Manipulation Of Qubit Based On Single Neutral Atoms

The minimum feature size of an integrated circuit has reached to 10nm.With the size of classical bits getting smaller and smaller, they will show quantum behavior and do not obey the classical theory. So scientists have proposed quantum computers based on quantum mechanics. A quantum computer uses qubits to store information and to carry out computation. A number of different quantum systems are currently being pursued to act as qubit, such as single photons, superconducting rings, quantum dots, single ions, nuclear spins, controlled neutral atoms, and so on. Compared to other physical systems, the quantum bits encoded in the ground state of the captured atoms are free of interaction with external electric field and magnetic field. More importantly the stable and clean ground states provide long coherent time in room temperature. And optical pump technique, the two-photon Raman process, the resonant microwave pulse, the resonant fluorescence detection technique and the Rydberg long-range interaction provide a powerful technical means for initializing, rotating and reading the atomic qubit with high accuracy. All these developments and the related techniques have helped to bring about the single neutral atoms being a powerful candidate for quantum information process.The thesis mainly focuses on manipulation of qubit based on single neutral atoms, lengthening the dephasing time and applying the techniques of manipulating qubits to the study of basic physical problems. The main works of the thesis are as follows:1). The construction of all-fibre magneto-optical trap;2). We capture single atom in micro-sized optical dipole trap formed by strongly focused a 1064nm laser beam. We lower the temperature of the single atoms by PGC cooling and measure the temperature by method of release and recapture;3). Based on single Cesium atoms trapped in a 1064 nm microscopic optical trap we have exhibited a single qubit encoded in the Cesium "clock states", The ground states Rabi flopping rate of 229.0 kHz is realized by a two-photon Raman process. A clock states dephasing time of 3.0 ms is measured, while an irreversible homogeneous dephasing time of 124 ms is achieved by using the spin-echo technique;4). We demonstrated trapping and quantum state manipulating of single cesium atoms in a 780 nm wave-length bottle beam trap?BBT? . The ground states Rabi flopping rate of 12.54 kHz is realized by a single resonant microwave pulse. A clock states coherence time of 10 ms is obtained, while an irreversible homogeneous dephasing time of 415 ms is achieved by using the spin-echo technique. We measured the fidelity of the prepared quantum qubit and quantum operation gates by using quantum state tomography and quantum process tomography5). The transition |6S_1/2,F= 3,mF = -1> to|651/2,F = 4,mF =1> is magnetic field independent. The homogeneous dephasing effect induced by fluctuation of magnetica fiels is suppressed. The homogeneous dephasing time is 1s;6). An experimental test of quantum complementarity principle based on single neutral atom trapped in a blue detuned bottle trap was performed. Imbalance losses influence to the complementarity relation is studied theoretically and experimentally.