3 papers
quant-ph2025
Is there a conflict between causality and diamagnetism?
Niclas Westerberg, Stephen M. Barnett
There is a long-standing apparent conflict between the existence of diamagnetism and causality as expressed through the Kramers-Kronig relations. In essence, using causality argume…
physics.optics2025
Quantised helicity in optical media
Neel Mackinnon, Jörg B. Götte, Stephen M. Barnett +1
We present a new approach to the definition of optical helicity in a medium. Our approach resolves the problem that duality transformations which simultaneously combine $\mathbf{E}…
quant-ph2025
Is diamagnetism really acausal?
Niclas Westerberg, Stephen M. Barnett
Diamagnetism, in which the magnetisation in a medium opposes the direction of an applied magnetic field, is a weak but familiar effect in a wide class of materials. Being weak it i…