Gabriele Raino1,2,Chenglian Zhu1,2,Malwina Marczak1,2,Leon Feld1,2,Simon Böhme1,2,Caterina Bernasconi1,2,Anastasiia Moskalenko1,2,Ihor Cherniukh1,2,Dmitry Dirin1,2,Maryna Bodnarchuk1,2,Maksym Kovalenko1,2
ETH Zürich1,Empa–Swiss Federal Laboratories for Materials Science and Technology2
Gabriele Raino1,2,Chenglian Zhu1,2,Malwina Marczak1,2,Leon Feld1,2,Simon Böhme1,2,Caterina Bernasconi1,2,Anastasiia Moskalenko1,2,Ihor Cherniukh1,2,Dmitry Dirin1,2,Maryna Bodnarchuk1,2,Maksym Kovalenko1,2
ETH Zürich1,Empa–Swiss Federal Laboratories for Materials Science and Technology2
Attaining pure single-photon emission is key for many quantum technologies,<sup>1</sup> from optical quantum computing<sup>2</sup> to quantum key distribution<sup>3</sup> and quantum imaging.<sup>4</sup> The past 20 years have seen the development of several solid-state quantum emitters, but most of them require highly sophisticated techniques (e.g., ultra-high vacuum growth methods and cryostats for low-temperature operation). The system complexity may be significantly reduced by employing quantum emitters capable of working at room temperature. Lead-halide perovskite APbX<sub>3</sub> (A=Cs or organic cation; X=Cl, Br, I) quantum dots (QDs) are one of the desired materials, of particular interest due to their low-cost synthesis, solution processability, tunability of the emission wavelength via size and composition, narrow-band emission, short radiative lifetime (~ns at RT) as well as high photoluminescence quantum yield (QY).<sup>5,6</sup> Here, we present a systematic study across ∼ 170 photostable single CsPbX<sub>3 </sub>(X: Br and I) colloidal QDs of different sizes and compositions, unveiling that increasing quantum confinement is an effective strategy for maximizing single-photon purity due to the suppressed biexciton quantum yield. Leveraging the latter, we achieve 98% single-photon purity (g<sup>(2)</sup>(0) as low as 2%) from a cavity-free, non-resonantly excited single 6.6 nm CsPbI<sub>3</sub> QDs, showcasing the great potential of CsPbX<sub>3</sub> QDs as room-temperature highly pure single-photon sources for quantum technologies.<br/><br/><b>References</b><br/>1. Aharonovich, I., Englund, D. & Toth, M. Solid-state single-photon emitters. <i>Nature Photonics</i> <b>10</b>, 631-641 (2016).<br/>2. Wang, H.<i> et al.</i> Boson sampling with 20 input photons and a 60-mode interferometer in a 1 0 14-dimensional hilbert space. <i>Phys. Rev. Lett.</i> <b>123</b>, 250503 (2019).<br/>3. Brassard, G., Lütkenhaus, N., Mor, T. & Sanders, B. C. Limitations on practical quantum cryptography. <i>Phys. Rev. Lett.</i> <b>85</b>, 1330 (2000).<br/>4. Tenne, R.<i> et al.</i> Super-resolution enhancement by quantum image scanning microscopy. <i>Nature Photonics</i> <b>13</b>, 116-122 (2019).<br/>5. Protesescu, L.<i> et al.</i> Nanocrystals of cesium lead halide perovskites (CsPbX3, X= Cl, Br, and I): novel optoelectronic materials showing bright emission with wide color gamut. <i>Nano Lett.</i> <b>15</b>, 3692-3696 (2015).<br/>6. Krieg, F.<i> et al.</i> Monodisperse long-chain sulfobetaine-capped CsPbBr3 nanocrystals and their superfluorescent assemblies. <i>ACS Cent. Sci.</i> <b>7</b>, 135-144 (2020).