| The Bose-Einstein condensate(BEC)formed at low temperatures provides an unique platform for exploring new physical phenomena and mechanisms at the condensed matter level on a quantum level due to its simplicity,purity,and high controllability in the environment.It has potential applications in fields such as high-energy physics,nuclear physics,quantum chemistry,and astrophysics.However,the BEC formed by neutral atoms cannot exhibit various quantum many-body phenomena like charged particles in a magnetic field,such as topological insulators,integer and fractional quantum Hall effects.The appearance of synthetic magnetic fields for neutral atoms provides the possibility of simulating gauge theories.The appearance of synthetic and orbital magnetic fields has also opened up new avenues for studying BEC.For example,effective synthetic gauge fields can be utilized by BEC to achieve complex hopping amplitudes and Peierls phases,which have been experimentally realized.Various implementation schemes for synthetic gauge fields have been proposed and realized in experiments.Among them,an adjustable artificial gauge field,that does not depend on the internal structure of the atom,has been experimentally realized in a tilted superlattice potential using laser-assisted tunneling.The characteristics of the artificial gauge potential also reveal that neutral single atoms can simulate the motion of charged particles in a gauge magnetic field.The quantum cyclotron orbit of neutral ultracold atoms has been observed in experiments,thus the tunneling dynamics of neutral atoms can reveal the potential properties of theoretical models.The quantum tunneling dynamics of ultracold atoms in an artificial gauge field has significant implications for studying new properties of quantum transport.In this paper,we study the tunneling dynamics of BEC in four-well potential under artificial gauge field,focusing on the non-reciprocity of tunneling,and studying the effects of the parameters of the system on the non-reciprocal quantum transport.The article is divided into four parts and covers the following main topics:The first chapter briefly introduces the theoretical background of ultracold atomic physics,the formation and preparation process of BEC,and the generation and experimental implementation of artificial gauge fields.The method of using laser-assisted transitions to implement artificial gauge fields is emphasized.The concepts of non-reciprocal transport and Floquet theory are introduced.Next,the quantum transport dynamics of BEC in a four-well potential with dissipative artificial gauge fields was investigated.The effects of dissipation,coupling strength,and artificial gauge fields on the quantum tunneling dynamics of BEC in the four-well potential were discussed,and the non-reciprocity of quantum transport under these parameter conditions was studied.It was found that by adjusting the artificial gauge field and other parameters,the system could exhibit the phenomenon of coherent population destruction and lead to the absence of ”transport” within a specific parameter range.Additionally,it was discovered that the reciprocal quantum transport characteristics of BEC in the four-well potential remained robust under different parameter conditions.Based on these phenomena and characteristics,a device for controlling BEC transport,a quantum reciprocity switch,is designed.Then,the robustness of the quantum reciprocal transport of BEC in a four-well potential is broken by introducing two opposite coherent drivings,thus realizing the nonreciprocal quantum transport of BEC in the system.In the absence of dissipation,the effects of the reduced strength of the direct current field,artificial gauge field,and coherent driving parameters on the quantum transport of the BEC were investigated.It was found that the unequal reduction strength of the direct current field was a necessary condition for the generation of non-reciprocal quantum transport in the system.The artificial gauge field,as a switch,jointly controlled the direction of the non-reciprocal transport with the reduced strength.In the presence of dissipation,it was found that the dissipation strength could enhance the non-reciprocity of quantum tunneling of the BEC to some extent.Moreover,under the joint action of other parameters,a smaller effective coupling strength was advantageous for achieving strong isolation and unidirectional non-reciprocal transport of the BEC.Additionally,when the trap-coupling amplitudes were equal and under certain phase conditions,the BEC had a half chance of stably occupying two adjacent traps,while the other half would dissipate to other traps.Notably,this phenomenon did not depend on the coherent driving or reduced strength.At last chapter summarizes the work of this dissertation and forecasts the research prospect and the next work in this field. |
