# Collection of fluorescence from an ion using trap-integrated photonics

## TL;DR

Researchers developed a chip-integrated method to collect photons from a trapped ion, improving stability and scalability for quantum information processing.

## Contribution

A new grating design technique enables efficient photon collection from a trapped ion into a single-mode waveguide.

## Key findings

- The integrated optic collects 0.043% of spontaneously emitted light into a single-mode waveguide.
- The method enables imaging and quantum state detection of the ion with high reproducibility.
- The grating design extends the effective aperture for improved photon collection.

## Abstract

Spontaneously emitted photons are entangled with the electronic and nuclear degrees of freedom of the emitting atom, so interference and measurement of these photons can entangle separate matter-based quantum systems as a resource for quantum information processing. Since confinement in a single-mode facilitates the photon interference needed for generating entanglement, the dipole emission patterns relevant in spontaneous emission present a mode-matching challenge. Current demonstrations rely on bulk photon-collection and manipulation optics that suffer from large component size and system-to-system variability—factors that impede scaling to the large numbers of entangled pairs needed for quantum information processing. To address these limitations, we demonstrate a collection method that enables passive phase stability, straightforward photonic manipulation, and intrinsic reproducibility. Specifically, we engineer a waveguide-integrated grating to couple photons emitted from a trapped ion into a single optical mode within a microfabricated ion-trap chip. Using the integrated collection optic, we characterize the collection efficiency, image the ion, and detect the ion’s quantum state. The integrated optic covers 2.18% of the solid angle and collects 1.97 ± 0.3% of the spontaneously emitted light incident on the grating for a total collection efficiency of 0.043% into a single-mode waveguide. This proof-of-principle demonstration lays the foundation for leveraging the inherent stability and reproducibility of integrated photonics to create, manipulate, and measure multipartite quantum states in arrays of quantum emitters.

We collect fluorescence photons from a trapped ion into a chip-integrated single waveguide. We introduce a new grating design technique to extend the effective aperture of a large grating.