Construction Of Quantum States And Study On The Decoherence

Decoherence is a universal essential problem in modern quantum information and quantum computation. Quantum decoherence is very important in quantum mechanics. In this thesis we study the decoherence of photon-added thermal state(PATS) in a thermal environment by deriving the analytical expression of Wiger function(Wigner函数) for photon-added thermal state(PATS), and then a new kind of three-mode entangled state in Fock space is constrcted. Our main contents are as follows:In chapter one, we introduce momentum representation, position representation , coherent state representation and their property. Chapter two introduces the IWOP technique. In chapter three, we shall introduce the PATS and explore theoretically the nonclassicality and the decoherence of PATS in thermal environment. The quantum statistical properties of the PATS is studied firstly ,such as Q-parameter, photon number distribution (PND) and analytical expression of the Wigner函数, and then its decoherence. In chapter four We analyse a two-mode squeezed state's physical properites, such as the cross-correlation function, the Wigner function, and its marginal distribution as well as the Husimi function in chapter four. In chapter five , a new kind of three-mode entangled state in Fock space is introduced, which can compose a new quantum mechanical representation. We can more explicitly show that the state is an entangled state by making Fourier transform and then realize teleportation scheme for single state. Finally. The chapter sixth summarized the whole thesis and some discussions are also given.