https://physicsworld.com/a/entangled-light-source-is-fully-on-chip/

Lots of interesting similarities to materials and methods Poet is adept at utilizing and we don't talk much about this vertical. But it has the potential to be the most groundbreaking of them all.

" “Photonic quantum computers have a big problem with loss,” says Elizabeth Goldschmidt, a quantum optics professor at the University of Illinois Urbana Champaign who was not involved in creating the new source. “Because interfaces are particularly lossy, going on-chip is very important.”

In their latest research, Haldar and colleagues have created a photonics system-on-a-chip that generates entangled photons. It consists of three main components: a laser; a filter ensuring laser stability at a narrow frequency band; and a non-linear medium generating entangled photon pairs. While lasers and quantum light sources requiring an external laser have been created on-chip before, putting both on the same chip has been a challenge. This is because the materials used for lasing are different from those required for filtering and entangled pair generation, and the manufacturing processes for the two materials are generally incompatible.

Hybrid integration

The team overcame this incompatibility using a technique called hybrid integration. The gain medium used for lasing was made from indium phosphide, while the filtering and photon-generation components were made from silicon nitride. To stick the two together, the team used the expertise of Klaus Boller’s group at the University of Twente. Boller’s team is adept at gluing different chips together with enough finesse that the microscopic light-guiding components line up and connect so perfectly that barely any light is lost at the interface. To avoid reflection at the interface, they added an anti-reflecting coating and tiled the end of the indium phosphide waveguide upwards off the chip by 9°. This allowed them to achieve less than 0.01 dB of loss across the interface."