Duality is the quantum principle that photons (and other particles) exhibit both wave-like and particle-like behaviour, as beautifully illustrated by the Hong-Ou-Mandel (HOM) dip. When two photons meet at a beamsplitter, the outcomes that they are both reflected or both transmitted cancel out due to wavelike quantum interference. But they are then detected as particles. The probability that the two photons are found at different detectors dips then vanishes as the two photons arrive at the beamsplitter at exactly the same time.
The HOM Dip shown in Duality’s logo is a fit to data taken by Anthony and Alberto in their PhDs, which showed near-perfect quantum interference on-chip for the first time: Laing et al. Appl. Phys. Lett. 97, 211109 (2010).
