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In late September, a Spanish military plane carrying the country’s defense minister to a base in Lithuania was reportedly the subject of a kind of attack—not by a rocket or anti-aircraft rounds, but by radio transmissions that jammed its GPS system. 

The flight landed safely, but it was one of thousands that have been affected by a far-reaching Russian campaign of GPS interference since the 2022 invasion of Ukraine. The growing inconvenience to air traffic and risk of a real disaster have highlighted the vulnerability of GPS and focused attention on more secure ways for planes to navigate the gauntlet of jamming and spoofing, the term for tricking a GPS receiver into thinking it’s somewhere else. 

US military contractors are rolling out new GPS satellites that use stronger, cleverer signals, and engineers are working on providing better navigation information based on other sources, like cellular transmissions and visual data. 

But another approach that’s emerging from labs is quantum navigation: exploiting the quantum nature of light and atoms to build ultra-sensitive sensors that can allow vehicles to navigate independently, without depending on satellites. As GPS interference becomes more of a problem, research on quantum navigation is leaping ahead, with many researchers and companies now rushing to test new devices and techniques. In recent months, the US’s Defense Advanced Research Projects Agency (DARPA) and its Defense Innovation Unit have announced new grants to test the technology on military vehicles and prepare for operational deployment. 

Tracking changes

Perhaps the most obvious way to navigate is to know where you started and then track where you go by recording the speed, direction, and duration of travel. But while this approach, known in the field as inertial navigation, is conceptually simple, it’s difficult to do well; tiny uncertainties in any of those measurements compound over time and lead to big errors later on. Douglas Paul, the principal investigator of the UK’s Hub for Quantum Enabled Precision, Navigation & Timing (QEPNT), says that existing specialized inertial-navigation devices might be off by 20 kilometers after 100 hours of travel. Meanwhile, the cheap sensors commonly used in smartphones produce more than twice that level of uncertainty after just one hour. 

“If you’re guiding a missile that flies for one minute, that might be good enough,” he says. “If you’re in an airliner, that’s definitely not good enough.” 

A more accurate version of inertial navigation instead uses sensors that rely on the quantum behavior of subatomic particles to more accurately measure acceleration, direction, and time.

Several companies, like the US-based Infleqtion, are developing quantum gyroscopes, which track a vehicle’s bearing, and quantum accelerometers, which can reveal how far it’s traveled. Infleqtion’s sensors are based on a technique called atom interferometry: A beam of rubidium atoms is zapped with precise laser pulses, which split the atoms into two separate paths. Later, other laser pulses recombine the atoms, and they’re measured with a detector. If the vehicle has turned or accelerated while the atoms are in motion, the two paths will be slightly out of phase in a way the detector can interpret. 

Last year the company trialed these inertial sensors on a customized plane flying at a British military testing site. In October of this year, Infleqtion ran its first real-world test of a new generation of inertial sensors that use a steady stream of atoms instead of pulses, allowing for continuous navigation and avoiding long dead times.

COURTESY INFLEQTION

Infleqtion also has an atomic clock, called Tiqker, that can help determine how far a vehicle has traveled. It is a kind of optical clock that uses infrared lasers tuned to a specific frequency to excite electrons in rubidium, which then release photons at a consistent, known rate. The device “will lose one second every 2 million years or so,” says Max Perez, who oversees the project, and it fits in a standard electronics equipment rack. It has passed tests on flights in the UK, on US Army ground vehicles in New Mexico, and, in late October, on a drone submarine. 

“Tiqker operated happily through these conditions, which is unheard-of for previous generations of optical clocks,” says Perez. Eventually the company hopes to make the unit smaller and more rugged by switching to lasers generated by microchips. 

Magnetic fields

Vehicles deprived of satellite-based navigation are not entirely on their own; they can get useful clues from magnetic and gravitational fields that surround the planet. These fields vary slightly depending on the location, and the variations, or anomalies, are recorded in various maps. By precisely measuring the local magnetic or gravitational field and comparing those values with anomaly maps, quantum navigation systems can track the location of a vehicle. 

Allison Kealy, a navigation researcher at Swinburne University in Australia, is working on the hardware needed for this approach. Her team uses a material called nitrogen-vacancy diamond. In NV diamonds, one carbon atom in the lattice is replaced with a nitrogen atom, and one neighboring carbon atom is removed entirely. The quantum state of the electrons at the NV defect is very sensitive to magnetic fields. Carefully stimulating the electrons and watching the light they emit offers a way to precisely measure the strength of the field at the diamond’s location, making it possible to infer where it’s situated on the globe. 

