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Chinese Journal of Quantum Electronics

Fidelity of two-level atom's quantum states in radiation field

Xie Li-Jun, Deng-Yu Zhang

Published Jan 1, 2008• 0 citations
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Abstract

The interaction between radiation and two-level atom was investigated by semi-classical theory and quantum theory respectively.The fidelity of the two-level atom's quantum state was written out, The influences of the radiation intensity in the case of semi-classical theory and the photon number of the radiation in the case of quantum theory on the fidelity were discussed for different atomic initial states.It is found that the fidelity of quantum state is independent of radiation intensity when the atom is initially in a superposition state and the atom interacts resonantly with the radiation field in semi-classical theory. The atom's quantum fidelity evolves periodically with time,and its frequency is modulated by radiation intensity.Furthermore,it can effectively change quantum information fidelity when the appropriate detuning is selected.

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The interaction between radiation and two-level atom was investigated by semi-classical theory and quantum theory respectively.The fidelity of the two-level atom's quantum state was written out, The influences of the radiation intensity in the case of semi-classical theory and the photon number of the radiation in the case of quantum theory on the fidelity were discussed for different atomic initial states.It is found that the fidelity of quantum state is independent of radiation intensity when the atom is initially in a superposition state and the atom interacts resonantly with the radiation field in semi-classical theory. The atom's quantum fidelity evolves periodically with time,and its frequency is modulated by radiation intensity.Furthermore,it can effectively change quantum information fidelity when the appropriate detuning is selected.
The interaction between radiation and two-level atom was investigated by semi-classical theory in this paper. The fidelity of the two-level atom’s quantum state was written out. The influence of the radiation intensity on the fidelity was discussed by using numerical calculation. It found that the evolvtion of atom’s quantum fidelity periodically, and its frequency was modulated by radiation intensity. Furthermore, the appropriate detuning was selected,and it can effectively change quantum information fidelity.
By means of numerical methods,the fidelity of the system of a fock state field interacting with the two two-level atoms have been studied.The effects of cavity-atoms detuning,photon number and manipulation of the atom on fidelity of the system are discussed.The results show that the information is undistorted completely in the initial moment in the absence of manipulation of the atom.Moreover the frequency of the oscillation,the peak and the period of fidelity of the system can be controlled by cavity-atoms detuning,photon number and manipulation of the atom.The Information is distorted in the initial moment in the presence of the manipulation of atom.Fidelity of the system can be controlled by the manipulation of the classical filed.
A model is built when the two two-level atoms is in thermal radiation field environment.By means of the density rectangular method,two two-level atoms'reducible density rectangular array is obtained when atoms by dipole-dipole interaction are put in a thermal reservoir.The problem of fidelity of two-level atoms is studied which are put in the strongly thermal radiation field.It is shown that the two two-level atoms initially situated in different coherent superposition states,quantum information may lose fidelities partly or may not lose fidelities during evolution in transmit process.The initial states may influence the losing fidelities speed obviously.
By means of numerical methods,we studied the fidelity of the system which contained a moving two-level atom and the binomial light field.The impact of different initial states is discussed to the fidelity of quantum states.The result showed that the velocity of atom effect the oscillation period of the fidelity,and different initial state of atom and the optical field parameters on the fidelity have a bigger influence.When the atom is in superposition state and the field has a bigger initial average number of photons the fidelity of the system has a higher value.
The time evolution properties of the quantum fidelity in a system of multi-mode coherent light field resonantly interacting with a two-level atom via any Nj-degenerate N∑-photon transition process are studied by the fully quantum theory and numerical calculations. The analytical expressions of the quantum fidelity of field and atom, and the numerical calculation results for three-mode field interacting with the atom are obtained. Our attention focuses on the discussion of the influences of the initial average photon number, the atomic distribution angle, the phase angle of the atom dipole, the field excitation angle, and the atomic degeneracy on the evolution of the quantum fidelity. The results obtained from the numerical calculation indicate that the above factors lead to the quantum fidelity changing with oscillation behavior. The quantum fidelity of field and atom will drastically decrease as the initial light increases, which is correlated sensitively with the fidelity. The speed change of quantum fidelity is strongly dependent on the atomic degeneracy and the intensity coupling between atoms and fields. The value and frequency of the quantum fidelity change lightly with the atomic distribution angle and the angle of light field excitation as well. The phase angles of the atom dipole almost have no influences on the quantum fidelity of field and atom. According to these properties of the quantum fidelity, we can control the speed and value of quantum fidelity in the system by these constraint conditions.