  We characterized stacked double-pyramidal quantum dots which showed biexciton
binding energies close to zero by means of photoluminescence and
cross-correlation measurements. It was possible to obtain a sequence of two
photons with (nearly) the same energy from the biexciton-exciton-ground state
cascade, as corroborated by a basic rate-equation model. This type of
two-photon emission is both of relevance for fundamental quantum information
theory studies as well as for more exotic applicative fields such as quantum
biology.
