MIT scientists have built an ultra-sensitive magnetic-field detector about 1,000 more energy efficient than current models. This new device could lead to a new generation of sensors for medical and security applications.

Magnetic-field detectors, or magnetometers, are widely utilized in medical imaging technologies and contraband detection at security checkpoints. But existing technologies have their limitations.

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Current magnetometers require massive and expensive gas chambers while some have limited usability as they only function in narrow frequency bands.

For their new device, MIT scientists successfully examined the use of synthetic diamonds with nitrogen vacancies (NVs). NVs are defects in diamonds extremely sensitive to magnetic fields.

The MIT magnetometer was equipped with a thumbnail sized diamond chip that has trillions of NVs. Each of these NVs can perform its own magnetic field detection.

The scientists then measured the magnetic state of the NVs by probing them with laser light. The light, which was swiftly absorbed and re-emitted, has the intensity that gave scientists some clues on the magnetic state of each defect.

When a light particle hits an electron in an NV, it jumps into a higher energy state. The electron then falls back down into its initial state, releasing its excess energy as another photon.

A magnetic field, however, can change the electron's magnetic spin. This can increase the difference between the electron's two energy states. Stronger magnetic fields can flip more spins, which can then change the intensity of light emitted by the NVs.

"In the past, only a small fraction of the pump light was used to excite a small fraction of the NVs," noted Dirk Englund , MIT's Jamieson Career Development Professor in Electrical Engineering and Computer Science. 

"We make use of almost all the pump light to measure almost all of the NVs," Englund added.

The MIT scientists noted they could be able to build a smaller version of the chip that could be used in devices powered by batteries .This, in turn, could make accurate magnetic field measurement for medical imaging, contraband detection and even geological exploration truly mobile.