Navigating when GPS is Unavailable

Navigating when GPS is Unavailable

The terms “tough” or “rugged” are rarely used to describe a quantum inertial sensor. The remarkable scientific instrument can measure motion thousand times more precisely than devices used to guide today’s missiles, aircraft, and drones. However, the technology’s delicate, table-sized array of components, which includes a complex laser and vacuum system, has largely kept it grounded and confined to the controlled settings of a lab.

Jongmin Lee wishes to alter this.

The atomic physicist is part of a Sandia team that sees quantum inertial sensors as game-changing onboard navigational aids. If the team is successful in reengineering the sensor into a small, rugged device, the technology could be used to safely guide vehicles in areas where GPS signals are jammed or lost.

The team has successfully built a cold-atom interferometer, a key component of quantum sensors that is much smaller and tougher than typical lab setups, which is a significant step toward realizing their vision. In the academic journal Nature Communications, the team describes their prototype, demonstrating how to integrate several normally separated components into a single monolithic structure. As a result, they were able to reduce the key components of a system that previously existed on a large optical table to a sturdy package roughly the size of a shoebox.

“Very high sensitivity has been demonstrated in the lab, but in practice, people need to shrink down the size, weight, and power, and then overcome various issues in a dynamic environment,” Jongmin explained.

The paper also includes a roadmap for further miniaturizing the system using emerging technologies. The prototype, which was funded by Sandia’s Laboratory Directed Research and Development program, shows significant progress toward getting advanced navigation technology out of the lab and into vehicles on the ground, underground, in the air, and even in space.

A monolithic structure having as few bolted interfaces as possible was key to creating a more rugged atom interferometer structure. The overall small, compact design naturally leads towards a stiffer more robust structure.

Ultrasensitive measurements drive navigational power

As a jet does a barrel roll through the sky, current onboard navigation tech can measure the aircraft’s tilts and 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, Jongmin said.

Quantum sensing would operate in the same way, but the much better accuracy would mean onboard navigation wouldn’t need to cross-check its calculations as often, reducing reliance on satellite systems.

Roger Ding, a postdoctoral researcher who worked on the project, said, “In principle, there are no manufacturing variations and calibrations,” compared to conventional sensors that can change over time and need to be recalibrated.

Aaron Ison, the lead engineer on the project, said to prepare the atom interferometer for a dynamic environment, he and his team used materials proven in extreme environments. Additionally, parts that are normally separate and freestanding were integrated together and fixed in place or were built with manual lockout mechanisms.

Navigating when GPS goes dark

“A monolithic structure having as few bolted interfaces as possible was key to creating a more rugged atom interferometer structure,” Aaron said. Furthermore, the team used industry-standard calculations called finite element analysis to predict that any deformation of the system in conventional environments would fall within required allowances. Sandia has not conducted mechanical stress tests or field tests on the new design, so further research is needed to measure the device’s strength.

“The overall small, compact design naturally leads towards a stiffer more robust structure,” Aaron said.

Photonics light the way to a more miniaturized system

Most modern atom interferometry experiments use a system of lasers mounted to a large optical table for stability reasons, Roger said. Sandia’s device is comparatively compact, but the team has already come up with further design improvements to make the quantum sensors much 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 and an expert in quantum sensing.

Photonic devices, such as a laser or optical fiber, use light to perform useful work and integrated devices include many different elements. Photonics are used widely in telecommunications, and ongoing research is making them smaller and more versatile. With further improvements, Peter thinks the space an interferometer needs could be as little as a few liters. His dream is to make one the size of a soda can.

In their paper, the Sandia team outlines a future design in which most of their laser setup is replaced by a single photonic integrated circuit, about eight millimeters on each side. Integrating the optical components into a circuit would not only make an atom interferometer smaller, it would also make it more rugged by fixing the components in place.

While the team can’t do this yet, many of the photonic technologies they need are currently in development at Sandia.

“This is a viable path to highly miniaturized systems,” Roger said. Meanwhile, Jongmin said integrated photonic circuits would likely lower costs and improve scalability for future manufacturing. “Sandia has shown an ambitious vision for the future of quantum sensing in navigation,” Jongmin said.