Just as early mariners used simple compasses to chart courses across the sea, today’s ships, planes, satellites, and smartphones can rely on Earth’s magnetic field to find their bearings. The difference is that today’s rather more sophisticated compasses have the aid of complex models, like the commonly used World Magnetic Model (WMM), that try to capture the multifaceted processes that create Earth’s magnetosphere. A compass can rely on the WMM or similar models to convert a needle pointing to magnetic north to a heading with respect to true north. (The two norths differ by ever-changing angles.)

These models are not perfect: There are differences between the magnetosphere that they predict and the magnetosphere that satellites observe. Scientists have traditionally ascribed these differences to space currents that flow through the magnetic field high in Earth’s upper atmosphere. But new research complicates the picture, suggesting that the differences are the result of observational biases, incomplete models, or both.

For craft that require sensitive navigation, particularly around Earth’s poles, any of these complications pose a problem. And those problems stand to grow as polar ice melts around the North Pole, opening up potential new shipping routes.

Earth’s magnetic field is multifaceted and complex, but models like the WMM can project it out a few years at a time. The WMM’s current edition, released in December 2019, contains estimates of Earth’s magnetic field from the start of 2020 to the end of 2024. (The next version, covering 2025 through 2029, is scheduled for release in December of this year.)

“Compasses need to account for space currents already, but this adds more complication and sources of noise that have to be dealt with.” —Mark Moldwin, University of Michigan

These models do not always account for space currents, which are often pushed around by extraterrestrial forces like the solar wind. But if space currents are responsible for the discrepancies between models and observations, scientists could identify them by simply finding the differences, which they call “residuals.” Moreover, there would then be little reason for one of Earth’s hemispheres to display more residuals than the other—except that’s what existing models predict.

But the new study’s authors, space physicists Yining Shi and Mark Moldwin from the University of Michigan, had been among a number of researchers who had spotted an imbalance in residuals. More residuals seemed to emerge from the magnetic woodwork, so to speak, in the southern hemisphere than in the Northern Hemisphere. “We wanted to take a closer look at them,” Moldwin said.

Shi and Moldwin compared estimates between 2014 and 2020 from another Earth magnetic field model, IGRF-13, with observations from the European Space Agency’s Swarm mission, a trio of satellites that have continually measured Earth’s magnetic field since their 2014 launch.

When they focused on residuals over that time period, they did indeed find about 12 percent more major residuals in the Southern Hemisphere than in the Northern. All of these large residuals were found in the polar regions. Many were concentrated at latitudes of 70 degrees north and south, where scientists expect to find space currents.

But another spate of residuals were concentrated closer to Earth’s geographic poles, about 80 degrees north and south, where they have no obvious geophysical explanation. Moreover, the distributions of these poles differed—matching the fact that Earth’s geographic poles map to different magnetic coordinates.

This second peak in particular led the researchers to consider alternative explanations. It is possible, for instance, that IGRF-13 simply does not capture all of the factors driving Earth’s magnetosphere around the poles. But another cause could be the satellites themselves. Shi and Moldwin say that, because Swarm satellites reside in orbits that cross the poles, Earth’s northern and southern polar regions are overrepresented in their magnetic measurements.

“Compasses need to account for space currents already, but this adds more complication and sources of noise that have to be dealt with,” Moldwin said.

Now, Shi is examining these residuals more closely to pick apart the causes of the residuals—which ones have actual geophysical explanations and which are the result of statistical errors.

Shi and Moldwin published their work on 6 May in Journal of Geophysical Research: Space Physics.

A short-haul aircraft in the United Kingdom recently became the first airborne platform to test delicate quantum technologies that could usher in a post-GPS world—in which satellite-based navigation (be it GPS, BeiDou, Galileo, or others) cedes its singular place as a trusted navigational tool. The question now is how soon will it take for this quantum tomorrow to actually arrive.

But is this tech just around the corner, as its proponents suggest? Or will the world need to wait until the 2030s or beyond, as skeptics maintain. Whenever the technology can scale up, potential civilian applications will be substantial.

