Studying On The Rotational State Collision Characteristics Of Ultracold ⁸⁵Rb¹³³Cs Molecules

Ultracold polar molecules are characterized by long-range dipole-dipole interaction,easy to be controlled by external fields,and long coherence time,so they usually have incomparable advantages in quantum computing,quantum simulation,and quantum precision measurement.The ultracold polar molecules in the ground state with stable physical and chemical properties are the basis of the above research.However,it is found that the polar molecules in the ground state still have non-negligible inelastic collision losses,no matter the molecules in the two-body exchange reaction or the molecules in the two-body exchange non-reaction.Therefore,it is of great significance to study the collision of ground state ultracold polar molecules,especially the collision characteristics of two-body exchange non-reactive molecules,to understand the inelastic collision of molecules,obtain the molecular samples with long life,chemical stability,quantum state degeneracy,and carry out the above-mentioned molecular applications.It has also become a research hotspot in the field of quantum control of ultracold molecules in recent years.In this paper,collision characteristics of the ultracold ⁸⁵Rb¹³³Cs molecule in the rotational states have been studied in order to understand the inelastic collisions of ultracold polar molecules in the ground state.First,⁸⁵Rb atoms and ¹³³Cs atoms are captured by laser cooling in a dark magneto-optical trap,and then ultracold ⁸⁵Rb¹³³Cs molecules are synthesized in the ground state by photoassociation which is an indirect method to prepare ultracold molecules,and finally the molecules prepared by the photoionization detection is carried out.In order to understand the information of molecular rotational energy level accurately,the population of molecular rotational states was measured by loss spectroscopy.And in order to manipulate the distribution of molecules in the rotational states,microwave pulses of different time were applied to ⁸⁵Rb¹³³Cs molecules in the initial state of pure rotational states.Besides,in order to study the properties of collisions between rotational states of molecules,the evolution of the number of molecules in pure and mixed states over time was measured,and the collision coefficients of rotational pure and mixed states were obtained.The main work and conclusion of this paper are as follows:1.Based on the samples of ultracold atoms,the population of rotational states in the ground state ultracold ⁸⁵Rb¹³³Cs molecules prepared by directly photoassociation was measured by loss spectroscopy and the high-resolution loss spectra of ultracold ⁸⁵Rb¹³³Cs molecules in X¹?⁺（=0）states were obtained,and the rotational constant of the molecules was obtained.2.A typical dissipative Rabi oscillation and molecular coherence time are obtained by using microwave pulse technique to manipulate the conversion between adjacent transformations of the ultracold ⁸⁵Rb¹³³Cs molecules.3.The evolution of the number of molecules with time in different pure and mixed states of the ultracold ⁸⁵Rb¹³³Cs molecules is studied.The rate equation is introduced to describe the molecular dynamics process.It is found that the collision coefficient of the rotational mixed state is higher than the pure rotational state,which is mainly caused by the dipole-dipole interaction between the neighboring rotational state.