Studies On Electrostatic Stark Deceleration And New Trapping Schemes Of Polar Molecules

In the past few decades,the research of cold atomic physics has revolutionized the field of atomic molecular and optical physics?AMO?.In the same way,the research on cold molecules will provide a new opportunity for the development of AMO.Compared with atoms,molecules have more abundant structures and more degrees of freedom.It is these rich and unique structures of molecules that make it possible to study new physical phenomena and discoveries.Using cold and ultracold molecules,people can explore many new fields,including high-resolution spectroscopy and precision measurements,cold collision,many-body physics,quantum computation.In this paper,we focus on the experimental study of electrostatic Stark deceleration of neutral polar molecules and the theoretical study of cold molecule trapping.The main contents and innovations of this paper are described as follows.The NH₃ molecule is a very important species in physical chemistry and has important applications in cold collisions,precision measurements and microwave frequency standard.We carried out the experimental study of Stark deceleration of NH₃ molecules with our homemade electrostatic Stark decelerator with 179 stages.Using normal operation mode,NH₃ molecular beam is decelerated from 333 m/s to 18m/s,resulting in a trappable cold molecular packet which can be applied in the following studies of cold collisions and high-resolution spectroscopy.In order to produce high-energy-resolved cold molecular beam,we use a new operation mode,the deceleration-bunching mode,and obtain a cold packet with the longitudinal velocity spread of only 2.8 m/s,corresponding to a temperature of 2.9 mK,which is one order of magnitude smaller than that of the cold packet obtained in the normal operation mode.This high-energy-resolved molecular beam with controllable velocity is an idea sample for cold molecular collisions.Although the traditional Stark decelerator can slow down some molecular species,its deceleration efficiency is very low.Besides,it can't perform effective decelerations on the molecules with tiny electric dipole moment or heavy atomic molecules which have important applications in physical chemistry and precision measurements,respectively.Here,we carried out experimental studie on a novel Stark decelerator,i.e.the ring Stark decelerator.The ring decelerator consists of a series of ring electrodes and works under DC high voltages,thus overcomes the faultiness of traditional decelerator and possesses the outstanding merits of the advanced traveling wave decelerator,while it is much easier to implement and operate than traveling wave decelerator.We described the principle of ring decelerator,and introduced the manufacture,alignment,high-voltage conditioning and switching of the decelerator in detail.Experimental guiding and bunching signals of ND₃ molecules traversing ring decelerator are observed.These experimental studies on ring decelerator have made a good contribution to the development of the Stark deceleration technique.Stark-decelerated cold molecules can be loaded and trapped in an electrostatic trap.Molecular trapping is the basis of many further studies and important applications.For this reason,we proposed two novel and efficient electrostatic trap schemes and a multi-loading method for pulsed beams of polar molecules.Monte Carlo simulation of the loading and trapping process of the two kinds of traps under different loading modes is performed.The results show that each of the new electrostatic traps can be efficiently loaded with Stark-decelerated cold molecules using single loading or multi-loading method.The number of trapped molecules is the prerequisite of sympathetic cooling or evaporative cooling.The highly efficient electrostatic trap provides the basis for the generation of ultracold molecules and even molecular Bose-Einstein condensates?BEC?.Cold molecules can also be trapped in a micropotential well on the chip.The polar cold molecules in the micropotential well can be used as quantum bits or molecular registers,which provides a new platform for quantum computing.Here,the first two-dimensional?2D?moving electrostatic lattice scheme for polar molecules is proposed.The design and operation principle of the electrostatic lattice are introduced in detail.Molecular loading,decelerating and trapping processes of the lattice were simulated.Numerical simulation results show that the 2D electrostatic lattice can decelerate the supersonic molecular beam to zero speed within a few centimeters,and make the molecular packages in the lattice move smoothly back and forth on the chip.The simulation results indicate that the 2D electrostatic lattice can be used as a molecular shift register,or simultaneously decelerate and trap two different molecular species.Therefore,the 2D moving electrostatic lattice on the chip has important applications in quantum computation and cold molecular collisions.