Propagation And Storage Of Squeezed Vacuum In EIT Atomic System

Based on the atomic interference phenomenon, the phenomena such as lasing without inversion (LWI), coherent population trapping (CPT) and so on can be realized. Especially, electromagnetically induced transparency (EIT) is the most important coherence phenomenon. EIT is one interference phenomenon in which the multi-level atoms driven by a strong coherent field is transparent for a probe field. Since the EIT phenomenon has been observed by Harrris, many researches have been explored. Recently, EIT has been developed into an important technique, which is widely used in slow propagation, storage of the optical quantum information, optical switch and quantum entanglement, etc. In this thesis, we mainly discuss the propagation and the storage of the quantum probe field in the EIT atomic system. The thesis is organized as follows:In chapter 1, the conception and the development for the EIT phenomenon has been reviewed. The various applications and present status of the EIT were presented.In chapter 2, the interaction between the fields and the atoms by using semi-classical and quantum theories has been introduced, respectively. We choose a three-levelΛatomic system as an example, the absorption and desperation of a probe field as well as its low group velocities are exhibited. Besides, the EIT phenomenon has been explained by using dark-state. In chapter 3, the conception of dark-state polariton is introdued, by which the realization of storage of optical quantum information has been interpretated.In chapter 4, the polariton picture in the interaction of three multi-mode quantized fields with a five-level triple-Λatomic ensemble driven by three classical control fields is derived. The storage (or retrieval) of the quantum state of light in (or from) the atomic polarization state is investigated: several entangled Fock states of light can be created in the process of retrieving photon state from atomic ensemble by modulating the control fields. Particularly, this system can be used to generate a class of W states, which have a potential application in quantum information processing.In chapter 5, we investigate the propagation and storage of a squeezed vacuum as the probe light in a collection of N four-level tripod configuration atoms under the condition of single or double electromagnetically induced transparency (EIT). The squeezing of the probe light is well preserved in both the single transparency channel and the double transparency one. On the other hand, the effects of the ground state dephasing rates on the propagation and storage of the squeezed vacuum are investigated. It is found that the maximum squeezing at the transparency points is suppressed by the dephasing rates in single or double EIT. Meanwhile, the mapping of the squeezing of the probe light onto the atomic ground coherences or onto the two atomic dark-state polaritons is also studied. In the absence of the Langevin atomic noise, the quasi-ideal squeezing transfer between the squeezed vacuum and the atomic ground coherences or the dark-state polaritons can be realized in such a system. When considering the Langevin atomic noise, the quantum characteristics of the atomic coherences at resonance are submerged by the Langevin noise, while in the scenario of the dark-state polariton, it is found that squeezing transfer onto one polariton is damaged, but the squeezing transfer onto the other polariton survives even in the presence of the Langevin noise.In chapter 6, the interaction of a collection of N four-level tripod configuration atoms with two orthogonally polarized probe fields is also investigated. Under the condition of electromagnetically induced transparency (EIT), we calculate the squeezing and entanglement spectra of the output probe fields. By analyzing the output spectrum, we find that the squeezing and entanglement of the probe fields can be well-preserved after passing through the optically thick medium. Additionally, the effects of the ground state dephasing rates of the atoms on the entanglement and squeezing of the output two-mode squeezed fields are investigated. It is shown that the dephasing rates will degrade the entanglement and squeezing, and these quantum properties can be lost when the dephasing rates increase up to a certain value. This will be useful in the quantum computation and quantum communication.