CSU's Du Jiangfeng's team achieves first sunlight-driven quantum magnetometer
While energy consumption has been a major concern for modern industry and society, quantum technologies have rarely taken energy consumption into account. In particular, the potential of quantum technologies driven directly by renewable energy sources has long been overlooked. The initialization, operation and readout of quantum systems usually require high energy-consuming devices such as dilution chillers, microwave power amplifiers and high-power lasers.
Paper forthcoming in the journal Physical Review X Energy
01Demonstration of a sunlight-driven quantum magnetometer
As a result of experiments, the team has discovered a direct pathway to use solar energy to direct the quantum state of negatively charged nitrogen-vacancy (NV) centers in diamond, one of the most promising solid-state quantum systems of the past few decades. In this way, the experimental team demonstrated sunlight-driven quantum magnetic measurements: the initialization and readout of this quantum magnetometer is achieved directly by sunlight, while traditional microwave operation can be eliminated by using a microwave-free scheme.
Conventional lasers consume around 100 watts of power: like keeping a bright light bulb burning; this innovation by the team has the potential to free quantum sensors from this energy requirement. By harnessing ambient energy directly, this approach presents a potential solution to the energy consumption problem of quantum technology. This technique can also be further extended to multiple quantum systems, thus opening the door to future environmentally sustainable quantum technologies and self-powered quantum sensing.
The light passes through a diamond sensor that is at the heart of a sunlight-driven quantum device that measures magnetic fields.
02How to use the sunlight? No need to convert solar energy into electricity
Academician Jiangfeng Du, a physicist at the University of Science and Technology of China, said [2], "The biggest difficulty is how the device uses sunlight: it does not use solar cells to convert light into electricity. Instead, sunlight is needed to do the work of a laser."
Quantum magnetometers typically include a powerful green laser to measure the magnetic field. The laser shines on a diamond containing atomic defects: when nitrogen atoms replace some carbon atoms in a pure diamond, "nitrogen-vacancy" defects are created. The green laser causes the nitrogen vacancies to fluoresce and the intensity emitted depends on the red light intensity of the surrounding magnetic field.
Green light shines on a diamond-based sensor in a quantum device that can be used to measure magnetic fields. In this prototype, a lens (top) collects sunlight, which is filtered to leave only green wavelengths of light. This green light provides an environmentally friendly alternative to the light produced by the high energy-consuming lasers on which conventional quantum devices rely.
New quantum sensors also require green light. A large amount of green light is present in sunlight, as seen in the green wavelengths reflected from leaves and grass. To collect enough green light to run their magnetometer, Jiangfeng Du's team replaced the laser with a 15-cm-wide lens to collect the sunlight; they then filtered the light to remove all colors except green and focused it on a diamond with a nitrogen atom defect. The end result was the generation of red fluorescence, which can show the strength of the magnetic field like a magnetometer equipped with a laser.
Changing energy from one type to another, as happens when solar cells collect light and generate electricity, is an inherently inefficient process. The researchers claim that not having to convert sunlight into electricity to run the laser makes their method three times more efficient than powering the laser with solar cells.
03A first step in the convergence of quantum and environmentally sustainable technologies
"I've never seen any other report linking solar research to quantum technology," said Yen-Hung Lin, a physicist at Oxford University who was not involved in the study. "This is likely to ignite a spark of interest in this unexplored direction, and we could see more interdisciplinary research in the energy field."
Quantum devices that are sensitive to other physical quantities (e.g., electric fields, pressure) could also benefit from a sunlight-driven approach, the researchers said. In particular, space-based quantum technologies may use the intense sunlight outside the Earth's atmosphere to provide tailored light for quantum sensors; the remaining light, in wavelengths not used by quantum sensors, could be relegated to solar cells to power the electronics that process quantum signals.
The sunlight-driven magnetometer is just the first step in the integration of quantum and environmentally sustainable technologies. Jiangfeng Du said, "In its current state, the device is primarily for development purposes; we expect that the device will be used for practical purposes, but there is still a lot of work to be done."
Reference links：
[1]https://journals.aps.org/prxenergy/accepted/9607cK25D4a18803a7914f5164e2f133eb90a6171
[2]https://www.sciencenews.org/article/quantum-sensor-sunlight-environment-magnetic-field
