  Solid-state quantum emitters have emerged as robust single-photon sources and
addressable spins: key components in rapidly developing quantum technologies
for broadband magnetometry, biological sensing, and quantum information
science. Performance in these applications, be it magnetometer sensitivity or
quantum key generation rate, is limited by the number of photons detected.
However, efficient collection of a quantum emitter's photoluminescence (PL) is
challenging as its atomic scale necessitates diffraction-limited imaging with
nanometer-precision alignment, oftentimes at cryogenic temperatures. In this
letter, we image an individual quantum emitter, an isolated nitrogen-vacancy
(NV) center in diamond, using a dielectric metalens composed of subwavelength
pillars etched into the diamond's surface. The metalens eliminates the need for
an objective by operating as a high-transmission-efficiency immersion lens with
a numerical aperture (NA) greater than 1.0. This design provides a scalable
approach for fiber coupling solid-state quantum emitters that will enable the
development of deployable quantum devices.
