Joseph Cotter, a researcher at Imperial College London's Centre for Cold Matter, has been seen on the London Underground armed with a stainless steel vacuum chamber, billions of rubidium atoms, and a series of lasers designed to cool the apparatus to just above absolute zero.

Users of the District Line have managed to ignore this, in a way that only the British can.

However, Cotter’s device aims to harness subatomic behaviours to create instruments that can precisely determine their location, regardless of placement, heralding a new era of subterranean and subaquatic sensors.

The London Underground has proven to be an ideal testing ground for this technology.

"In the lab, our new quantum-based sensors are showing significant promise," Dr. Cotter shared with the Observer.

 "Yet, their accuracy diminishes outside controlled environments. That's why we're bringing them into the Underground — it's the optimal environment for refining our devices for real-world application."

An accelerometer is central to the quantum compass, anticipated to be ready for broad deployment within a few years. This instrument measures changes in velocity over time, which, when combined with an object's initial location, enables the prediction of its future positions.

While mobile phones and laptops have accelerometers, they lack long-term precision. Quantum mechanics offers a solution by allowing precise measurements of supercooled atoms' properties. At near absolute zero temperatures, atoms exhibit quantum behaviour, displaying particle and wave characteristics.

 "Ultra-cold atoms allow us to apply quantum mechanics to their movement, granting us the ability to make precise measurements that inform us of our device's positional changes," explained Cotter.

The devices, tested on London Underground's track-testing trains (not commuter services), incorporate rubidium into their core vacuum chamber. Intense lasers cool these atoms to a fraction above absolute zero (-273.15°C). Under these conditions, the vehicle's acceleration alters the rubidium atoms' wave properties, enabling precise detection of these subtle shifts.

Cotter added that while the system performs well in stable lab settings, it requires further testing under more challenging conditions to evolve into a portable, independent device suitable for use in remote or intricate locations.