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We present the first observation of the quantum nature of the Cherenkov effect, by phasematching light & electron waves. Interacting coherently along hundreds of microns, each electron simultaneously absorbs and emits hundreds of photon quanta.

We demonstrate nanophotonic enhancement of the intrinsic spontaneous emission of X-ray-driven scintillation. By designing a 16-layers nanophotonic scintillator structure, we present the first observation of Purcell-enhanced scintillation, expressed by enhanced angular emission of visible photons.

The stability of spin of macroscopic quantum states to intrinsic noise is studied for non-resonantlypumped optically-trapped polariton condensates. We demonstrate flipping between the two spinpolarised states with >10 4 slow-down of the flip rate by tuning the optical pump power. Individual spin flips faster than 50 ps are time resolved using single-shot streak camera imaging. We reproduce our results within a mean-field model accounting for cross-spin scattering between excitons and polaritons, yielding a ratio of cross-to co-spin scattering of ∼0.6, in contrast with previous literature suggestions.