London Underground hosts tests for 'quantum compass' that could replace GPS

What the device is

• Described as a “quantum compass” but participants say it’s essentially a quantum-enhanced inertial navigation system (INS) / dead-reckoning device.
• Core component is a highly sensitive accelerometer; combines known starting position with integrated acceleration to track motion without external signals.
• London Underground is mainly a convenient moving lab; primary envisioned uses are in GPS-denied environments (submarines, underground, underwater, other planets).

How it works (technical discussion)

• Uses cold atoms (rubidium) and laser cooling: atoms are slowed and trapped, then their motion is probed via laser light.
• Because the atoms are referenced to extremely stable laser wavelengths, the accelerometer can, in principle, be more accurate than conventional MEMS or light-based sensors.
• Atoms sit in ultra-high vacuum; cooling is via lasers and traps, not cryogenic liquids.

Accuracy, drift, and recalibration

• All INS approaches accumulate error due to double integration of noisy acceleration data; participants emphasize this remains true here.
• Sampling limits (Nyquist issues) and missed high-frequency accelerations still cause drift.
• Example commercial quantum accelerometer cited with precision that would drift tens of centimeters per hour, hundreds of meters per day if never recalibrated.
• Some note that reduced drift could make recalibration infrequent, especially when combined with known track layouts or station references.

Relationship to GPS/GNSS

• Strong pushback on the idea that this “replaces” GPS; more accurate framing is “GNSS-independent backup” or “augmentation.”
• Devices still require a starting reference and periodic corrections (e.g., from known positions, wireless networks, beacons).
• Counterargument: for military or critical applications in jammed or wartime scenarios, such systems could function as a de facto GPS replacement.

Use cases and deployment contexts

• Suggested uses: submarines, long-range missiles, autonomous underwater/underground vehicles, pipelines, fiber routes, arctic navigation.
• For trains, many argue odometers plus track maps and station resets already provide excellent inertial navigation; quantum tech is overkill.

Miniaturization and practicality

• Current systems are large; bulk comes from optics and electronics, not cryogens.
• Some are optimistic about shrinking to “orange-sized” units over time; others think they’ll remain backpack-scale and niche.
• Several see this as an incremental but important improvement, while a few suspect hype and easy funding rather than transformative tech.