A lone erbium atom sits on a silver substrate, and its spin, the electron's internal rotation, stores quantum information. Previously, flipping this spin required a magnetic pulse: a blunt tool that disturbs neighbors and works slowly. Now physicists from Germany and Korea have shown that a single electric voltage suffices.

The secret lies in a neighboring titanium atom. It sits next to the erbium and is coupled to it by exchange interaction — the same force that holds atoms together in a molecule. When voltage is applied to the tip of a scanning tunneling microscope, the electric field slightly shifts the titanium. Acting like a lever, it pulls the erbium's spin and flips it. The whole operation takes less than a nanosecond.

The authors measured how quickly the spin responds to an electric jolt. It turns out that the Rabi frequency, the rate at which the spin oscillates between 'up' and 'down' states, reaches nearly a billion cycles per second. For rare-earth spins, this is a record: the previous result was ten times more modest. Moreover, the control works equally well in any direction of the magnetic field, which is rare for such systems.

Such an electric steering wheel opens the door to quantum circuits where each spin is addressed individually and quickly. Rare-earth ions are renowned for long memory: their spins can store information for seconds, while neighboring qubits lose it in milliseconds. If they can now also be switched quickly, the combination of long memory and high speed looks promising.