Quantum prospects for hybrid thin-film lithium niobate on silicon photonics.

Photonics is poised to play a unique role in quantum technology for computation, communications and sensing. Meanwhile, integrated photonic circuits-with their intrinsic phase stability and high-performance, nanoscale components-offer a route to scaling. However, each integrated platform has a unique set of advantages and pitfalls, which can limit their power. So far, the most advanced demonstrations of quantum photonic circuitry has been in silicon photonics. However, thin-film lithium niobate (TFLN) is emerging as a powerful platform with unique capabilities; advances in fabrication have yielded loss metrics competitive with any integrated photonics platform, while its large second-order nonlinearity provides efficient nonlinear processing and ultra-fast modulation. In this short review, we explore the prospects of dynamic quantum circuits-such as multiplexed photon sources and entanglement generation-on hybrid TFLN on silicon (TFLN/Si) photonics and argue that hybrid TFLN/Si photonics may have the capability to deliver the photonic quantum technology of tomorrow.

Programmable four-photon graph states on a silicon chip.

Future quantum computers require a scalable architecture on a scalable technology-one that supports millions of high-performance components. Measurement-based protocols, using graph states, represent the state of the art in architectures for optical quantum computing. Silicon photonics technology offers enormous scale and proven quantum optical functionality. Here we produce and encode photonic graph states on a mass-manufactured chip, using four on-chip-generated photons. We programmably generate all types of four-photon graph state, implementing a basic measurement-based protocol, and measure high-visibility heralded interference of the chip's four photons. We develop a model of the device and bound the dominant sources of error using Bayesian inference. The combination of measurement-based quantum computation, silicon photonics technology, and on-chip multi-pair sources will be a useful one for future scalable quantum information processing with photons.