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Motion of a Gaussian Through a 2D Dilute BEC Droplet

Kuhrij, Zhanna LU (2020) FYSK02 20201
Mathematical Physics
Department of Physics
Abstract
In the last decades, Bose-Einstein Condensates (BECs) have been a research topic of great interest. In 2015, a new type of liquid was found - dilute self-bound BEC droplets that have orders of magnitude lower density than air. These droplets are not predicted by classical van der Waals theory, but are stabilised by quantum fluctuations. In this bachelor thesis, these droplets were numerically studied when colliding with a Gaussian obstacle in two-dimensions. This is interesting because below a certain velocity, dilute BECs can behave like superfluids. This is called Landau's criterion. Several droplet velocities and Gaussian widths were tested with special focus on two cases: one where the droplet starts outside the Gaussian and one where... (More)
In the last decades, Bose-Einstein Condensates (BECs) have been a research topic of great interest. In 2015, a new type of liquid was found - dilute self-bound BEC droplets that have orders of magnitude lower density than air. These droplets are not predicted by classical van der Waals theory, but are stabilised by quantum fluctuations. In this bachelor thesis, these droplets were numerically studied when colliding with a Gaussian obstacle in two-dimensions. This is interesting because below a certain velocity, dilute BECs can behave like superfluids. This is called Landau's criterion. Several droplet velocities and Gaussian widths were tested with special focus on two cases: one where the droplet starts outside the Gaussian and one where the droplet starts with the Gaussian inside of it. The droplet was then propagated until the Gaussian was approximately at the centre of the droplet. In none of the collisions simulated, laminar- attached vortices- or vortex street flow patterns were observed. These are flow patterns one can see in similar classical examples and/or with trapped dilute BECs. However, it appeared that in all the cases the droplet did not fully behave like a superfluid. It might have been quantum fluctuations that created a drag force. Further, a large deformation of the droplet could be seen when the droplet started outside a broad Gaussian. This is believed to have been caused by the Gaussian piercing the surface of the droplet. Finally, suggestions for future research are given at the end of this thesis. (Less)
Popular Abstract
The difference between a gas and a liquid is relatively simple. A gas fills the whole space available to it, while a liquid does not necessarily. Gasses also usually have lower densities than liquids. Now, imagine a mixture of atoms that has orders of magnitude lower density than air, but still forms liquid droplets. This new type of liquid was theoretically proposed in 2015 and has since then also been created in the lab. It is stabilised by quantum mechanical effects, one of the most counterintuitive branches of physics. In my bachelor thesis, I studied how this liquid flows past an obstacle.
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author
Kuhrij, Zhanna LU
supervisor
organization
course
FYSK02 20201
year
type
M2 - Bachelor Degree
subject
keywords
Bose-Einstein Condensate, BEC, Droplet, Dilute, Liquid, Quantum Mechanics, Fluid Dynamics, Superfluid, Superfluidity, Quantum Fluctuations, LHY-correction, Flow patterns, Gaussian, 2D, Vortices, Gross-Pitaevskii Equation
language
English
id
9024798
date added to LUP
2020-07-10 10:57:35
date last changed
2020-07-10 10:57:35
@misc{9024798,
  abstract     = {{In the last decades, Bose-Einstein Condensates (BECs) have been a research topic of great interest. In 2015, a new type of liquid was found - dilute self-bound BEC droplets that have orders of magnitude lower density than air. These droplets are not predicted by classical van der Waals theory, but are stabilised by quantum fluctuations. In this bachelor thesis, these droplets were numerically studied when colliding with a Gaussian obstacle in two-dimensions. This is interesting because below a certain velocity, dilute BECs can behave like superfluids. This is called Landau's criterion. Several droplet velocities and Gaussian widths were tested with special focus on two cases: one where the droplet starts outside the Gaussian and one where the droplet starts with the Gaussian inside of it. The droplet was then propagated until the Gaussian was approximately at the centre of the droplet. In none of the collisions simulated, laminar- attached vortices- or vortex street flow patterns were observed. These are flow patterns one can see in similar classical examples and/or with trapped dilute BECs. However, it appeared that in all the cases the droplet did not fully behave like a superfluid. It might have been quantum fluctuations that created a drag force. Further, a large deformation of the droplet could be seen when the droplet started outside a broad Gaussian. This is believed to have been caused by the Gaussian piercing the surface of the droplet. Finally, suggestions for future research are given at the end of this thesis.}},
  author       = {{Kuhrij, Zhanna}},
  language     = {{eng}},
  note         = {{Student Paper}},
  title        = {{Motion of a Gaussian Through a 2D Dilute BEC Droplet}},
  year         = {{2020}},
}