Deterministic coupling of site-controlled quantum emitters in monolayer WSe2 to plasmonic nanocavities

Solid-state single-quantum emitters are crucial resources for on-chip photonic quantum technologies and require efficient cavity-emitter coupling to realize quantum networks beyond the single-node leve(1)(,2). Monolayer WSe2, a transition metal dichalcogenide semiconductor, can host randomly located quantum emitters(3-6), while nanobubbles(7) as well as lithographically defined arrays of pillars in contact with the transition metal dichalcogenide act as spatially controlled stressors(8,9). The induced strain can then create excitons at defined locations. This ability to create zero-dimensional (0D) excitons anywhere within a 2D material is promising for the development of scalable quantum technologies, but so far lacks mature cavity integration and suffers from low emitter quantum yields. Here we demonstrate a deterministic approach to achieve Purcell enhancement at lithographically defined locations using the sharp corners of a metal nanocube for both electric field enhancement and to deform a 2D material. This nanoplasmonic platform allows the study of the same quantum emitter before and after coupling. For a 3 x 4 array of quantum emitters we show Purcell factors of up to 551 (average of 181), single-photon emission rates of up to 42 MHz and a narrow exciton linewidth as low as 55 mu eV. Furthermore, the use of flux-grown WSe2 increases the 0D exciton lifetimes to up to 14ns and the cavity-enhanced quantum yields from an initial value of 1% to up to 65% (average 44%).