The new 3D quantum accelerometer leaves classic sensors in the dust

At the smallest scale, our universe gets weird. Particles act like billiard balls or waves in water, depending on how you detect them. Properties cannot be measured simultaneously or tend to be smeared with uncertainty over a range of values. Human intuition fails us.

For much of the last century, all this weirdness was primarily the domain of physicists. More recently, however, the theoretical and the experimental have moved towards the practical. This trend is most visible in the growing menagerie of early quantum computers, but the strange quantum behavior is useful for more than just computation. Some scientists and engineers are building quantum communications networks that cannot be hacked. others have their eyes on the sensors.

In a recent preprint published on arXiv, a team at France’s National Center for Scientific Research describes a quantum accelerometer that uses lasers and ultracold rubidium atoms to measure motion in all three dimensions with extreme precision.

The work extends quantum accelerometers into the third dimension and could provide precise navigation without GPS and reliable detection of valuable mineral deposits underfoot.

Atomic Waves

We already rely on accelerometers every day. Pick up a phone and the screen lights up. Turn it sideways and the page you’re reading changes orientation. A tiny mechanical accelerometer—basically a mass attached to a spring-like mechanism—makes these actions possible (along with other sensors, like gyroscopes). Whenever a phone moves through space, its accelerometer tracks that movement. This includes short periods of time when the GPS goes down, such as in tunnels or cell signal dead spots.

As useful as they are, mechanical accelerometers tend to get out of hand. If left long enough, they will accumulate kilometer-scale errors. This is not critical for phones that are briefly out of GPS contact, but is an issue when devices travel out of range for long periods. For both industrial and military applications, precise positioning would be useful in submarines—which do not have access to GPS underwater—or as back-up navigation on ships in case they lose GPS.

Researchers have long been developing quantum accelerometers to improve positioning accuracy. Instead of measuring a mass compressing a spring, quantum accelerometers measure the wavelike properties of matter. The devices use lasers to slow down and cool clouds of atoms. In this state, atoms behave like light waves, creating interference patterns as they move. More lasers trigger and measure how these patterns change to track the device’s position in space.

At first these devices, called atom interferometers, were a mess of wires and instruments spread across lab benches that could only measure one dimension. But as lasers and know-how have advanced, they’ve gotten smaller and tougher—and now they’re 3D.

A quantum upgrade

The new 3D quantum accelerometer, developed by the team in France, looks like a metal box about the length of a laptop. It uses lasers along all three spatial axes to manipulate and measure a cloud of rubidium atoms trapped in a small glass box and frozen to near absolute zero. Like earlier quantum accelerometers, these lasers cause ripples in the cloud of atoms and interpret the resulting interference patterns to measure motion.

To improve stability and bandwidth—requirements for use outside the lab—the new device combines measurements from classical and quantum accelerometers in a feedback loop that leverages the strengths of both technologies.

Because the team can screen people with extreme precision, they can make similarly precise measurements. To test the accelerometer, they attached it to a table adapted to shake and rotate, and found the system to be 50 times more accurate than classic navigation sensors. Within hours, the device’s position as measured by a classic accelerometer was off by a kilometer. the quantum accelerometer nailed it at 20 meters.

Shrink Ray

The accelerometer, which is still relatively large and heavy, won’t be ready for your iPhone anytime soon. However, made a bit smaller and more robust, the team says it could be installed on ships or submarines for precise navigation. Or it may find its way into the hands of field geologists hunting for mineral deposits by measuring subtle changes in gravity.

Other groups are also working on miniaturizing and enhancing quantum sensors for the field. A team at Sandia National Laboratory recently built a cold atom interferometer—like the one used here—in a durable package the size of a shoebox. In a paper describing the project, Sandia researchers say further miniaturization will likely be driven by advances in photonic chips. In the future, they say, the necessary optical components for a cold-atom interferometer like theirs may fit on a chip just eight millimeters on a side.

More quantum sensors, such as gyroscopes, may join the party. Although they’ll also need a few rounds of shrinking and hardening before they escape the lab.

For now, the move to 3D is a step forward.

“Measuring in three dimensions is a big deal, a necessary and extraordinary engineering step toward any practical use of quantum accelerometers,” John Close of the Australian National University said recently. Young Scientist.

Image credit: Interference patterns appear in a cloud of cold rubidium atoms trapped in a quantum gyroscope / National Institute of Standards and Technology (NIST)

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