| The controllable interaction of the ultracold Fermi gas provides an ideal experimental platform for studying the physics of the strong interaction.In par-ticular,when at low temperature the strength of the collision interaction can be tuned to infinity by using the so-called Feshbach resonance,the strong interac-tion of the quantum gases allowed by quantum mechanics.This ensures that the behavior of the gas is independent of the microscopic details of the inter-actions between the particles and exhibits the same universal thermodynamic properties as the various strong interaction systems.The strongly interacting two-component Fermi gas is the prototype for other exotic systems in nature,including High-temperature superconductivity,quark gluon plasma,and neutron stars.Modulation instability(MI)is a long-standing research topic in physics.This nonlinear effect leads to the formation of random wave patterns in various systems.The patterns resulted from modulation instability are ubiquitous and have been widely studied in optics and Bose-Einstein condensate,such as soli-tons,Faraday waves,spatiotemporal crystals,etc...However,they have not been realized experimentally in ultracold Fermi gases although there are a lot of theoretical interest in the field.In this thesis,a nonlinear control method is used,which is different from that report before.We report an experimental observation of space-time patterns in a superfluid Fermi gas excited by a red-detuning laser light.The longitudinally spatially-fluctuating laser beams induce the spontaneous emergence of two dif-ferent kinds of the patterns.Interaction plays an important role in the formation and propagation of patterns.For the strongly interacting Fermi gas,due to non-linear coupling,the induced patterns accompanied by phonon excitations show a striking“X”-type dispersion relation between the frequency and wavevector.The propagation of such patterns in the crossover of the BEC and BCS is investigated,which is related to the sound speed and consistent with the mean field and Monte Carlo calculations.The observed patterns at the non-interacting Fermi gas are from the ground-state density modulation and there are stationary without excitations.In this thesis,we focus on the nonlinear space-time pattern caused by the spatially-fluctuating laser beams,taking the strong interaction of the ultra-cold Fermi gas as the main line.In Chapter 1,the development of the field is briefly introduced,and in Chapter 2 and 3,the preparation and properties of~6Li ul-tracold atoms with different interactions are introduced in detail.In Chapter4,5 and 6,the space-time pattern caused by the spatially-fluctuating laser beams and its underlying physics are introduced in detail,including the experimental scheme,the calibration process and results of basic thermodynamic parameters such as temperature,energy and other parameters,data acquisition and analysis.Finally is the summary and the outlook. |
