*Article* **Description of Dressed-Photon Dynamics and Extraction Process**

**Suguru Sangu 1,\* and Hayato Saigo 2**

> 2

	- Department of Bioscience, Nagahama Institute of Bio-Science and Technology, Nagahama 526-0829, Japan; h\_saigoh@nagahama-i-bio.ac.jp

**Abstract:** Several interesting physical phenomena and industrial applications explained by the dressed photon have been reported in recent years. These require a novel concept in an off-shell science that deviates from the conventional optics, satisfying energy and momentum conservation laws. In this paper, starting from an original model that captures dressed-photon characteristics phenomenologically, the dynamics of the dressed photon in a nanomatter system and the mechanism for extracting internal degrees of freedom of the dressed photon to an external space have been examined by theoretical and numerical approaches. Our proposal is that basis states of the dressed photon can be transformed to the form that reflects the spatial distribution of the dressed-photon steady state in the system, and some of basis states with predetermined spatial distribution can relate to the dissipation components in the external space by means of the renormalization technique. From the results of numerical simulation, it is found that quasi-static states are regarded as the photon with light mass or massless, and the extraction of active states strongly affects the spatial distribution in a new steady state. The concept for extracting dressed-photon energy to an external space will contribute to a detailed understanding of dressed-photon physics and future industrial applications.

**Citation:** Sangu, S.; Saigo, H. Description of Dressed-Photon Dynamics and Extraction Process. *Symmetry* **2021**, *13*, 1768. https:// doi.org/10.3390/sym13101768

Academic Editor: Motoichi Ohtsu

Received: 3 September 2021 Accepted: 20 September 2021 Published: 23 September 2021

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**Keywords:** dressed photon; localization; dissipation; off-shell science; non-equilibrium open system; quantum master equation; quantum density matrix; projection operator; renormalization
