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Dynamics of Bose-Einstein Condensates
Thesis

Dynamics of Bose-Einstein Condensates

Chen, Po-Sung
Masters, 國立清華大學, 物理學系
2017

Abstract

玻色 愛因斯坦 凝態 雷射冷卻 BEC condensate laser cooling
The dynamics of bosonic quantum degenerate gas (Bose-Einstein condensate, BEC) in a magnetic potential well was reported. A BEC is considered as a giant microscopic matter wave that can be investigated by direct optical imaging with a time-scale of millisecond to second. In comparison with a single particle wave function, it can be closely observed, as a slow-motion movie. The evolution of matter wave in and out of a trap potential is equivalent to “binding” and “ionization” processes. In our experiment, a BEC with 3×〖10〗^5 rubidium (87Rb) atoms was produced in a magneto-optic hybrid trap with a typical temperature < 100nK. Two kinds of BEC dynamics were then investigated in our experiment. Firstly, the BEC was “shaken” out of the trap, forming droplets and generating a pulsed atom laser. We take advantage of the internal dynamics of BEC to generate pulses with a repetition rate equal to the trap frequency. A simple model was presented to explain the droplet-like density distribution. Secondly, the BEC acquires initial kinetic energy via free fall in gravity, and then the magnetic trap was turned on to load the BEC, which then periodically moved up-and-down in the trap. Combining with the gravity, it was confined in an asymmetric V-type potential well. The wave function of atoms bounces inside the trap, enriching the dynamics of the system. The matter wave with an initial gaussian profile evolved to a long strip with interference pattern. During the bouncing, the collapses and revivals of BEC were also observed. Numerical simulations based on Schrodinger equation agree quantitatively with the experimental observation. In the thesis, we explore the possibility of quantum simulation for molecular physics using BEC.

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