Quantum Optics Seminar by Tom Wolterink

Large-scale linear optical networks based on silicon nitride waveguides

Quantum photonics experiments require ultimate control over the propagation of light in linear optical networks. Because of their phase stability and reconfigurability, on-chip universal linear optical networks based on tunable beam splitters and phase shifters are particularly suited for quantum information processing, enabling a variety of quantum communication, computation, and simulation protocols. Out of all the major integrated photonic platforms, silicon nitride seems to be especially promising, as this platform offers a unique combination of high index contrast, enabling a dense waveguide arrangement, low propagation loss, and a wide spectral transparency range from the visible to the mid-infrared. 

In this talk, I will present our work on a reconfigurable 8x8 photonic integrated circuit based on silicon nitride waveguides. This circuit contains 128 programmable elements that are arranged in a novel architecture inspired by microwave engineering, enabling the realization of arbitrary transformations, unitary and non-unitary. To demonstrate its versatility, we have performed some quantum information processing primitives, in the form of Hong-Ou-Mandel interference and high-dimensional single-photon gates. Exploiting the freedom allowed by non-unitary optical networks, we show how the well-known Hong-Ou-Mandel bunching of photons can be transformed into antibunching. Finally, I will present our work on programmable quantum interference in a massively multichannel network, consisting of an array of thousands of coupled waveguides. These results show the high potential of the silicon nitride platform for large-scale photonic quantum information processing.