Application Of Two-level System In Quantum Battery

The interaction between light and matter is one of the most fundamental physical processes.Among various models involving the interaction between light and matter,the semi-classical Rabi model and the quantum Rabi model are two basic and important models,which have been widely used in the research and control of various quantum systems,including nuclear magnetic resonance,cavity quantum electrodynamics(QED)and circuit QED.The semi-classical Rabi model describes the interaction between a quantum bit and a classical field of a single mode.As a small quantum mechanical system for temporarily storing energy,the quantum battery can be used as a medium to transfer energy from the source of energy to the source of energy consumption.It has attracted wide attention because it can enhance charging power by using quantum effect and requires less charging time and has better performance compared with classical batteries.Originally,the concept of QB was originally proposed as a two-stage system for temporarily storing energy transferred from an external field.In the quantum battery,the charging process means that the two-level system will change from a low energy state to a high energy state,while the discharge process means that the two-level system will change from a high energy state to a low energy state.In a quantum battery,the two-level system can be used as a device to store energy,and the external light field can be used as a charger to charge the quantum battery.The semi-classical Rabi model can be regarded as a description of the quantum battery system.Recently,people are more and more interested in the analysis of quantum battery performance,and in Dicke battery system,it has been proved by theoretical research that multi-qubit entanglement can improve the charging power and accelerate the charging time.The quantum relationships between atoms depend on the interactions between atoms.In the case that there is no interaction between the atoms constituting QB,the charging of QB can reach the state of full charge,and the analytical solution of the optimal driving frequency of the harmonic charger is obtained.We introduce the dynamic process of charging a quantum battery composed of N two-level atoms with the harmonic drive field as an energy charger.Compared with previous static charging studies,the quantum battery without interacting atoms can be fully charged by selecting the best driving frequency.After charging,each two-level atom ends up in an upper energy state.Therefore,the use of harmonic field as charging field has a great improvement compared with the previous static charging field.When we take into account the repulsive interactions between the atoms that make up QB,we find that the atoms that make up QB charge faster than if there were no interactions between the atoms that make up QB.However,with the increase of coupling strength,the optimal charging period of the attractive interacting QB is longer than before.When there is a strong attractive interaction,a quantum phase change occurs,accompanied by the degeneracy of the ground state energy.We find that the maximum stored energy of the atom in the degenerate state decreases from the value of full charge,which indicates that the gap state plays a negative role in the charging process.This is due to the degeneracy of energy levels between the ground state and the excited state,and the excited state is not conducive to the improvement of energy during charging.The repulsion interaction between multi-atoms can shorten the charging cycle and improve the complete charging efficiency of the battery.When we consider charging in an open system,we eliminate the influence of the evolution of the external environment by using a dynamic equation that includes the influence of the surrounding environment on the state of the system.We find that for a single atom,the steady-state storable energy is relatively high when the dissipation is smaller and the driving amplitude is larger.When considering charging multiple non-interacting atoms,there is an optimal number of charging atoms as N increases.