Observation of light thermalization to negative temperature Rayleigh-Jeans equilibrium states in multimode optical fibers

Abstract

Although the temperature of a thermodynamic system is usually believed to be a positive quantity, under particular conditions, negative temperature equilibrium states are also possible. Negative temperature equilibriums have been observed with spin systems, cold atoms in optical lattices and two-dimensional quantum superfluids. Here we report the observation of Rayleigh-Jeans thermalization of light waves to negative temperature equilibrium states. The optical wave relaxes to the equilibrium state through its propagation in a multimode optical fiber, i.e., in a conservative Hamiltonian system. The bounded energy spectrum of the optical fiber enables negative temperature equilibriums with high energy levels (high order fiber modes) more populated than low energy levels (low order modes). Our experiments show that negative temperature speckle beams are featured, in average, by a non-monotonous radial intensity profile. The experimental results are in quantitative agreement with the Rayleigh-Jeans theory without free parameters. Bringing negative temperatures to the field of optics opens the door to the investigation of fundamental issues of negative temperature states in a flexible experimental environment.

12 pages, 14 figures

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• Obstruction to ergodicity in nonlinear Schrödinger equations with resonant potentials
• Random matrix model of Kolmogorov-Zakharov turbulence
• Resolving the Debate Between Boltzmann and Gibbs Entropy: Relative Energy Window Eliminates Thermodynamic Inconsistencies and Allows Negative Absolute Temperatures
• Spatio-temporal thermalization and adiabatic cooling of guided light waves
• Onsager coefficients in a coupled-transport model displaying a condensation transition
• Universal Routing of Light via Optical Thermodynamics
• Thermodynamic criteria for signaling in quantum channels
• Dynamic thermalization on noisy quantum hardware
• Dynamical thermalization and turbulence in social stratification models
• Irreversible thermalization vs reversible dynamics mediated by anomalous correlators: Wave turbulence theory and experiments in optical fibers
• Spatio-temporal equilibrium thermodynamics of guided optical waves at positive and negative temperatures