High-rate intercity quantum key distribution with a semiconductor single-photon source
Light: Science & Applications volume 13, Article number: 150 (2024 ) Cite this article
Quantum key distribution (QKD) enables the transmission of information that is secure against general attacks by eavesdroppers. The use of on-demand quantum light sources in QKD protocols is expected to help improve security and maximum tolerable loss. Semiconductor quantum dots (QDs) are a promising building block for quantum communication applications because of the deterministic emission of single photons with high brightness and low multiphoton contribution. Here we report on the first intercity QKD experiment using a bright deterministic single photon source. A BB84 protocol based on polarisation encoding is realised using the high-rate single photons in the telecommunication C-band emitted from a semiconductor QD embedded in a circular Bragg grating structure. Utilising the 79 km long link with 25.49 dB loss (equivalent to 130 km for the direct-connected optical fibre) between the German cities of Hannover and Braunschweig, a record-high secret key bits per pulse of 4.8 × 10−5 with an average quantum bit error ratio of ~ 0.65% are demonstrated. An asymptotic maximum tolerable loss of 28.11 dB is found, corresponding to a length of 144 km of standard telecommunication fibre. Deterministic semiconductor sources therefore challenge state-of-the-art QKD protocols and have the potential to excel in measurement device independent protocols and quantum repeater applications.
Realms of communication that transcend the limitations of traditional networks can be accessed by establishing a ‘quantum internet’1,2 through the distribution of quantum light states. Sharing quantum bits of information with distant nodes via optical fibre or free space (satellite) enables new applications such as quantum teleportation3,4,5, quantum cloud computing6,7 or quantum sensor networks8,9. A primary advantage of quantum communication lies in its ability to ensure unambiguous security for modern communication networks, a security that is increasingly threatened by the rapid advancement of quantum computing technologies10,11,12. Hence, Quantum Key Distribution (QKD) has attracted worldwide attention for its unique ability to provide security based on the principles of quantum mechanics13, surpassing the capabilities of classical cryptography14.
