Studies On Electrostatic Stark Deceleration And Three-dimensional Electric Lattice Theory Of Polar Molecules

Cold molecules have important significance and promising applications in the fields of precision measurements,high-resolution spectroscopy,and cold collisions.Since 1998,the group of Dolye from Harvard University first obtained the sample of cold molecules in the gas phase by buffer gas cooling technique,many significant scientific advances have been made in the field of cold molecules,resulting in a series of techniques and methods for preparing cold molecules.Ranging from electrostatic Stark deceleration to laser cooling,from buffer gas cooling to evaporative cooling,these techniques allow the preparation of cold molecules at temperatures below 1 K as well as ultra-cold molecular samples at temperatures below 1 m K.This paper focuses on the preparation of cold molecules by Stark deceleration techniques,and the study of cooling and trapping for the decelerated molecules.In 1999,Meijer team successfully developed the first polar molecular electrostatic Stark decelerator（traditional Stark decelerator）in the world,and realized the molecular deceleration experiment.In this paper,a comprehensive experimental study was carried out on the traditional electrostatic Stark decelerator,and the conditions and parameters of the deceleration experiment were optimized.Under the deceleration voltage of 8 k V,the ND₃ molecule with the initial velocity of 337 m/s was decelerated to the final velocity of 9 m/s,removing about 99.9%of kinetic energy,and realizing the control of the molecule at any speed.This paper also studies a method to reduce molecular loss and increase the number of molecules after deceleration by changing the control mode of traditional decelerator.This paper first introduces the working principle of the new control mode,then introduces the modification of timing and control program,so that the control can work in the current system.Finally,the experiment of the new control mode is implemented,and the experimental results are consistent with the theoretical simulation,which verifies the feasibility of the scheme.At the same time,the new control scheme is compared with the traditional mode,and the improvement effect of this control is more obvious at a higher final velocity,and the molecular beam density under the bunch is about 2.5 times that of the traditional mode.The cold molecules obtained by the deceleration technology can be trapped in the electrostatic wells or electrostatic lattices for subsequent experimental research.In this paper,a three-dimensional electrostatic trap lattice scheme is proposed to trap cold molecular beams from Stark deceleration.The three-dimensional electrostatic lattice is an extension of the three-dimensional optical lattice,and the ultra-cold polar molecular system trapped in the three-dimensional electrostatic lattice can be used for quantum simulation of many-body physics.Since the depth of three-dimensional electrostatic lattices is typically several orders than that of the optical lattices,thus allowing for powerful control of polar molecules over comparatively large energy scales.In this paper,the processes of loading,trapping,and evaporative cooling of ND₃ molecules in the lattices are investigated in detail by theoretical analysis and Monte-Carlo simulations.The simulation results in this paper show that the loading efficiency of ND₃ molecules is about 3.3%from the Stark decelerator to the three-dimensional electrostatic lattice.The sample temperature of the ND₃ molecule in the lattice is reduced from 24 m K to about 7.6 m K by evaporative cooling,and the filling ratio of the lattice is gradually reduced from 100%to 6%during the evaporative cooling process.These results verify the feasibility of this three-dimensional electrostatic lattice.In addition,due to the flexibility of design,the three-dimensional electrostatic lattice can be derived from a variety of topologies,such as triangular,hexagonal,and Kagome topological electrostatic lattices,which provide an ideal platform for exploring new materials and other research.Periodically driven quantum systems can achieve many important physical experiments that cannot be performed by static quantum systems,such as the study of coherent manipulation of the tunneling amplitude for single particles in periodically driven optical lattices.In addition to the three-dimensional electrostatic lattice,a driven three-dimensional electric lattice scheme is proposed in this paper.By adjusting the voltage,the potential well in the three-dimensional electric lattice can move in one direction,remain stationary,or move back and forth.So the polar molecules can be decelerated,be trapped,and move back and forth in the lattices.In this paper,the manipulation of light polar molecules（ND₃）and heavy polar molecules（Pb F）in the lattice is investigated by theoretical analysis and numerical simulation.The results show that the driven three-dimensional lattice can decelerate these two polar molecules from 330 m/s to rest and can trapped them in the lattice stably,respectively.And then by driving the lattice,the molecules in the lattice can move back and forth.These studies validated the feasibility of our scheme.As a supplement to the driven optical lattice,the driven three-dimensional electric lattice is expected to provide a new platform for the study of the driving cold molecule quantum system.