Authored by Atharva Gosavi via Interesting Engineering,
US Army scientists have demonstrated a new quantum sensor that can measure the full 3D direction of radio-frequency electromagnetic fields, a milestone that could reshape how signals are detected on the battlefield.
The breakthrough was achieved by scientists at the U.S. Army Combat Capabilities Development Command, known as DEVCOM, Army Research Laboratory.
According to the researchers, the sensor could improve situational awareness, strengthen secure communications, and help soldiers make faster, better-informed decisions in complex battlefield environments.
"Our work in quantum science is about giving our Soldiers new ways to sense and understand the world around them," said David Meyer, ARL research physicist.
"This research opens the door to detecting and pinpointing signals over a broad frequency range in a single sensing package, even in the most challenging environments,"
Measuring Radio Waves in 3D
The new sensor is based on Rydberg atoms, which are atoms placed in a highly excited state that makes them extremely sensitive to electric fields.
The researchers described how the device can determine not only electromagnetic field strength but also the 3D polarization orientation and propagation direction, known as the k-vector.
According to ARL, this is the first time such a measurement has been achieved using a quantum sensor.
Traditional sensors usually measure the strength of an electromagnetic field in only one direction at a time. The ARL-developed quantum sensor, however, can "see" both the direction and motion of the electromagnetic field, providing a complete 3D picture.
Despite being only a few centimeters across, the sensor can determine the direction of incoming signals with an accuracy of about two degrees.
This could make it a highly flexible platform for detecting and locating radio-frequency signals in contested environments.
A Tiny Sensor for a Crowded Spectrum
Unlike conventional antennas, which often need to be physically comparable in size to the signals they detect and are typically limited to narrow frequency ranges, ARL's sensor is independent of signal size. It can also operate across the entire radio-frequency spectrum.
This capability comes from the broadband nature of Rydberg atoms, which can operate from direct current to terahertz frequencies.
"The modern battlefield is an extremely complicated radio frequency environment," Meyer said.
"With the proliferation of autonomous systems, there can be hundreds of distinct signal sources. Having a single sensor platform that covers the entire radio-frequency spectrum and can measure the 3D direction of those fields represents a potentially transformative capability, especially in spectrum awareness," he continued.
Building on Years of Quantum Research
The sensor works by using a tiny glass cell filled with rubidium atom vapor. Researchers shine lasers through the cell to put the atoms into Rydberg states.
When a radio wave passes through, the atoms respond in a way that reveals the field's strength, direction, and movement in three dimensions.
The latest work builds on ARL's earlier development of the Rydberg electrometer. In 2024, the team demonstrated its ability to measure radio-frequency field polarization and decode information encoded in that polarization.
The research was published in a paper called Physical Review Applied.