Sandia Labs uses SiPh microchip for atom interferometry quantum sensing

14 Aug 2024

Toward the development of a “quantum compass” for navigation when GPS signal unavailable.

Scientists are attempting to make a motion sensor so precise it could minimize reliance on global positioning satellites. For the first time, researchers from Sandia National Labs, Albuquerque, NM, have used silicon photonic microchip components to perform a quantum sensing technique called atom interferometry.

Sandia comments that this is “an ultra-precise way of measuring acceleration”, and the latest milestone toward developing a kind of quantum compass for navigation when 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 — in Science Advances. The research, supported by Sandia’s Laboratory Directed Research and Development program, took place, in part, at the U.S. National Security Photonics Center.

“Accurate navigation becomes a challenge in real-world scenarios when GPS signals are unavailable,” said Sandia scientist Jongmin Lee. For example, in a war zone, such challenges pose national security risks, as electronic warfare units can jam or spoof satellite signals to disrupt troop movements and operations.

“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,” Jongmin added.

Modulator as centerpiece

Typically, an atom interferometer is a sensor system that fills a small room. A complete quantum compass — more precisely called a quantum inertial measurement unit — would require six atom interferometers.

But Jongmin and his team have been finding ways to reduce its size, weight and power needs. They already have replaced a large, power-hungry vacuum pump with an “avocado-sized vacuum chamber” and consolidated several components usually delicately arranged across an optical table into a single, rigid apparatus.

The new modulator is the centerpiece of a laser system on a microchip. Rugged enough to handle heavy vibrations, it would replace a conventional laser system typically the size of a refrigerator. 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 mitigated. Sandia’s suppressed-carrier, single-sideband modulator reduces these sidebands by an unprecedented 47.8 decibels, resulting in a nearly 100,000-fold drop.

“We have significantly improved the performance compared to what’s out there,” said Sandia scientist Ashok Kodigala.

Mass-producible, affordable

Besides size, cost has been a major obstacle to deploying quantum navigation devices. Every atom interferometer needs a laser system, and laser systems need modulators. “Just one full-size single-sideband modulator, a commercially available one, costs more than $10,000,” Jongmin said.

Miniaturizing bulky, expensive components into silicon photonic chips helps drive down these costs. “We can make hundreds of modulators on a single 8-inch wafer and even more on a 12-inch wafer,” Ashok said.

“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,” Jongmin said.

The team is exploring other uses beyond navigation. Researchers are investigating whether it could help locate underground cavities and resources by detecting the tiny changes these make to Earth’s gravitational force. They also see potential for the optical components they invented, including the modulator, in lidar, quantum computing and optical communications.