196 research outputs found
Detection of Zak phases and topological invariants in a chiral quantum walk of twisted photons
Topological insulators are fascinating states of matter exhibiting protected
edge states and robust quantized features in their bulk. Here, we propose and
validate experimentally a method to detect topological properties in the bulk
of one-dimensional chiral systems. We first introduce the mean chiral
displacement, and we show that it rapidly approaches a multiple of the Zak
phase in the long time limit. Then we measure the Zak phase in a photonic
quantum walk, by direct observation of the mean chiral displacement in its
bulk. Next, we measure the Zak phase in an alternative, inequivalent timeframe,
and combine the two windings to characterize the full phase diagram of this
Floquet system. Finally, we prove the robustness of the measure by introducing
dynamical disorder in the system. This detection method is extremely general,
as it can be applied to all one-dimensional platforms simulating static or
Floquet chiral systems.Comment: 10 pages, 7 color figures (incl. appendices) Close to the published
versio
Red light-emitting Carborane-BODIPY dyes: Synthesis and properties of visible-light tuned fluorophores with enhanced boron content
A small library of 2,6- and 3,5-distyrenyl-substituted carborane-BODIPY dyes was efficiently synthesized by
means of a Pd-catalyzed Heck coupling reaction. Styrenyl-carborane derivatives were exploited as molecular
tools to insert two carborane clusters into the fluorophore core and to extend the π-conjugation of the final
molecule in a single synthetic step. The synthetic approach allows to increase the molecular diversity of this class
of fluorescent dyes by the synthesis of symmetric or asymmetric units with enhanced boron content. The
structural characterization and the photoluminescence (PL) properties of synthesized dyes were evaluated, and
the structure/properties relationships have been investigated by theoretical calculations. The developed compounds
exhibit a significant bathochromic shift compared to their parent fluorophore scaffolds, and absorption
and emission patterns were practically unaffected by the different substituents (Me or Ph) on the Ccluster atom
(Cc) of the carborane cage or the cluster isomer (ortho- or meta-carborane). Remarkably, the presence of carborane
units at 2,6-positions of the fluorophore produced a significant increase of the emission fluorescent
quantum yields, which could be slightly tuned by changing the Cc-substituent and the carborane isomer, as well
as introducing ethylene glycol groups at the meso-position of the BODIPY
Distilling the topology of the Hofstadter model through a diffraction experiment
In two and three spatial dimensions, the transverse response experienced by a
charged particle on a lattice in a uniform magnetic field is proportional to a
topological invariant, the first Chern number, characterizing the energy bands
of the underlying Hofstadter Hamiltonian. In four dimensions, the transverse
response is also quantized, and controlled by the second Chern number. These
remarkable features solely arise from the magnetic translational symmetry. Here
we show that the symmetries of the two-, three- and four-dimensional Hofstadter
Hamiltonians may be encrypted in optical diffraction gratings, such that simple
photonic experiments allow one to extract the first and the second Chern
numbers of the whole energy spectra. This result is particularly remarkable in
three and four dimensions, where complete topological characterizations have
not yet been achieved experimentally. Side-by-side to the theoretical analysis,
in this work we present the experimental study of optical gratings analogues of
the two- and three-dimensional Hofstadter models
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