BRISTOL, England, Sept. 4, 2020 — Researchers at the University of Bristol have developed a new CMOS-compatible silicon photon source that satisfies all the requirements necessary for large-scale photonic quantum computing. To meet the stringent requirements for single-photon sources used in quantum computing, the researchers based their source on intermodal spontaneous four-wave mixing in a multimode silicon waveguide.

The intermodal approach to on-chip photon sources, where an interplay between multiple optical pump fields is used to generate photons, enables novel degrees of freedom to control the photon emission. By tailoring the geometry of a low-loss multimode waveguide and the on-chip temporal delay between the pump fields, the research team showed that the properties of the spontaneous photon emission could be engineered to achieve near-ideal photons.

To test their design, the researchers fabricated single-photon devices on standard silicon-on-insulator using CMOS-compatible lithography processes on a commercial wafer. Tests of the devices showed that the multimode waveguides significantly reduced transmission losses, enabling an intrinsic heralding efficiency of the source by approximately 90%. A high heralding efficiency is necessary to scale up quantum processing.

The researchers tested another feature essential for quantum computations — on-chip photon interference. Those experiments showed a raw data visibility of 96%, which the OSA reports is the highest so far in integrated photonics.

The achievement enables on-chip quantum operations between photons at an unprecedented level of precision, establishing the possibility to scale up low-noise photon processing in near-term quantum photonic devices.

According to the researchers, using a pump laser and increasing the uniformity of the fabrication process could improve the single-photon source.

The research will be presented at OSA Frontiers in Optics + Laser Science APS/DLS Sept. 14-17.