https://www.nature.com/articles/s41566-024-01394-2
This appears to be the same paper published on arxiv:
https://arxiv.org/abs/2302.00793
The abstract describes the actual problem that these photonic chips solve:
> We designed and experimentally demonstrated a vector–matrix product for a 2 × 2 matrix and a 3 × 3 matrix. We also designed a 10 × 10 matrix using the proposed 2D computational method. These examples demonstrate that these techniques have the potential to enable larger-scale wave-based analogue computing platforms.
It appears the main contribution of this paper is not so much a new chip technology, but a new way to efficiently model the flow of light through a particular kind of chip (using raised and lowered bumps of silicon) that makes designing photonic chips that compute matrix multiplications practical.
For a fixed matrix, they can design a chip that approximately multiplies that matrix by an input query vector, using light.
Being a fixed matrix severely limits the usefulness of this for now, especially at the 2x2 and 3x3 sizes, but it could be useful if it could be made much larger, or ways to vary the contents of the matrix are discovered.