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Chinese Journal of Quantum Electronics

Evolution of the fidelity in the degenerateRaman process

Yanli Zhang

Published Jan 1, 2004• 0 citations
OpenAlex

Abstract

Fidelity is an important concept in quantum optics and information optics, the study on fidelity is meaningful for the development of quantum teleportation and quantum calculation. The properties of the evolution of the fidelity and fidelity amplitude for degenerate Raman process in the presence of the Stark shift were investigated by means of quantum theory, the influence of the Stark shift parameter and average photon number on the fidelity were discussed. Results show that the less the Stark shift is, which will weaken the interaction between the field and atom, and the higher the fidelities of the three systems are. On the other hand, the more the initial photons are, which strengthen the interaction between the field and atom, and the lower the fidelities of the system and atom.

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Fidelity is an important concept in quantum optics and information optics, the study on fidelity is meaningful for the development of quantum teleportation and quantum calculation. The properties of the evolution of the fidelity and fidelity amplitude for degenerate Raman process in the presence of the Stark shift were investigated by means of quantum theory, the influence of the Stark shift parameter and average photon number on the fidelity were discussed. Results show that the less the Stark shift is, which will weaken the interaction between the field and atom, and the higher the fidelities of the three systems are. On the other hand, the more the initial photons are, which strengthen the interaction between the field and atom, and the lower the fidelities of the system and atom.
By considering the dynamic Stark shift,the effects of dynamic Stark shift of level and the squeezed light field factorsγon the fidelity of quantum state are discussed.It is shown that the evolutions of the fidelity obviously exhibit the oscillations of quantum collapse and revival.Taking the Stark shift into consideration,a comparative study of the two processes for the fidelity is presented.The fidelities of the atom,the field and the system are higher than those in the absence of the dynamic Stark shift when manipulating and communicating quantum information.Meanwhile,the periodicities of the fidelity evolutions of atom,field and the system are modulated by the intensity of the initial light field,and the impulse of the oscillation of fidelity for the field become smaller.The energy between field and atom is influenced by the squeezed light field factors.
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.
The evolution process of atomic entangled state is discussed in the interaction of light-field with atoms by use of the complete quantum theory.The influence of multi-parameter on atomic fidelity is studied.Taking advantage of computation,the results show that atoms are always in partly entangled states during the process of interaction atoms with light fields.The evolution properties of fidelity of the atomic quantum state with time appear oscillatory and collapse-revert in a manner similar to Rabi oscillation.Its oscillatory frequency is mainly modulated by the radiation intensity or photon numbers,the coupling intensity between atoms and fight field,the complex probability amplitude of atoms jump,and the complex probability amplitude of annihilate a photon in the light field.And other factors hardly effect on the atomic fidelity.Hence,the entanglement degree and fidelity of atoms could be enhanced or weakened through controlling the three above parameters.