Scientists at Sandia National Laboratories, Albuquerque, N. M., are attempting to make a motion sensor so precise it could minimize the nation\u2019s reliance on global positioning satellites. Until recently, such a sensor \u2014 a thousand times more sensitive than today\u2019s navigation-grade devices \u2014 would have filled a moving truck. But advancements are dramatically shrinking the size and cost of this technology.<\/p>\n
For the first time, researchers have used silicon photonic microchip components to perform a quantum sensing technique called atom interferometry, an ultra-precise way of measuring acceleration. It is the latest milestone toward developing a kind of quantum compass for navigation when GPS signals are unavailable.<\/p>\n
\u201cBy 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,\u201d said Sandia scientist Jongmin Lee.<\/p>\n
Typically, an atom interferometer is a sensor system that fills a small room. A complete quantum compass \u2014 more precisely called a quantum inertial measurement unit \u2014 would require six atom interferometers. But Lee 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.<\/p>\n
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. Lasers perform several jobs in an atom interferometer, and the Sandia team uses four modulators to shift the frequency of a single laser to perform different functions.<\/p>\n
However, modulators often create unwanted echoes called sidebands that need to be mitigated. Sandia\u2019s suppressed-carrier, single-sideband modulator reduces these sidebands by an unprecedented 47.8 decibels, resulting in a nearly 100,000-fold drop.<\/p>\n
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. \u201cJust one full-size single-sideband modulator, a commercially available one, is more than $10,000,\u201d Lee said.<\/p>\n
So, miniaturizing bulky, expensive components into silicon photonic chips helps drive down these costs. Hundreds of modulators could be made on a single 8-inch wafer and even more on a 12-inch wafer.<\/p>\n
And since they can be manufactured using the same process as virtually all computer chips, \u201cThis sophisticated four-channel component, including additional custom features, can be mass-produced at a much lower cost compared to today\u2019s commercial alternatives, enabling the production of quantum inertial measurement units at a reduced cost,\u201d said Lee.<\/p>\n
As the technology gets closer to field deployment, 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\u2019s gravitational force. They also see potential for the optical components they invented, including the modulator, in LIDAR, quantum computing, and optical communications.<\/p>\n