Quantum measurement and orientation tracking of fluorescent nanodiamonds inside living cells

Abstract

Fluorescent particles are routinely used to probe biological processes 1. The quantum properties of single spins within fluorescent particles have been explored in the field of nanoscale magnetometry 2-8, but not yet in biological environments. Here, we demonstrate optically detected magnetic resonance of individual fluorescent nanodiamond nitrogen-vacancy centres inside living human HeLa cells, and measure their location, orientation, spin levels and spin coherence times with nanoscale precision. Quantum coherence was measured through Rabi and spin-echo sequences over long (>10 h) periods, and orientation was tracked with effective 1° angular precision over acquisition times of 89 ms. The q..