Programmable Spatiotemporal Quantum Parametric Mode Sorter

Photons are ideal information carriers for sensing, communication, and computing. In principle, a single photon can carry much in its spatiotemporal modes; the challenge is to read it out, as linear optical elements not sensitive subtle differences among those modes. This study demonstrates nonlinear-optical approach which pass through LiNiO${}_{3}$ waveguide separate photons according their detailed profiles or superpositions, even if they completely overlap with each other. provides access photons' large Hilbert spaces, pointing applications free-space quantum computing, sensing.