USTC achieves high-efficiency single-photon source above loss-tolerant threshold

Research teams led by Prof. PAN Jianwei, LU Chaoyang, HU Yongheng, and others have realized a high-performance single-photon source with an efficiency beyond the scalable linear optical quantum computing loss tolerance threshold for the first time, and the comprehensive indicators have reached the international advanced level. The results were published in Nature Photonics on February 28^th.

Photons, as important carriers for quantum information processing, have the advantages of fast speed and strong resistance to environmental interference. However, for scalable linear optical quantum computing to be feasible, apart from the challenges like photons’ being easily lost, the efficiency of a single-photon source must exceed the tricky threshold of 2/3. Previous studies had never broken through this threshold, becoming a key obstacle restricting the development of optical quantum computing.

To overcome this challenge, the research teams have developed a tunable open optical microcavity, achieving precise coupling of quantum dots and microcavities in both resonance frequency and spatial positioning. The microcavity solved the detuning problem of traditional fixed microcavities.

In addition, the teams employed tailor shaped laser pulse excitation on a high-quantum efficiency single quantum dot. The excitation significantly improved the overall performance of the single photon source. The related comprehensive index has reached the international advanced level.

To be more specific, the single-photon property of the single photon source went beyond 98.0%, the photon indistinguishability excelled 98.5%, and the system efficiency reached 71.2%.

Also, the extraction efficiency transcended 80.6%, the loss tolerance threshold of 2/3 was broken through for the first time.

With this source developed, the researchers further reported 1.89(14) dB intensity squeezing, and consecutive 40-photon events with a count rate of 1.67 mHz.

The study achieves a source system efficiency above the threshold required for compensating for photon loss in photonic quantum computing is certainly a milestone, showing another significant step towards the ideal single-photon source, according to the reviewer of the journal.