Experimental Study On Spin Entanglement With Ultracold Atoms In Optical Lattices

This dissertation reports on the experimental study of quantum spin en-tanglement between ultracold atoms in optical periodic potential. Many-body quantum entanglement has been identified as the essential resource for quantum computation. With the recently developed optical lattices technique, we may able to manipulate multi-particle entanglement for quantum information processing.The Mott insulator state of ultracold atoms is a scalable platform for many-body entanglement generation. In the experiment, a Bose-Einstein condensate of 87Rb atoms is loaded into a single layer of two-dimensional optical superlat-tices. In such a system we have been able to in situ observe the Mott insulator state, manipulate the superexchange interaction and realize two particle entangled states.Experimental realization of Bose-Einstein condensate phase transition allows us to enter the quantum gas region. An ensemble of 87Rb atoms is first captured in the magneto-optical trap, then transported into an ultra-high vacuum chamber,and evaporative cooled in the magnetic quadrupole trap and optical dipole trap,we finally achieve a nearly pure Bose-Einstein condensate with an atom number of 2 × 105.The Bose-Hubbard model, which predict the superfluid to Mott insulator phase transition, is experimentally realized by loading ultracold quantum gas into a two-dimensional optical lattice. We load the Bose-Einstein condensate into a single layer of optical periodic potential, then reach the Berezinsky—Kosterlitz-Thouless transition region in such a two-dimensional quantum gas. By slowly ramping up the other two optical standing wave potential, atomic ensemble enters different many-body quantum phase. Time of flight imaging of the momentum distribution tells the correlation difference between superfluid and Mott insulator states. In situ high resolution imaging together with spin relaxation collision tech-nique resolve the atom filling number in the optical lattice. From the occupation probabilities we deduce the atomic ensemble temperature in Mott insulator region is around 0.2U/kB.Based on the above achievement, we separate atoms into arrays of double wells by controlling a bichromatic optical lattice, this double well system serve as a minimum building block of Bose-Hubbard model. A novel technique for selective addressing the spin states in double wells is developed. By controlling the superlattice potential and manipulating the atomic spin states, we in situ observed the single atom tunneling process and spin exchange dynamics. At the quarter period of spin exchange evolution the atoms form entangled states. We are able to realize the Bell states by tuning the relative spin-dependent potential.This experiment lay important foundations for future studies of many-body entangled state and measurement-based quantum computation.