Dramatically more sensitive motion sensors could help ships keep track of their positions at sea, even in rough weather or when a military opponent jams GPS signals. However, these advanced sensors are typically lab-scale in size. Now researchers have developed a new laser system to help make these sensors fit in a shoebox, as well as potentially mass-producible.
Motion sensors in wearable devices are usually sensitive to accelerations in the range of thousandths of a g. Bigger, more expensive accelerometers, which help ships, airplanes, and other vehicles navigate without GPS existence, are about the size of a grapefruit and “have sensitivities on the order of a hundred micro-gs,” says Ashok Kodigala, a research scientist at Sandia National Laboratories in Albuquerque, N.M.
More accurate than either of these mobile accelerometers are cold-atom interferometers. These currently have sensitivities of billionths of a g, with future potential for trillionths of a g, Kodigala says.
Atom interferometers are examples of quantum sensors, which rely on the strange phenomena that emerge at the universe’s tiniest scales. These quantum effects are extraordinarily fragile to outside interference, and quantum sensors capitalize on this vulnerability in order to respond to the slightest disturbances in the environment. Quantum sensors are reaching unprecedented levels of sensitivity and accuracy for use in potential applications such as detecting the magnetic fields of thoughts.
How Atom Interferometers Work
Atom interferometers rely on a quantum effect known as superposition, in which one atom can essentially exist in two or more places at the same time. The sensors have these Schrödinger’s cat–like states of the atoms travel along different paths and then it recombines them. Due to wave-particle duality—the quantum phenomenon where particles can act like waves, and vice versa—these atoms interfere with each other, with their waves’ peaks and troughs augmenting or suppressing one other. Analyzing the nature of this interference can reveal the extent of the slightly different motions experienced on their separate paths.
Atom interferometers could lead to GPS-free navigation. The satellite links that help enable global navigation satellite systems do not work underground or underwater, and where they do work, they’re vulnerable to jamming, spoofing, and even the weather. A quantum motion sensor can help serve as the foundation of an inertial navigation system that does not rely on any outside signals.
“Aside from navigation, the precision and stability of a quantum inertial sensor would also make it suitable for mapping Earth’s gravity from space, to study the movements of water, ice sheets, and sea levels for climate analysis,” Kodigala says.
However, atom interferometers are typically large enough to fill a small room. “Even mobile units are the size of a mini-refrigerator,” Kodigala says.
The laser systems in atom interferometers that, among other things, drive atoms into states of superposition are the most complex components within the instruments. They are each typically about the size of a refrigerator.
Shrinking Atom Interferometers
Now Kodigala and his colleagues have developed a silicon photonic modulator—a device to control the light in an atom interferometer—that can fit on a microchip. “Ultimately, this will miniaturize a quantum inertial sensor to the size of a shoebox or smaller, making it much more fieldable for a variety of applications,” Kodigala says.
Previously, Kodigala and his colleagues explored ways to reduce the size, weight, and power needs of atom interferometers. For instance, they 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.
In a new study, the researchers used four of their new modulators in a laser system on a chip “that is about the size of a penny,” Kodigala says. The devices shifted the frequency of a single laser to help it perform the roles that multiple lasers play in an atom interferometer.
Photonic modulators often create unwanted echoes called sidebands that can disrupt sensor performance. The new modulator reduces these sidebands by an unprecedented 47.8 decibels—a measure often used to describe sound intensity, but also applicable to light intensity. This resulted in a nearly 100,000-fold drop in the modulator’s sideband intensity.
Miniaturizing an atom interferometer’s laser system may also help reduce costs. Hundreds of modulators can be fabricated on a single 8-inch wafer using the same process as virtually all computer chips, at a much lower cost than their bulky, expensive counterparts in conventional atom interferometers, the researchers say.
“There’s still more work to be done on integrating other photonic components to chip-scale, but this is a great start and first of its kind,” Kodigala says of the team’s latest research.
The researchers did integrate their new modulators into an atom interferometer. Although they did not measure its sensitivity directly, “the final performance of this accelerometer doesn’t yet compete with the best laboratory quantum inertial sensor out there,” Kodigala says. “We’re continuing to make progress on this front.”
The scientists detailed their findings on 10 July in the journal Science Advances.
From Your Site Articles
Related Articles Around the Web