Finite-Time Quantum Thermodynamics In Ultracold Fermi Gas

In recent years,with the rapid development of evaporative cooling in mag-netic trap,high resolution imaging,optic lattice and other techniques,ultracold quantum gas has become a simulation experimental platform for many body and few body quantum physics research.In particular,degenerate Fermi gas,through controllable Feshbach resonance technique,could precision control the interactions between atoms that could realize the transition from noninteract-ing many body quantum system to strongly interacting many body quantum system,and study novel phase transitions,and the transformation of diatomic molecular Bose Einstein condensation pairs to BCS cooper pairs could be used to simulate nuclear matter,condensed matter physics and the quark-gluon plasma.Especially the Fermi gas is at resonance,the scattering length between atoms tends to infinity,which is called unitary region,the interactions of Fermi gas no longer depend on the scattering length between atoms,are only related to the energy of the system.Except the space distance between atoms,the system has non other characteristic length which is a scale invariance system with universal thermodynamic properties.The main research of this thesis is the dynamics in strongly interacting ultra-cold Fermi gas of⁶Li.The experiment system is composed of ultra-high vacuum system,high power frequency doubling laser cooling system,ultra-stable crossed dipole trap,high-precision Feshbach resonance magnetic field and high-resolution absorption imaging system which is used for high field imaging.During my doc-toral study period,I participated in the construct of the precision controllable experiment platform of ultra-cold quantum gas,which has realized the quantum degeneracy and molecular Bose Einstein condensation of⁶Li.Vacuum degree of our ultrahigh vacuum system can reach 10^-12Torr,which can effectively reduce the atoms loss and heating due to the background gas collisions,so it is a good experiment environment for the preparation of ultracold Fermi gas;according to the laser cooling and trapping process of⁶Li,we developed a powerful 671-nm laser system with 2.5W high output power which is based on laser injection,Ra-man amplification and internal cavity frequency doubling technology,and this laser system simplified the experiment setup of⁶Li laser cooling and operation process a lot,finally could be able to get large number cold atoms closing to the doppler cooling limit of⁶Li;point noise and power noise of our ultra-stable crossed dipole trap is precision controlled,which could restrain the heating and loss of the atom resulting from the noise of laser field effectively,and the life of the atoms in the dipole trap can achieve nearly hundred seconds with an efficient loading of⁶Li cold atoms;the magnetic field strength of self designed high accu-racy magnetic field can reach 1500 G,whose stability is about 10 mG based on the control of current and feedback technique of magnetic field detection,so the interaction between atoms can be accurate controlled both in the BEC side and BCS region of the ultracold Fermi gas of⁶Li;combined with the beat locking technique,high resolution imaging system can precisely detect the information of the ultracold Fermi gas of⁶Li which can covered the magnetic field from 0G to 1500 G.This thesis mainly focused on the research of non-equilibrium dy-namics of many body system and finite-time quantum dynamics in the strongly interacting Fermi gas of⁶Li.The research of Efimovian and Super-Efimovian non-equilibrium expansion dynamics in a scale invariant many body quantum system of⁶Li.According to the scale invariance in the unitary and noninteracting Fermi gas,by controlling the frequency of external harmonic potential of Fermi quantum gas to vary as a special function of time,the cloud size behaves as scale symmetry of discrete time and space during the Efimovian non-equilibrium expansion dynamics process,which is very similar to mathematical representation of the three body Efimov effect in the Bose gas,and the time inversion symmetry of this dynamic behavior in scale invariant system is verified by our experiment;a double log periodicity relationship between the cloud size and experiment time is measured in the Super-Efimovian non-equilibrium dynamics process,which is similar to the mathematical description of the Super-Efimov effect in the Fermi gas.More importantly,both Efimovian and Super-Efimovian non-equilibrium expansion dynamics are universal,which can be observed in other scale-invariant quantum system.Research of superadiabatic finite-time thermodynamics in the strong coupled many body system.The quantum dissipation of the non-equilibrium process is greatly suppressed by scale invariant symmetry.Based on the dynam-ics evolution of Fermi gas with strong interaction,the fast adiabatic transfer between different equilibrium states of unitary Fermi gas is realized by the pre-cision designed capture frequency of the gas.At the same time,it is proved that Fermi gas with non interaction and strong interaction can obey the same dynamic evolution rule.The finite-time expansion and compression dynamics in the ultracold strong interaction Fermi gas at low temperature is studied.Com-bined with counterdiabatic driving technique,the quantum dissipation caused by excitation of non-equilibrium dynamics process is greatly suppressed,which can increase the output work of the many body system,and researched the re-lation between the fluctuation of output power and finite time,which confirmed that it is limited by the Heisenberg uncertainty principle.At high temperature,the quantum viscosity coefficient has great influence on Fermi gas.The influ-ence of viscosity coefficient on the finite-time thermodynamic control at finite temperature is studied with viscosity hydrodynamics.It is found that viscosity coefficient has no effect on the isotropic Fermi gas,while in the anisotropic Fermi gas viscosity coefficient increases the quantum dissipation during the dynamics process.The research of interactions between near resonant light and⁶Li ultracold atoms.The D2 line absorption spectrum of⁶Li is precision measured when the light goes through the ultracold Fermi gas of⁶Li with a single photon detection technique,the width of the spectral line is measured with different atomic density or optical depth.The result indicated that the spectral line width dependence of the optical depth does not agree with the classical prediction which is based on the lorentz-lorenz model,but is coincide with a modified self-broadening theory with carefully consideration of the effects of light induced dipole-dipole interactions in the ultracold dense atomic cloud.This thesis mainly studies the strongly interacting ultracold Fermi gas of⁶Li,carried out the researches of Efimovian and Super-Efimovian non-equilibrium dynamics in the scale invariant Fermi gas,finite-time quantum thermodynamics of strong interacting Fermi gas and the interactions between near resonant light and⁶Li ultracold Fermi gas.The results show novel dynamics properties,which can open up new ideas for the research of many body non-equilibrium dynamics physics and many body quantum heat engine with demonstration effects,and provides valuable reference for the application technique of atomic molecular optical physics in high-density atoms.