New breakthrough in quantum navigation! New 3D quantum sensor improves accuracy by 50 times

In a recent preprint paper published on the arXiv [1], a team from the French National Center for Scientific Research describes a quantum accelerometer that uses a laser and ultracold rubidium atoms; it can measure three-dimensional motion with 50 times superior accuracy compared to classical devices. This work extends quantum accelerometers to the third dimension, which can bring precise navigation without GPS.

013D-mode atomic interferometer to measure the wave-like properties of matter

We already rely on accelerometers on a daily basis. Pick up a phone and the display lights up; turn it around and the page you are reading switches direction. A tiny (basically a mass attached to a spring-like mechanism) mechanical accelerometer along with other sensors, such as a gyroscope, make these movements possible. Whenever the phone moves through space, its accelerometer tracks this movement: even for brief periods when the GPS drops out, such as in tunnels or dead spots in the phone's signal.

As useful as they are, mechanical accelerometers tend to drift out of tune. Meaning, leave them in place long enough and they will accumulate into kilometer-level errors. This doesn't matter for phones that are briefly out of touch with GPS, but it becomes a problem when devices travel outside of GPS range for long periods of time. For industrial and military applications, accurate position tracking is useful on submarines, where GPS is not available underwater; or, as backup navigation when a ship loses GPS.

Researchers have long been developing quantum accelerometers to improve the accuracy of position tracking: instead of measuring the mass of a compressed spring, quantum accelerometers measure the wave-like properties of matter. These devices use lasers to slow and cool clouds of atoms; in this state, the atoms behave like light waves, creating interference patterns as they move. More lasers induce and measure how these patterns change in order to track the device's position in space.

In the early days, these devices, called atomic interferometers, were a "mess" of wires and instruments spread across lab benches, measuring only one dimension. But with advances in lasers and specialized technology, they have become smaller and more robust: now they are in 3D mode.

02The first 3D quantum accelerometer: 50 times more accurate

Developed by a French team, the new 3D quantum accelerometer looks like a metal box and is about the length of a laptop. It uses a laser along all three spatial axes to manipulate and measure a cloud of rubidium atoms trapped in a small glass box and cooled to absolute zero. Like earlier quantum accelerometers, these lasers cause ripples in the atomic cloud and measure motion by interpreting the resulting interference patterns. This is the first Quantum Accelerometer Triad (QuAT), which measures acceleration along three mutually orthogonal directions.

(a) Design concept and geometry of the quantum accelerometer triplet (QuAT). The acceleration components are measured along the bands kx, ky and kz perpendicular to the bands. (b) Three-dimensional model of the sensor head mounted on a rotating platform.

To improve stability and bandwidth for use outside the laboratory, the new device combines classical and quantum accelerometer readings in a feedback loop that takes advantage of both techniques.

Because the team can control the atoms with extreme precision, they can make similarly accurate measurements. To test the accelerometer, they attached it to a shaking and rotating table and found that the system was 50 times more accurate than classical navigation-level sensors. Over the course of a few hours, the position of the device measured by the classical accelerometer was off by a kilometer; the quantum accelerometer "nailed" the error to within 20 meters.

A hybrid scheme between quantum and classical accelerometers. The open-loop scheme on the left describes how the filtered classical accelerometer is used to correct the vibration of the quantum accelerometer. At rest, the quantum accelerometer provides a discrete measurement of the projected gproj due to gravity. The closed-loop scheme on the right shows how the classical accelerometer is periodically bias corrected by comparing its output with that of the quantum accelerometer. Here, the output of the hybrid accelerometer is continuous and functions in both static and dynamic situations: providing the sum of the projections of the acceleration aproj due to gravity and motion.

033D sensors are an engineering advance

Despite the significant results, accelerometers are still relatively large and heavy and will not soon step into practical use. But if made smaller and more robust, the team says it could be mounted on ships or submarines for precise navigation; or, it could get into the hands of field geologists searching for mineral deposits by measuring subtle changes in gravity.

More quantum sensors, such as gyroscopes, could join the ranks. Although they will need a few more rounds of shrinkage and reinforcement before they leave the lab.

For now, 3Ding is a step forward.

John Close of the Australian National University had this to say about the results [2], "3D measurement is a big deal and a necessary and excellent engineering step towards any practical use of quantum accelerometers."

Reference links

[1]https://arxiv.org/abs/2209.13209

[2]https://singularityhub.com/2022/10/31/new-3d-quantum-accelerometer-leaves-classical-sensors-in-the-dust/