Coherent Manipulation Of Magnetically Insensitive Cesium State In Blue Dipole Trap

Recently,quantum computation and quantum communication has been one of the important research fields.A qubit is the basic cell to save quantum information and perform quantum computation,and its coherence time is a critical parameter for these applications.There are lots of quantum physical systems,e.g.trapped ions,superconducting rings,quantum dots,and neutral atoms can be used to encode qubit.Qubit encoded in controlled single atomic ground states has longer coherence time due to the weak coupling to external electronic and magnetic field.Meanwhile,single neutral atom trapped in a far-detuned optical dipole trap(FORT)has great advantage on the scalability.Therefore,the neutral single atom has been a promise physical system to demonstrate QIP.In recent years,the scaled single atom arrays with arbitrary structure have been achieved.At the same time,the one-qubit two-bit logic operations lay a strong foundation to realize neutral atomic quantum computation.However,the coherent time has yet to be improved compared to ion system,whose coherence time has reached to around ten minutes.The major factors that limit atomic coherence time include inhomogeneous dephasing due to atomic thermal motion and homogeneous dephasing due to interactions with ODT and external electronic and magnetic fields.Some of the homogeneous dephasing factors,like ODT beam pointing noise,ODT beam power,can be greatly suppressed by 'magic' conditions.In any situation,the inhomogeneous dephasing dominates the dephasing process By using CPMG sequences(Carr-Purcell-Meiboom-Gill sequences)and spin-echo sequences the inhomogeneous dephasing can be suppressed,and the coherent time is then extended.In this thesis we mainly focus on the experiment of extending the coherent time by using the "magic" magnetic field in a blue dipole trap.In addition,the theoretical and experimental preparations for Raman sideband cooling of single neutral atom trapped in a red detuned dipole trap are also demonstrated.The main content focus on the following:1).Basing on the system of single cesium atom captured in 780 nm blue-detuned dipole trap,we encode qubit in the magnetically insensitive ground state(|0>-|6S1/2,F=3,m=-1)and|1>)=|6S1/2,F=4,mF=+1)).The differential energy shift versus magnetic field is measured by two-photon process with a microwave photon and a rf photon.The magic magnet field B=1.4(2)Gauss is then determined By setting the magnetic field to this "magic" point a coherence time up to 1 s can be obtained by using spin-echo techniques.2).We theoretically analyze Raman sideband cooling of single cesium atom in 1064 nm red detuned dipole trap and experimentally construct the Raman laser system.