Our research investigates the potential of colloidal semiconductor quantum shells (CQSs) as quantum light sources (QLSs) for quantum information processing, particularly in the generation of entangled photon pairs. Epitaxially grown quantum dots (QDs) have been widely used as deterministic single-photon emitters, but their reliance on molecular-beam epitaxy introduces scalability challenges. Colloidal semiconductor quantum dots (CQDs) offer a scalable alternative but suffer from Auger recombination and surface nonradiative decay effects, leading to photoluminescence (PL) spectral fluctuations, poor coherence, and PL flickering. These issues limit the spectral distinction between exciton and biexciton states, reducing their effectiveness for entanglement-based applications.
(a) A diagram illustrating exciton−exciton repulsion in a quantum shell structure. (b) Low temperature (10 K), time dependent PL spectra of an individual QS showing energyseparated X and XX emission bands. The integration time of each frame is 1 s. The inset shows an energy diagram of a two-exciton state of a QS. (c) Room temperature emission and absorption profiles of a 6.0 nm core CdS-CdSe-CdS QS. (d) Characteristic TEM image of 6.0 nm core CdS-CdSe-CdS QSs. (e) High angle annular dark field (HAADF)-STEM images of 6.0 nm core quantum shells, illustrating the location of the CdSe shell layer.
By employing CQSs with a CdS/CdSe/CdS structure, we achieve stable and spectrally distinct exciton-biexciton emissions, which exhibit photon bunching behaviors indicative of strong temporal correlations—an essential characteristic for entanglement-based quantum optics. Low-temperature single-particle measurements confirm biexciton cascade relaxation, a process often utilized in the creation of entangled photon pairs. Compared to epitaxial QDs, the improved spectral separation and stability of exciton-biexciton pairs in quantum shells make them promising candidates for entanglement-based applications. (ACS Nano 2024, 18, 44, 30863–30870)
(a) Single QS spectra taken at 10 K. Shaded bars show the bandpass filters used to separate the emission for correlation measurements. Blue and brown solid lines are Gaussian fits to XX and X lines, respectively. (b) 3D intensity plot of the same QS taken over 30 s and indicating the spectral stability of the XX and X lines.
Our work aims to advance the understanding of quantum shells as multi-photon emitters, positioning them as viable QLS candidates for quantum information technologies. Their ability to reliably produce and manipulate photon pairs, along with the potential for spectrally filtering single-photon emission, opens new pathways for scalable quantum photonics.