A quantum sensing milestone is approaching that promises incredibly precise navigation without GPS. Take apart your smartphone, fitness tracker, or VR headset and you’ll find a tiny motion sensor inside that tracks its location and movement. Larger and more expensive versions of the same technology, about the size of a grapefruit and a thousand times more precise, are helping guide ships, planes, and other vehicles using GPS.

Scientists are now working to make the motion sensor sensitive enough to minimise the country’s reliance on global positioning satellites. Until recently, such a sensor, a thousand times more sensitive than modern navigation devices, could have filled a moving truck. But progress is dramatically reducing the size and cost of the technology.

Researchers at Sandia National Laboratories have used silicon photonic microchip components for the first time to perform a quantum technique called atom interferometry, a highly sensitive way to measure acceleration. It’s the latest milestone in developing a type of quantum compass for navigation when GPS signals aren’t available.

The team published their findings and presented their new, highly efficient silicon photonic modulator (a device that controls light on a microchip) as the journal’s cover story. Science Developments.

The research was supported by Sandia’s Laboratory Directed Research and Development program at the National Security Photonics Center, a collaborative research center that develops integrated photonic solutions to complex problems primarily in the national security sector.

Navigation without GPS is a matter of national security

“In real-world scenarios where GPS signals are not available, precision navigation becomes a challenge,” said Sandia scientist Jongmin Lee. In a war zone, these challenges pose a threat to national security, as electronic warfare units can jam or spoof satellite signals to disrupt troop movements and operations.

A quantum sensor offers a solution.

“Using the principles of quantum mechanics, these advanced sensors provide unprecedented accuracy in measuring acceleration and angular velocity, enabling precise navigation even in places where GPS is prohibited,” Lee said.

The modulator is the central part of a laser system on a chip

Typically, an atom interferometer is a sensor system that fills a small room. A complete quantum compass (more accurately called a quantum inertial measurement unit) requires six atomic interferometers.

But Lee and his team found ways to reduce its size, weight, and power requirements. They replaced the already power-hungry large vacuum pump with a vacuum chamber the size of an avocado and combined several components, usually precisely positioned on an optical table, into a single rigid apparatus.

The new modulator is the central part of a laser system on a microchip. The device, which is strong enough to withstand strong vibrations, will replace a traditional refrigerator-sized laser system.

Lasers perform various tasks in an atom interferometer, and the Sandia team uses four modulators to change the frequency of a single laser to perform different functions. But the modulators often create unwanted echoes called sidebands that must be attenuated.

Sandia’s single-band suppressed carrier modulator reduces these sidebands by an unprecedented 47.8 decibels, a measurement commonly used to describe the intensity of sound but which can also be applied to light intensity, resulting in a reduction of approximately 100,000 times.

“We achieved a significant performance improvement over what was available,” said Sandia scientist Ashok Kodigala.

The silicone device is mass produced and more affordable

Besides size, the biggest obstacle to deploying quantum navigation devices has been cost. Each atom interferometer needs a laser system, and laser systems need modulators.

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

Miniaturizing bulky, expensive components in silicon photonic chips helps reduce these costs.

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

Because they can be manufactured using nearly the same process as all computer chips, “this complex four-channel component, which also includes additional specialized features, can be mass-produced at a significantly lower cost compared to today’s commercial alternatives, enabling quantum fabrication,” Lee said. “We will sell the inertial measurement device units at a discounted price.”

As the technology moves closer to field deployment, the team is exploring uses beyond navigation. The researchers are investigating whether it could help find underground cavities and resources by detecting tiny changes they make to Earth’s gravity. They also see potential for optical components they’ve invented, including LIDAR, quantum computing and modulators in optical communications.

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

Multidisciplinary team turns quantum compass concept into reality

Lee and Kodigala represent two halves of a multidisciplinary team. Half, including Lee, are experts in quantum mechanics and atomic physics. The other half, like Kodigala, are experts in silicon photonics—think of a microchip, but with light beams instead of electricity in its circuits.

These teams collaborate in Sandia’s Microsystems Engineering and Science Facility, where researchers design, manufacture and test chips for national security programs.

“We have colleagues who we can come into the room with and talk about this and figure out how we can solve these fundamental challenges to get this technology into the field,” said Peter Schwindt, a quantum sensing scientist at Sandia.

The team’s ambitious plan to turn atomic interferometers into a compact quantum compass bridges the gap between fundamental research at academic institutions and commercial development at technology companies. Atomic interferometers are a proven technology that could be a great tool for non-GPS navigation. Sandia’s ongoing efforts are to make it more stable, usable, and commercially viable.

The National Security Photonics Center works with industry, small business, academia and government to develop new technologies and help bring new products to market. Sandia has hundreds of patents in support of its mission, with dozens more pending.

“I am really excited to see these technologies move into real-world applications,” Schwindt said.

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