Phys. Rev. X (in the press); preprint at

Since its discovery more than eighty years ago, Čerenkov radiation has been treated as a classical phenomenon: a charged particle travels through a dielectric medium faster than the speed of light in that medium, producing a characteristic bluish glow. But what if the particle is described as a quantum wavepacket? This question was addressed back in the 1940s and the general agreement at the time was that the quantum and classical treatments would yield the same results for the wavelengths of interest. But Ido Kaminer and colleagues have now revisited the problem to find that in fact quantum corrections do matter.

Kaminer et al. predict that the orbital angular momentum and spin of the particle would come into play, leading to intriguing effects such as a radiation frequency cut-off in the optical region, the splitting of the Čerenkov cone into two, and the backward propagation along a reverse cone. These predictions could be observed in electron vortex beams and may also be put to use in designing new types of Čerenkov detectors.