3,397 research outputs found
Floquet engineering of optical solenoids and quantized charge pumping along tailored paths in two-dimensional Chern insulators
The insertion of a local magnetic flux, as the one created by a thin
solenoid, plays an important role in gedanken experiments of quantum Hall
physics. By combining Floquet engineering of artificial magnetic fields with
the ability of single-site addressing in quantum-gas microscopes, we propose a
scheme for the realization of such local solenoid-type magnetic fields in
optical lattices. We show that it can be employed to manipulate and probe
elementary excitations of a topological Chern insulator. This includes
quantized adiabatic charge pumping along tailored paths inside the bulk, as
well as the controlled population of edge modes.Comment: 6 pages, 4 figures. Discussions and references are update
Hopf characterization of two-dimensional Floquet topological insulators
We present a topological characterization of time-periodically driven
two-band models in 2+1 dimensions as Hopf insulators. The intrinsic periodicity
of the Floquet system with respect to both time and the underlying
two-dimensional momentum space constitutes a map from a three dimensional torus
to the Bloch sphere. As a result, we find that the driven system can be
understood by appealing to a Hopf map that is directly constructed from the
micromotion of the drive. Previously found winding numbers are shown to
correspond to Hopf invariants, which are associated with linking numbers
describing the topology of knots in three dimensions. Moreover, after being
cast as a Hopf insulator, not only the Chern numbers, but also the winding
numbers of the Floquet topological insulator become accessible in experiments
as linking numbers. We exploit this description to propose a feasible scheme
for measuring the complete set of their Floquet topological invariants in
optical lattices.Comment: 6 pages, 3 figures + 2 pages, 1 figure supplementar
A sub-basin scale dust plume source frequency inventory for southern Africa, 2005-2008
We present a dust plume source inventory for southern Africa. In order to locate and track the local, short-lived plume events, source and frequency data have been derived from Meteosat Second Generation (MSG) thermal infrared composite data (4 km data using 8.7, 10.8, and 12.0 µm) and Moderate Resolution Imaging Spectroradiometer (MODIS) visible composite data (0.25 km data utilizing 0.620 – 0.670 µm, 0.545 – 0.565 µm, and 0.459 – 0.479 µm). Between January 2005 and December 2008, a total of 328 distinct daytime dust plumes more than 10 km in length were detected. These plumes were attributed to 101 distinct point sources, consisting largely of ephemeral inland lakes, coastal pans as well as dry river valleys in Namibia, Botswana, and South Africa. These data also provided sub-basin scale source observations for large basins such as Etosha and Makgadikgadi Pans
Superfluid-insulator transition in a periodically driven optical lattice
We demonstrate that the transition from a superfluid to a Mott insulator in
the Bose-Hubbard model can be induced by an oscillating force through an
effective renormalization of the tunneling matrix element. The mechanism
involves adiabatic following of Floquet states, and can be tested
experimentally with Bose-Einstein condensates in periodically driven optical
lattices. Its extension from small to very large systems yields nontrivial
information on the condensate dynamics.Comment: 4 pages, 4 figures, RevTe
How to Directly Measure Floquet Topological Invariants in Optical Lattices
The classification of topological Floquet systems with time-periodic
Hamiltonians transcends that of static systems. For example, spinless fermions
in periodically driven two-dimensional lattices are not completely
characterized by the Chern numbers of the quasienergy bands, but rather by a
set of winding numbers associated with the quasienergy gaps. We propose a
scheme for measuring these winding numbers in a system of fermionic cold atoms
in a periodically driven optical lattice efficiently and directly. It is based
on the construction of a one-parameter family of experimentally feasible
drives, continuously connecting the Floquet system of interest to a trivial
reference system. The winding numbers are then determined by the identification
and the tomography of the band-touching singularities occurring on the way. As
a byproduct, we also propose a method for probing spectral properties of time
evolution operators via a time analog of crystallography.Comment: 6 pages, 5 figure
Epitaxial growth of deposited amorphous layer by laser annealing
We demonstrate that a single short pulse of laser irradiation of appropriate energy is capable of recrystallizing in open air an amorphous Si layer deposited on a (100) single-crystal substrate into an epitaxial layer. The laser pulse annealing technique is shown to overcome the interfacial oxide obstacle which usually leads to polycrystalline formation in normal thermal annealing
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