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ACTA PHOTONICA SINICA

Evolution of the Field Entropy and Preparation of Quantum States in the Control of Atomic Motion and Fieldfrequency Variation

刘小娟 LIU Xiaojuan, 刘一曼 LIU Yi-man, 刘敏 Liu Min

Published Jan 1, 2011• 1 citation
Publisher

Abstract

In the rotating-wave approximation,the evolution of the field quantum entropy in the system that consists of a two-level atom interacting with a single-mode field was studied,considering the atomic motion and the field frequency varying with the time in the form of sine-function at the same time.In two cases of neglecting atomic motion and considering atomic motion,figures of the time evolutions of the field entropy were plotted respectively using numerical calculations.Influences of the atomic motion,the field-model structure parameter,amplitude and angular frequency of the field-frequency variation on the field entropy were also discussed.The atom-field entangled states,field fock states and atomic high fidelity states were prepared by analytic method according to the decomposition theorem of Schmidt,and the related system parameters of these quantum states operation were acquired.The results show that:the time evolution behavior of the field entropy is modulated by the frequency variation of field;the interaction between the field and atom will weaken with the increase of the amplitude of variation of the field frequency;the period of the field entropy agrees with the period of field-frequency variation;the atomic motion will result in the period of the field entropy doubled;the evolution of the field entropy is related to the parity of field-mode structure parameter;the approximate EPR states of field-atom can be prepared periodically whether the atom moves or not.

DOI
10.3788/gzxb20114003.0458

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In the rotating-wave approximation,the evolution of the field quantum entropy in the system that consists of a two-level atom interacting with a single-mode field was studied,considering the atomic motion and the field frequency varying with the time in the form of sine-function at the same time.In two cases of neglecting atomic motion and considering atomic motion,figures of the time evolutions of the field entropy were plotted respectively using numerical calculations.Influences of the atomic motion,the field-model structure parameter,amplitude and angular frequency of the field-frequency variation on the field entropy were also discussed.The atom-field entangled states,field fock states and atomic high fidelity states were prepared by analytic method according to the decomposition theorem of Schmidt,and the related system parameters of these quantum states operation were acquired.The results show that:the time evolution behavior of the field entropy is modulated by the frequency variation of field;the interaction between the field and atom will weaken with the increase of the amplitude of variation of the field frequency;the period of the field entropy agrees with the period of field-frequency variation;the atomic motion will result in the period of the field entropy doubled;the evolution of the field entropy is related to the parity of field-mode structure parameter;the approximate EPR states of field-atom can be prepared periodically whether the atom moves or not.
By using the multiphoton Jaynes-Cummings model,the dynamical properties of the field entropy in the system that consists of a two-level atom interacting with a single-mode field via multiphoton transition are studied.The frequency of the field varying with time in the form of u sin wt has been considered.The results show that the time-evolution behavior of the field entropy is modulated by the frequency variation of field using the numerical.The modulation intensity is enchanced as the amplitude u of frequency variation of field increases.When the amplitude u of the time varying fields is larger than a fixed value,the time-evolution behavior of the field entropy will display periodic oscillation behavior.Its oscillation period agrees with the period of frequency varying.It shows that the evolution of field entropy is influenced by the frequency parameters w and u of the field varying with time.
The field entropy evolution in a system which is composed of two moving entangled atoms interacting with the squeezed coherent state is studied by means of the full quantum theory.The influences of the coherent amplitude factor,the squeezing factor,the atomic motion and the field-model structure parameter on the field entropy are discussed.The result shows that the atomic motion leads to the periodic evolution of the field entropy.An increase of coherent amplitude factor weaken the degree of entanglement between the atoms and the light field.However,an increase of squeezing factor of light strengthen the degree of entanglement between the atoms and the light field.With increasing atomic speed or field-model structure parameter,the evolution period of the field entropy becomes shorter,and the degree of entanglement between field and moving atoms becomes smaller.
Under on-resonance condition and far-off-resonance condition, at first, we used the full quantum theory to educe the wave function of the system. Secondly, we utilized entropy theory, in virtue of the wave function, to discuss the effects of the initial mean photon number?the atomic motion and the field-mode structure on the evolution of the field(atom) entropy at length in the interaction of a three-level moving atom with field. The results show that the atomic motion leads to the periodic evolution of the field entropy, this periodicity does not depend on the statistical distribution and the intensity of the initial field mode, but depend on the atomic motion and the field-mode structure parameters ep. Both on-resonance condition and far-off-resonance condition, when making a suitable choice for parameter ep (this choice is experimentally possible),we can get pure field state for a long time.
We investigate the preparation and the control of entangled states in a system with the two-mode coherent fields interacting with a moving two-level atom via the two-photon transition. We discuss entanglement properties between the two-mode coherent fields and a moving two-level atom by using the quantum reduced entropy, and those between the two-mode coherent fields by using the quantum relative entropy. In addition, we examine the influences of the atomic motion and field-mode structure parameter p on the quantum entanglement of the system. Our results show that the period and the duration of the prepared maximal atom-field entangled states and the frequency of maximal two-mode field entangled states can be controlled, and that a sustained entangled state of the two-mode field, which is independent of atomic motion and the evolution time, can be obtained, by choosing appropriately the parameters of atomic motion, field-mode structure, initial state and interaction time of the system.
According to the complete quantum theory,the quantum field-entropy evolution properties in a system of the two coupled two-level atoms interacting with a single-mode odd-coherent state light field are studied.Through numerical calculation the influence of the initial mean photon number n_0,the coupled intensity g of interaction between the single-mode field and atoms,and the coupled intensity g_a of dipole-dipole interaction between the two coupled atoms on the quantum field-entropy evolving while the initial state of the light field is a single-mode odd-coherent and the two coupled two-level atoms lay in different Einstein Poclolsky Rosen(EPR) entangled state respectively.The results indicate that the time evolving of quantum field-entropy is closely related to the initial atoms state.The quantum field-entropy evolution can display the phenomena of entanglement and disentanglement while they are periodically under the condition of intensity field(n_01). Meanwhile the phenomena of quantum interference is also discovered.The periodicity of the quantum field-entropy anomalous oscillation decreases gradually with the increasing of g values.When g_a is an especial constant,it is shown that the phenomena of period collapse-reversion can present.
The field entropy evolution of a system which is composed of two moving entangled atoms interacting with the Schrdinger cat state is studied by means of the full quantum theory.The influences of the strength of light field,the phase angle between the two coherent states,the atomic motion and the field-model structure parameter on the field entropy are discussed.The result shows that the atomic motion leads to the periodic evolution of the field entropy.When the strength of light field is small,the degree of entanglement is maximum in a system of the moving atoms interacting with an odd coherent state;it is intermediate for a system of the the moving atoms interacting with Yurke-Stoler coherent state,and it is minimum in a system of the moving atoms interacting with an even coherent state.When the strength of light field is large enough,the degrees of entanglement between the moving atoms and the three different states of the light fields become equal,and the properties of field entropy evolvement are also same.With increasing atomic speed or field-model structure parameter,the evolution period of the field entropy is shortter,the degree of entanglement between field and moving atoms is weaker.