185 research outputs found
Collective optomechanical effects in cavity quantum electrodynamics
We investigate a cavity quantum electrodynamic effect, where the alignment of
two-dimensional freely rotating optical dipoles is driven by their collective
coupling to the cavity field. By exploiting the formal equivalence of a set of
rotating dipoles with a polymer we calculate the partition function of the
coupled light-matter system and demonstrate it exhibits a second order phase
transition between a bunched state of isotropic orientations and a stretched
one with all the dipoles aligned. Such a transition manifests itself as an
intensity-dependent shift of the polariton mode resonance. Our work, lying at
the crossroad between cavity quantum electrodynamics and quantum optomechanics,
is a step forward in the on-going quest to understand how strong coupling can
be exploited to influence matter internal degrees of freedom.Comment: 6 pages, 3 figure
Matter wave coupling of spatially separated and unequally pumped polariton condensates
Spatial quantum coherence between two separated driven-dissipative polariton
condensates created non-resonantly and with a different occupation is studied.
We identify the regions where the condensates remain coherent with the phase
difference continuously changing with the pumping imbalance and the regions
where each condensate acquires its own chemical potential with phase
differences exhibiting time-dependent oscillations. We show that in the mutual
coherence limit the coupling consists of two competing contributions: a
symmetric Heisenberg exchange and the Dzyloshinskii-Moriya asymmetric
interactions that enable a continuous tuning of the phase relation across the
dyad and derive analytic expressions for these types of interactions. The
introduction of non-equal pumping increases the complexity of the type of the
problems that can be solved by polariton condensates arranged in a graph
configuration. If equally pumped polaritons condensates arrange their phases to
solve the constrained quadratic minimisation problem with a real symmetric
matrix, the non-equally pumped condensates solve that problem for a general
Hermitian matrix.Comment: 3 figures, 16 page
Time-Delay Polaritonics
Non-linearity and finite signal propagation speeds are omnipresent in nature,
technologies, and real-world problems, where efficient ways of describing and
predicting the effects of these elements are in high demand. Advances in
engineering condensed matter systems, such as lattices of trapped condensates,
have enabled studies on non-linear effects in many-body systems where exchange
of particles between lattice nodes is effectively instantaneous. Here, we
demonstrate a regime of macroscopic matter-wave systems, in which ballistically
expanding condensates of microcavity exciton-polaritons act as picosecond,
microscale non-linear oscillators subject to time-delayed interaction. The ease
of optical control and readout of polariton condensates enables us to explore
the phase space of two interacting condensates up to macroscopic distances
highlighting its potential in extended configurations. We demonstrate
deterministic tuning of the coupled-condensate system between fixed point and
limit cycle regimes, which is fully reproduced by time-delayed coupled
equations of motion similar to the Lang-Kobayashi equation
Spinning nanorods - active optical manipulation of semiconductor nanorods using polarised light
In this Letter we show how a single beam optical trap offers the means for
three-dimensional manipulation of semiconductor nanorods in solution.
Furthermore rotation of the direction of the electric field provides control
over the orientation of the nanorods, which is shown by polarisation analysis
of two photon induced fluorescence. Statistics over tens of trapped
agglomerates reveal a correlation between the measured degree of polarisation,
the trap stiffness and the intensity of the emitted light, confirming that we
are approaching the single particle limit.Comment: 7 pages, 4 figure
Enhanced coupling between ballistic exciton-polariton condensates through tailored pumping
We propose a method to enhance the spatial coupling between ballistic
exciton-polariton condensates in a semiconductor microcavity based on available
spatial light modulator technologies. Our method, verified by numerically
solving a generalized Gross-Pitaevskii model, exploits the strong
nonequilibrium nature of exciton-polariton condensation driven by localized
nonresonant optical excitation. Tailoring the excitation beam profile from a
Gaussian into a polygonal shape results in refracted and focused radial streams
of outflowing polaritons from the excited condensate which can be directed
towards nearest neighbors. Our method can be used to lower the threshold power
needed to achieve polariton condensation and increase spatial coherence in
extended systems, paving the way towards creating extremely large-scale quantum
fluids of light
High-energy optical transitions and optical constants of CHNHPbI measured by spectroscopic ellipsometry and spectrophotometry
Optoelectronics based on metal halide perovskites (MHPs) have shown
substantial promise, following more than a decade of research. For prime routes
of commercialization such as tandem solar cells, optical modeling is essential
for engineering device architectures, which requires accurate optical data for
the materials utilized. Additionally, a comprehensive understanding of the
fundamental material properties is vital for simulating the operation of
devices for design purposes. In this article, we use variable angle
spectroscopic ellipsometry (SE) to determine the optical constants of
CHNHPbI (MAPbI) thin films over a photon energy range of 0.73
to 6.45 eV. We successfully model the ellipsometric data using six Tauc-Lorentz
oscillators for three different incident angles. Following this, we use
critical-point analysis of the complex dielectric constant to identify the
well-known transitions at 1.58, 2.49, 3.36 eV, but also additional transitions
at 4.63 and 5.88 eV, which are observed in both SE and spectrophotometry
measurements. This work provides important information relating to optical
transitions and band structure of MAPbI, which can assist in the
development of potential applications of the material.Comment: 18 pages, 4 figure
- …