High-dimensional quantum key distribution by a spin-orbit microlaser

Quantum key distribution (QKD) enabled by the fundamental quantum no-cloning theorem is by far the most attractive solution to enable secure information networks. While the two-level quantum bits (qubits) have been widely adopted, their N-dimensional (N>2) counterparts, qudits, provide higher information capacity and stronger noise-resilience, leading to high-dimensional QKD (HD-QKD) scheme. Despite that various qudit systems have been demonstrated for HD-QKD, a robust and compact HD-QKD system is still missing, due to the underlying challenge of integrated generation and stable propagation of qudits, of which the solution would be of fundamental interest in quantum information technology. Here, we integrate high-dimensional quantum communication into chips leveraging spin-orbit photon qudits, which are dynamically generated and manipulated via a non-Hermitian-physics-driven integrated microlaser quantum transmitter, enabling fast and precise qudit reconfigurability. The uniform spatial-temporal structure of the four spin-orbit eigenstates emitted by the microlaser ensures homogeneity between all qudit states used for key distribution, eliminating propagation dephasing and walk-off problems, and thus promises a compact and high-capacity quantum link.