458 research outputs found
Field-induced topological pair-density wave states in a multilayer optical lattice
We study the superfluid phases of a Fermi gas in a multilayer optical lattice
system in the presence of out-of-plane Zeeman field, as well as spin-orbit (SO)
coupling. We show that the Zeeman field combined with the SO coupling leads to
exotic topological pair-density wave (PDW) phases in which different layers
possess different superfluid order parameters, even though each layer
experiences the same Zeeman field and the SO coupling. We elucidate the
mechanism of the emerging PDW phases, and characterize their topological
properties by calculating the associated Chern numbers.Comment: 7 pages, 6 figures, accepted by Phys. Rev.
Hybrid air bearings for high speed turbo machinery
This PhD project is set out to develop a type of hybrid journal air bearings with reduced reliance on the supply of compressed air for mobile turbomachinery applications. The research work covers hydrostatic and hybrid journal air bearings with non-compliant clearance boundaries. The approach adopted combined numerical analysis based on CFD and experimental verification of the designs.
The research can be divided into three sections. In the
first section, numerical approaches to model hydrostatic
and hybrid journal air bearings with a fixed clearance
boundary were developed based on finite difference method
(FDM) and finite volume method (FVM) respectively. In the
second and third section, theoretical and experimental
studies were performed on hydrostatic and hybrid journal
air bearings. Performance of the bearings was
investigated in non-rotational and rotational conditions.
The analysis on stability and natural frequencies of
rotor bearing system was performed using the linear
bearing model. The unbalance responses of the rotor in the test rig were predicted using non-linear transient analysis and measured experimentally from 50k rpm to 120k rpm in rotor speed. Through the theoretical and experimental investigations of the hybrid journal air bearings, the objectives of the project have been implemented and the aims have been met
Synthetic Landau levels and spinor vortex matter on Haldane spherical surface with magnetic monopole
We present a flexible scheme to realize exact flat Landau levels on curved
spherical geometry in a system of spinful cold atoms. This is achieved by
Floquet engineering of a magnetic quadrupole field. We show that a synthetic
monopole field in real space can be created. We prove that the system can be
exactly mapped to the electron-monopole system on sphere, thus realizing
Haldane's spherical geometry for fractional quantum Hall physics. The scheme
works for either bosons or fermions. We investigate the ground state vortex
pattern for an -wave interacting atomic condensate by mapping this system to
the classical Thompson's problem. We further study the distortion and stability
of the vortex pattern when dipolar interaction is present. Our scheme is
compatible with current experimental setup, and may serve as a promising route
of investigating quantum Hall physics and exotic spinor vortex matter on curved
space.Comment: 11 pages, 4 figure
Two-component polariton condensate in optical microcavity
We present a scheme for engineering the extended two-component Bose-Hubbard
model using polariton condensate supported by optical microcavity. Compared to
the usual two-component Bose-Hubbard model with only Kerr nonlinearity, our
model includes a nonlinear tunneling term which depends on the number
difference of the particle in the two modes. In the mean field treatment, this
model is an analog to a nonrigid pendulum with a variable pendulum length whose
sign can be also changed. We study the dynamic and ground state properties of
this model and show that there exists a first-order phase transition as the
strength of the nonlinear tunneling rate is varied. Furthermore, we propose a
scheme to obtain the polariton condensate wave function.Comment: 9 pages, 8 figure
Dynamically manipulating topological physics and edge modes in a single degenerate optical cavity
We propose a scheme to simulate topological physics within a single
degenerate cavity, whose modes are mapped to lattice sites. A crucial
ingredient of the scheme is to construct a sharp boundary so that the open
boundary condition can be implemented for this effective lattice system. In
doing so, the topological properties of the system can manifest themselves on
the edge states, which can be probed from the spectrum of an output cavity
field. We demonstrate this with two examples: a static Su-Schrieffer-Heeger
chain and a periodically driven Floquet topological insulator. Our work opens
up new avenues to explore exotic photonic topological phases inside a single
optical cavity.Comment: 6 pages, 5 figure
Quantum phase transition of Bose-Einstein condensates on a ring nonlinear lattice
We study the phase transitions in a one dimensional Bose-Einstein condensate
on a ring whose atomic scattering length is modulated periodically along the
ring. By using a modified Bogoliubov method to treat such a nonlinear lattice
in the mean field approximation, we find that the phase transitions are of
different orders when the modulation period is 2 and greater than 2. We further
perform a full quantum mechanical treatment based on the time-evolving block
decimation algorithm which confirms the mean field results and reveals
interesting quantum behavior of the system. Our studies yield important
knowledge of competing mechanisms behind the phase transitions and the quantum
nature of this system.Comment: 12 pages, 7 figure
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