Experimental Studys Of Many-body Spin System In Optical Lattices

With the vigorous development of experimental techniques,ultracold quantum gas is becoming an increasingly important research area.Due to the clean system,explicit theory and high controllability,it is widely studied in various fields,such as atomic and molecular physics,condensed matter physics and quantum in information science.Especially,the techniques of optical lattices,which provide periodic potentials and en-hance the strength of interaction,open up the research of strongly correlated physics with ultracold atoms.Meanwhile,ultracold atoms in optical lattices constitute an im-portant platform for realizing quantum simulaton of solid state models and performing large-scale quantum information processing tasks.However,the cooling of strongly correlated atoms in optical lattices is a current ex-perimental bottleneck constraining the further application of optical lattice techniques.In the first stage,this thesis investigates the refrigeration of the strongly correlated atomic system in optical lattices and experimentally realize a low-entropy unit-filling Mott insulator.On this basis,we also carry out experimental explorations towards both quantum simulation and quantum computation.We realize parallel high-fidelity two-body quantum gates entangling ultracold bosons in optical lattices.On the other hand,we investigate the lattice magnetic model in optical lattice and generates the bosonic antiferromagnetic Heisenberg state.First of all,we develop the techniques for cooling strongly correlated bosons in optical superlattices and realize a low-entropy two-dimensional Mott insulator state with high filling ratio.Based on the precise munipulation of the superlattice poten-tial,the staggered-immersion cooling proposal is designed and performed,where the superfluid phase and the Mott insulator phase are prepared alternatively in the bosonic optical lattice.Subsequently,we adiabatically engineer the cooled state by sweeping the superlattice phase,which achieves the two-dimensional unit-filling Mott insulator in a high-fidelity way.In the final stage,a optical-lattice system containing 104 sites with the averaged unit-filling ratio of 0.992(1)is obtained,which consititutes an advan-tageous experimental platform for both quantum simulation and quantum information process with ultracold atoms.Secondly,in the defect-free optical lattice system,we realize the high-fidelity two-body quantum gate and generate roughly 1250 pairs of entangled atoms.This thesis,a new(?)gate is designed by matching the four-state inteference,which greatly shortens the operation time and results in a high gate fidelity.In the experiment,the gate operation time is reduced to 0.8 ms amd the averaged gate fidelity is measured to be 0.993(1)in a region containing 1250 pairs of atoms.This gate fidelity is beyond the error thresholds of topological quantum error correction protocols,laying a basis for the scalable quantum computation with ultracold netural atoms in optical lattices.Thirdly,the bosonic one-dimensional lattice magnetic model is investigated in the defect-free optical lattice system.Using the staggered superlattice potential,a one-dimensional isotropic antiferromagnetic Heisenberg model is in implemented,which is verified by the post-quench dynamics of an initial Neel ordered state.On this basis,the adiabtic preparation is of a Heisenberg antiferromagnetic(AF)state is realized.For as-sessing the Heisenberg AF state,we develop the spin-correlated measurement methods without the single-site resolution,detecting the nearest-neighboring and next-nearest-neighboring spin correlation.Finally,the spin rotational invariance and decoherence mechanism of the Heisenberg AF state are also explored.The study of 1D heisenberg model is an important step of the quantum simulation of bosonic magnetism,and the coherent state transfer also provides new ways for realizing of other many-body states.In summary,the cooling and the entropy removal of strongly correlated bosonic system is studied in optical lattices.Based on the defect-free Mott insulator platform,the high-fidelity quantum gate and the bosonic Heisenberg antiferromagnet are realized,which lay a basis for the further researches of many-body spin systems.