A Massachusetts Institute of Technology team has developed a new, ultrasensitive magnetic-field detector. The device could lead to miniaturized, battery-powered devices for medical imaging.

Synthetic diamonds with nitrogen vacancies (NVs) — defects that are extremely sensitive to magnetic fields — have long held promise as the basis for efficient, portable magnetometers.

A diamond chip about one-twentieth the size of a thumbnail could contain trillions of nitrogen vacancies, each capable of performing its own magnetic-field measurement. The problem has been aggregating all of the measurements.

The MIT researchers used almost all the pump light to measure the majority of the NVs. The team calculated the angle at which the laser beam should enter the crystal so that it will remain confined, bouncing off the sides in a pattern that spans the length and breadth of the crystal before all of its energy is absorbed.

Because of the geometry of the nitrogen vacancies, the re-emitted photons emerge at four distinct angles. A lens at one end of the crystal can collect 20 percent of them and focus them onto a light detector, which is enough to yield a reliable measurement.