ESSENS · Efficient Detection of Squeezed Light on Nanophotonic Chips using Subwavelength-Engineered Superconducting Nanowire Avalanche Photodetectors

Efficient Detection of Squeezed Light on Nanophotonic Chips using Subwavelength-Engineered Superconducting Nanowire Avalanche Photodetectors

The ESSENS project aims at implementing a photonic integrated chip that features high system detection efficiency to exploit the potential of squeezed states of light for quantum simulation, communication and sensing applications. Light in a squeezed state exhibits reduced quantum uncertainty, which can, for example, be employed in super-sensitive gravitational-wave detectors and has been utilized for Gaussian boson sampling experiments. However, squeezed light is very delicate, as interaction with the environment (i.e., photon loss) rapidly degrades quantum correlations. This inconvenience limits the scalability and stability of systems based on bulk optical components such as beamsplitters and mirrors. Photonic integrated circuits offer novel means for overcoming such current limitations because recent advances in design and nanofabrication benefit compact realizations of processing loss-sensitive squeezed light on silicon chips: on the one hand, very low propagation loss is achievable in wideband-transparent moderate-index-contrast platforms (e.g., silicon nitride on insulator); on the other hand, monolithic chips provide interferometric stability even when the component count increases. Thus, in the ESSENS project a photonic integrated system is developed that paves the way for exploiting squeezed states of light on a chip. The key components of such a system are a surface grating coupler with sub-decibel coupling efficiency and a waveguide-integrated superconducting nanowire single-photon detector (SNSPD) with high on-chip detection efficiency (OCDE) and low jitter. The specific goals of the project align with the independent design of both key components. In order to achieve the required high performance, direct-laser-writing (DLW) fabrication technology and subwavelength-grating (SWG) metamaterial engineering are considered. The former facilitates the fast fabrication of any 3D shape, thereby expanding the design space beyond planar geometries that result from standard electron-beam lithography and reactive ion etching processes; the latter enable the synthesis of anisotropic metamaterials with tailorable optical properties, which also expands the design space by enlarging the range of usable refractive indices.

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