講題:Entropy of Waves 摘要:While entropy is elusive, it is an indispensable physical quantity for identifying direction of evolution of thermodynamic many-body systems, measuring decoherence of quantum systems, evaluating the amount of information loss, and so on. Originally it was introduced in order to describe irreversibility of equilibrium thermodynamic systems. The idea of entropy has been expanded into various fields such as quantum computing, information science, evaluation of networks and so on as well as to nonequilibrium systems. In this talk, we consider entropy of classical wave turbulence systems. The concept of wave turbulence, that describes nonlinearly interacting waves, covers areas of fluid turbulence, optical turbulence, plasma turbulence, and so on. In the field of wave turbulence, wave action, which represents the number of waves as a function of a quantum number such as frequency or wave number, has been a subject of investigation. I propose a new idea representing wave field entropy, that doesn’t require conventional random-phase approximation (RPA). The idea is application of the concept of the von Neumann entropy to classical wave turbulence systems and it is a natural extension of Gibbs entropy (equivalently Shannon entropy in information science). For that purpose, a concept of a density matrix of classical wave fields is introduced together. I show validity of the classical von Neumann entropy to distinguish turbulent states and coherent state having broad spectrum quantitively. Examples, to which my idea is fit, include supercontinuum, optical turbulence, rogue waves, drift wave turbulence and so on, that are recognized as wave turbulence. |

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