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Congratulations to Becca VanDrunen, Juanjuan Ren, and Stephen Hughes, along with German collaborator Sebastian Franke for their new paper titled , which has been highlighted on the front cover of the April edition of the new gold-standard journal in quantum optics: Optica Quantum.

This work showcases a rigorous mode theory for gain-compensated plasmonic cavities and demonstrates how quality factors and Purcell factors (spontaneous emission enhancements from quantum emitters) can be drastically improved, yielding enhanced quality factors from 10 to over 26,000 and peak Purcell factors from approximately 3000 to over 10 billion, far beyond what has been realized or predicted before. We provide full three-dimensional calculations for gold dimers in a finite-size game medium, which allows one to easily surpass fundamental Purcell factor limits of lossy media. Remaining within a regime of linear system response, we show how the Purcell factors are modified by contributions from the projected local density of states and non-local gain, fully described within the framework of quasinormal modes.

Purcell factors (enhanced spontaneous emission rates) for a quantum dipole emitter placed inside the gap of a metal dimer cavity, in a finite gain medium (see cover), showing the usual local density of states (LDOS) values with small gain (a) [dashed line is no gain] and increasing amounts of gain (b), as well as (c) our corrected total Purcell factors that also include a non-local contribution from the gain medium, which results in a substantial increase (the dashed line here shows a drastic failure of the usual LDOS theory result). Symbols are numerically exact simulations and solid lines are the predictions from our single quasinormal mode theory, showing quantitative agreement with no fitting parameters.