US Army researchers have built a so-called “quantum sensor,” which can analyze the full RF spectrum and real-world signals, a report on Physics.org says. The quantum sensor — technically a Rydberg sensor — can sample the RF spectrum from 0 to 20 GHz and is able to detect AM and FM radio signals, as well as Bluetooth, Wi-Fi, and other RF communication protocols. The peer-reviewed Physical Review Applied published the researchers’ findings, “Waveguide-coupled Rydberg spectrum analyzer from 0 to 20 Gigaherz,” coauthored by Army researchers David Meyer, Paul Kunz, and Kevin Cox.

“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 article explains. “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.”

Cox, a researcher at the US Army Combat Capabilities Development Command (DEVCOM) Army Research Laboratory, called the development “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 electromagnetic battlespace.”

Cox said earlier demonstrations of Rydberg atomic sensors were only 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.” The technology uses rubidium atoms, which are excited to high-energy Rydberg states. These interact strongly with the circuit’s electric fields, allowing detection and demodulation of any signal received into the circuit.

The report says the Rydberg spectrum analyzer has the potential “to surpass fundamental limitations of traditional electronics in sensitivity, bandwidth, and frequency range.

According to Meyer, “Devices that are based on quantum constituents are one of the Army's top priorities to enable technical surprise in the competitive future battlespace. Quantum sensors in general, including the one demonstrated here, offer unparalleled sensitivity and accuracy to detect a wide range of mission-critical signals.”

The researchers plan additional development to improve the signal sensitivity of the Rydberg spectrum analyzer, aiming to outperform existing state-of-the-art technology. “Significant physics and engineering effort is still necessary before the Rydberg analyzer can integrate into a field-testable device,” Cox said.