Fluctuations in Light-Matter Interactions: Emerging Quantum and Thermal Regimes

Quantum and thermal electromagnetic fluctuations give rise to macroscopic phenomena such as Casimir–Lifshitz forces and radiative heat transfer. In this colloquium, I will introduce the common theoretical framework underlying these effects and discuss how they can be shaped and controlled through geometry, material properties, and nonequilibrium conditions.

I will first discuss the giant Casimir torque arising between rotated metallic gratings, where a geometric transition at zero relative angle produces an anomalous torque enhancement and points toward the realization of a contactless quantum-vacuum torsional spring. I will then present a Kapitza-like mechanism for near-field radiative heat transfer, showing how rapid modulation of the vacuum gap or of the material response can alter the time-averaged thermal dynamics, shift stationary temperatures, and can stabilize or destabilize thermal steady states. Together, these examples illustrate emerging strategies for controlling mechanical forces and heat transport through shaping light–matter interactions.