Physics – a “green” quantum sensor

    Vadim Vorobyov

    • Institute of Physics, University of Stuttgart, Stuttgart, Germany

Physics 15, 158

The researchers demonstrated a quantum sensor that can turn itself on using sunlight and the surrounding magnetic field, a feat that could help reduce the energy costs of this energy-hungry technology.

Figure 1: The newly designed diamond flawless quantum sensor can work without external power supply.

No longer in the realm of science fiction, today’s quantum sensors are used in applications ranging from timekeeping and gravitational wave detection to nanomagnetometers. [1]. When making new quantum sensors, most researchers focus on creating devices as accurate as possible, which usually requires the use of advanced — power-hungry — technologies. This high power consumption can be a problem for sensors designed for use in remote locations on Earth, in space, or in IoT sensors not connected to the mains electricity grid. To reduce the dependence of quantum sensors on external energy sources, Yunbin Zhu of the University of Science and Technology of China and colleagues now demonstrate a quantum sensor that directly exploits renewable energy sources to obtain the energy it needs to operate. [2]. The new device could greatly expand the use of quantum sensors as well as help reduce the energy costs of quantum sensors in current applications.

Today quantum technologies are largely found in research laboratories, which have virtually unlimited access to energy. A typical device operates in extremely cold temperatures and requires powerful lasers, microwave frequency amplifiers, and waveform generators. Such a device can consume thousands of watts and operate 24 hours a day. One way to reduce these energy costs is to make sensors from systems that do not require cryogenic cooling, such as diamond defects known as nitrogen vacant (NV) centers. However, these sensors still require a powerful laser, which can easily consume 100-1000 watts, and a microwave source that needs about 100 watts. The researchers are also working on miniaturizing the sensors, a process that typically reduces power consumption. But current versions of these smaller sensors still get their power off the grid [3].

Zhu and colleagues are taking a different approach by developing a quantum sensor that generates its own power from a renewable energy source, in this case solar energy (Fig. 1). The team’s sensor consists of an array of NV centers in diamond, a well-established solid-state quantum sensing platform that can operate over a wide range of temperatures (0-600 K), pressures (up to 40 GPa), and magnetic fields (0-12 T). .

Vacant nitrogen centers are defects usually created by implanting nitrogen ions into the diamond network. The centers trap charge carriers – such as electrons or holes – creating a local electronic state. Users can read the rotation of this state by triggering the fault with the laser. The NV center then emits radiation, via fluorescence, the intensity of which is related to the rotation of the system. Researchers typically use a green laser for this excitation, as this color of light produces the strongest fluorescence in the system (the radiation emitted in red).

For use in quantitative applications, NV cores are ideal because they operate at room temperature, so no cooling device is required. However, they require a laser to excite the NV center. It also requires a magnetic field generator and a microwave frequency amplifier: the fluorescence frequency of the NV center can be divided into two by applying a bias magnetic field, and the two resulting emission peaks can be reached by scanning the microwave amplifier through these frequencies. The exact positions of these peaks encode information about any changes in the surrounding magnetic field with respect to bias as well as changes in device temperature or stress.

Zhu and colleagues’ device eliminates both the laser and the amplifier. Instead of using laser light to excite the center of the NV, the researchers use sunlight, filtering it with an optical band-pass filter so that only green wavelengths are recorded at the center of the NV. They also use a so-called iron center of flux to amplify the Earth’s magnetic field to about 100-300 G. At these magnetic field strengths, the energy structure of the NV centers allows for full visual detection of changes in the surrounding magnetic field. Just by observing the brightness of the device’s brilliance. This ability allows the team to operate the sensor without a separate magnetic field generator or separate external microwave frequency amplifier.

The team’s device requires only 0.1 watts to operate – and that power is required to operate a low-powered spin-reading photodetector. The researchers showed that they could have reasonable sensitivity to detect ground-level changes in the Earth’s resulting magnetic field, for example, by having power lines or trains nearby. This sensitivity – less than 1 nT/sqrt (Hz) – is on par with that achieved for diamonds with normal concentrations of carbon isotopes – diamonds typically contain two isotopes, C12 and c13. Higher sensitivities were achieved using iso-pure diamond, lab-grown, best with around 1 penny/square foot (Hz) – a level suitable for detecting changes in biomagnetic fields in the heart or in skeletal muscle. I imagine they could reach this sensitivity level by increasing the energy of sunlight entering the device or by allocating both the isotopic content of the diamond and the focus of the NV center.

This demonstration is a first step towards powering quantum technologies directly with renewable energy, eliminating the need to connect to an external power source. By doing so, Zhu and his colleagues showed that their devices had much higher energy efficiency than similar networked devices.

references

  1. CL Digen et al.“quantum sensing,” Rev. DoD. Phys. 89035002 (2017).
  2. Y. Zhu et al.“Sunlight-Driven Quantum Magnetism Measurement,” PRX power 1033002 (2022).
  3. FM Turner et al.“An integrated, portable magnetometer based on diamond-free nitrogen clusters,” case. Quantum technology. 42000111 (2021).

About the author

Vadim Vorobyov's photo

Vadim Vorobyov studied physics at the Moscow Institute of Physics and Technology and received his Ph.D. He received his Ph.D. from the Lebedev Physical Institute of the Russian Academy of Sciences in 2017. Since 2018, he has been a researcher at the University of Stuttgart, Germany. It studies quantum solid-state defects and their applications, with a focus on quantum sensing and quantum information processing.


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Subject areas

Quantum physics and energy research

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