A new type of sensor was developed that uses atoms to receive commonly used communications signals. Cesium atoms were used to receive digital bits (1s and 0s) in the most common communications format used in cellphones, Wi-Fi, and satellite TV. In this format, called phase shifting or phase modulation, radio signals or other electromagnetic waves are shifted relative to one another over time. The information (or data) is encoded in this modulation. The method works across a wide range of frequencies.
The quantum sensor received signals based on real-world phase-shifting methods. A 19.6-gigahertz transmission frequency was chosen because it could be used in future wireless communications systems. Researchers use two different color lasers to prepare atoms contained in a vapor cell into high-energy (“Rydberg”) states, which 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 was used to convert input signals into new frequencies. One radio-frequency (RF) signal acts as a reference and a second RF signal serves as the modulated signal carrier. Differences in frequency and the offset between the two signals were detected and measured by probing the atoms. Depending on the encoding scheme, the atom-based system received up to about 5 megabits of data per second. This is close to the speed of older, third-generation (3G) cellphones. The researchers also measured the accuracy of the received bit stream based on a conventional metric called error vector magnitude (EVM), which compares a received signal phase to the ideal state and thus gauges modulation quality.
Tiny lasers and vapor cells are already used in some commercial devices such as chip-scale atomic clocks, suggesting it might be feasible to build practical atom-based communications equipment.
With further development, atom-based receivers may offer benefits over conventional radio 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. The atom-based mixer also can measure weak electric fields precisely.