Heralded Generation\nof Correlated Photon Pairs from\nCdS/CdSe/CdS Quantum Shells

Quantum information processing demands efficient quantum\nlight\nsources (QLS) capable of producing high-fidelity single photons or\nentangled photon pairs. Single epitaxial quantum dots (QDs) have long\nbeen proven to be efficient sources of deterministic single photons;\nhowever, their production via molecular-beam epitaxy presents scalability\nchallenges. Conversely, colloidal semiconductor QDs offer scalable\nsolution processing and tunable photoluminescence, but suffer from\nbroader linewidths and unstable emissions. This leads to spectrally\ninseparable emission from exciton (X) and biexciton (XX) states, complicating\nthe production of single photons and triggered photon pairs. Here,\nwe demonstrate that colloidal semiconductor quantum shells (QSs) achieve\nsignificant spectral separation (∼75–80 meV) and long\ntemporal stability of X and XX emissive states, enabling the observation\nof exciton-biexciton bunching in colloidal QDs. Our low-temperature\nsingle-particle measurements show cascaded XX-X emission of single\nphoton pairs for over 200 s, with minimal overlap between X and XX\nfeatures. The X-XX distinguishability allows for an in-depth theoretical\ncharacterization of cross-correlation strength, placing it in perspective\nwith photon pairs of epitaxial counterparts. These findings highlight\na strong potential of semiconductor quantum shells for applications\nin quantum information processing.