Aerospace & Defense Technology - April 2021 - 26

RF & Microwave Technology

Army Detects Broadest Frequencies Ever with Quantum Receiver

new quantum sensor can analyze the full spectrum of
radio-frequency and real-world signals, unleashing new
potential for soldier communications, spectrum awareness,
and electronic warfare.
Army researchers built the quantum sensor, which can sample the radio-frequency spectrum - from zero frequency up
to 20 GHz - and detect AM and FM radio, Bluetooth, Wi-Fi,
and other communication signals.

How it Works
The Rydberg sensor uses laser beams to create highly excited Rydberg atoms directly above a microwave circuit to
boost and home 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.
" 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 (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
electromagnetic battlespace. "
The Rydberg spectrum analyzer has the potential to surpass fundamental limitations of traditional electronics in
sensitivity, bandwidth, and frequency range. Because of
this, the lab's Rydberg spectrum analyzer and other quantum sensors have the potential to unlock a new frontier of
Army sensors for spectrum awareness, electronic warfare,
sensing, and communications - part of the Army's modernization strategy.
" Devices that are based on quantum constituents are one of
the Army's top priorities to enable technical surprise in the
competitive future battlespace, " said Army researcher Dr.
David Meyer. " Quantum sensors in general, including the one
demonstrated here, offer unparalleled sensitivity and accuracy
to detect a wide range of mission-critical signals. "

A Rydberg receiver and spectrum analyzer detects a wide range of real-world
radio-frequency signals above a microwave circuit including AM radio, FM
radio, Wi-Fi, and Bluetooth. (U.S. Army illustration)

Researchers excite rubidium atoms to high-energy Rydberg states. The atoms
interact strongly with the circuit's electric fields, allowing detection and
demodulation of any signal received into the circuit. (U.S. Army illustration)

The Future
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. " One of the first steps will be understanding how to retain and improve the device's performance as
the sensor size is decreased. The Army has emerged as a leading developer of Rydberg sensors and we expect more cuttingedge research to result as this futuristic technology concept
quickly becomes a reality. "
For more information, contact the Army DEVCOM Army
Research Laboratory Public Affairs at 703-693-6477.
26

Researchers use a Rydberg spectrum analyzer experimental apparatus at the
DEVCOM Army Research Lab. (U.S. Army)

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