Scientists identify light as a quantum brake for nanoscale systems

Researchers from Germany and India have established that light can function as a quantum brake, significantly slowing the movement of particles at the nanoscale. The findings, published in the journal Nature, demonstrate that light can exert a drag force on fluorescent carbon-mesh nanotubes suspended in water, countering the conventional understanding that illumination primarily imparts energy and motion to matter.

The phenomenon, described by the scientific team from Ruhr-University Bochum and their collaborators as "light-induced quantum friction," occurs when the nanotubes absorb light. This absorption generates mobile excitons—energetic pairings of an electron and a corresponding electron hole. As these charges fluctuate within the nanotube, they couple with the surrounding water molecules in the aqueous solution.

This continuous coupling results in a transfer of momentum from the nanotubes to the water. The interaction creates a substantial drag force, causing the carbon-mesh structures to decelerate as though they were moving through a much thicker, more viscous liquid.

The discovery challenges fundamental assumptions in physics regarding the interaction between light and matter. While photons are routinely understood to energise or accelerate particles, the ability to induce deceleration through quantum friction introduces a previously undocumented mechanism for manipulating molecular behaviour.

By proving that light can actively restrict motion rather than solely driving it, the researchers have established a new theoretical and practical framework. According to the published research, this principle of light-induced drag opens new avenues for the precise control and regulation of complex nanoscale systems.