Science Advances posts quantum photon extraction

Science Advances on May 22 posted a paper describing a laboratory method to pull more usable light from quantum emitters embedded in bulk semiconductors. The study, published online this week, reported that inverse-designed nanostructures created “photonic nanojets” that both isolated individual emitters and increased the number of photons collected from them. The work focused on solid-state quantum emitters, which are used in efforts to build quantum communication, sensing and information-processing devices. The paper said a persistent problem is that high-refractive-index host materials trap much of the emitted light, reducing collection efficiency. ### What exactly did the researchers build? The authors said they used free-form topology optimization to design monolithic photonic structures inside high-refractive-index materials. (science.org) Those fabricated structures generated tightly confined photonic nanojets — concentrated optical fields that can selectively excite individual emitters. The paper said the structures were made with standard top-down patterning techniques rather than requiring unusually pure samples or precise defect implantation. (science.org) It also reported that the optimized geometries reduced background photoluminescence from near-surface defects and other randomly distributed emitters in the bulk. ### What was the main experimental result? The team demonstrated the approach using negatively charged nitrogen-vacancy, or NV-, centers in diamond at room temperature. (science.org) In confocal microscopy measurements, the paper reported selective single-emitter excitation with a 10-fold power enhancement and more than 15-fold improvement in photon extraction efficiency for photoluminescence collection. Those results matter because single-photon sources and optically addressable spin defects are among the components being studied for quantum networks, memories and sensors. (science.org) The paper described diamond NV centers as a case study, not the only intended target. ### Where was the work done? The corresponding authors listed on the paper and supplementary materials were Behrooz Semnani and Michal Bajcsy, both using University of Waterloo email addresses. (science.org) Bajcsy is an associate professor at the Institute for Quantum Computing and the Department of Electrical and Computer Engineering at the University of Waterloo, according to the university profile page. The author list also included Sai Sreesh Venuturumilli, Mohammad Soltani, Pratik Adhikary, Abdolreza Pasharavesh, Nikolay Videnov, Paul Anderson, Supratik Sarkar and Vinodh Raj Rajagopal Muthu. (science.org) University of Waterloo pages and conference materials tie multiple co-authors to the institute and Bajcsy’s Nano-Photonics and Quantum Optics Laboratory in Waterloo, Ontario. ### Why is photon extraction such a bottleneck? (science.org) The paper said quantum emitters can be useful only if their photons can be efficiently collected and directed into measurement or device architectures. In bulk semiconductors, much of that light is lost before it reaches the optics, which limits brightness and readout. The authors wrote that their approach could extend beyond NV centers in diamond to other semiconductor materials containing emitters, and could also be generalized to fiber-integrated platforms. (uwaterloo.ca) That claim was presented as a future application rather than a demonstrated device product. ### What comes next from here? Science Advances has published the paper online under the title “Probing individual quantum emitters in bulk semiconductors via photonic nanojets.” The next public step is likely to come from follow-on demonstrations in other emitter materials or fiber-integrated systems, which the authors named in the paper as possible extensions. (science.org)