Schemes In Cold Atoms About Quantum Simulation And Quantum Computation

Quantum information science is a subject combined by applying the basic prin-ciples and theories of quantum mechanics to information science. It contains many relating research areas, including quantum computation, quantum simulation, quantum communication, etc. Due to the quantum property, quantum computer and the algo-rithms based on it have tremendous advantages to classical computer; the schemes of quantum simulation also solve the problem that the existing algorithms on classical computer can not simulate quantum many body system precisely; quantum communi-cation plays an important role in secure communication due to the no-cloning theorem and collapse after observation. so the quantum information science has been paid great attention since the date of birth and attracts many scientists working on it.In this paper, we first introduce the general principles of quantum computation and quantum simulation. In the quantum computation part, we show the importance of high-fidelity quantum gates to quantum computer and propose a scheme to realize two qubit phase gate; we also explain that the preparation of entangled states is a crucial part of quantum network as well as other applications relating to computation and propose a scheme to purify general mixed entangled states. For the quantum simulation part, we emphasize on optical lattice system and synthetic gauge field:we propose a scheme to realize directed quantum transport in optical lattice and study the property of Rashba type spin orbit coupled system with an in-plane magnetic field. Precisely,1:We propose a scheme to realize directed quantum transport of ultracold atoms in one dimensional optical lattice. In this proposal, the effective tunneling between neighboring sites can be adjusted via coherent destruction of tunneling by tuning the phase of the external field, instead of the driving field intensity or the frequency, thus the directed quantum transport of ultracold atoms can be coherently controlled in a much easier manner. Our proposal overcomes the major drawback of the idea by Creffield et al [Phys. Rev. Lett.99,110501(2007)], and can be implemented, in principle, in any one dimensional optical lattice. Some potential applications of the scheme are also discussed.2:We propose a scheme for purification of general mixed entangled state. In this scheme, we start from a large number of general mixed entangled states and end up, after local operation and classical communication, with a smaller number of Bell diagonal states with higher entanglement. In particular, the scheme can purify one maximally entangled state from two entangled pairs prepared in a class of mixed entangled state. Furthermore we propose a linear optical implementation of present scheme with polar- ization beam splitters and photon detectors.3:We propose an experimental feasible scheme for implementing two-qubit quan-tum phase gate with atoms trapped in an optical cavity. The scheme is based on the dispersive interaction between the optical cavity mode and three-level atoms in (?) con-figuration, which has been demonstrated in recent experiment. We also discuss the influence of the cavity decay on the gate fidelity. It is shown that the fidelity of the phase gate is robust to the cavity decay and high-fidelity quantum phase gate can be implemented with current experimental technology.4:We study the system of pure Rashba spin-orbit coupled Bose gas with in-plane magnetic field. Based on mean field theory, we obtain the zero temperature phase di-agram of the system which exhibits three phases identified by Plane Wave phase(PW), Striped Wave phase(SW) and Zero Momentum phase(ZM). It is shown that with a grow-ing in-plane field, both SW and ZM phases will eventually turn into PW phase. Fur-thermore, we adopt Bogoliubov theory to study the excitation spectrum as well as the sound speed.