| In the present, the problems of exchange, transmission and maintain of quantum entangled information is always one of the foremost and important research topic in the regime of quantum optics and quantum informatics, its achievements is of broadening application prospects and great application values in the fields of Hi-technologies such as quantum optics and quantum informatics. In this thesis, the complete quantum theory is utilized to study the problems of exchange, transmission and maintain of quantum entangled information systematically within the various systems of atoms-cavities-fields interaction, and a series of new important research results is obtained that is rather different from the current scientific reports. The main research results are as follows:1. By using numerical calculating method, the time evolution characteristic of quantum entanglement degree of different field-atom interaction systems are studied in detail, such as the two coupled two-level atoms with dipole-dipole interaction interacting with a single-mode odd coherent state light-field, interacting with a singled-mode even coherent state light-field, and interacting with two state superposition-a single-mode Schr?dinger-cat state light-field, respectively. It is showed that the time evolution properties of quantum entanglement degree of field-atom system are decided by such major factors as the initial mean photon-number of light-field, the coupled intensity between field-atom, the coupled intensity between atom-atom, the frequency detune, and the initial state of atom. In general, the time evolution of quantum entanglement degree can present the property of oscillation; under the condition of initial intensive-field, the phenomena of entanglement and disentanglement present periodically and alternatively, and the phenomenon of quantum interference follows in the same time; with the increasing of coupled intensity between field-atom, the anomalous oscillating period of quantum entanglement degree decreases gradually; if the coupled intensity between atom-atom is some certain and fixed value, the time evolution of quantum entanglement degree can display the phenomenon of periodical collapse-reversion, while the dipole-dipole interaction between atom-atom is weaker the time evolution characteristic of quantum field-entropy is similar to the situation of one-photon Jaynes-Cummings model, while it is strong enough that is very similar to the situation of two-photon Jaynes-Cummings model. From what had said above, we can see that it is possible to make atom and light-field staying in the maximum quantum entanglement state long time, which is benefited for the transmission of quantum entangled information.2. The physical model of interaction system composed of multi-independent atom-cavity-field is established. The complete quantum theory is used to study the processes of M two-level atoms interacting with M single-model (or M multi-model) light-field with intensity-dependent coupling through one-photon (or any multi-photon) interaction, and M pairs of coupled two-level atoms interacting with M single-model (or M multi-model) light-field through one-photon (or any multi-photon) interaction, respectively. The general expressions evolving with time of the combined state vector of the systems mentioned is given in different situations, and the conditions to realize exchange and transfer of quantum entangled information by using the interaction process among atom-cavity-field are found out. It is found that the quantum entangled information of light-field can transfer to atom, by controlling the interacting time of atom-cavity-field system and the flying velocity of atom through cavity, and by the interaction between the atom stayed in the ground state initial and the cavity-field to be stored the quantum entangled information initially, for the different model the atom flying out of the cavity sometimes need to be detected; contrary, the quantum entangled information of atom stayed in the entangled state initially can also transfer to the cavity-field which is initially stayed in the vacuum state. Meanwhile, the ground atom as flying qubit can also transfer the quantum entangled information from one cavity to another. Otherwise, the initial quantum entanglement information possessed by cavity-field or atom can be maintained completely or partially, by controlling the interaction time between atom and cavity-field. For the different atom-cavity-field interaction system, the factors of condition to affect realizing exchange, transmission and maintain of quantum entangled information are rather different. For example, the quantum entangled information can be exchanged, transferred and maintained completely by controlling the frequency detuning, but the dipole-dipole interaction between the two coupled two-level atoms can lead the quantum entangled information to transfer and maintain incompletely. It can be seen that when the atom stayed in the ground state initially and flying at a fixed velocity passes through the cavity-field, it can possess the quantum entangled information of light-field; contrary, when atom stayed in quantum entangled state initially and flying at a fixed velocity passes through the vacuum state cavity-field, it can release its quantum entangled information to the cavity-field, so one can realize the exchange and transmission of quantum entangled information of atom-cavity-field system. By utilizing the properties of atom picking up and giving off quantum entangled information, one can further realize the transmission of that from one cavity to another.3. The synthesized physical model consisting of coherent cavity-fields and coherent atoms is proposed, the processes of coherent atom-beam interacting with a single-model (or multi-model) coherent state light-field through one-photon (or any multi-photon) resonant and nonresonant interaction is researched, and the characteristic of time evolution on the system of coherent atom-beam interacting with coherent cavity-field is given by using time evolution operator. The results show that the cavity-field entangled state and the atom entangled state can convert periodically each other in the process of cavity-field interacting with atom, and this can realize the exchange and transmission of quantum entangled information. It is pointed out that transform period mentioned above is closely related to the following factors, such as the coupled-interacting between atom and cavity-field, the interacting time t, the complex probability amplitude Aξ,kof atomic operator, he complex probability amplitude Aη,k of photon annihilation operator, the photon-number N j, k and n j, k of interaction of each model light-field at initial time, and the total longitudinal mode number q, and so forth. It is also found that in general case, the condition of exchange and transmission of quantum entangled information are related to the circular frequencyωa,k of atomic transition and its relative phaseξ, to the circular frequencyωf ,k of light-field and its relative phaseη, and to coupled-intensity g and interaction time t between the cavity-field and atom, especially when atom interacting with cavity-field resonantly, the conditions mentioned are related to the parameter g and t too. Therefore the general characteristic of transferring the quantum entangled information is revealed in the process of coherent atom-beam interacting with coherent cavity-field. Under the proper condition, the initial atomic entangled state and the cavity-field entangled state cab be also maintained. So the results of incoherent interaction are only the specific examples of these universal results under different conditions.4. Considering nonlinear optical effects, the combined system state vector is solved exactly, which is made up of multi-atoms interacting with multi-cavity-field and evolving with time. By utilizing the complete quantum theory and numerical calculating method, that the Kerr effect, Stark effect and the imaginary light-field effect have important influences upon the periodical exchange and transfer of quantum entangled information between atom and cavity-field are further studied systematically. It is found that①. Kerr media have no any influence upon the entangled state which is made of initial vacuum state cavity-field or entangled superposition state of the lowest Fock state, for the general Fock state n k( n k≠0), Kerr effect can change the phase and period of transferring quantum entangled information, and the intensive Kerr effect is, the shorter converting period, vice versa. So one can control the converting rate of exchange and transfer of quantum entangled information by changing the intensity of Kerr effect. Besides, when considering Kerr effect, the phase change is also related to the photon-number n k(k=1,2,3,…,M) within cavity.②. Stark effect and initial intensity of light-field have direct influence on exchange and transmission of that, the quantum entanglement degree of light-field can increase with increasing of initial light-field intensity, the quantum entanglement degree of light-field can also present the phenomenon of collapses-revivals periodically under the condition of intensive field, the greater the Stark drift, the faster the oscillation of quantum entanglement degree of light-field. So, it is show that the time stability of quantum entanglement degree of light-field is broken.③.The Rotating-Wave Approximation(RWA) has no any influences upon the exchange, transmission and maintain between atomic entangled state and cavity-field entangled state, but the imaginary light-field effect have evident influences upon the process of entangled state converting between cavity-field and atom under the condition without RWA. After the entangled information of cavity-field transmits to atom, it can not be restored to the initial vacuum state, and its phase is changed and many disturbance items appear in the processes of transforming and maintaining entangled state.
|
PDF Full Text Request