Preparation And Application Of Multi-photon States

Quantum information science attracts much attention recently. In the past decade, with the development of technology, people have developed the theoretical work to experimental work. As the foundation of quantum information, the preparation of two-particle and multi-particle entangled states is urgently needed. To date, many systems have been suggested to prepare entanglement, such as linear optical system, cavity-quantum-electronics-dynamic system, nuclear magnetic resonance, ion-trap, quantum dot and superconductor josephsen junction. Among them, linear optical system has more advantages: photons as the information carrier can be easily transformed, single bit operation can be performed easily and good resistance to environment fluctuation. Many theories based on two particles have been realized based on linear optical system, such as state preparation, single qubit operation and two-qubit nonlinear operation.On the other hand, multi-photon high dimensional system has more advantages than two-photon system in the field of quantum information and quantum computation. People have developed the linear optical system to multi-photon high dimensional system, and have made some progresses in multi-photon high dimensional system, while the difficulties arose along with the photon number increasing. Much groundwork, including multi-photon preparation and state measurement, has not been well studied and has no good reliable ideas. These are the reasons we concentrate on the subject of multi-photon state preparation and its applications. We get some valuable results:1. Providing a promising method to prepare multi-photon state.Preparation of multi-photon state plays a role in the process of quantum information. To data, the only way to prepare multi-photon state is using interference and can achieve only a few types of photon state. Here we provide a promising method using same mode multi-photon state to prepare arbitrary polarized multi-photon state. Our method dose not need optical interferometer and has good stability. Many important states such as W state, GHZ state and their superposition can be easily achieved. We also give some experimental realization for this work. 2. Experimental demonstration of controllable temporal distinguishability for three photon state using two pieces of down-conversion srystals.The distinguishability of photons reduces the purity of multi-photon state and the visibility of multi-photon interference. There should be a good way to quantify the distinguishability of photons. Because of the difficulty of multi-photon preparation, there has no report about completely temporal distinguishability of multi-photon states. Here we use two pieces of down-conversion crystals and achieve a temporal controllable three photon state, and demonstrate a completely controllable temporal distinguishablity. We also give some valuable experience about the stimulated emission in our experimental system.3. Demonstration of three photon de Broglie wavelength using projection measurementThe experimental progress on multi-photon de Broglie wavelength always excites scientists because of its precise phase measurement. The usual way to demonstrate multi-photon de Broglei wavelength is to use maximum entangled multi-photon state called NOON state, and is difficulty to realize experimentally. Here we using projection measurement to demonstrate three photon de Broglie wavelength and get good results. Our method is scalable and does not need maximum entangled multi-photon state.4. Extending projection measurement to asymmetric projection and using it to demonstrate four photon interference and three photon temporal distinguishablity.The difficulties of multi-photon experiment come from the state preparation process and the low counts rate of multi-photon state. The second one is the motivity for high bright photon source. A good solution for these problems may be the tradeoff of the two parts. Here we use asymmetric beamsplitter to build up an asymmetric projection measurement and overcome both of the difficulties: get high counts rate without maximum entangled multi-photon states.