Parabolic Diamond Scanning Probes for Single-Spin Magnetic Field Imaging

Abstract

Enhancing the measurement signal from solid-state quantum sensors such as the nitrogen-vacancy (N-V) center in diamond is a challenge for sensing and imaging of condensed-matter systems. Here we design and fabricate diamond scanning probes with a truncated parabolic profile that optimizes the photonic signal from single, near-surface, embedded N-V centers, forming a high-sensitivity probe for nanoscale magnetic field imaging. These structures operate over the full N-V photoluminescence spectrum with the emission being directed into a measured numerical aperture of 0.44. Furthermore, they yield a median saturation count rate of 2.1 MHz, a fivefold improvement in measurement signal over the state of the art in scanning-probe-based N-V sensors. We additionally introduce a charge-state-registered pulsed-excitation method for measuring the detection efficiency of photons from the N-V's metrologically relevant negative charge state, finding an overall detection efficiency of 12%. We demonstrate the excellent properties of these diamond scanning probes by imaging thin-film ferromagnetic stripes with a spatial resolution better than 50 nm.