Kealy says these quantum magnetometers have a few big advantages over traditional ones, including the fact that they measure the direction of the Earth’s magnetic field in addition to its strength. That additional information could make it easier to determine location. 

The technology is far from commercial deployment, but Kealy and several colleagues successfully tested their magnetometer in a set of flights in Australia late last year, and they plan to run more trials this year and next. “This is where it gets exciting, as we transition from theoretical models and controlled experiments to on-the-ground, operational systems,” she says. “This is a major step forward.” 

Delicate systems

Other teams, like Q-CTRL, an Australian quantum technology company, are focusing on using software to build robust systems from noisy quantum sensors. Quantum navigation involves taking those delicate sensors, honed in the placid conditions of a laboratory, and putting them in vehicles that make sharp turns, bounce with turbulence, and bob with waves, all of which interferes with the sensors’ functioning. Even the vehicles themselves present problems for magnetometers, especially “the fact that the airplane is made of metal, with all this wiring,” says Michael Biercuk, the CEO of Q-CTRL. “Usually there’s 100 to 1,000 times more noise than signal.” 

After Q-CTRL engineers ran trials of their magnetic navigation system in a specially outfitted Cessna last year, they used machine learning to go through the data and try to sift out the signal from all the noise. Eventually they found they could track the plane’s location up to 94 times as accurately as a strategic-grade conventional inertial navigation system could, according to Biercuk. They announced their findings in a non-peer-reviewed paper last spring. 

In August Q-CTRL received two contracts from DARPA to develop its “software-ruggedized” mag-nav product, named Ironstone Opal, for defense applications. The company is also testing the technology with commercial partners, including the defense contractors Northrop Grumman and Lockheed Martin and Airbus, an aerospace manufacturer. 

COURTESY Q-CTRL

“Northrop Grumman is working with Q-CTRL to develop a magnetic navigation system that can withstand the physical demands of the real world,” says Michael S. Larsen, a quantum systems architect at the company. “Technology like magnetic navigation and other quantum sensors will unlock capabilities to provide guidance even in GPS-denied or -degraded environments.”

Now Q-CTRL is working on putting Ironstone Opal into a smaller, more rugged container appropriate for deployment; currently, “it looks like a science experiment because it is a science experiment,” says Biercuk. He anticipates delivering the first commercial units next year. 

Sensor fusion

Even as quantum navigation emerges as a legitimate alternative to satellite-based navigation, the satellites themselves are improving. Modern GPS III satellites include new civilian signals called L1C and L5, which should be more accurate and harder to jam and spoof than current signals. Both are scheduled to be fully operational later this decade. 

US and allied military users are intended to have access to far hardier GPS tools, including M-code, a new form of GPS signal that is rolling out now, and Regional Military Protection, a focused GPS beam that will be restricted to small geographic areas. The latter will start to become available when the GPS IIIF generation of satellites is in orbit, with the first scheduled to go up in 2027. A Lockheed Martin spokesperson says new GPS satellites with M-code are eight times as powerful as previous ones, while the GPS IIIF model will be 60 times as strong.

Other plans involve using navigation satellites in low Earth orbit—the zone inhabited by SpaceX’s internet-providing Starlink constellation—rather than the medium Earth orbit used by GPS. Since objects in LEO are closer to Earth, their signals are stronger, which makes them harder to jam and spoof. LEO satellites also transit the sky more quickly, which makes them harder still to spoof and helps GPS receivers get a lock on their position faster. “This really helps for signal convergence,” says Lotfi Massarweh, a satellite navigation researcher at Delft University of Technology, in the Netherlands. “They can get a good position in just a few minutes. So that is a huge leap.”

Ultimately, says Massarweh, navigation will depend not only on satellites, quantum sensors, or any other single technology, but on the combination of all of them. “You need to think always in terms of sensor fusion,” he says. 

The navigation resources that a vehicle draws on will change according to its environment—whether it’s an airliner, a submarine, or an autonomous car in an urban canyon. But quantum navigation will be one important resource. He says, “If quantum technology really delivers what we see in the literature—if it’s stable over one week rather than tens of minutes—at that point it is a complete game changer.”