Suppressed Magnitude of Spectral Diffusion in Cube-Shaped CdSe/CdS Core/Shell Nanocrystals with Exceedingly Stable Photoluminescence.

Colloidal semiconductor nanocrystals are promising candidates for quantum light sources, yet their application has been impeded by photoluminescence instability due to blinking and spectral diffusion. This study introduces a new category of cube-shaped CdSe/CdS core/shell nanocrystals with exceptionally stable photoluminescence characteristics. Under continuous excitation, the emissive quantum state remained consistent without alterations of the charge state for 4000 s, and the average photon energy variation stayed within the bounds of spectral resolution throughout this extended duration. Systematic examination of single-nanocrystal photoluminescence, upon variation of the core and shell dimensions, revealed that a thicker CdS shell and increased core edge length significantly curtail spectral diffusion, considering that the nanocrystals possess well-controlled CdSe-CdS and facet-ligand interfaces. This study advances the optimization of colloidal semiconductor nanocrystals as high-performance quantum light sources.

Room-Temperature Single-Photon Sources Based on Colloidal Quantum Dots: A Review.

Single-photon sources (SPSs) play a crucial role in quantum photonics, and colloidal quantum dots (CQDs) have emerged as promising and cost-effective candidates for such applications due to their high-purity single-photon emission at room temperature. This review focuses on various aspects of CQDs as SPSs. Firstly, a brief overview of the fundamental optical properties of CQDs is provided, including emission wavelength engineering and fluorescence intermittency, and their single-photon emission properties. Subsequently, this review delves into research concerning CQDs as SPSs, covering topics such as the coupling of single CQDs to microcavities, both in weak and strong coupling regimes. Additionally, methods for localizing and positioning CQDs are explored, which are critical for on-chip SPSs devices.

Double-Pulse Generation of Indistinguishable Single Photons with Optically Controlled Polarization.

Single-photon sources play a key role in photonic quantum technologies. Semiconductor quantum dots can emit indistinguishable single photons under resonant excitation. However, the resonance fluorescence technique typically requires cross-polarization filtering, which causes a loss of the unpolarized quantum dot emission by 50%. To solve this problem, we demonstrate a method for generating indistinguishable single photons with optically controlled polarization by two laser pulses off-resonant with neutral exciton states. This scheme is realized by exciting the quantum dot to the biexciton state and subsequently driving the quantum dot to an exciton eigenstate. By combining with a magnetic field, we demonstrated the generation of photons with optically controlled polarization (the degree of polarization is 101(2)%), laser-neutral exciton detuning up to 0.81 meV, high single-photon purity (99.6(1)%), and indistinguishability (85(4)%). Laser pulses can be blocked using polarization and spectral filtering. Our work makes an important step toward indistinguishable single-photon sources with near-unity collection efficiency.