Quantum Radio could be used to map out GPS-resistant underground and underwater areas

Digital maps and GPS tracking systems have made it far more difficult for people to truly get lost. Soon, even remote areas where GPS or radio signals don't work at all, such as underground or underwater, could also be mapped out using quantum physics. Scientists are developing a "Quantum radio" of sorts, which may help track areas that are currently unreachable for GPS systems.

Scientists at the National Institute of Standards and Technology (NIST), experimenting with very low frequency (VLF) magnetic signals found that these signals can travel farther than traditional electromagnetic communications signals, even penetrating through soil, building materials and water.

Although VLF electromagnetic fields are already used in submarine communications, it allows for limited data transfer – just one-way texts. It is also a cumbersome procedure as submarines must first rise to periscope depth, reduce travelling speed and also carry antenna cables to communicate.

"The big issues with very low-frequency communications, including magnetic radio, is poor receiver sensitivity and extremely limited bandwidth of existing transmitters and receivers. This means the data rate is zilch," Dave Howe, the lead researcher of the new study, which has been published in the Review of Scientific Instruments, said in a statement.

"The best magnetic field sensitivity is obtained using 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 cellphone has. We need bandwidth to communicate with audio underwater and in other forbidding environments," Howe added.

Using atomic magnetometers that rely on the quantum properties of rubidium atoms, the researchers demonstrated how digitally attuned magnetic signals – messages that are basically digital 0s and 1s – or coded messages can be received.

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

According to Howe, the quantum method could also be used to detect weaker signals or even increase the signal range. Researchers used "optimally pumped" magnetometers, which involved using polarised light to detect the spinning movements of rubidium atoms. These sensors were successful in detecting digitally modulated signals as weak as 1 picotesla – which is one-millionth of the Earth's magnetic field strength.

What is more, these incredibly faint signals were detected at extremely low frequencies, below 1 kilohertz. To put this in perspective – government and military VLF radios used to communicate under the radar span around 3 to 30 kilohertz.

The research could have military applications, allowing soldiers to communicate in situations and areas where radio frequencies and GPS technology cannot be relied on.

According to Howe, the new method would involve combining quantum physics and low-frequency magnetic radio. Researchers are now developing and testing an atomic clock-like quantum magnetometer that could boost the range of low-frequency magnetic field signals. They also plan to further determine how to use quantum physics to expand the existing bandwidth limits.