Abstract
Quantum gases of atoms and exciton-polaritons are now well-established theoretical and experimental tools for fundamental studies of quantum many-body physics and suggest promising applications to quantum computing. Given their technological complexity, it is of paramount interest to devise other systems where such quantum many-body physics can be investigated at lesser technological expense. Here we examine a relatively well-known system of laser light propagating through thermo-optical defocusing media: based on a hydrodynamic description of light as a quantum fluid of interacting photons, we investigate such systems as a valid room-temperature alternative to atomic or exciton–polariton condensates for studies of many-body physics. First, we show that by using a technique traditionally used in oceanography it is possible to perform a direct measurement of the single-particle part of the dispersion relation of the elementary excitations on top of the photon fluid and to detect its global flow. Then, using a pump-and-probe setup, we investigate the dispersion of excitation modes of the fluid: for very long wavelengths, a sonic, dispersionless propagation is observed that we interpret as a signature of superfluid behavior.
Highlights
Quantum gases, i.e., systems in which the thermal de Broglie wavelength is larger than the average particle distance, are an ever-increasingly important area of theoretical and experimental study, with applications as diverse as quantum computing and quantum simulation of general relativity models
Building on these latter studies, an ever-growing community is active on the study of the so-called quantum fluids of light, where the many-photons forming the beam are seen as a gas of interacting particles via the optical nonlinearity of the medium [1]
Among the many hydrodynamic effects that are presently being studied in such fluids of light, we can mention turbulence [2], where the general physical processes found in a fluid or superfluid can be found in many other systems, such as plasmas or in astrophysical systems
Summary
I.e., systems in which the thermal de Broglie wavelength is larger than the average particle distance, are an ever-increasingly important area of theoretical and experimental study, with applications as diverse as quantum computing and quantum simulation of general relativity models. After early work on liquid helium, the physics of condensates has been experimentally studied in ultracold atomic gases and, more recently, in exciton–polariton fluids in semiconductor microcavities Building on these latter studies, an ever-growing community is active on the study of the so-called quantum fluids of light, where the many-photons forming the beam are seen as a gas of interacting particles via the optical nonlinearity of the medium [1]. As an alternative to actual flowing fluids, optical analogues obtained using laser beams propagating through nonlinear self-defocusing media or confined in nonlinear optical cavities have been proposed to create a photon fluid with the desired flow pattern In these systems the fluid properties can be controlled through the phase and intensity of the incident optical field, as well as by the refractive index profile and the structural boundaries of the medium [7,8,9]. An important result of this study is the experimental verification of the existence of a (phonon) wavelength regime in which, using the terminology introduced by Chiao and Boyce, photon superfluidity can be observed [15]
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