New method generates nearly indistinguishable photons for quantum communication

Researchers from Paderborn University, the University of Basel, and Ruhr University Bochum have developed a new method for generating nearly indistinguishable photons, which could significantly improve quantum communication. The breakthrough, published in the journal Physical Review Letters, utilizes special semiconductor nanostructures to produce individual photons and pairs of photons that are almost perfectly identical.

Indistinguishable photons are crucial for quantum entanglement and interference, which are key components in quantum information processing. Traditional photon sources have faced issues with temporal correlations and spatial misalignment, limiting their indistinguishability and overall quality. To address this, the team employed a process called biexciton decay within semiconductor quantum dots housed in an optical resonator.

This process involves a molecule composed of two bound excitons (each containing an electron and an electron hole) decaying into a single exciton and a photon. Additionally, the study introduced the concept of a biexciton cascade, where a quantum dot, when doubly excited, emits two photons in succession. By integrating the quantum dot into a specialized optical cavity, the researchers accelerated and controlled the light emission process, resulting in an unprecedented 90% indistinguishability of the photons generated.

Compared to previous methods, this represents a significant improvement, with photon indistinguishability previously reaching only around 60%. The researchers note that the quality of these photons is heavily influenced by the controlled environment provided by the optical cavity. They also identified a phenomenon known as cavity feeding, which involves vibrations in the semiconductor's crystal lattice and can limit the purity of the generated photons. By minimizing these vibrations, further enhancement of photon quality can be achieved.

The findings demonstrate that biexciton decay in semiconductor quantum dots, when properly controlled using an optical cavity, can produce high-quality photons with vastly improved indistinguishability. This advancement lays the groundwork for more efficient quantum communication systems and paves the way for future developments in this field.