The Expansion Dynamics In Strongly Interacting Ultracold Fermi Gas

A impressive development of the ultracold Fermi gas has been realized in the past 20 years.Lots of cooling methods,such as evaporative cooling in a magnet-ic trap,sympathetic cooling with bosons,all optical production,are applied to achieve the ultracold gases in nK and pK scale,which permit us to observe the quantum behavior of Fermi gases.The scattering length of the Fermi gas could be precisely controlled by a magnetic controlled or optical induced Feshbach reso-nance,being applied to study the molecular condensation,Fermi resonant super-fluid and condensed matter physics.The molecular Bose-Einstein condensation and Fermi Barteen-Cooper-Schriefier superfluid crossover(BEC-BCS crossover),which was theoretically predicted thirty years ago,had be experimentally ob-served by adjusting the scattering length.Especially when the Fermi gas is at resonance,the scattering length diverges and no intrinsic length scale define the Fermi many-body systems except for the inter-particle spacing.Acting as the most strongly interacting superfluid,the Fermi gases exhibit universal quantum thermal properties and the symmetry of scale invariance.By precisely controlling the external potential and interaction strength between atoms,the scale invari-ant ultracold Fermi gas is a test bed for testing the fundamental few body and many body physics.This dissertation mainly talks about the universal expansion dynamics in strongly interacting Ferrmi gas.After designing and constructing the experiment machines for cooling the Fermi gas,we realized the all Optical production of quantum degeneracy and molecular Bose-Einstein condensation with two com-ponet Fermi gas and studied the Fermi resonant superfluid.The experiment setup consists of a high power laser system,an ultr-ahigh vacuum system,an ultra-stable dipole trap system and a high resolution imaging system.A new high power laser system,including the seeder laser,Raman amplifier and a fre-quency doubler,is set up to solve the problems in cooling 6Li due to the indis-tinguishable energy levels of excited states and large recoiling momentum.The laser system with a high power up to 2.5 watts,greatly simplified the experi-ment conditions and avoided complex operations,leads to a large number cold atoms(109)whose temperature approaches the doppler limitation.An ultra-high vacuum system approaching 10-12 Torr is prepared to suppress the atoms loss and heating induced by collisions with background gases.Under such ultra-high vacuum situation,an ultra-stable high power dipole trap system is well prepared for realizing the ultracold Fermi gas.The atoms in the dipole trap have a high loading efficiency and long life time.A high magnetic field(larger than 1200 gauss),whose stability is better than 10 mGauss,is employed to realize the moleculax Bose-Einstein condensation and BCS superfluid crossover by precisely controlling the interaction strength between atoms.Based on the ultracold strongly interacting Fermi system,a new expansion dynamics is found in scale invariant unitary Fermi gas(infinity scattering length)and non-interacting Fermi gas.And the universal dynamics is also investigated.Considered the harmonic trap frequencies change as a function of inverse of time,the continuous symmetry of the expansion dynalmics in ultracold Fermi gas would change to be discrete symmetry if the change of the frequencies goes across a critical value.A series of discrete quantum plateaus would appear with the time and spatial geometric sequence.This new expansion dynamics connects with the famous Efimov effect in three body physics predicted in 1970s.Most importantly,the expansion dynamics is universal to all scale invariant state of matters,such as 2D quantum gas and 1D Tonks gas.The other research in this dissertation is the shortcut to adiabaticity(STA)in ultracold Fermi atomic gas.We present the first experimental investigation on the STA in strongly interacting quantum fluids.By changing the trap potential,the many-body state could be adiabatically transfered from one stationary state to another in short time scale without any excitation.A thermodynamic cycle demonstrates the entropy does not change during the STA process.An STA trajectory is also performed in non-interating Fermi gas,indicating the univer-sality of the STA protocol.The STA method permits adiabatic transferring by non-adiabatic process.This protocol could be applied to all scale invariant quan-tum many-body system and has great significance in studying the equilibrium dynamic evolution of the strongly correlated Fermi gas.In this dissertation the equilibrium thermodynamic properties and non-equilibrium dynamics in strongly interacting ultracold Fermi gas are studied by the precise control of interaction and external trap potential.In particular,the Efimovian expansion dynamics and STA are investigated in scale invariant quan-tum many-body system.This researches can open up new research field and establish foundations for new many-body dynamics such as symmetry breaking and quantum thermalization.