26 research outputs found
First-principles quantum simulations of many-mode open interacting Bose gases using stochastic gauge methods
Many-mode interacting Bose gases (1D,2D,3D) are simulated from first
principles. The model uses a second-quantized Hamiltonian with two-particle
interactions (possibly ranged), external potential, and interactions with an
environment, with no further approximations. Simulations are of a set of
stochastic equations that in the limit of many realizations correspond exactly
to the full quantum evolution. These are obtained using the stochastic gauge
method (derived here), an extension of the positive P phase-space
representation.
The systems investigated are: 1) Dynamics of spatial correlations in uniform
1D and 2D Bose gases after the rapid appearance of significant two-body
collisions (e.g. after entering a Feshbach resonance). 2) Dynamics of
stimulated Bose enhancement of scattered atom modes during the collision of two
Bose-Einstein condensates with a mean of 150 000 atoms. 3) Dynamics of trapped
bosons, where the size of the trap is of the same order as the range of the
interparticle potential. 4) Grand canonical thermodynamics of uniform 1D Bose
gases for a variety of temperatures and collision strengths. Observables
calculated include 1st-3rd order spatial correlation functions (including
finite separation) and momentum distributions.
The stochastic gauge method is derived, and its application to interacting
Bose gases investigated in detail. It is found to improve simulation
effectiveness under many conditions, and to be capable of overcoming
instability and boundary term problems. Additionally, conditions under which
very generalized phase-space represntations can be used to obtain tractable
many-body simulations are analysed.Comment: PhD thesis, The University of Queensland (2005), 342 pages, 61
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Liquid Thread Breakup and the Formation of Satellite Droplets
The breakup of liquid threads into smaller droplets is a fundamental problem
in fluid dynamics. In this study, we estimate the characteristic wavelength of
the breakup process by means of many-body dissipative particle dynamics. This
wavelength shows a power-law dependence on the Ohnesorge number in line with
results from stability analysis. We also discover that the number of satellite
droplets exhibits a power-law decay with exponent in the
product of the Ohnesorge and thermal capillary numbers, while the overall size
of main droplets is larger than that based on the characteristic wavelength
thanks to the asynchronous breakup of the thread. Finally, we show that the
formation of satellite droplets is the result of the advection of pinching
points towards the main droplets in a remaining thinning neck, when the
velocity gradient of the fluid exhibits two symmetric maxima.Comment: 18 pages, 9 figure