Quantum Sensor Hits Nanosecond Resolution

Making certain that tiny, nanoscale transistors are performing correctly, understanding the properties of nanomaterials, or testing nanoscale medical devices all require the ability to measure magnetic fields quickly and precisely.

Researchers have now unlocked the secret to doing so with a tabletop quantum sensor that can capture magnetic fields with nanosecond resolution. Konstantin Herb, a physicist at ETH Zurich, presented the demonstration at the American Physical Society’s Global Physics Summit last week, in Anaheim, Calif.

In data storage, companies developing magnetic racetracks—ultrahigh-density nonvolatile memory systems—could benefit from the ability to study ultrafast magnetization dynamics. Similarly, spintronics research in memory and computing applications stands to gain from enhanced temporal resolution.

Traditionally, examining dynamic magnetization processes that occur on timescales of a few nanoseconds requires beamtime at large-scale X-ray synchrotron facilities, such as those at the Diamond Light Source in the United Kingdom or the Paul Scherrer Institute in Switzerland. “We think we now have the ability to do this on a tabletop experiment,” says Herb.

A Quantum Trade-off Between Speed and Precision

The design is based on nitrogen-vacancy (NV) centers in diamond, a workhorse in the world of quantum sensing. These tiny, engineered defects in a diamond’s crystal lattice act as highly sensitive quantum sensors, detecting minuscule changes in magnetic and electric fields, and responding to these changes in a measurable way.

NV-based quantum magnetometers have become crucial for magnetic imaging. But their application has mostly been limited to static magnetization structures. Previous methods could measure with time resolution of 20 nanoseconds at best, but many other dynamic magnetization processes—such as those in magnetic racetracks—occur on timescales of only a few nanoseconds, beyond the reach of existing NV sensing techniques.

Last year Herb and Christian Degen explored the interplay between Heisenberg’s famous uncertainty principle and the achievable time resolution in a quantum sensing experiment. The “quantum speed limit” (QSL)—the minimum time that a quantum system requires to transition between two states—has remained mainly a concept in information theory for the last decade. But the researchers’ 2024 study established a direct link between QSL and the achievable time resolution in sensing. “We show that sensitivity and time resolution can be traded off,” explains Herb.

Now they’ve put this trade-off to the test. Herb, Degen, and the ETH Zurich team have demonstrated magnetic-field sensing with a record time resolution of just one nanosecond. This allowed them to capture fast signals such as domain wall motion and magnetization reversal. The result constitutes a more than tenfold advance compared to previous work, bringing them significantly closer to real-time imaging of magnetization dynamics.

This is a microscope image of the antenna used by the researchers.ETH Zurich

Tabletop Technology

In the experiments, the team used an off-the-shelf NV probe from QZabre to detect fields similar to those arising from magnetization reversals and domain-wall propagation in thin magnetic nanostructures. By applying a sequence of microwave pulses, they manipulated the electronic spin of a single NV center in the diamond probe tip, generating a photoluminescent signal in response to tiny external magnetic field changes. Monitoring photoluminescence variations allowed them to interpret the local magnetic-field density.

Their ability to measure nanosecond-scale changes boiled down to how the microwave pulses were delivered, and the fact that sensing occurs simultaneously with microwave excitation. “You need a strong enough antenna to drive the transition of the NV center,” explains Herb, but without delivering excessive heat. The researchers accomplished that by designing an efficient antenna that maximized microwave field per ampere, achieving a pulse duration of 2 ns and therefore enabling an instantaneous bandwidth of 0.9 gigahertz for magnetic sensing.

“We’re excited because quantum sensing has traditionally prioritized sensitivity and precision over speed,” says Herb. “Yet as quantum technologies progress toward real-world applications, exploring their speed limits becomes essential.”

Startups like QZabre and QNami are already bringing NV-based quantum sensing to the market. Their ready-to-use tabletop systems have made these advanced techniques more accessible to researchers in spintronics and magnetism. For the last few years, they’ve commercialized full scanning microscope systems that can be mounted on a computer rack for academia and industry. Herb believes that accessing ultrafast measurements in these compact, room-temperature machines is not too far away.

QZabre is already working on an integrated antenna design that will help to improve the switching speed of their scanning microscopes. “Now that everything is in principle available, it should be just an engineering problem,” says Herb.

For the ETH Zurich team, the primary motivation was proving that such fast sensing is possible. It’s also opened the ability to study new memory systems, as well as dynamic magnetization processes. “Our vision is that you’ll be able to do ultrafast science without needing a synchrotron,” Herb says.