Research On Hyperradiance And Entanglement In Qubit Cavity QED System

In the development of quantum mechanics,people combined quantum theory and information science to develop a new research field,quantum information science and technology,including quantum communication,quantum metrology,and quantum cryptography.In quantum information science and technology,cavity quantum electrodynamics(QED)system has the advantages of long coherence time,high integration and strong stability,which are used to study the nonclassical effects such as photon blockade and collective radiation of the system.These novel results can be extended extensively and have good application prospects in quantum computing,quantum information and other fields.Since the proposed of black body radiation,energy quantization,wave-particle duality,photoelectric effect and other theories,people have carried out a lot of research based on quantum.Quantum state is the basis of quantum information transmission,and it is an indispensable carrier of quantum communication in the process of quantum teleportation,dense coding and quantum cloning.Therefore,the preparation and manipulation of quantum state has become the focus of attention.A lot of research has been done in nuclear magnetic resonance,ion trap,etc.At present,the preparation of photon states has been achieved by using methods such as the nonlinear effect between photons and optical devices.Magnon has the characteristics of long lifetime and high spin density,and has always been an important research object of macroscopic quantum effects.The preparation of arbitrary magnon states has also become the focus of current study.In this paper,based on the qubit-cavity QED system,we have studied the quantum statistical properties of light,the enhancement of collective radiation,the entanglement between qubits,and the preparation of arbitrary magnon states.The details are as follows:First,we theoretically study the electromagnetic field controlled photon correlation and radiation properties in a two atoms cavity quantum electrodynamics(QED)system with different atom-cavity coupling strengths.Here,two identical threelevel ladder-type atoms are embedded in a single mode cavity,driven by a weak probe field and a strong control field simultaneously,forming a typical ladder type electromagnetically induced transparency(EIT)configuration.In the presence of the control field,the system dressed states are significantly changed and additional excitation pathways appear in one and two photon spaces,respectively.When the resonant single-photon and two-photon excitation are achieved,the third-order correlation function g(3)(0)can be reduced to 10-3,which means the strong two photon blockade.At the same time,significantly enhanced mean photon number and superradiance or hyperradiance behavior of two atoms can be achieved in such a system,which can be used as a converter of a weak coherent field to two correlated photons.Then we propose a novel physical mechanism for realizing dipole blockade without the dipole-dipole interaction by using the cavity QED,and two qubits are antisymmetrically coupled to each other.Under the strong coupling regime,the symmetric Dicke state is decoupled with other states in the one-photon space.By adjusting the relative decay strengths of the qubits and cavity field,the population of the doubly excited state is transferred quickly to the cavity mode.Thus,the symmetric Dicke state is significantly populated,resulting in the dipole blockade behavior.Moreover,this effect can be detected by measuring the second-order photon correlation function.Using the mean field method,we also show strongly entangled two qubits can be achieved under the conditions of g02≥2(?)ηκ and(?)η>>γ.Finally,we discuss a scheme to realize the preparation of arbitrary magnon states,which made up for the shortcomings in the preparation and manipulation of magnon states in the current research,and also realized the strong entanglement between magnons and qubits.Based on the qubit and Yttrium Iron Garnet(YIG)hybrid cavity system,the qubit can couple to YIG through the excitation of the virtual photon in the cavity.When the qubit is initially prepared in the excited state,the perturbation effect of the pump field yields the energy level crossings in the energy spectrum transform into energy level avoiding crossings,which leads to the phenomenon of the quantum beat.At the silent point of the quantum beat,the equal-weight superposition of the magnon state can be realized,so as to realize the preparation of arbitrary magnon state,including the realization of cat state.In addition,we also found that in such a hybrid cavity QED system,there is strong entanglement between the magnon and the qubit,and the concurrence exceeds 0.9.