Researchers address photon extraction limits

Science Advances published a paper on May 21 describing a way to get more usable light out of solid-state quantum emitters embedded in bulk semiconductors. The study, led by Behrooz Semnani and Michal Bajcsy, addresses a longstanding problem in quantum photonics: many promising emitters sit inside high-refractive-index materials, where much of the light stays trapped instead of escaping into an optical system. The authors reported a monolithic nanostructure design that improves photon extraction while also helping isolate individual emitters in samples that are not specially purified. The work appears in the journal under the title “Probing individual quantum emitters in bulk semiconductors via photonic nanojets.” ### Why is photon extraction such a bottleneck in bulk materials? The paper says high-refractive-index host materials often cause low-efficiency photon collection from embedded quantum emitters. That matters because solid-state emitters are used as building blocks for quantum information processing, quantum telecommunication and quantum-enhanced sensing, according to the study. The authors also wrote that isolating individual emitters usually requires high-purity samples and precise defect implantation, which adds fabrication complexity. (science.org) In practical terms, that means researchers often face a trade-off between scalable fabrication and optical performance. ### What did the researchers build to get around that problem? The researchers used free-form topology optimization to design broadband monolithic photonic structures inside high-index materials containing relatively dense, randomly distributed quantum emitters. (science.org) The structures were fabricated with standard top-down patterning techniques, the paper said. The study reports that those inverse-designed nanostructures generate tightly confined “photonic nanojets.” According to the paper, the nanojets enable selective excitation of individual emitters and improve photon extraction efficiency, while the optimized geometries suppress background photoluminescence from near-surface defects and other emitters in the bulk. (science.org) ### What was the actual experimental result? (science.org) The authors demonstrated the approach using negatively charged nitrogen-vacancy, or NV−, centers in a low-cost diamond sample at room temperature. In that setup, they reported selective single-emitter excitation with a 10-fold power enhancement and more than 15-fold improvement in photon extraction efficiency for photoluminescence collection in confocal microscopy. (science.org) The room-temperature diamond result is central because NV centers are a widely studied platform for quantum memory and sensing experiments. The paper says diamond defects such as NV centers can support coherent control and optical readout of spin states, including at room temperature. ### Does the paper claim this works beyond diamond? The authors said the method is not limited to NV centers or diamond-embedded emitters. (science.org) The paper states that inverse-designed structures producing subwavelength photonic nanojets can be applied to other semiconductor materials containing emitters and can be generalized to fiber-integrated platforms. That claim is important for researchers trying to move from one-off laboratory devices to repeatable component fabrication. (science.org) The study frames the design strategy as compatible with standard nanofabrication rather than bespoke assembly around single preselected emitters. ### Who did the work, and where can readers find it? Science Advances lists Behrooz Semnani and Michal Bajcsy as corresponding authors on the article. (science.org) External profile pages identify Bajcsy with the University of Waterloo’s Institute for Quantum Computing and Electrical and Computer Engineering department, while ORCID records the paper under DOI 10.1126/sciadv.aea5936. The paper was published on May 20 in the journal’s record and was being highlighted by Science Advances on May 21. (science.org) Readers looking for the next step can find the full article and supplementary materials through the Science Advances entry for DOI 10.1126/sciadv.aea5936, where the corresponding authors’ contact details are also listed. (orcid.org) (uwaterloo.ca)