Beyond single-photon emission, generating correlated N-photon bundles, e.g., a photon pair, is essential for various quantum technologies including quantum teleportation and metrology. A widely explored approach exploits the radiative biexciton cascade in individual (mainly epitaxially grown) quantum dots (QDs). Here, we investigate such a cascade in colloidal CsPbBr3 QDs, a scalable and solution-processable quantum-light emitter. By matching their size-dependent biexciton binding energies to their size-independent phonon energies, we demonstrate the generation of time-correlated and energy-degenerate photon pairs in large (>15 nm) QDs. Under pulsed excitation at 4 K, we observe pronounced photon bunching, with a g(2)(0) of up to 7 in Hanbury Brown and Twiss measurements. The excitation-density-dependent bunching is quantitatively reproduced by multicolor numerical calculations, suggesting the cascade involving biexciton and phonon-mediated exciton decay as origin of the photon pair. Our findings provide new insights into energy-degenerate photon-pair generation in these highly engineerable quantum-light emitters, marking important steps toward their application in quantum-information technologies.

Greatly enhanced light absorption is reported in large perovskite quantum dots by realizing a transition with a giant oscillator strength at the optical bandgap.

Swiss Summer School on Materials Chemistry 2025: Materials characterization through X-ray total scattering. Villars-sur-Glâne, Fribourg, June 23-24, 2025.