Milestone in quantum sensing brings high-precision navigation without GPS closer

If you take apart a smartphone, fitness tracker or virtual reality headset, you’ll find a tiny motion sensor inside that tracks position and movement. 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 GPS-enabled vehicles.

Scientists are trying to develop a motion sensor so precise that it could minimize the country’s dependence on global positioning satellites. Until recently, such a sensor – a thousand times more sensitive than today’s navigation devices – would have filled a moving truck. But advances are dramatically reducing the size and cost of this technology.

Researchers at Sandia National Laboratories have for the first time used silicon photonics microchip components to perform a quantum sensing technique called atom interferometry, an ultra-precise method of measuring acceleration. It’s the latest milestone toward developing a type of quantum compass for navigation when GPS signals aren’t available.

The team published their results and introduced a new high-performance silicon photon modulator – a device that controls light on a microchip – as a cover story in the journal Scientific advances.

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

GPS-free navigation a matter of national security

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

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

Quantum sensing offers a solution.

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

Modulator as the heart of a chip-scale laser system

An atom interferometer is usually a sensor system that fills a small space. A complete quantum compass – or more precisely a quantum inertial measurement unit – would require six atom interferometers.

But Lee and his team have found ways to reduce size, weight and energy requirements. They have already replaced a large, energy-hungry vacuum pump with an avocado-sized vacuum chamber and combined several components that would normally be carefully arranged on an optical table into a single, rigid device.

The new modulator is the heart of a laser system on a microchip. It is robust enough to withstand strong vibrations and could replace a conventional laser system the size of a refrigerator.

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

However, modulators often produce unwanted echoes, so-called sidebands, which must be attenuated.

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

“We have dramatically improved performance compared to what exists before,” said Sandia scientist Ashok Kodigala.

Silicon components can be produced in large quantities and are cheaper

In addition to size, cost has been a major obstacle to the deployment of quantum navigation devices. Each atom interferometer requires a laser system, and laser systems require modulators.

“A full-size commercially available single-sideband modulator alone costs more than $10,000,” Lee said.

The miniaturization of bulky, expensive components in silicon photonics chips helps reduce these costs.

“We can produce 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 compared to today’s commercial alternatives, enabling the manufacture of quantum inertial measurement units at a lower cost,” Lee said.

As the technology gets closer to being used in the field, the team is also exploring other uses beyond navigation. The researchers are studying whether it could help locate underground cavities and resources by detecting the tiny changes they make to Earth’s gravity. They also see potential for the optical components they invented, including the modulator, in the areas of LIDAR, quantum computing and optical communications.

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

Interdisciplinary team makes quantum compass concept a reality

Lee and Kodigala represent the two halves of a multidisciplinary team. One half, which includes Lee, consists of experts in quantum mechanics and atomic physics. The other half, like Kodigala, are specialists in silicon photonics – imagine a microchip in whose circuits, however, light rays flow instead of electricity.

These teams work together at Sandia’s Microsystems Engineering, Science and Applications Complex, where researchers design, manufacture and test chips for national security applications.

“We have colleagues we can talk to in the hallway and figure out how we can solve these key problems to put this technology into practice,” said Peter Schwindt, a quantum sensor researcher at Sandia.

The team’s grand plan – to transform atom interferometers into a compact quantum compass – bridges the gap between basic research at academic institutions and commercial development at technology companies. An atom interferometer is a proven technology that could be an excellent tool for GPS-free navigation. Sandia’s ongoing efforts aim to make it more robust, deployable and commercially viable.

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

“I am excited about translating these technologies into real-world applications,” said Schwindt.

Michael Gehl, a Sandia scientist who studies silicon photonics, shares this passion. “It’s great to see our photonics chips being used in practice,” he said.