Defence researchers have been experimenting with quantum technologies for decades, with some results and capabilities proving more promising than others. The question is not whether quantum will proliferate the defence world, but when and to what extent. Norbert Neumann investigates what quantum computing and sensing mean for militaries.

Defence researchers have been experimenting with quantum technologies for decades, with some results and capabilities proving more promising than others. The question is not whether quantum will proliferate the defence world, but when and to what extent. Norbert Neumann investigates what quantum computing and sensing mean for militaries.

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The four main areas of quantum research are computing, imaging, communication and sensing, with sensors being the most advanced and most promising for military applications. Quantum sensors could be used for position, navigation and timing without the need for external references such as a GPS. A mature quantum sensing capability could make it possible to detect submarines and stealth aircraft.

The University of Birmingham-led UK Quantum Technology Hub and BAE Systems announced in 2020 that they were collaborating to develop and integrate quantum sensing technologies.

Head of innovation at the University of Birmingham School of Physics and Astronomy and researcher on the programme Michael Holynski says: “The hub and our partners are building sensors and preparing them for application trials. We are connecting to defence companies, such as BAE Systems, who are telling us what they need in applications and what steps need to be taken to validate the technology.”

Quantum sensors generally work by measuring physical parameters like gravitational forces, magnetic or electric fields, time and temperature. There are existing technologies that measure similarly, but by fusing these methods with quantum capabilities users can significantly outperform their established counterparts.

The project is experimenting with various sensors that hold promise for the defence sector, including measuring time in new ways, magnetometry and activity on inertial sensing. A sensor or a radar enhanced with quantum capabilities could play a big role in projects like the UK-led Future Combat Air System.

“On the timing side, our focus is on developing precision oscillators in radar by using quantum clocks. Having improved oscillators would improve overall radar performance and may allow resolution of finer details,” Holynski explains.

The motivation for experimenting with quantum and inertial sensing comes from the potential to create reliable navigation systems. Regular inertial stabilisation systems integrate an accelerometer and a gyroscope with an algorithm to determine where the vehicle is. Holynski says a problem with such sensors is that, due to drift and noise, the reading on the sensors can change meaning it can produce less accurate location predictions.

“Quantum might provide a way to make sensors with lower noise and better drift. In principle, quantum can achieve low drift. Improving the underpinning sensors may help improve inertial navigation systems and there’s really a lot of promise there. But the reality is yet to be seen,” he says.

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Czech Technical University high energy physics and quantum technologies researcher Michal Krelina says: “Quantum technologies will allow us to reach higher efficiency, sensitivity and resolution, but many of these experiments are only at the laboratory level. Quantum gravity gradiometers, for instance, allow the exploration of underground or the sub-surface. They are great for geophysical research to find minerals, but less so for locating a nuclear submarine.”

Krelina believes that although the sensitivity of a quantum sensor positioned in low-Earth orbit may be sufficient to find a massive piece of steel in the water, it would lack sufficient spatial resolution. Improving spatial resolution is possible, but it would distort and reduce sensitivity.

Militaries currently use classic magnetometers on vessels and aircraft to detect submarines, so we can assume they will use quantum magnetometers once such technologies are mature enough. The question is how big of an advantage will they provide.

“It’s very difficult to tell because you don’t only need to do very detailed simulations on the technology itself, like measuring inner noise and quantum efficiency, but also conduct direct simulations of the environment itself,” says Krelina.

“If you want to detect a submarine by its magnetic field, you need to consider that the propagation of magnetic field in water is a thousand times slower than in the air. There are loads of questions in this area and it can be a long time before we see results.”

The delivery timescale for capabilities can differ depending on the quantum device in question, but Holynski is optimistic that the first trials of quantum sensing that are relevant to more general defence applications can be expected in the next two to three years.

Whereas classic computers execute calculations using the binary digits 0 and 1, a quantum computer performs tasks using quantum bits (qubits). Qubits can be in a superposition of both states – 0 and 1 – at the same time. This allows quantum computers to carry out multiple complex calculations simultaneously at high efficiency.

The quantum algorithm that can solve digital infrastructure encryptions has existed since 1994, but a mature quantum computer capable of using it is expected to be developed in 10 to 15 years. Hackers could then use the technology to steal sensitive encrypted information from governments and militaries.

Krelina says: “They [quantum computers] can break asymmetric encryptions. That is a huge threat as we use that kind of encryption for all of our communication systems and even for the internet. But we cannot assume that classical hacking will disappear.”

Just like conventional hacking won’t disappear, quantum computers will be used alongside classic computers. As quantum computers are good at specific tasks, hybrid use of classic and quantum computing is a more effective solution.

In the case of quantum sensors, it is only a matter of replacing one piece of equipment with another, possibly larger one. Quantum computers, however, require robust cooling systems. Countries with an infrastructure capable of supporting quantum computing capabilities include China, the US, the UK, Germany and France, but the European Union as a whole has also started to invest more in such technologies.

There are two ways to counter the threats quantum computers pose: develop quantum communication and implement post-quantum cryptography (PQC). One is more challenging than the other. PQC requires huge computation power and is unlikely to be developed before the first quantum attacks could take place.

“Quantum communication methods, such as quantum key distribution, in theory, could work. But it requires the building of new infrastructure,” Krelina explains.

“Fortunately, the quantum algorithm was discovered a very long time ago, so we had plenty of time to come up with countermeasures.”

// Main image: Precision oscillators using quantum clocks would improve overall radar performance. Credit: Petair. Shutterstock