Integrated optical entangled quantum vortex emitters

Abstract

Quantum vortices of light carrying orbital angular momentum stand as essential resources for quantum photonic technologies. Recent advancements in integrated photonics offer the potential to create and control quantum vortices using fully integrated circuits, eliminating the need for intricate free-space alignment, modulation and the stabilization of bulky optical elements. However, generating quantum vortices in planar optical waveguides and circuits poses challenges, owing to the complexities of confining and guiding twisted photons and, importantly, the difficulties in preparing the quantum superposition and entanglement of vortex states. Here we report the realization of entangled quantum vortex emitters, leveraging programmable integrated nanophotonic circuits. These circuits enable the generation and arbitrary control of resilient vortex entanglement in free space, coherently transitioning from on-chip-created path entanglement. This capability is facilitated by a chip-to-free-space interfacing quantum technology that combines reprogrammable integrated quantum photonics with advanced classical free-space beam structuring. The emitters operate in a plug-and-play manner, enabling swift reconfiguration within microseconds. Validation of multidimensional genuine entanglement is achieved through quantum tomography and measurement of the dimension witness. Our work demonstrates integrated quantum vortex devices that combine the versatility of the on-chip processing quantum information with the robustness of transmitting quantum vortices in free space, opening new avenues for applications in quantum communication, quantum light detection and ranging, and quantum computation and storage. Combining on-chip photon-pair sources, two sets of linear integrated circuits for path entanglements and two path-to-orbital angular momentum converters, free-space-entangled orbital angular momentum photon pairs can be generated in high-dimensional vortex states, offering a high level of programmable dynamical reconfigurability.