Navigate when GPS turns off

Quantum inertial sensors could serve as revolutionary on-board navigational aids if they can be redesigned into compact and rugged devices. When GPS signals are blocked or lost, they can guide vehicles safely.

High-tech quantum sensors could guide vehicles without satellites, if they can handle the journey.

When talking about quantum inertial sensors, words like “tough” or “robust” are unlikely to be spoken. These remarkable scientific instruments can measure motion a thousand times more accurately than the devices that help navigate today’s missiles, drones and planes. However, its delicate array of table-top-sized components that includes a complex laser and vacuum system has essentially kept the technology grounded and confined to the controlled parameters of a laboratory.

Jongmin Lee wants to change that.

The atomic physicist is part of a Sandia team that envisions quantum inertial sensors as revolutionary on-board navigational aids. The team is working to redesign the sensor into a compact and rugged device, where the technology could safely guide vehicles when GPS signals are blocked or lost.

In an important step towards realizing their vision, the team successfully built a cold-atom interferometer. It is a core component of quantum sensors, and their version is designed to be much smaller and stronger than typical lab setups. The team describes their prototype in an article recently published in the academic journal Nature Communication, showing how to integrate several normally separate components into a single monolithic structure. In doing so, they reduced key components from a system that existed on a large optical table to a rugged enclosure the size of a shoebox.

Jongmin Lee cold atom interferometer

PRETTY HARD? — Sandia atomic physicist Jongmin Lee examines the sensor head of a cold atom interferometer that could help vehicles stay on course where GPS is unavailable. Credit: Photo by Bret Latter

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

The document also outlines a roadmap to further miniaturize the system using technologies under development.

The prototype, funded by Sandia’s lab-led research and development program, demonstrates significant progress toward moving advanced navigation technologies out of the lab and into vehicles on the ground, underground, in the air and even in the air. ‘space.

The Global Positioning System (GPS) is a constellation of orbiting satellites that provides position, navigation, and timing data to military and civilian users around the world. GPS satellites orbit the Earth every 12 hours, continuously transmitting navigation signals. With the proper equipment, users can receive at least four satellite signals to calculate time, location, and speed. The signals are so precise that time can be calculated to less than a millionth of a second, speed to less than a fraction of a mile per hour, and location to less than 100 feet.

Ultra-sensitive measurements boost navigation power

As a jet barrels through the sky, current in-vehicle navigation technology can measure the plane’s tilts, turns and accelerations to calculate its position without GPS, for a period of time. Small measurement errors gradually push a vehicle off course unless it periodically synchronizes with satellites, Jongmin said.

Quantum sensing would work the same way, but so much the better precision would mean that onboard navigation would not 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 which can change over time and need to be recalibrated.

Aaron Ison, the project’s lead engineer, said that to prepare the atomic interferometer for a dynamic environment, he and his team used materials proven in extreme environments. Additionally, parts that are normally separate and free-standing have been integrated together and fixed in place or have been constructed with manual locking mechanisms.

“A monolithic structure with as few bolted interfaces as possible was key to creating a more robust atomic interferometer structure,” Aaron said.

Additionally, 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 tolerances. Sandia did not perform mechanical stress tests or field tests on the new design, so further research is needed to gauge the strength of the device.

“The overall small and compact design naturally leads to a stiffer and sturdier structure,” Aaron said.

Photonics opens the way to a more miniaturized system

Most modern atom interferometry experiments use a system of lasers mounted on a large optical table for stability, Roger said. Sandia’s device is relatively compact, but the team has already proposed other design improvements to make the quantum sensors much smaller using integrated photonics technologies.

“There are tens to hundreds of elements that can fit on a chip smaller than a penny,” said Peter Schwindt, the project’s principal investigator and an expert in quantum sensing.

Photonic devices, such as a laser or fiber optic, use light to do useful work, and integrated devices include many different elements. Photonics is widely used in telecommunications, and ongoing research is making it 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 describes a future design in which most of their laser setup is replaced by a single photonic IC, about eight millimeters on each side. Integrating the optical components into a circuit would not only make an atom interferometer smaller, but also make it more robust by fixing the components in place.

Although the team can’t do it yet, many of the photonic technologies they need are currently under development at Sandia.

“It’s a viable route to highly miniaturized systems,” Roger said.

Meanwhile, Jongmin said integrated photonic circuits would likely reduce costs and improve scalability for future manufacturing.

“Sandia has shown an ambitious vision for the future of quantum sensing in navigation,” Jongmin said.

Reference: “A Compact Cold Atom Interferometer with a High Data Rate Array Magneto-Optical Trap and Laser System Compatible with Photonic Integrated Circuits” by Jongmin Lee, Roger Ding, Justin Christensen, Randy R. Rosenthal, Aaron Ison , Daniel P. Gillund, David Bossert, Kyle H. Fuerschbach, William Kindel, Patrick S. Finnegan, Joel R. Wendt, Michael Gehl, Ashok Kodigala, Hayden McGuinness, Charles A. Walker, Shanalyn A. Kemme, Anthony Lentine, Grant Biedermann and Peter DD Schwindt, September 1, 2022, Nature Communication.
DOI: 10.1038/s41467-022-31410-4

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