Heralded Generation of Correlated Photon Pairs from CdS/CdSe/CdS Quantum Shells*

Non-classical states of light are essential for quantum information processing. Single epitaxial quantum dots have already demonstrated the ability to produce single deterministic photons and shown promise for generation of entangled photon pairs at cryogenic temperature. They, however, suffer from scalability issues since they are produced via expensive molecular-beam epitaxy technology. On the other hand, colloidal semiconductor nanocrystal quantum dots offer a more scalable solution via wet-chemical synthesis. These, however, have traditionally suffered from broader emission lines, photoluminescence spectral flickering, and short coherence time. Here, we demonstrate that colloidal semiconductor quantum shells (QSs) achieve significant spectral separation (~ 75-80 meV) and long temporal stability of X and XX emissive states, enabling the observation of exciton-biexciton bunching in colloidal QDs. The distinguishability between X and XX emission lines allows for an in-depth theoretical characterization of cross-correlation strength, placing it in perspective with photon pairs generated by the epitaxial counterparts. Such findings show great promise of colloidal nanocrystals in applications for future quantum information technologies.