Non-locally sensing the spin states of individual atomic-scale nanomagnets
Quantum spin systems can provide unprecedented accuracy and sensitivity compared to classically-based sensors. Here we used a quantum spin sensor consisting of three Fe atoms on a monolayer copper nitride surface to probe the magnetic states of nearby nanomagnets. We detect minute magnetic interactions by measuring variations in the spin relaxation time of the spin sensor. The distance between the nanomagnets and the sensor can be changed discretely by atom manipulation using a low-temperature scanning tunneling microscope. We can sense nanomagnets as far away as 3 nanometers, that couple to the sensor with interaction strengths as low as 6 micro-electron volts. By making use of weak inter-atomic exchange interaction the Fe-atom-based sensor can detect nanomagnets possessing no net spin. This scheme permits simultaneously sensing the magnetic states of multiple nanomagnets with a single quantum spin sensor.