Biophotons, coherence and photocount statistics: a critical review

TL;DR

This review critically examines the current understanding of biophoton emission from biological samples, focusing on its statistical properties, coherence, and nonclassical features, concluding that evidence for quantum coherence remains unconfirmed.

Contribution

It provides a comprehensive categorization of experimental claims on biophoton statistics and highlights the lack of reliable evidence for coherence or nonclassicality in UPE.

Findings

UPE from biological systems is well established experimentally.

No reliable evidence for coherence or nonclassicality of UPE has been found.

The paper suggests future research directions in biophoton statistical properties.

Abstract

Biological samples continuously emit ultra-weak photon emission (UPE, or "biophotons") which stems from electronic excited states generated chemically during oxidative metabolism and stress. Thus, UPE can potentially serve as a method for non-invasive diagnostics of oxidative processes or, if discovered, also of other processes capable of electron excitation. While the fundamental generating mechanisms of UPE are fairly elucidated together with their approximate ranges of intensities and spectra, statistical properties of UPE is still a highly challenging topic. Here we review claims about nontrivial statistical properties of UPE, such as coherence and squeezed states of light. After introduction to the necessary theory, we categorize the experimental works of all authors to those with solid, conventional interpretation and those with unconventional and even speculative interpretation. The conclusion of our review is twofold; while the phenomenon of UPE from biological systems can be considered experimentally well established, no reliable evidence for the coherence or nonclassicality of UPE was actually achieved up to now. Furthermore, we propose perspective avenues in the research of statistical properties of biological UPE.