Chaotic Vortex Dynamics in Bose-Einstein Condensates
Master thesis
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http://hdl.handle.net/11250/2467021Utgivelsesdato
2017Metadata
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- Institutt for fysikk [2653]
Sammendrag
Quantum vortices in superfluid Bose Einstein condensates (BECs) are excellent candidatesfor studying hydrodynamic phenomena, such as turbulence and chaos, due to thequantization of vortex circulation and the absence of dissipation in BECs. Since the early2000s, many experimental groups have successfully observed vortices in dilute atomicBECs.
This work mainly focuses on creating quantum chaos with a few vortices in a twodimensionalBEC of Rubidium87. We use graphics processing unit (GPU) computing methods to simulate our BEC trapped inside a harmonic potential with tight trapping in one direction. The quantum vortices are created by rotating the condensate. After generating the ground state of the BEC with a small number of singly charged vortices with positive phase winding, we imprint a 4\pi phase winding on top of one vortex in the opposite orientation to that of the original vortex. This phase imprinting annihilates the preexisting vortex and creates a new singly-charged vortex with negative phase winding. Due to the high resolution of our system and an excellent vortex tracking algorithm, the location of phase imprinting can be delicately controlled.
Both the individual vortex dynamics and the dynamics of the entire system of vorticesafter flipping a vortex have shown strong signs of chaos. This chaotic nature isfurther confirmed both qualitatively and quantitatively by employing two chaos indicatorson our numerical results. These chaos indicators are the Lyapunov exponent spectrumand the Smaller ALignment Index (SALI). The Lyapunov exponent remains positive andconverges to a positive value during an experimentally realistic time period, which is thesmoking gun for chaotic behaviour.