New theory explains how lasers create entangled light

Ivan Gonoskov, Christian Hünecke and Stefanie Gräfe of the Institute of Physical Chemistry at Friedrich Schiller University Jena have developed an analytical framework revealing how entangled light arises from intense laser interactions with matter. The researchers began with a Pauli-Fierz description to model the dynamics of electrons and light, identifying that nonlinearities in the electronic dipole response directly correlate to nonclassicality as measured by Wigner-function negativity. This work establishes a predictive link between strong-field electron behavior and the quantum properties of emitted light, offering a path toward generating high-photon-number nonclassical radiation in high-order harmonic generation. The results provide a basis for engineering nonclassical states in intense laser-matter interactions. The analytical framework begins with a Pauli-Fierz Hamiltonian, offering a fully quantum description of charged particles interacting with electromagnetic fields, and departs from previous approaches by directly using the time-dependent Schrödinger equation without conditioning or post-selection techniques. This foundation allows for a specific factorization of the light-matter system into a field-driven electronic state and a quantized light state, a method that implicitly accounts for the influence of…