Fully integrated quantum frequency processor on a silicon chip

TL;DR

This paper presents the first fully integrated silicon photonic chip capable of generating, manipulating, and measuring high-dimensional quantum frequency states, advancing scalable quantum photonic processing.

Contribution

It introduces a monolithic silicon chip integrating sources, filters, modulators, and spectral shapers for quantum frequency processing, enabling complex quantum state control on-chip.

Findings

Achieved tunable frequency beamsplitters with >94% success probability.

Demonstrated high-fidelity (>99.9%) quantum operations.

Performed on-chip quantum state tomography with 95.7% fidelity.

Abstract

Frequency-bin encoding has recently emerged as a powerful approach for photonic quantum information processing, offering high dimensionality, gate-parallelization, and compatibility with existing telecommunication infrastructure. However, its scalable deployment has so far been hindered by the lack of an integrated platform capable of unifying quantum state generation, coherent frequency mixing, and programmable spectral control.\\ Here, we report the first fully integrated quantum frequency processor, monolithically integrating on the same silicon photonic chip a microresonator-based biphoton quantum frequency comb source, a pump-rejection filter, high-speed phase modulators, and a four-channel, line-by-line pulse shaper. We demonstrate key functionalities, such as tunable frequency beamsplitters with success probabilities exceeding $94\%$ and fidelities above $99.9\%$, as well as the ability to synthesize more general single-qubit gates. Finally, we generate and coherently manipulate high-dimensional frequency-bin entangled states entirely on chip, showcasing control over two-photon quantum walks and performing the first on-chip frequency-bin quantum state tomography of a Bell-state with a fidelity of $95.7(3)\%$. By integrating all key functional elements on the same $4\times7\,\textrm{mm}^2$ chip, with the possibility of scaling to a larger number of modes, our work marks an important step toward large-scale frequency-domain photonic processors for both classical and quantum applications.