Tube trains of the future may soon know exactly where they are underground — even in places where GPS is blind — by tapping into the strange rules of the quantum world.
Most modern tracking systems rely on satellites to pinpoint location, backed up by accelerometers that measure tiny movements between GPS updates. It works well enough above ground, but those accelerometers gradually drift, which is why they constantly need satellite corrections.
However, in tunnels or urban areas surrounded by tall buildings where GPS signals don’t reach, that safety net disappears.
So researchers are turning to something far more exotic: quantum accelerometers.
Instead of relying on conventional sensors, these devices use clouds of atoms cooled to near absolute zero. At those temperatures, atoms start to behave strangely — acting as both particles and waves. As the atoms “fall” through a sensor, their wave patterns shift in response to acceleration. Using what’s effectively an ultra-precise optical ruler, the system can read these changes with extraordinary accuracy, without needing satellites at all.
That technology is now moving closer to the railway. Research firm MoniRail has secured an additional £1.25 million from the UK government’s quantum technology programme to advance the work. The funding supports the next phase of the Rail Quantum Inertial Navigation System (RQINS) roadmap, aimed at developing quantum navigation for the London Underground — and potentially the wider national rail network.
MoniRail’s approach goes beyond simple positioning. Sensors fitted to trains already provide a non-intrusive way to monitor track condition, collecting ride-quality data and flagging emerging faults in real time.
Naturally, trains already have track-based location systems, but they are usually based on a train being within a “moving block”, so their accuracy is down to metres rather than centimetres. If you want to monitor track conditions, the more accurate the location of the suspected fault, the less time staff spend repairing it.
Quantum navigation could shrink that uncertainty to centimetres, making it far quicker to pinpoint exactly where a defect lies. Underground, it could deliver the sort of location precision passengers have come to expect above ground — while also acting as a robust fallback above ground if GPS is unavailable.
It might seem like a nice-to-have, but in troubled times, it would not be unrealistic to expect a hostile government (or solar flares) to knock out satellite networks, with substantial impacts on society, especially as estimates suggest that a single day of GPS disruption could cost the UK economy more than £1.4 billion. A system that can keep working independently of space-based infrastructure suddenly looks less like a luxury and more like an insurance policy.
As long as the vehicle has a known starting point, quantum accelerometers can continue tracking its movement accurately, regardless of what’s happening above the atmosphere. In other words, the future of mobile navigation may depend on supercold atoms behaving very strangely.
The project is being carried out in collaboration with Transport for London, QinetiQ, PA Consulting, Imperial College London and University of Sussex.
Steve Venables, Senior Engineer at Transport for London, said: “Being a partner in the RQINS project has highlighted the transformative potential of quantum navigation and the importance of continued investment and collaboration to bring these innovations to life. We commit our support and partnerships with industry and academia to deliver tangible benefits to the UK rail infrastructure, with a focus on real-world impact and long-term resilience. We look forward to being part of the development roadmap in this next phase of UKRI funding.”