Miniature cold-atom inertial sensors help navigation without GPS

A quantum inertial sensor is designed to measure motion more accurately than devices that help navigate missiles, aircraft and drones. However, its delicate array of components that includes a laser and vacuum system has kept the technology grounded and confined to the controlled settings of a lab.

Atomic physicist Jongmin Lee, part of a team at Sandia National Laboratories, aims to reengineer the sensor into a compact, rugged device that can safely guide vehicles where GPS signals are jammed or lost.

The research team has built a cold-atom interferometer, a core component of quantum sensors, designed to be smaller and tougher than typical lab set-ups. The prototype was described in Nature Communications, with researchers showing how to integrate several normally separated components into a single monolithic structure. In doing so, the researchers reduced the key components of a system that existed on a large optical table down to a sturdy package roughly the size of a shoebox. The paper also describes a roadmap for further miniaturising the system using technologies under development.

“Very high sensitivity has been demonstrated in the lab, but the practical matters are, for real-world application, that people need to shrink down the size, weight and power, and then overcome various issues in a dynamic environment,” Lee said.

The prototype demonstrates the strides taken towards moving advanced navigation technology out of the lab and into vehicles on the ground, underground, in the air and even in space. As a jet does a barrel roll through the sky, current onboard navigation technology can measure the aircraft’s tilts, turns and accelerations to calculate its position without GPS, for a time. Small measurement errors gradually push a vehicle off course unless it periodically syncs with the satellites. Quantum sensing would operate in the same way, but the improved accuracy would mean onboard navigation wouldn’t need to cross-check its calculations as often, reducing its reliance on satellite systems.

Roger Ding, a postdoctoral researcher on the project, said that in principle, there are no manufacturing variations and calibrations, compared to conventional sensors that can change over time and require recalibration. Aaron Ison, the lead engineer on the project, said to prepare the atom interferometer for a dynamic environment, the team used materials suitable for extreme environments. Parts that are normally separate and freestanding were integrated together and fixed in place, or built with manual lockout mechanisms. “A monolithic structure having as few bolted interfaces as possible was key to creating a more rugged atom interferometer structure,” Ison said.

The team used calculations called finite element analysis to predict that any deformation of the system in conventional environments would fall within required allowances. “The overall small, compact design naturally leads towards a stiffer more robust structure,” Ison said.

Most modern atom interferometry experiments use a system of lasers mounted to a large optical table for stability reasons. While Sandia’s device is comparatively compact, the team has also devised further design improvements to make the sensors smaller using integrated photonic technologies. “There are tens to hundreds of elements that can be placed on a chip smaller than a penny,” said Peter Schwindt, the principal investigator on the project.

In their paper, the researchers outlined a future design in which most of their laser set-up is replaced by a single photonic integrated circuit, about eight millimetres on each side. Integrating the optical components into a circuit would make the atom interferometer smaller and more rugged, by fixing the components in place. While the researchers can’t do this yet, the necessary technologies are in development at Sandia. Lee said that integrated photonic circuits would lower costs and improve scalability for future manufacturing. “Sandia has shown an ambitious vision for the future of quantum sensing in navigation,” Lee said.

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