Researchers at Massachusetts Institute of Technology were able to develop an ultra-sensitive magnetometer that is nearly 1,000 more energy efficient than current devices.
Magnetometers, or magnetic-field detectors, have a wide range of applications in medicine, but they are also used by the police to detect arms trafficking and geologists that want to have a more accurate image of the variations in the Earth magnetic field.
A more powerful device means that super-powerful magnetometers will shrink in size and become portable. Moreover, producers will have room to equip them with more safety features. Some current models use gas-filled chambers, while others have limited usability since they only work in narrow frequency bands.
In their new device, MIT scientists managed to successfully test man-made diamonds with nitrogen vacancies (NVs). NVs are point defects in diamonds that are very sensitive to magnetic fields. MIT magnetometers will be equipped with a very tiny diamond chip which would contain trillions of NVs. A single NV will be able to create its own magnetic-field detection.
MIT researchers measured the nitrogen vacancies’ magnetic state by zapping them with laser-light, which was quickly absorbed and re-emitted. The intensity of the resulted light gave scientists some clues on each defect’s magnetic state.
“In the past, only a small fraction of the pump light was used to excite a small fraction of the NVs. We make use of almost all the pump light to measure almost all of the NVs,”
said Dirk Englund, one of the designers of the device and electrical engineering and computer science professor at the institute.
Scientists published a paper on their findings in the journal Nature Physics. The experiment involved experienced researchers such as Danielle Braje and Dirk Englund, their former or current students including Matthew Trusheim, Hannah Clevenson and Carson Teale, and Tim Schröder, a MIT postdoctoral fellow.
A pure-state diamond does not sense magnetic fields since its dense structure of carbons doesn’t allow it to. But an artificial diamond with trillions of nitrogen vacancies in it suddenly becomes a very powerful magnetic-field detector. Within a nitrogen vacancy, electrons are able to interact with electric fields.
MIT scientists explained that the light a NV can re-emit is influenced by the intensity of a nearby magnetic field. When the research team used a laser to strike an electron in a NV, they found that a photon in the laser beam can kick the NV electron into a higher energy state.
However, the electron quickly relapsed to its initial energy state, but released the excess energy as another photon. Since a magnetic field can flip the electron’s magnetic spin and boost the difference between its energy states, the stronger the field, the brighter the light re-emitted by NVs.
Yet, researchers had to solve first a technical problem. By directing the laser light at the surface of a diamond chip, that light went straight through the diamond, and only a small fraction was absorbed and re-emitted. By adding a small prism facet to the corner of the chip and attaching the laser into the side, all light was absorbed.
Image Source: MIT