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Chinese Journal of Quantum Electronics

Fidelity evolution of quantum state for atom and field in the two-photon process

He An-Zhi

Published Jan 1, 2009• 0 citations
OpenAlex

Abstract

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.

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In this paper,the Tavis-Cummings(TC) model is generalized to simultaneously consider atomic motions and fields via intensity dependent coupling.Evolution of the fidelity of quantum states of entangled two-atom with motion interacting with light field via intensity-dependence coupling is investigated by means of the full quantum theory.The effects on the evolution of the fidelity of quantum states from the initial entanglement factor  of the two-atom and the average photon number n-and field-mode structure parameter p of the field are researched by numerical calculations.The formation rule of quantum echoes of two-atoms is analyzed,and its physical essence is revealed.The results show that period quantum echo of the two-atom is always produced in the case of field-mode structure parameter p=1,independent of light intensity n-and the initial entanglement factor  of the two-atom.Bell-state atoms can produce quantum echo with 2π/p cycle on the conditions of strongly coherent field,via changing the p of from 1 to any value less than 800.When p≥800,no matter what value of  takes,the light field is a vacuum field,weakly coherent field or strong coherent field,the fidelity of quantum states of the two-atom is always 1,that is the first class Bell state-atoms is in the fidelity state continuously.But when the initial entanglement factor  of two-atom is 3π/4,no matter how both values of n-,p are,the fidelity of quantum states of the two-atom maintains 1,namely the two-atom is in the fidelity state of the second class Bell-state continuously.The conclusions show that the extension model has good properties of periodic quantum echoes of two-atom,and provides the theoretical parameters and physical carrier for high fidelity output of entangled two-atoms information and experimental implementation of quantum information processing in the noise environment.

ACTA PHOTONICA SINICA•Jan 1, 2012•1 citation
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.
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.
In this paper the evolution characteristics of the fidelity of quantum information for the V-type three-level atom interacting with number state light field in Kerr medium are investigated. It shows that the periodicity of the evolution of fidelity of quantum information is influenced by the Kerr coefficient, the photon number of the initial field and intensity of light. The evolutions of the fidelity of quantum information are modulated by the initial number state field. The Rabi oscillation frequency and the modulation frequency of fidelity for the field and the system vary with the value of the Kerr coefficient. The evolutions of fidelity of quantum information obviously show the quantum collapse and revival behaviours in the system of atom interacting with light field.
The evolution of quantum information of light field fidelity in the percedure interaction between two atoms and light field under considering atom-atom coupling and intensity-dependent coupling are investigated by mean of full quantum theory and numerical computation method.The results show that the light field fidelity relates closely with intensity of initial light field,coefficient of field-atom coupling,and coefficient of atom-atom coupling.The influence of these factors leads to fidelity oscillation.It is advantageous of improving the light field fidelity if controlling and making intensity of light weak and atom-atom coupling strong.The more stronger initial light intensity or atom-field coupling,the faster the frequency of light field fidelity and the more obvious varying regularity.The fidelity present also collapse-revert when initial light intensity or atom-atom coupling is strong.The light field could keep steady state during strongly coupling between atom and light field.
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.
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.
In this paper,the Tavis-Cummings(TC) model is generalized to simultaneously consider atomic motions and fields via intensity dependent coupling.Evolution of the fidelity of quantum states of entangled two-atom with motion interacting with light field via intensity-dependence coupling is investigated by means of the full quantum theory.The effects on the evolution of the fidelity of quantum states from the initial entanglement factor  of the two-atom and the average photon number n-and field-mode structure parameter p of the field are researched by numerical calculations.The formation rule of quantum echoes of two-atoms is analyzed,and its physical essence is revealed.The results show that period quantum echo of the two-atom is always produced in the case of field-mode structure parameter p=1,independent of light intensity n-and the initial entanglement factor  of the two-atom.Bell-state atoms can produce quantum echo with 2π/p cycle on the conditions of strongly coherent field,via changing the p of from 1 to any value less than 800.When p≥800,no matter what value of  takes,the light field is a vacuum field,weakly coherent field or strong coherent field,the fidelity of quantum states of the two-atom is always 1,that is the first class Bell state-atoms is in the fidelity state continuously.But when the initial entanglement factor  of two-atom is 3π/4,no matter how both values of n-,p are,the fidelity of quantum states of the two-atom maintains 1,namely the two-atom is in the fidelity state of the second class Bell-state continuously.The conclusions show that the extension model has good properties of periodic quantum echoes of two-atom,and provides the theoretical parameters and physical carrier for high fidelity output of entangled two-atoms information and experimental implementation of quantum information processing in the noise environment.