Unjammable Quantum Sensors Navigate by Earth's Magnetic Field

In March 2024, a plane carrying the UK defense minister had its GPS signal jammed as it travelled close to the Russian exclave of Kaliningrad on a journey between the UK and Poland. The UK government later said the plane was never in danger but that jamming incidents were not unusual in the region. However, this incident highlights the vulnerability of global navigation satellite systems (GNSS) to interference and jamming.

For decades, inertial navigation has been the standard backup for navigational failures caused by GNSS signal loss. But these systems have an inherent weakness: tiny errors add up over time, causing position estimates to drift, potentially by many kilometers over long journeys. This makes them unacceptable in many critical applications. What navigators desperately need is a new way to work out where they are that does not rely on satellite signals that can be jammed.

A New Era of Navigation: Quantum-Assured MagNav

Murat Muradoğlu and colleagues at Q-CTRL, a quantum technology company with offices in Sydney, Australia, have demonstrated just such a technology. Their approach is to sense anomalies in the Earth’s magnetic field and compare them with a known map of the field to work out their position. And because they use quantum sensors for this process, they can detect magnetic anomalies with much greater sensitivity than previously possible.

The Q-CTRL system uses a proprietary quantum magnetometer that measures the way an external field influences the spin of rubidium atoms. This compact, lightweight package is about the size of a Rubik’s cube and has the potential to revolutionize how vehicles find their way in environments where GNSS are unavailable.

The Concept Behind MagNav

The concept behind MagNav isn’t new. The Earth's magnetic field isn't perfectly uniform; superimposed on the main field of up to 65,000 nanotesla generated by the planet’s core are small, localized variations known as magnetic anomalies. These anomalies typically range in size from 10 to 100 nanoteslas over a few kilometers.

Just like landmarks allow visual navigation, these magnetic features can serve as signposts. If a vehicle carries a sensitive magnetometer and has access to a map of these anomalies, it can determine its position by matching its real-time magnetic field measurements to the map. Global magnetic anomaly maps already exist, compiled from decades of geophysical surveys.

However, translating this elegant concept into a practical system has been challenging. The magnetic noise inside a vehicle can be so high that it interferes with the anomaly signal, making accurate navigation difficult.

Quantum-Assured MagNav: A Game-Changer in Navigation

In the ground trials, the Q-CTRL MagNav system achieved a final accuracy of 180 meters over an 18 km route, despite magnetic noise inside the van reaching levels 50 times greater than the anomaly signal. This is impressive work with significant implications.

Given the increasing vulnerability of GNSS systems, much work has gone into alternative forms of navigation but all have limitations. Camera-based terrain navigation and star trackers can fail when the weather is poor; radar and lidar are resilient options but reveal their position and beacon-based navigation systems based on mobile phone towers work poorly over oceans or in remote areas.

Q-CTRL's quantum-assured MagNav has the potential to leapfrog these technologies. It can outperform inertial navigation systems across a wide range of conditions, making it an attractive solution for future UK defense ministers and others who need reliable navigation.

Challenges Ahead

However, there are challenges ahead for Q-CTRL's quantum-assured MagNav. The resolution and coverage of public domain magnetic maps need to be improved, particularly over oceans where magnetic anomalies tend to be smaller than over land.

An important question is how accurate these maps can be made. Additionally, geomagnetic storms caused by solar activity can generate fields that dwarf anomalies this system depends on for navigation. It may become necessary to integrate predictive models of geomagnetic activity for path planning.

Furthermore, there is the possibility that military capabilities developed in secret may outperform Q-CTRL's making it obsolete. Other "unjammable" quantum technologies could also compete, such as quantum inertial navigation, which is currently being tested by the UK technology company Infleqtion.

A New Era of Navigation Dawns

All this work suggests a new era of quantum-enabled navigation is dawning that should protect future UK defense ministers and others from jamming attacks. Of course, a new era of hacking, jamming and other nefarious activity cannot be far behind.

But for now, Q-CTRL's quantum-assured MagNav has opened up new possibilities for reliable navigation in the face of GNSS interference. It is an exciting development that could have significant implications for various industries, including defense, transportation, and beyond.