Ultracompact quantum splitter of degenerate photon pairs

Integrated sources of indistinguishable photons have attracted a lot of attention because of their applications in quantum communication and optical quantum computing. Here, we demonstrate an ultracompact quantum splitter for degenerate photon pairs based on a monolithic silicon chip. It incorporates a Sagnac loop and a microring resonator with a total footprint of 0.011 mm2, generating and deterministically splitting indistinguishable photon pairs using two-photon interference. The ring resonator provides an enhanced photon generation rate, and the Sagnac loop ensures the photons travel through equal path lengths and interfere with the correct phase to enable the reversed Hong–Ou–Mandel (HOM) effect to take place. In the experiment, we observed a HOM dip visibility of 94.5±3.3%, indicating the generated photons are in a suitable state for further integration with other components for quantum applications, such as controlled-NOT gates.