Generation Of A Single-photon Source Via A Four-wave Mixing Process In A Cavity

Since the concept of light quanta was put forward in 1905, photons, as a basic quantum object, has been active in the research of fundamental physics. Many important fundamental quantum problems, such as the nature of quantum correlation and the test of the EPR paradox, have been investigated via photon experiments. Meanwhile, as an easy-controllable information-carrier and a flying qubit, single photon sources have been widely used in quantum information and quantum computaion, especially quantum cryptography.Currently, there are two main ways to prepare a single-photon source. One way is the parametric down conversion (PDC) and single-photons are generated either by the technique of heralding due to the simultaneity of the photon pairs. The other way is to use single microscopic emitters, such as single atoms, sin-gle molecules and single quantum dots. The disadvantage of the former way is that the photons come randomly, and therefore they are usually not on demand. Preparing a single-photon source via the latter way usually needs exact and com-plicated controlling. The second chapter of this thesis, we propose a scheme for the generation of an efficient and pure single-photon source via a four-wave mixing in a cavity. In our scheme, one just controls the strength of the two input states and the resonance between the cavity and the pump field. We first analytically demonstrate that the four-wave mixing process in our system is equivalent to a two-photon absorption process and single photons will be obtained at the out-put. Then, we make the simulation by the Monte Carlo-Wave Function (MCWF) method, and the numerical result agrees well with the analytical one. In the last section of this chapter, to remove the vacuum state from the source, we optimize our source via the post-process method and the odd cat state input.One of the main applications of single-photon sources is the quantum cryp-tography, or exactly, the quantum key distribution (QKD). The QKD protocols and the available QKD system are mostly based on the point-to-point, or one-to-one network, while the real communication needs one to many, many-to-many network. Therefore, several groups suggested wave division multiplexing (WDM) technique combining with the QKD system. The third chapter first recalls the WDM technique and the quantum key distribution (QKD). Then, we introduce the wave division multiplexing-quantum key distribution (WDM-QKD) system and review two typical schemes of generating a WDM-QKD source. In the sec-ond section, we propose the generation of a quantum optical comb, that is, a coherent multi-wavelength single-photon source by introducing optical comb to our system. This source might be an ideal candidate for the WDM-QKD system.