Single-photon emitters (SPEs) are crucial in quantum communication and information processing. In 2D transition metal dichalcogenides (TMDs), SPEs are realized through inhomogeneous strain, while in combination with 2D magnets, a high spontaneous out-of-plane magnetization can be induced due to proximity effects. Here, an alternative is proposed that consists of suspending a TMD monolayer (WSe₂) on a few-layer antiferromagnet (CrSBr) with in-plane magnetic ordering. The resulting heterostructure exhibits localization centers at lower energies than expected. Among them, a bright SPE with a high degree of polarization selection is identified. This suffers a clear energy shift driven by an in-plane magnetic field, and interestingly, this shift is correlated with the metamagnetic transition of CrSBr, suggesting a new kind of proximity-type effect. Unlike regular SPEs in WSe₂ (sensitive to out-of-plane magnetic fields), our SPE demonstrates sensitivity to both in-plane and out-of-plane magnetic fields. The added tunability at significantly lower fields offers a promising direction for developing magnetically responsive quantum emitters, paving the way for more practical applications in quantum technologies.

Intervalley excitons with electron and hole wavefunctions residing in different valleys determine the long-range transport and dynamics observed in many semiconductors. However, these excitons with vanishing oscillator strength do not directly couple to light and, hence, remain largely unstudied. Here, we develop a simple nanomechanical technique to control the energy hierarchy of valleys via their contrasting response to mechanical strain. We use our technique to discover previously inaccessible intervalley excitons associated with K, Γ, or Q valleys in prototypical 2D semiconductors WSe2 and WS2. We also demonstrate a new brightening mechanism, rendering an otherwise “dark” intervalley exciton visible via strain-controlled hybridization with an intravalley exciton. Moreover, we classify various localized excitons from their distinct strain response and achieve large tuning of their energy. Overall, our valley engineering approach establishes a new way to identify intervalley excitons and control their interactions in a diverse class of 2D systems.