ONE OF THE SURPRISES OF QUANTUM MECHANICS IS ZERO POINT FLUCTUATIONS WHICH PERVADE BOTH VACUUM AND MATTER.
Far from just theoretical interest, practical consequences exist at the nanoscale when these fluctuations cause forces that attract or repel macroscopic bodies. They are also manifested at the molecular level where tiny fluctuating dipoles lead to molecular attractive or repulsive forces and energy transfer. However these forces are often small and difficult to enhance. In this issue, Guo et. al. have pointed out a giant fluctuational force between moving bodies caused by a singular Fabry-Perot mode.
Vacuum can interestingly exert a drag force between moving media if they are sufficiently close to each other. This is very much like the frictional force we all experience but with one key difference: no physical contact is needed, just a nanoscale vacuum gap! The force arises due to photons exchanged between the moving media which can be driven by a temperature difference. What is non-intuitive is that even when the temperatures of the two moving bodies are assumed to be same, an interesting effective temperature difference develops solely due to Doppler shifted frequencies. Think of it like a nanoscale circuit, where the energy carriers are photons instead of electrons and the potential difference of a battery is provided by the Doppler shifted distribution of photons inside the moving bodies.
Our article puts forth a giant enhancement in this vacuum frictional force arising due to a singular Fabry-Perot resonance. The canonical example of moving bodies is a pair of Fabry-Perot plates with a nanoscale gap between them. Light bouncing back and forth between FabryPerot plates is a textbook example every optical scientist studies. However, when the plates are set into motion the amplitude and phase of evanescent waves reflected from the plates develop fundamentally unique properties causing a giant increase in vacuum friction. This phenomenon requires energy from the mechanical motion of the plates and bears an uncanny similarity to lasing. The singular resonance causes a giant increase in the number of photons exchanged between the plates, enough to cause a fire due to vacuum friction! The effect is robust to loss and dispersion but the velocity of motion needs to be of the order of the Fermi velocity of electrons in the metal, a daunting task.