Mainz 2026 – scientific programme
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Q: Fachverband Quantenoptik und Photonik
Q 78: Quantum Optics and Control III
Q 78.6: Talk
Friday, March 6, 2026, 15:45–16:00, P 3
Quantized helicity in optical media — Neel Mackinnon1, •Jörg Götte1,2, Stephen Barnett1, and Niclas Westerberg1 — 1University of Glasgow, University Avenue, Glasgow G12 8QQ, United Kingdom — 2Max-Planck-Institut für Physik komplexer Systeme, Nöthnitzer Str. 38, 01187 Dresden, Germany
We present a novel approach to defining optical helicity in dispersive media that resolves the fundamental incompatibility between duality transformations and linear constitutive relations. By treating electromagnetic and matter degrees of freedom equally, we derive a helicity density that explicitly includes contributions from polarization and magnetization fields. Our formalism, based on duality transformation of vector potentials and matter fields, naturally expresses helicity in terms of polariton excitations. In dual-symmetric media, each circularly polarised polariton carries helicity equal to total energy density divided by frequency, generalising the free-space result. For arbitrary media, single-polariton states exhibit wave-vector-dependent helicity, reflecting different electric and magnetic responses. Remarkably, when helicity is not conserved, superpositions of polariton branches exhibit temporal oscillations analogous to neutrino oscillations. States initially prepared in helicity eigenstates evolve with time-dependent helicity, oscillating at frequency differences between polariton branches. Unlike previous approaches, our definition naturally extends to inhomogeneous, lossy, chiral, and nonreciprocal media, providing a unified framework for understanding helicity transfer in light-matter interactions and chiroptical effects.
Keywords: Helicity; Polaritons; Chirality