Atomic fluorescence collection into planar photonic devices

TL;DR

This paper presents a theoretical and experimental study of efficient fluorescence photon collection into planar photonic devices for quantum emitters, including design, fabrication, and characterization of collection elements with practical efficiencies.

Contribution

It introduces a simple reciprocity-based method to evaluate collection efficiency and demonstrates practical diffractive collection elements with measurable efficiencies for quantum applications.

Findings

Collection efficiencies of 0.25% and 1.14% into waveguides achieved

Design and fabrication of diffractive collection elements validated experimentally

Close agreement between simulated and measured emission patterns

Abstract

Fluorescence collection from individual emitters plays a key role in state detection and remote entanglement generation, fundamental functionalities in many quantum platforms. Planar photonics have been demonstrated for robust and scalable addressing of trapped-ion systems, motivating consideration of similar elements for the complementary challenge of photon collection. Here, using an argument from the reciprocity principle, we show that far-field photon collection efficiency can be simply expressed in terms of the fields associated with the collection optic at the emitter position alone. We calculate collection efficiencies into ideal paraxial and fully vectorial focused Gaussian modes parameterized in terms of focal waist, and further quantify the modest enhancements possible with more general beam profiles, establishing design requirements for efficient collection. Towards practical implementation, we design, fabricate, and characterize two diffractive collection elements operating at $\lambda=397$ nm; a forward emitting design is predicted to offer 0.25% collection efficiency into a single waveguide mode, while a more efficient reverse-emitting design offers $1.14\%$ collection efficiency, albeit with more demanding fabrication requirements. Close agreement between simulated and measured emission for both designs indicates practicality of these collection efficiencies, and we indicate avenues to improved devices approaching the limits predicted for ideal beams. We point out a particularly simple integrated waveguide configuration for polarization-based remote entanglement generation enabled by integrated collection.