Tech
NIST team shows atoms can receive common
communications signals
NIST researcher Chris Holloway adjusts a mirror to align
a laser beam used in an atom-based receiver for digitally
modulated communication signals. Credit: Burrus/NIST
Researchers at the National Institute of Standards and Technology (NIST) have demonstrated a new
type of sensor that uses atoms to receive commonly used communications signals. This atom-based
receiver has the potential to be smaller and work better in noisy environments than conventional
radio receivers, among other possible advantages.
The NIST team used cesium atoms to receive digital bits (1s and 0s) in the most common
communications format, which is used in cell phones, Wi-Fi and satellite TV, for example. 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 point is to demonstrate one can use atoms to receive modulated signals,” project leader Chris
Holloway said. “The method works across a huge range of frequencies. The data rates are not yet the
fastest out there, but there are other benefits here, like it may work better than conventional
systems in noisy environments.”
As described in a new paper, the quantum sensor received signals based on real-world phase-
shifting methods. A 19.6 gigahertz transmission frequency was chosen because it was convenient for
the experiment, but it also could be used in future wireless communications systems, Holloway said.
The NIST team previously used the same basic technique for imaging and measurement
applications. 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.
In the new experiments, the team used a recently developed atom-based mixer 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.
While many researchers have previously shown that atoms can receive other formats of modulated
signals, the NIST team was the first to develop an atom-based mixer that could handle phase
shifting.
Wireless communications often use a format called phase shifting or phase modulation, in which the
signals are shifted relative to one another in time. In this example, the communications signal (blue)
contains periodic reversals relative to the reference signal (red). These reversals are the blips that
look like cats’ ears. The information (or data) is encoded in this modulation. Credit: Holloway/NIST
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) cell phones.
The researchers also measured the accuracy of the received bit stream based on a conventional
metric called error vector magnitude (EVM). EVM compares a received signal phase to the ideal state
and thus gauges modulation quality. The EVM in the NIST experiments was below 10 percent, which
is decent for a first demonstration, Holloway said. This is comparable to systems deployed in the
field, he added.
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 many benefits over conventional radio
technologies, according to the paper. 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.
Researchers now plan to improve the new receiver by reducing laser noise and other unwanted
effects.
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Paper: C.L. Holloway, M.T. Simons, J.A. Gordo and D. Novotny. 2019. Detecting and Receiving Phase
Modulated Signals with a Rydberg Atom-Based Receiver. IEEE Antennas and Wireless Propagation
Letters. September 2019 issue. DOI: 10.1109/LAWP.2019.2931450
- Dan Romanchik, KB6NU