In the crystal lattice of diamond, defects occasionally appear: a nitrogen atom grabs a foreign spot, and next to it gapes a void. Such a flaw turns into a supersensitive diamond compass: its magnetic needle quivers at the slightest external field. Paradoxically, a blemish that lowers a stone's value has become a coveted tool for physicists.

To see this atom-sized compass, scientists built a tiny platform unfazed by temperature fluctuations. They 'hailed' the defect with a series of magnetic pulses and caught the echo — a faint response. Magnetic scanning decoded the signal and pinpointed the spot with staggering precision of 0.28 nanometers — smaller than the distance between atoms in a crystal.

Underpinning this is the quantum nature of the defect: its magnetic moment can act as a qubit — the information unit of a quantum computer. Now we can probe such 'compasses' inside proteins and living cells, bringing us closer to the era of molecular medicine.