Modul: MAT675 PDE and Mathematical Physics

## Optical nonclassicality, decoherence and entanglement

Talk by Prof. Dr. Stephan De Bievre

**Date:** 03.03.22 **Time:** 16.00 - 17.00 **Room:** ETH HG G 19.1

A state (density matrix) of a bosonic quantum field, such as an n-mode optical field, is said to be optically classical if it is a mixture of coherent states. Whereas this definition is straightforward, a simple characterization of the optically classical density matrices is not available. A variety of witnesses have been introduced to characterize optical (non)classicality. Optically classical states have, for example, a positive Wigner function, but the opposite is not true. In this talk I will review some of the recent and not so recent literature on this question and present a new such witness, the Quadrature Coherence Scale (QCS). Using the QCS and other nonclassicality witnesses, the link between optical nonclassicality, entanglement and decoherence will be elucidated.