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Register a new userReal-space collapse of a polariton condensate
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Added by
Lorenzo Dominici dr
Publication date
2013
fields
Physics
and research's language is
English
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Polaritons in microcavities are versatile quasi-2D bosonic particles with a high degree of coherence and strong nonlinearities, thanks to their hybrid light-matter character. In their condensed form, they display striking quantum hydrodynamic features analogous to atomic Bose-Einstein condensates, such as long-range order coherence, superfluidity and quantized vorticity. Their variegated dispersive and dissipative properties, however, set significant differences from their atomic counterpart. In this work, we report the unique phenomenology that is observed when a pulse of light impacts the polariton vacuum: the condensate that is instantaneously formed does not splash in real space but instead coheres into an enigmatic structure, featuring concentric rings and, most notably, a sharp and bright peak at the center. Using a state-of-the-art ultrafast imaging with 50 fs time steps, we are able to track the dynamics of the polariton mean-field wavefunction in both real and reciprocal space. The observation of the real-space collapse of the condensate into an extremely localized---resolution limited---peak is at odd with the repulsive interactions of polaritons and their positive effective mass. An unconventional mechanism is therefore at play to account for our observations. Our modeling suggests that self-trapping due to a local heating of the crystal lattice---that can be described as a collective polaron formed by a polariton condensate---could be involved. These observations hint at the fascinating fluid dynamics of polaritons in conditions of extreme intensities and ultrafast times.
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We study the collapse of an attractive atomic Bose-Einstein condensate prepared in the uniform potential of an optical-box trap. We characterise the critical point for collapse and the collapse dynamics, observing universal behaviour in agreement with theoretical expectations. Most importantly, we observe a clear experimental signature of the counterintuitive weak collapse, namely that making the system more unstable can result in a smaller particle loss. We experimentally determine the scaling laws that govern the weak-collapse atom loss, providing a benchmark for the general theories of nonlinear wave phenomena.
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We consider a condensate of exciton-polaritons in a diluted magnetic semiconductor microcavity. Such system may exhibit magnetic self-trapping in the case of sufficiently strong coupling between polaritons and magnetic ions embedded in the semiconductor. We investigate the effect of the nonequilibrium nature of exciton-polaritons on the physics of the resulting self-trapped magnetic polarons. We find that multiple polarons can exist at the same time, and derive a critical condition for self-trapping which is different to the one predicted previously in the equilibrium case. Using the Bogoliubov-de Gennes approximation, we calculate the excitation spectrum and provide a physical explanation in terms of the effective magnetic attraction between polaritons, mediated by the ion subsystem.
We report the experimental observation and control of space and time-resolved light-matter Rabi oscillations in a microcavity. Our setup precision and the system coherence are so high that coherent control can be implemented with amplification or switching off of the oscillations and even erasing of the polariton density by optical pulses. The data is reproduced by a fundamental quantum optical model with excellent accuracy, providing new insights on the key components that rule the polariton dynamics.
Quantum vortices, the quantized version of classical vortices, play a prominent role in superfluid and superconductor phase transitions. However, their exploration at a particle level in open quantum systems has gained considerable attention only recently. Here we study vortex pair interactions in a resonant polariton fluid created in a solid-state microcavity. By tracking the vortices on picosecond time scales, we reveal the role of nonlinearity, as well as of density and phase gradients, in driving their rotational dynamics. Such effects are also responsible for the split of composite spin-vortex molecules into elementary half-vortices, when seeding opposite vorticity between the two spinorial components. Remarkably, we also observe that vortices placed in close proximity experience a pull-push scenario leading to unusual scattering-like events that can be described by a tunable effective potential. Understanding vortex interactions can be useful in quantum hydrodynamics and in the development of vortex-based lattices, gyroscopes, and logic devices.
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