Milestone in quantum sensing moves closer to extremely precise, GPS-free navigation

Take apart a smartphone, fitness tracker, or virtual reality headset and you’ll find a tiny motion sensor inside that tracks its location and movements. Larger, more expensive versions of the same technology, about the size of a grapefruit and a thousand times more accurate, help navigate ships, planes, and other vehicles with GPS assistance.

Today, scientists are trying to create a motion sensor so accurate that it could reduce the country’s dependence on global positioning satellites. Until recently, such a sensor, a thousand times more sensitive than current navigation devices, would have filled a moving truck. But technological advances 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 implement a quantum sensing technique called atom interferometry, an ultra-precise method of measuring acceleration. It’s the latest step toward developing a kind of quantum compass for navigation when GPS signals aren’t available.

The team published their findings and presented a new high-performance silicon photonic modulator, a device that controls light on a microchip, as the journal’s cover article. Scientific progress.

The research was funded by Sandia’s Laboratory Directed Research and Development program and took place, in part, at the National Security Photonics Center, a collaborative research center that develops integrated photonics solutions for complex national security problems.

Navigation without GPS: a matter of national security

“Precise navigation becomes a challenge in real-world scenarios when GPS signals are not available,” said Sandia scientist Jongmin Lee.

In a war zone, these challenges pose national security risks, as electronic warfare units can jam or spoof satellite signals to disrupt troop movements and operations.

Quantum sensing offers a solution.

“By leveraging the principles of quantum mechanics, these advanced sensors deliver unparalleled accuracy in measuring acceleration and angular velocity, enabling precise navigation even in areas without GPS,” Lee said.

The modulator, the centerpiece of a chip-scale laser system

Typically, an atomic interferometer is a system of sensors that fills a small room. A full quantum compass, more accurately called a quantum inertial measurement unit, would require six atomic interferometers.

But Lee and his team have found ways to reduce the device’s size, weight and power requirements. They’ve already replaced a bulky, power-hungry vacuum pump with a vacuum chamber the size of an avocado and consolidated several components that would normally be delicately arranged on an optical table into a single, rigid device.

The new modulator is the centerpiece of a laser-on-a-chip system. Robust enough to withstand strong vibrations, it would replace a conventional laser system the size of a refrigerator.

Lasers perform multiple tasks in an atomic interferometer, and the Sandia team uses four modulators to shift the frequency of a single laser to perform different functions.

However, modulators often create unwanted echoes called sidebands that need to be attenuated.

Sandia’s suppressed-carrier single-sideband modulator reduces these sidebands by an unprecedented 47.8 decibels (a measure often used to describe sound intensity but also applicable to light intensity), resulting in a reduction of nearly 100,000 times.

“We’ve significantly improved performance over what’s already out there,” said Sandia scientist Ashok Kodigala.

Silicon device that can be mass-produced and more affordable

Besides size, cost is a major obstacle to deploying quantum navigation devices. Each atom interferometer requires a laser system, and laser systems require modulators.

“A single, standard-size, commercially available single-sideband modulator costs over $10,000,” Lee said.

Miniaturization of large and expensive components into silicon photonic chips helps reduce these costs.

“We can fabricate hundreds of modulators on a single 8-inch wafer and even more on a 12-inch wafer,” Kodigala said.

And because they can be manufactured using the same process as virtually all computer chips, “this sophisticated four-channel component, including additional custom features, can be mass-produced at a much lower cost than current 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 other uses beyond navigation. The researchers are investigating whether it could help locate caverns and underground resources by detecting the tiny changes they cause in Earth’s gravitational pull. They also see potential for the optical components they invented, including the modulator, in LIDAR, quantum computing and optical communications.

“I think it’s really exciting,” Kodigala said. “We’re making great strides in miniaturization for many different applications.”

Multidisciplinary team turns quantum compass concept into reality

Lee and Kodigala are two halves of a multidisciplinary team. The first half, which includes Lee, is made up of experts in quantum mechanics and atomic physics. The other half, like Kodigala, is made up of specialists in silicon photonics: imagine a microchip, but instead of electricity running through it, it has beams of light running through it.

These teams collaborate within Sandia’s Microsystems Engineering, Science and Applications Complex, where researchers design, produce and test chips for national security applications.

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

The team’s grand project, which involves transforming atomic interferometers into a compact quantum compass, bridges the gap between basic research at academic institutions and commercial development at technology companies. An atomic interferometer is a proven technology that could be a great tool for GPS-free navigation. Sandia’s ongoing efforts are aimed at making it more stable, more usable and more commercially viable.

The National Security Photonics Center collaborates with industry, small businesses, academia and government agencies to develop new technologies and help launch new products. Sandia has hundreds of issued patents and dozens more in process that support its mission.

“I have a passion for seeing these technologies evolve into real-world applications,” Schwindt said.

Michael Gehl, a Sandia scientist who works on silicon photonics, shares the same passion. “It’s great to see our photonic chips being used for real-world applications,” he said.