Researchers demonstrated an atom-based sensor that can determine the direction of an incoming radio signal, another key part for a potential atomic communications system that could be smaller and work better in noisy environments than conventional technology.
The capability to measure a signal’s “angle of arrival” helps ensure the accuracy of radar and wireless communications, which need to sort out real messages and images from random or deliberate interference. A true atom-based communication system would benefit 5G and beyond.
Two different-colored lasers prepare gaseous cesium atoms in a tiny glass flask, or cell, in high-energy (Rydberg) states that have novel properties such as extreme sensitivity to electromagnetic fields. The frequency of an electric field signal affects the colors of light absorbed by the atoms. An atom-based “mixer” takes input signals and converts them into different frequencies. One signal acts as a reference while a second signal is converted or detuned to a lower frequency. Lasers probe the atoms to detect and measure differences in frequency and phase between the two signals. Phase refers to the position of electromagnetic waves relative to one another in time.
The mixer measures the phase of the detuned signal at two different locations inside the atomic vapor cell. Based on the phase differences at these two locations, researchers can calculate the signal’s direction of arrival. To demonstrate the approach, the team measured phase differences of a 19.18-Gigahertz experimental signal at two locations inside the vapor cell for various angles of arrival. They compared these measurements to both a simulation and a theoretical model to validate the new method.
Atom-based sensors in general have many possible advantages including measurements that are both highly accurate and universal; that is, the same everywhere because the atoms are identical. Measurement standards based on atoms include those for length and time.
With further development, atom-based radio receivers may offer many benefits over conventional technologies. For example, there is no need for traditional electronics that convert signals to different frequencies for delivery because the atoms do the job automatically. The antennas and receivers can be physically smaller, with micrometer-scale dimensions. In addition, atom-based systems may be less susceptible to some types of interference and noise.
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