Using an angle-resolved heterodyne four-wave-mixing technique, we probe the low momentum excitation spectrum of a coherent polariton gas. The experimental results are well captured by the Bogoliubov transformation which describes the transition from single particle excitations of a normal fluid to soundlike excitations of a superfluid. In a dense coherent polariton gas, we find all the characteristics of a Bogoliubov transformation, i.e., the positive and negative energy branch with respect to the polariton gas energy at rest, soundlike shapes for the excitations dispersion, intensity, and linewidth ratio between the two branches in agreement with the theory. The influence of the nonequilibrium character of the polariton gas is shown by a careful analysis of its dispersion.
The Bogoliubov transformation of a polariton quantum fluid has recently been revealed in the four-wave mixing response of a driven microcavity polariton gas. In this work, we investigate the modifications that the dual nature of microcavity polaritons produce on the excitations of this particular half-light-half-matter quantum fluid. We discuss in particular the Bogoliubov character of the excitations of a lower polariton superfluid when it coexists with upper polaritons. We show unique effects resulting from the interplay between polariton decay and Bogoliubov transformation such as the modification of the Bogoliubov dispersion or the slowing down of the four-wave mixing dynamics.
We have fabricated all-dielectric high-Q optical pillar resonators with embedded colloidal CdSe/ZnS quantum dots or rods as light emitters by focused ion beam milling. Three-dimensional light confinement and distinct pillar microcavity modes are observed. Results from a waveguide model for the mode patterns and their spectral positions are in excellent agreement with the experimental data. Cavities with elliptical cross sections show higher quality factors in the short axis direction than do circular resonators of the same cross-sectional area.
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