6,311 research outputs found
Vortex-vortex control in exciton-polariton condensates
Vortices are widely studied in fields ranging from nonlinear optics to
magnetic systems and superconductors. A vortex carries a binary information
corresponding to its topological charge, `plus' or `minus', that can be used
for information storage and processing. In spatially extended optical and
condensed many-particle systems, achieving full control over vortex formation
and its charge is particularly difficult and is not easily extended to systems
of multiple vortices. Here we demonstrate the optical creation of multiplets of
phase-locked vortices in polariton condensates using off-resonant excitation
with ring-shaped pump beams. We find that the vorticity of one vortex can be
controlled solely using the phase-locking with other nearby vortices. Using
this mechanism, we demonstrate how an existing vortex with a specific
topological charge can be inverted to the oppositely charged state, and how the
charge state of one reference vortex can be copied to a neighboring vortex.
This way we can optically encode any set of binary information onto a chain of
vortices. We further show that this information can be modified later by using
the possibility to address and manipulate each vortex in the chain
individually.Comment: Physical Review B, in pres
Circular polarization reversal of half-vortex cores in polariton condensates
Vortices are topological objects carrying quantized orbital angular momentum
and have been widely studied in many physical systems for their applicability
in information storage and processing. In systems with spin degree of freedom
the elementary excitations are so called half-vortices, carrying a quantum
rotation only in one of the two spin components. We study the spontaneous
formation and stability of localized such half-vortices in semiconductor
microcavity polariton condensates, non-resonantly excited by a linearly
polarized ring-shaped pump. The TE-TM splitting of optical modes in the
microcavity system leads to an effective spin-orbit coupling, resulting in
solutions with discrete rotational symmetry. The cross-interaction between
different spin components provides an efficient method to realize all-optical
half-vortex core switching inverting its circular polarization state. This
switching can be directly measured in the polarization resolved intensity in
the vortex core region and it can also be applied to higher order half-vortex
states.Comment: 8 pages, 8 figure
Structuring co- and counter-flowing currents of polariton condensates in concentric ring-shaped potentials
We investigate the current flow of microcavity polariton condensates loaded
into concentric ring-shaped potentials. The tunneling of the condensates
between different potential rings results in different phase-locked states,
depending on the separation of the potential rings. As a consequence, the
condensate currents in different rings can flow either in the same or opposite
direction depending on the specific configuration of the ring-shaped
potentials. In two concentric standard ring-shaped potentials, the condensates
always circulate in the same direction (co-flowing current) and the vortices
formed in the two rings share the same topological charge because of the
azimuthally uniform distribution of their phase difference. In this case,
increasing the number of the potential rings enables the excitation of
Bessel-like solutions. If the two ring-shaped potentials are engineered into an
eye shape with the inner ring being standard ring-shaped and the outer ring
being elliptically ring-shaped, the phase differences of the condensates in the
two rings along the major and minor axes of the ellipse can be opposite, which
gives rise to a counter-flowing condensate currents
Spiraling vortices in exciton-polariton condensates
We introduce the phenomenon of spiraling vortices in driven-dissipative
(non-equilibrium) exciton-polariton condensates excited by a non-resonant pump
beam. At suitable low pump intensities, these vortices are shown to spiral
along circular trajectories whose diameter is inversely proportional to the
effective mass of the polaritons, while the rotation period is mass
independent. Both diameter and rotation period are inversely proportional to
the pump intensity. Stable spiraling patterns in the form of complexes of
multiple mutually-interacting vortices are also found. At elevated pump
intensities, which create a stronger homogeneous background, we observe more
complex vortex trajectories resembling Spirograph patterns
Tilting flat bands in an empty microcavity
Recently microcavities with anisotropic materials are shown to be able to
create novel bands with non-zero local Berry curvature. The anisotropic
refractive index of the cavity layer is believed to be critical in opening an
energy gap at the tilted Dirac points. In this work, we show that an
anticrossing between a cavity mode and a Bragg mode can also form within an
empty microcavity without any birefringent materials. Flat bands are observed
within the energy gap due to the particular refractive index distribution of
the sample. The intrinsic TE-TM splitting and XY splitting induce the squeezing
of the cavity modes in momentum space, so that the flat bands are
spin-dependently tilted. Our results pave the way to investigate the spin orbit
coupling of photons in a simple microcavity without anisotropic cavity layers
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