Manipulation Of Photons Based On Coherent Atomic Ensemble

Manipulation of photons has attracted a lot of interest in the fields of information science and precise measurment. In this thesis, we have investigated the atomic coherence between the two hyperfine ground states based on double-lambda configuration in rubidium ensemble. The utilization of atomic coherence results in reduced absorption and spontaneous emission, as well as enhanced nonlinearity, which make the four-wave mixing (FWM) process based on double-lambda configuration more efficient. These lead to new developments in the research of photonic manipulation based on coherence in atomic ensemble.We have realized the FWM parametric amplification process and FWM generated quantum states process, both of which have attractive properties for novel photonic manipulation technology. The FWM parametric amplification process can provide large nonlinearity and steep dispersion, resulting in optical logic gates using coherent feedback and single-photon level induced all-optical delays at two different frequencies. In the situation of FWM generated quantum states process, as the lights are coupled through atomic coherence between ground states, the near-resonant absorption and the spontaneous emission are reduced. Combined with large optical gain without cavity enhancement, FWM can make the spatial-multi-mode entangled images experimentally available. Four detail projects are listed as follows:1. Based on double-lambda configuration in hot rubidium ensemble, we have experimentally realized nondegenerate FWM parameric amplification process. The two resulted nondegenerate modes have coherence between each other. After the two nondegenerate optical modes been coherently fed back to the double-lambda configuration, with the atomic coherence acting as the mediator, FWM can be enhanced. We can realize an optical "NOR" gate for the feedback-suppressed state and an optical "OR" gate for the feedback-boosted state simultaneously. The logic gates exhibit transition times faster than previously demonstrated in rubidium vapor. Coherent photon conversion between the two logic states is observed in the coherent feedback process.2. In the double-lambda configuration based on hot rubidium ensemble, lights are coupled through atomic coherence, which allows one to reduce near-resonant losses and increase the relevant nonlinearity. Through increasing the power of pump beam and atomic density, the gain due to FWM parametric amplification can be enhanced. In this situation, single-photon level input is able to induce nondegenerate FWM happen, leading to all-optical delays at two different frequencies. These delays have properties with long-time delay, fractional delay that larger than unity, while preserving to a large degree the input pulse shape. Furthermore, the delay time is strongly dependent on the input photon-number state, which enables an all-optical way to do the photon-number resolving detection.3. As FWM generated quantum states process can provide large enough gain without resonant cavity, the spatial-multimode quantum entangled images are experimentally available. We compared two techniques, the quantum noise image technique and the classical noise image technique, to do a parameter estimation of a mask. The conclusion is using the quantum noise image technique has the higher sensitivity.4. We have made progress on the image storage. Two images can be stored and released by the use of gradient echo memory, while to a large degree(88%) preserving the similarity between the input image and released image.