Back in July 2019 we posted about a new development in radio technology known as "Atomic Radio" or "Quantum Radio". In that post we discussed an article that explained the concept and science behind the idea and noted how some researchers described the possibility of a very wideband capable receiver.
Recently the US Army has described how they built a quantum radio that can receive from DC to 20 GHz. If you're interested in the science, the paper is published in the Journal of Physics B: Atomic, Molecular and Optical Physics and it is available on sci-hub. The radio uses something called a Rydberg sensor which they describe below.
The Rydberg sensor uses laser beams to create highly-excited Rydberg atoms directly above a microwave circuit, to boost and hone in on the portion of the spectrum being measured. The Rydberg atoms are sensitive to the circuit's voltage, enabling the device to be used as a sensitive probe for the wide range of signals in the RF spectrum.
Army researcher Kevin Cox notes how this is the first implementation that can operate over such a wide frequency range:
"All previous demonstrations of Rydberg atomic sensors have only been able to sense small and specific regions of the RF spectrum, but our sensor now operates continuously over a wide frequency range for the first time," said Dr. Kevin Cox, a researcher at the U.S. Army Combat Capabilities Development Command, now known as DEVCOM, Army Research Laboratory. "This is a really important step toward proving that quantum sensors can provide a new, and dominant, set of capabilities for our Soldiers, who are operating in an increasingly complex electro-magnetic battlespace."
Quantum radios may be one of the next big leaps in radio technology. However as they require lasers and the space of a small laboratory the technology will probably be restricted to the military and institutions for the time being.