Theoretical Researches On Novel And High-efficient Electrostatic Stark Decelerator And Trapping Of Cold Molecules

After nearly 20 years of development, cold molecules as an emerging subject has been given more and more attention by scientific workers, and this is based on the potential applications in many fields, such as the high resolution spectrum and fundamental physical constants of precision measurement, chemical and cold collisions, quantum computation and so on. And how to product the reliable source of cold molecular beam is the basis of many experiments, so far, like electrostatic Stark deceleration, Zeeman deceleration, buffer gas cooling, and the latest molecular laser cooling technology have been more and more mature in the experiments. And in this paper, we are mainly devoted to use electrostatic Stark deceleration technology to product the cold molecules, and how to realize the electrostatic trap on a chip.First, we have proposed a simple and high-efficient decelerator scheme to slow neutral polar molecules, and this scheme has increased the transverse bunching effect based on the traditional decelerator. Then we calculate the electric filed distribution in free space and simulate ND3 molecules in the state|J,KM)=|1,-1> by using a simple analytic model and Monte-Carlo method. Our research shows that a subsonic molecular beam passes 108 stages, the length of 486 mm of decelerator, the final velocity is decreased from 320m/s to 6m/s, and we can obtain a number of molecules is 4.5×103. In addition, we make a comparison with the s=1 and s=3 modes of the traditional decelerator and the travelling-wave ring one. And find that our scheme is higher than the s=1 mode of the traditional decelerator by about a factor of 7 to 10 and is far higher than the s=3 mode by about two orders of magnitude at a high phase angles. Even with travelling-wave decelerator, our scheme is only slightly less than it.The success of the deceleration of light molecules (e.g., ND3 molecules) inspires us to focus on the heavier weight molecules (e.g., PbF molecules) or the light polar molecules with a tiny electric dipole moment (EDM) molecules (e.g., NO molecues). Especially for PbF molecules, it plays an important role in electronic electric dipole moment measurement. So we calculate the the Stark shift and the population in the different rotational levels of PbF molecules, and simulate the PbF molecues in the J= 5/2 and J= 7/2 states. We obtain the corresponding slowing efficiency are 1.5×10-4 and 4.5 ×10-4, respectively. In order to further focus and cooling PbF molecules, we make a bunch with a cold packet of PbF molecules, and a longitudinal velocity spread of 0.69m/s and the corresponding longitudinal temperature of 2.35mK will be produced. In final, we have also demonstrated the feasibility to slow light polar molecules with a tiny EDM, when the phase angle of 54°, and found that our proposed decelerator can be used to efficiently slow NO molecules from 315m/s to 28m/s after passing 1040 stages. Especially at low velocities, our new decelerator has a better transverse stability, compared with conventional decelerator, so more cold molecules can be obtained.Next, we have proposed a novel electrostatic Stark decelerator on a chip. Based on the similar decelerator by Meijer’s group, our scheme has been increased the quadrupole guidance function. Using the finite element software, we calculated the two transverse potential well depths and the longitudinal potential well depth. Due to the effect of transverse guidance of the quadrupole, we have obtained the well depth more than 2K in the x direction, even in the y direction, the well depth is around 400mK. When applied the electrodes voltage of +8kV, the longitudinal deceleration of the depth can reach 0.17cm-1. Then, using the 3D Monte-Carlo method, we simulate the ND3 molecules in the |J,KM>=|1,-1> state, the initial 106 molecules after 400 stages, and the final velocity is slowed from 320 m/s to 8 m/s, and the corresponding deceleration efficiency is 0.18%.Finally, we have proposed an electrostatic surface trapping scheme for cold polar molecules on a chip. We calculate the corresponding electric field distribution and the effective Stark trapping potential for ND3 molecules. Then we have also analyzed the dependences of the trapping center position and the effective trapping potential on the geometric parameters of our charged-wire layout respectively. Next we have studied the dynamic loading and trapping processes of cold ND3 molecules in the |J,KM>= |1,-1> state by using Monte-Carlo method to obtain the optimal trapping efficiency, the initial and final velocity distributions of cold molecules in the trap. Our study shows that when the initial longitudinal velocity of incident ND3 molecule is 12.5m/s, and the loading time tloading is 0.829ms, the maximum loading efficiency can reach 11.5%, and the temperature of the trapped cold molecules is about 26.4mK. In addition, we also simulate a simple surface electrostatic trap that consists of a U-shaped electrode, and its feasibility is verified.