Optical Control Feshbach Resonance And Observation Of Floquet Band Topology Change In Ultracold Fermi Gases

In recent years,with the development of experimental tecnology,the spin-orbit coupling for ultracold atomic gases provides a powerful platform for exploring many interesting quantum phenomena.Spin-orbit coupling can be used to simulate many interesting phenomena in condensed matter physics,such as spin Hall effect,topological insulators,topological superconductor and Majorana fermions.Magnetic-field-induced Feshbach resonance and optical Feshbach resonance are such powerful tools and has been widely used in studying strongly correlated degenerate atomic gases.The following is a summary of the main contents of this article:First of all,we measured two key parameters of spin-orbit coupling:the spin-orbit coupling strength and the lifetime of the ⁸⁷Rb BEC.We measured the influence of laser polarization to the spin-orbit coupling strength in ultracold fermi gas.We perform our experiments employing a fermionic gas of ⁴⁰K in hyperfine state|F=9/2,8)=3/2?and|F=9/2,8)=1/2?.Then,we study the influence of the phase noises of far detuning single frequency lasers on the lifetime of Bose-Einstein condensation?BEC?of ⁸⁷Rb in optical dipole trap.As a comparison,we shine continuous-wave single-frequency Ti:sapphire laser,external-cavity diode laser and phase locked diode laser on BEC respectively.We measured the heating and lifetime of BEC in two different hyperfine states:|F=2,8)=2?and|F=1,8)=1?.In order to reduce the phase noise of external-cavity diode laser,we use an optical phase-locked loop for external-cavity diode laser to be locked on Ti:sapphire laser.We experimentally study the spin exchange collision in ultracold ⁴⁰K Fermi gases.The quadratic Zeeman shift,trap potential and temperature of atomic cloud will influence on the spin changing dynamics.Dependences of the spin components populations on the external bias magnetic field,the optical trap depth and the temperature of atomic cloud are experimentally investigated.The spin exchange from the initial states to the final state are observed for different initial states.This work shows an interesting process of reaching equilibrium by redistribution among the spin states with the spin exchange collision in an ultracold large-spin Fermi gas.We report the experimental results on the optical control of a p-wave Feshbach resonance by utilizing a laser-driven bound-to-bound transition to shift the energy of a closed-channel molecule state.The magnetic field location for the p-wave resonance as a function of laser detuning can be captured by a simple formula with essentially one parameter,which describes how sensitively the resonance depends on the laser detuning.The key result of this work is to demonstrate,both experimentally and theoretically,that the ratio between this parameter for the m=0 component of the resonance and that for the m=±1 component,to a large extent,is universal.We also show that this optical control can create intriguing situations where interesting few-and many-body physics can occur,such as a p-wave resonance overlapping with an s-wave resonance or the three components of a p-wave resonance being degenerate.We directly measure Floquet band dispersions in a periodically driven spin-orbit coupled ultracold Fermi gas.Using spin injection radio-frequency spectroscopy,we observe that the Dirac point originating from two dimensional spin-orbit coupling can be ma-nipulated to emerge at the lowest or highest two dressed bands by fast modulating Raman laser frequencies,demonstrating topological change of Floquet bands.Our work will provide a powerful tool for understanding fundamental Floquet physics as well as engineering exotic topological quantum matter.