This environmentally friendly quantum sensor runs on sunlight

Quantum technology is going green.

The new look at highly sensitive magnetic field sensors ditches the energy-hungry lasers that previous devices relied on for measurements and replaces them with sunlight. Lasers can absorb 100 watts or so of power – like keeping a light bulb burning brightly. The innovation potentially frees quantum sensors from this energy requirement. As a result, an environmentally friendly prototype at the cutting edge of technology, researchers report in the next issue X Energy Physical Review.

Big turn in how the device uses sunlight. It does not use solar cells to convert light into electricity. Instead, sunlight does the work of laser light, says Jiangfeng Du, a physicist at the University of Science and Technology of China in Hefei.

Quantum magnetometers often include a powerful green laser to measure magnetic fields. The laser shines on a a diamond containing atomic defects (ЗН: 26.02.08). Defects occur when nitrogen atoms replace some of the carbon atoms that make up pure diamonds. The green laser causes the nitrogen defects to fluoresce, emitting red light with an intensity that depends on the strength of the surrounding magnetic fields.

The new quantum sensor also needs the green light. There is a lot of this in sunlight, as seen in the green waves reflected from the leaves of trees and grass. To collect enough of it for the magnetometer to operate, Du and his colleagues replaced the laser with a 15-centimeter-diameter lens to collect sunlight. They then filtered the light to remove all colors except green and focused it on a diamond with nitrogen atom defects. The result is red fluorescence that detects magnetic field strength in the same way that laser-equipped magnetometers do.

The prototype lens filters green light from sunlight onto a diamond sensor underneath.
The green light shining on the diamond sensor of the quantum device can be used to measure magnetic fields. In this prototype, a lens (top) collects sunlight, which is filtered to leave only green waves of light. This green light provides an environmentally friendly alternative to the light produced by the energy-intensive lasers that conventional quantum devices rely on.Yunbin Zhu/University of Science and Technology of China

The change of energy from one type to another as it occurs when solar cells collect light and produce electricityis an inherently inefficient process (ZN: 07/26/17). Avoiding converting sunlight into electricity to run the lasers makes their approach three times more efficient than would be possible with solar cells that power the lasers, the researchers say.

“I’ve never seen any other reports linking solar research to quantum technology,” says Yen-Hung Lin, a physicist at the University of Oxford who was not involved in the research. “This could ignite a spark of interest in this unexplored direction, and we may see more interdisciplinary research in the field of energy.”

Quantum devices sensitive to other factors, such as electric fields or pressure, could also benefit from a sunlight-driven approach, the researchers say. In particular, space-based quantum technology can use the intense sunlight available outside the Earth’s atmosphere to provide light tailored for quantum sensors. The remaining light, with wavelengths that quantum sensors do not use, can be fed to solar cells that power electronics to process quantum signals.

A magnetometer driven by sunlight is just the first step in combining quantum and environmentally sustainable technology. “As it stands, this device is primarily for development,” says Du. “We expect the devices to be used for practical purposes. But there is [is] a lot of work needs to be done.”

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