Photon-efficient high-dimensional quantum key distribution
Tian Zhong, Hongchao Zhou, Robert D. Horansky, Catherine Lee, Varun B. Verma, Adriana E. Lita, Alessandro Restelli, Joshua C. Bienfang, Richard P. Mirin, Thomas Gerrits, Sae Woo Nam, Francesco Marsili, Zhenshen Zhang, Ligong Wang, Dirk Englund, Gregory Wornell, Jeffrey Shapiro, Franco N. Wong
Quantum key distribution (QKD) is a secure communication technology whose security is guaranteed by the laws of physics. However, its widespread use has been hindered in part by low secure-key throughput due to the inherent loss and de-coherence of photons during transmission. Most existing protocols use binary key encoding, with photon information efficiency (PIE) of at most 1 bit per photon and a key rate limited by the photon flux reaching the receiver. High dimensional QKD (HDQKD) promises to significantly improve photon efficiency and key throughput, but its implementation within a framework of proven security for multiple bits per photon has remained a long-standing challenge. Here,we report the first complete implementation of HDQKD protocols, yielding high PIE up to 8.8 secure bits per photon at telecom wavelength, with 7.0 bits per photon maintained after 20 km of fibre transmission. With its throughput of as much as 7.1 Mb/s, our work represents a viable approach to real-world high rate QKD by efficiently utilizing available photonic entanglement and detection resources.