Scientists are now working to create a motion sensor so precise that it could reduce the nation's dependency on GPS. Such a sensor-thousands of times more sensitive than current navigation-grade devices-used to require equipment that would fill a moving truck. Recent advancements, however, are dramatically reducing the size and cost of this technology.

For the first time, researchers at Sandia National Laboratories have used silicon photonic microchip components to perform atom interferometry, a quantum sensing technique that provides extremely precise measurements of acceleration. This is a significant step toward developing a quantum compass for navigation in areas where GPS signals are unavailable.

The team published its findings and introduced a new high-performance silicon photonic modulator, a device that controls light on a microchip, as the cover story in 'Science Advances'.

The research was supported by Sandia's Laboratory Directed Research and Development program and conducted at the National Security Photonics Center, a collaborative research center focused on integrated photonics solutions for national security challenges.

Ensuring Navigation Accuracy in GPS-Denied Environments
"Accurate navigation becomes a challenge in real-world scenarios when GPS signals are unavailable," explained Sandia scientist Jongmin Lee.

In conflict zones, the loss of GPS signals poses significant risks to national security, as enemy forces can jam or spoof satellite signals, disrupting troop movements and operations.

Quantum sensing provides a potential solution.

"By harnessing the principles of quantum mechanics, these advanced sensors provide unparalleled accuracy in measuring acceleration and angular velocity, enabling precise navigation even in GPS-denied areas," Lee said.

Compact, Chip-Scale Laser System for Quantum Sensing
Traditionally, an atom interferometer-a type of sensor-fills a small room, and a fully functioning quantum compass, or quantum inertial measurement unit, would require six of these interferometers.

Lee and his team have been developing methods to reduce the size, weight, and power requirements of these systems. They have already replaced a large vacuum pump with a vacuum chamber the size of an avocado and combined multiple components that were typically spread out across an optical table into a single, rigid unit.

The newly developed modulator is the core of a laser system on a microchip, rugged enough to withstand heavy vibrations. It could replace a conventional laser system that is typically the size of a refrigerator.

Lasers have several roles in an atom interferometer, and the Sandia team uses four modulators to shift the frequency of a single laser for different functions.

However, these modulators often create unwanted echoes, known as sidebands, which need to be minimized.

Sandia's new suppressed-carrier, single-sideband modulator reduces these sidebands by an unprecedented 47.8 decibels-a unit of measure commonly used for sound intensity but also applicable to light intensity-resulting in a nearly 100,000-fold reduction.

"We have drastically improved the performance compared to what's out there," said Sandia scientist Ashok Kodigala.

Making Quantum Navigation Affordable
In addition to size, cost has been a major barrier to the widespread deployment of quantum navigation devices. Every atom interferometer needs a laser system, and laser systems require modulators.

"Just one full-size single-sideband modulator, a commercially available one, is more than $10,000," Lee said.

By miniaturizing these components into silicon photonic chips, the costs can be significantly reduced.

"We can make hundreds of modulators on a single 8-inch wafer and even more on a 12-inch wafer," Kodigala noted.

Because these modulators can be manufactured using the same processes as nearly all computer chips, "this sophisticated four-channel component, including additional custom features, can be mass-produced at a much lower cost compared to today's commercial alternatives, enabling the production of quantum inertial measurement units at a reduced cost," Lee said.

As the technology moves closer to field deployment, the team is exploring additional applications beyond navigation. Researchers are investigating whether the technology could help detect underground cavities and resources by sensing tiny changes in Earth's gravitational force. The optical components, including the modulator, could also be used in LIDAR, quantum computing, and optical communications.

"I think it's really exciting," Kodigala said. "We're making a lot of progress in miniaturization for a lot of different applications."

Collaborative Efforts Bringing Quantum Compass to Reality
Lee and Kodigala are part of a multidisciplinary team at Sandia. Lee's team focuses on quantum mechanics and atomic physics, while Kodigala's group specializes in silicon photonics, where light, instead of electricity, flows through microchips.

These teams work together at Sandia's Microsystems Engineering, Science and Applications complex, where they design, produce, and test chips for national security applications.

"We have colleagues that we can go down the hall and talk to about this and figure out how to solve these key problems for this technology to get it out into the field," said Peter Schwindt, a quantum sensing scientist at Sandia.

The team's ultimate goal is to transform atom interferometers into a compact quantum compass, bridging the gap between academic research and commercial development. While atom interferometry is a proven technology for GPS-denied navigation, Sandia's efforts aim to make it more stable, practical, and commercially viable.

The National Security Photonics Center collaborates with industry, small businesses, academia, and government agencies to develop new technologies and support product launches. Sandia holds hundreds of issued patents, with many more pending, that contribute to its mission.

"I have a passion around seeing these technologies move into real applications," Schwindt said.

Michael Gehl, another Sandia scientist working with silicon photonics, shares this enthusiasm. "It's great to see our photonics chips being used for real-world applications," he said.

Research Report:High-performance silicon photonic single-sideband modulators for cold-atom interferometry

Related Links
Sandia National Laboratories
Understanding Time and Space