Army-Maryland Researchers Measure Electromagnetic Field Direction in 3D Using Rydberg Atoms

Researchers at DEVCOM Army Research Laboratory (ARL), in collaboration with the University of Maryland at College Park and the Army-Maryland Partnership for Quantum Electrodynamics (AMPED), have demonstrated three-dimensional characterization of a radio-frequency electromagnetic (EM) field using a quantum sensor based on Rydberg atoms.

An EM field is characterized by field and propagation directions oriented in  3-dimensional space, but typical sensors only report the field amplitude along a particular axis.

 The new sensor developed at ARL measures the EM field’s 3D vector orientation and propagation direction.  This demonstration is the first of its kind using a quantum sensor, based on laser-interrogated rubidium Rydberg atoms.  The sensor demonstrated an impressive resolution of approximately two degrees in every direction.

ARL’s Rydberg sensor consists of a dilute gaseous vapor of rubidium atoms contained in a few-centimeter-sized glass cell.  The atoms are prepared into Rydberg states and detected using two counter-propagating laser beams.  The Rydberg states, which have one electron orbiting the atom at a much larger distance than usual, give the atoms exquisite sensitivity to the incoming electric fields.  

A surprising and important feature of ARL’s new technology is that the sensor measures the field and propagation direction even though the sensor’s size can be much smaller than the field’s wavelength.  In contrast, most antennas must be comparable in size to the wavelength of the EM field to measure directionality.

This work has wide-ranging long-term applications in the field of EM field detection, and the work was published in two recent articles published in Physical Review Applied.