Scientists build quantum dot device, emits photon pairs with record purity

Chinese researchers have developed a semiconductor quantum dot device that emits photon pairs with unprecedented purity, achieving 98.3% of emitted light as photon pairs—one of the highest efficiencies recorded for a solid-state source. Unlike traditional nonlinear crystal sources that probabilistically generate photon pairs by splitting laser photons, this device produces pairs from a single quantum emitter, offering more deterministic and noise-free photon generation. Photon pairs are crucial for quantum technologies because their correlated or entangled nature enables applications in ultra-secure communications, precision measurements, quantum imaging, and advanced sensing. The breakthrough hinges on embedding a single quantum dot inside a microscopic optical pillar cavity, which enhances photon emission via the Purcell effect. The researchers innovatively manipulated the quantum dot into a long-lived "dark exciton" state using polarization-selective p-shell excitation with finely tuned laser pulses. This dark state acts as a temporary holding area that allows two electrons to occupy the quantum dot simultaneously, forming a biexciton state that decays by emitting two photons in