Quantum radio may enable receivers with weakest radio signals and mapping in locations where GPS and ordinary cellphones and radios don’t work

Quantum sensing has become a distinct and rapidly growing branch of research within the area of quantum science and technology, with the most common platforms being spin qubits, trapped ions and flux qubits. Quantum sensors are measuring device that takes advantage of quantum correlations, such as states in a quantum superposition or entanglement, for better sensitivity and resolution than can be obtained by classical systems.

 

When measurements are based on quantum phenomena, such as the energy difference between two well-defined quantum states, sensors have the ability to reach unprecedented precision and accuracy that doesn’t drift over time. High sensitivity and stability in combination with a small form factor provide transformational capabilities with applications spanning from GPS-free global navigation and cryogen-free high-precision magnetometry to sensing within mesoscale structure and measurements of individual nuclear or electron spins. Quantum sensors are just becoming commercially available.

 

Researchers at the National Institute of Standards and Technology (NIST) have demonstrated that quantum physics might enable communications and mapping in locations where GPS and ordinary cellphones and radios don’t work reliably or even at all, such as indoors, in urban canyons, underwater and underground.

 

The NIST team is experimenting with low-frequency magnetic radio—very low frequency (VLF) digitally modulated magnetic signals—which can travel farther through building materials, water and soil than conventional electromagnetic communications signals at higher frequencies. The lower a signal’s frequency, the farther it travels, but at the expense of the precision afforded with higher frequencies.

 

The researchers built a direct-current magnetometer that detects the “spin” of certain atoms using polarized light. Because the atoms are highly sensitive and respond quickly, the resulting quantum sensors would be able to enhance very low-frequency radio with the best of both worlds—precise signals at an ideal bandwidth. A paper detailing the work was published in the Review of Scientific Instruments.

 

VLF electromagnetic fields are already used underwater in submarine communications. But there’s not enough data-carrying capacity for audio or video, just one-way texts. Submarines also must tow cumbersome antenna cables, slow down and rise to periscope depth (18 meters, or about 60 feet, below the surface) 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,” NIST project leader Dave Howe said.

 

“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,” he said.