Scalable, efficient ion-photon coupling with phase Fresnel lenses for large-scale quantum computing

TL;DR

This paper demonstrates that phase Fresnel lenses with high numerical aperture can significantly improve ion-photon coupling efficiency in large-scale quantum computing, offering scalable and high-quality optical solutions.

Contribution

The study introduces a scalable approach using phase Fresnel lenses for efficient ion-photon coupling, with experimental characterization showing improved coupling over traditional methods.

Findings

Measured diffraction-limited spot with NA=0.64 and mode quality M^2≈1.08.

Estimated ion-photon coupling efficiency of 0.64%, twice previous best.

Evaluated techniques to enhance entanglement fidelity with high-NA lenses.

Abstract

Efficient ion-photon coupling is an important component for large-scale ion-trap quantum computing. We propose that arrays of phase Fresnel lenses (PFLs) are a favorable optical coupling technology to match with multi-zone ion traps. Both are scalable technologies based on conventional micro-fabrication techniques. The large numerical apertures (NAs) possible with PFLs can reduce the readout time for ion qubits. PFLs also provide good coherent ion-photon coupling by matching a large fraction of an ion's emission pattern to a single optical propagation mode (TEM00). To this end we have optically characterized a large numerical aperture phase Fresnel lens (NA=0.64) designed for use at 369.5 nm, the principal fluorescence detection transition for Yb+ ions. A diffraction-limited spot w0=350+/-15 nm (1/e^2 waist) with mode quality M^2= 1.08+/-0.05 was measured with this PFL. From this we estimate the minimum expected free space coherent ion-photon coupling to be 0.64%, which is twice the best previous experimental measurement using a conventional multi-element lens. We also evaluate two techniques for improving the entanglement fidelity between the ion state and photon polarization with large numerical aperture lenses.