arXiv subjects

Ivan Amelio

Publications and source records attributed to Ivan Amelio.

22 records · Page 2Linked to original sources

arXiv2020

Galilean boosts and superfluidity of resonantly driven polariton fluids in the presence of an incoherent reservoir

We theoretically investigate how the presence of a reservoir of incoherent excitations affects the superfluidity properties of resonantly driven polariton fluids. While in the absence of reservoir the two cases of a defect moving in a fluid at rest and of a fluid flowing against a static defect are linked by a formal Galilean transformation, here the reservoir defines a privileged reference frame attached to the semiconductor structure and causes markedly different features between the two settings. The consequences on the critical velocity for superfluidity are highlighted and compared to experiments in resonantly driven excitons polaritons.

cond-mat.quant-gas↗

arXiv2019

New perspectives on superfluidity in resonantly--driven polariton fluids

In this paper we discuss, within the Gross--Pitaevskii framework, superfluidity, soliton nucleation, and instabilities in a non-equilibrium polariton fluid injected by a spatially localized and continuous-wave coherent pump and flowing against a defect located outside the pump spot. In contrast to equilibrium condensates, the steady-state solutions of the driven-dissipative equations in this specific geometry hardly show a clean superfluid flow around the defect and rather feature a crossover from shallow to deep soliton-like perturbation. This is explained in terms of the properties of one-dimensional flows, in particular their weak dependence on the pump parameters and their rapid transition to a super-sonic regime under the effect of the quantum pressure; such a highly nonlinear behaviour calls for quantitative experimental tests of the underlying Gross--Pitaevskii equation. The role of disorder and of a incoherent reservoir in inducing non-stationary behaviours with moving vortices is also highlighted.

cond-mat.quant-gas↗

arXiv2019

Dispersion relation of the collective excitations in a resonantly driven polariton fluid

Exciton-polaritons in semiconductor microcavities constitute the archetypal realization of a quantum fluid of light. Under coherent optical drive, remarkable effects such as superfluidity, dark solitons or the nucleation of hydrodynamic vortices have been observed. These phenomena can be all understood as a specific manifestation of collective excitations forming on top of the polariton condensate. In this work, we performed a Brillouin scattering experiment to measure their dispersion relation $ω(\mathbf{k})$ directly. The result, such as a speed of sound which is apparently twice too low, cannot be explained upon considering the polariton condensate alone. In a combined theoretical and experimental analysis, we demonstrate that the presence of a reservoir of long-lived excitons interacting with polaritons has a dramatic influence on the nature and characteristic of the quantum fluid, and that it explains our measurement quantitatively. This work clarifies the role of such a reservoir in the different polariton hydrodynamics phenomena occurring under resonant optical drive. It also provides an unambiguous tool to determine the condensate-to-reservoir fraction in the quantum fluid, and sets an accurate framework to approach novel ideas for polariton-based quantum-optical applications.

cond-mat.quant-gas↗

arXiv2018

Probing quantum turbulence in $^4$He by quantum evaporation measurements

Theory of superfluid $^4$He shows that, due to strong correlations and backflow effects, the density profile of a vortex line has the character of a density modulation and it is not a simple rarefaction region as found in clouds of cold bosonic atoms. We find that the basic features of this density modulation are represented by a wave--packet of cylindrical symmetry in which rotons with positive group velocity have a dominant role: The vortex density modulation can be viewed as a cloud of virtual excitations, mainly rotons, sustained by the phase of the vortex wave function. This suggests that in a vortex reconnection some of these rotons become real so that a vortex tangle is predicted to be a source of non-thermal rotons. The presence of such vorticity induced rotons can be verified by measurements at low temperature of quantum evaporation of $^4$He atoms. We estimate the rate of evaporation and this turns out to be detectable by current instrumentation. Additional information on the microscopic processes in the decay of quantum turbulence will be obtained if quantum evaporation by high energy phonons should be detected.

cond-mat.other↗