MIT researchers have developed a new, ultrasensitive magnetic-field detector that is 1,000 times more energy-efficient than its predecessors. It could lead to miniaturized, battery-powered devices for medical and materials imaging, contraband detection, and even geological exploration. Magnetic-field detectors, or magnetometers, are already used for all those applications. But existing technologies have drawbacks: Some rely on gas-filled chambers; others work only in narrow frequency bands, limiting their utility.

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 those measurements. Probing a nitrogen vacancy requires zapping it with laser light, which it absorbs and re-emits. The intensity of the emitted light carries information about the vacancy's magnetic state.

"In the past, only a small fraction of the pump light was used to excite a small fraction of the NVs," says Dirk Englund, the Jamieson Career Development Assistant Professor in Electrical Engineering and Computer Science and one of the designers of the new device. "We make use of almost all the pump light to measure almost all of the NVs."

The MIT researchers report their new device in the latest issue of Nature Physics. First author on the paper is Hannah Clevenson, a graduate student in electrical engineering who is advised by senior authors Englund and Danielle Braje, a physicist at MIT Lincoln Laboratory. They're joined by Englund's students Matthew Trusheim and Carson Teale (who's also at Lincoln Lab) and by Tim Schröder, a postdoc in MIT's Research Laboratory of Electronics.