Quantum Sensors Could Be Used Where GPS Doesn't Work

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Thanks to GPS we can work out our position anywhere on the surface of the Earth, but this technology doesn’t work well in certain environments. Inside buildings, underground, underwater, and outside among skyscrapers, the signal can get lost, so researchers are looking at alternatives.

One emerging technology uses very low frequency (VLF) magnetic signals and quantum sensors, atoms of rubidium that are capable of detecting these specific magnetic fields. As reported in Review of Scientific Instruments, VLF magnetic fields could be used as GPS alternatives in submarines, mines, and more.

"The big issues with very low-frequency communications, including magnetic radio, is poor receiver sensitivity and extremely limited bandwidth of existing transmitters and receivers," NIST project leader Dave Howe said in a statement. "This means the data rate is zilch." 

"Atoms offer very fast response plus very high sensitivity. Classical communications involve a tradeoff between bandwidth and sensitivity. We can now get both with quantum sensors.

"The increased sensitivity leads in principle to longer communications range. The quantum approach also offers the possibility to get high bandwidth communications like a cell phone has."

The sensors work like a magnetometer. As the magnetic fields reach the rubidium, the spin rate of the atoms changes and this creates a current that can be measured. The sensor is capable of detecting magnetic signals a million times smaller than Earth’s magnetic field.

The advantages of this approach vary. The quantum sensors work at room temperature, they are small, they consume very little power, and they should be relatively cheap to make. They also don’t require calibration as the system uses a naturally occurring property of the atoms. These facts make them a really strong contender to go beyond the limitations of GPS.

But despite the advantages, there are still challenges ahead. There are many magnetic fields around, so the signal can sometimes become lost in the noise. Currently, the system has an indoor range of tens of meters, which is better than what’s currently possible, but not really a universal and versatile technology just yet. It also struggles with accurate positioning. The uncertainty is about 16 meters (52 feet), which is still significantly off the 3-meter (10-foot) target that the researchers hope to achieve.

The scientists are working on ways to increase the signal-to-noise ratio by improving how the magnetic field is produced, among other things.

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