A quantum pathway to overcome the trilemma of magnetic data storage

The three essential pillars of magnetic data storage devices are readability, writeability, and stability. However, these requirements compete as magnetic domain sizes reach the fundamental limit of single atoms and molecules. The proven magnetic bistability of individual holmium atoms on magnesium oxide appeared to operate within this magnetic trilemma, sacrificing writeability for unprecedented stability. Using the magnetic stray field created by the tip of a spin-polarized scanning tunneling microscope (SP-STM), we controllably move the Ho state into the quantum regime, allowing us to write its state via the quantum tunneling of magnetization (QTM). We find that the hyperfine interaction causes both the excellent magnetic bistability, even at zero applied magnetic field, and the avoided level crossings which we use to control the magnetic state via QTM. We explore how to use such a system to realize a high-fidelity single atom NOT gate (inverter). Our approach reveals the prospect of combining the best traits of the classical and quantum worlds for next generation data storage.