“The very first application or very valuable application is going to be autonomous shipping,” says Max Perez, vice president for strategic initiatives at the Boulder, Colo.–based company Infleqtion. “As we get these systems down smaller, they’re going to start to be able to address other areas like autonomous mining, for example, and other industrial settings where GPS might be degraded. And then, ultimately, the largest application will be generalized, personal autonomous vehicles—whether terrestrial or air-based.”

The big idea Infleqtion and its U.K. partners are testing is whether the extreme sensitivity that quantum sensors can provide is worth the trade-off of all the expensive kit needed to miniaturize such tech so it can fit on a plane, boat, spacecraft, car, truck, or train.

Turning Bose-Einstein Condensates Into Navigational Tools

At the core of Infleqtion’s technology is a state of matter called a Bose-Einstein condensate (BEC), which can be made to be extremely sensitive to acceleration. And in the absence of an external GPS signal, an aircraft that can keep a close tally on its every rotation and acceleration is an aircraft that can infer its exact location relative to its last known position.

As Perez describes it—the company has not yet published a paper on its latest, landmark accomplishment—Infleqtion’s somewhat-portable BEC device occupies 8 to 10 rack units of space. (One rack unit represents a standard server rack’s width of 48.3 centimeters and a standard server rack depth of 60–100 cm.)

Scientists tested delicate Bose-Einstein condensates in their instruments, which could one day undergird ultrasensitive accelerometers.Qinetiq

In May, the company flew its rig aboard a British Aerospace 146 (BAe 146/Avro RJ100) tech demonstrator aircraft. Inside the rig, a set of lasers blasted a small, supercooled cloud of rubidium atoms to establish a single quantum state among the atoms. The upshot of this cold atom trap is to create ultrasensitive quantum conditions among the whole aggregation of atoms, which is then a big enough cloud of matter to be able to be manipulated with standard laboratory equipment.

Using the quantum wave-particle duality, in which matter behaves both like tiny billiard balls and wave packets, engineers can then use lasers and magnetic fields to split the BEC cloud into two or more coherent matter-wave packets. When later recombined, the interference patterns of the multiple wave packets are studied to discover even the most minuscule accelerations—tinier than conventional accelerometers could measure—to the wave packets’ positions in three-dimensional space.

That’s the theoretical idea, at least.

Real-World Conditions Muddy Timetables

In practice, any BEC-based accelerometer would need to at least match the sensitivity of existing, conventional accelerometer technologies.

“The best inertial systems in the world, based on ring laser gyroscopes, or fiber-optic gyroscopes, can...maintain a nautical mile of precision over about two weeks of mission,” Perez says. “That’s the standard.”

The Infleqtion rig has provided only a proof of principle for creating a manipulable BEC state in a rubidium cloud, Perez adds, so there’s no one-to-one comparison yet available for the quantum accelerometer technology. That said, he expects Infleqtion to be able to either maintain the same nautical-mile precision over a month or more mission time—or, conversely, increase the sensitivity over a week’s mission to something like one-tenth of a nautical mile.

The eventual application space for the technology is vast, says Doug Finke, chief content officer at the New York City–based market research firm Global Quantum Intelligence.

“Quantum navigation devices could become the killer application for quantum-sensing technology,” Finke says. “However, many challenges remain to reduce the cost, size, and reliability. But potentially, if this technology follows it similar path to what happened in computing, from room-size mainframes to something that fits inside one’s pocket, it could become ubiquitous and possibly even replace GPS later this century.”

The timeframe for such a takeover remains an unanswered question. “It won’t happen immediately due to the engineering challenges still to be resolved,” Finke says. “And the technology may require many more years to reach maturation.”

Dana Goward, president of the Alexandria, Va.–based Resilient Navigation and Timing Foundation, even ventures a prediction. “It will be 10 to 15 years at least before we see something that is practical for broad application,” he says.

Perez says that by 2026, Infleqtion will be testing the reliability of its actual accelerometer technology—not just setting up a BEC in midflight, as it did in May. “It’s basically trading off getting the technology out there a little faster versus something that is more precise for more demanding applications that’ll be just behind that,” Perez says.

UPDATE 4 June 2024: The story was updated to modify the accuracy estimate for the best inertial navigation systems today—from one nautical mile per one-week mission (as a previous version of this story stated) to one nautical mile per two-week mission.