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

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

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

High-energy optical transitions and optical constants of CH3_3NH3_3PbI3_3 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 CH$_3$NH$_3$PbI$_3$ (MAPbI$_3$) 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$_3$, which can assist in the development of potential applications of the material.Comment: 18 pages, 4 figure

Spontaneous symmetry breaking in a polariton and photon laser

We report on the simultaneous observation of spontaneous symmetry breaking and long-range spatial coherence both in the strong and the weak-coupling regime in a semiconductor microcavity. Under pulsed excitation, the formation of a stochastic order parameter is observed in polariton and photon lasing regimes. Single-shot measurements of the Stokes vector of the emission exhibit the buildup of stochastic polarization. Below threshold, the polarization noise does not exceed 10%, while above threshold we observe a total polarization of up to 50% after each excitation pulse, while the polarization averaged over the ensemble of pulses remains nearly zero. In both polariton and photon lasing regimes, the stochastic polarization buildup is accompanied by the buildup of spatial coherence. We find that the Landau criterion of spontaneous symmetry breaking and Penrose-Onsager criterion of long-range order for Bose-Einstein condensation are met in both polariton and photon lasing regimes.Comment: 5 pages, 3 figure