driving strength.When the dipole coupling strength is larger and larger,the driving strength required to achieve the anti-bunching effect is much larger.