Quantum Sensing Unleashed: How Rydberg Sensors Will Disrupt Telecom

Quantum sensors are fascinating instruments that reveal nature to us in ways that were unthinkable just a few years ago. These are relatively small devices that help investigate items of scientific interest ranging from the infinitesimal specks of energy called photons to the unimaginably large web of galaxies that span the universe. Through the lens of these small quantum devices we can appreciate the breadth of nature and its secrets.

In this article, I’ll talk about how we came to understand Rydberg atoms, which enable an especially promising type of quantum sensor. I’ll also explain how Rydberg-based devices are being developed and commercialized by a company called Rydberg Technologies—and how Rydberg sensors could revolutionize telecommunications in the years to come.

Early Rydberg Sensor Research

In general, Rydberg radio-frequency sensors use atoms that have a single electron in their outer orbits that has been energized artificially, causing the electron to occupy an orbit much farther away from the nucleus. That makes the atom very sensitive to changes in external electrical fields.

Scientists were aware of Rydberg atoms as far back as 1885. The atoms were named after Swedish physicist Johannes Rydberg, who did important early work that helped to describe these atoms. But initial research into their use in sensors started in the 1970s with the development of tunable dye lasers. Serious scientific research became possible once laser trapping and cooling allowed researchers to use lasers like tweezers to hold and manipulate atoms. This was a turning point in our understanding of Rydberg atoms. It was so important that the Nobel Prize for Physics was awarded in 1997 for this breakthrough.

Personally, I became interested in quantum sensing about six years ago, largely because of my background in experimental high-frequency radio as it relates to the ionosphere and micro-HF devices.

The U.S. government began experimenting with the concept of quantum radios in 2017. In the period that followed, I spoke with a team of researchers at the U.S. Army Combat Capabilities Development Command’s Army Research Laboratory about their development of a prototype quantum radio receiver using Rydberg atoms. I wrote a Forbes article about the Army’s groundbreaking work in mid-2020. At that time, the Army concluded it would take several more years of research for the technology to become useful.

Rydberg, The Technology

Rubidium is an alkali metal atom that is a good candidate for Rydberg atoms because it has a single valence electron in the outer shell and 36 inner core electrons. This is important because the inner electrons act as a shield and weaken the attraction between the single outer electron and the atom’s nucleus.

To create the Rydberg atoms, energy is added to a rubidium atom using lasers. The additional energy moves the outermost electron into a higher orbit, where the attraction of the nucleus is weakened. This makes the atom increasingly susceptible to external magnetic and electrical fields.

In addition to quantum RF sensors, Rydberg atoms play important roles in other areas of science. They can be used as qubits in quantum computing. Their sensitivity to oscillating electromagnetic fields makes them useful in high-resolution imaging and the detection of electromagnetic signals. Rydberg atoms have also been used in astrophysics research.

How Rydberg Atoms Are Being Used Now

Research on quantum sensors has come a long way in just the past two years. A company called Rydberg Technologies recently announced that it has developed the world’s first long-range radio communications device using a Rydberg quantum sensor. The device was demonstrated at the U.S. Army Network Modernization Experiment 2023 event—a reliable, no-hype test for next-gen communications and intelligence technology.

A Rydberg atomic receiver has very high sensitivity across the range of high-frequency to super high-frequency bands of the electromagnetic spectrum. Rydberg sensors check every box needed for a superior receiver: high signal selectivity, low detection probability and the ability to reject unwanted electromagnetic interference.

In my discussion with Dr. David A. Anderson, founder and CEO of Rydberg Technologies, I learned he had been experimenting with Rydberg technology for many years. He said that development of the recently deployed Rydberg quantum sensor device was supported by DARPA and the National Security Innovation Capital, a funding initiative sponsored by the Defense Innovation Unit.

“It has been a long and exciting road for us so far,” he said. “We founded Rydberg Technologies in 2015 with an initial focus on R&D to bring to bear Rydberg quantum sensing capabilities for real-world applications. One significant early challenge was establishing a supply chain to develop the hardware needed to build functional devices.”

Over the past eight years, Rydberg Technologies has been able to shrink the sensors from refrigerator-sized devices in 2018 to today’s briefcase-sized sensors that can receive signals from more than a kilometer away.

Practical Applications Of Rydberg-Based Technology

Rydberg devices can address needs beyond the capabilities of classical devices. Potential markets for Rydberg Technologies’ products include defense applications for electronic warfare and surveillance, along with commercial applications such as electromagnetic testing and spectrum monitoring.

Unlike many companies investigating quantum applications, Rydberg Technologies offers commercially available products:

• The Rydberg Field Measurement System is a Rydberg atomic spectroscopy system that can measure and characterize RF fields over a wide range of frequencies and intensities. It measures E-field characteristics over an RF frequency range that would otherwise require multiple receiver antennas.
• MiniSatSpec is a compact device used for atomic referencing, laser frequency stabilization and calibration.
• Rydberg Technologies also offers atomic vapor cells and vacuum chambers for other companies to use with their quantum and photonic devices.

Rydberg Technologies is one of eight industry and university research teams chosen by DARPA for its Science of Atomic Vapors for New Technologies (SAVaNT) program.

“We have demonstrated the capability of a Rydberg atomic sensor to receive electromagnetic waves over an unprecedented frequency range spanning from near DC [i.e., almost zero wavelength] to well above 100 gigahertz,” Dr. Anderson said. “The DARPA SAVaNT program is driving fundamental advances to push the sensitivity of Rydberg sensors closer to their fundamental quantum limits.”

Wrapping Up

As a quantum technology analyst and an RF expert with over forty years of experience, I see the demonstrated performance of Rydberg RF sensors as more than just a milestone. I see it as a seismic shift. Quantum sensors have the potential to disrupt today’s most advanced wideband software defined receivers, as well as to replace the large classical-physics-based antennas that SDRs use for signal detection. A single quantum sensor can perform as both an antenna and a receiver.

Compared to traditional antennas that have a limited range of tuned frequencies, broadband Rydberg atomic receivers can operate across a huge span of frequencies ranging from HF long-wavelength to millimeter-wavelength frequencies in the terahertz spectrum. Servicing these collective frequencies with classical technology would require hundreds of physical antennas installed on acres of land—compared to a future scenario using a few quantum sensors the size of a laptop computer or smaller.

Dr. Anderson summed it up this way: “Having a compact version of these devices marks a significant milestone in Rydberg RF sensing. The device demonstrates both sensitivity and a wide operational range. We have shown that this atomic receiver is capable of tasks that are challenging to achieve even in controlled laboratory experiments.”

I agree with Dr. Anderson’s assessment. The deployment of Rydberg atom quantum sensors in the electromagnetic domain will create sweeping changes in wireless technology. It will usher in an entirely new approach to telecommunications and provide capabilities superior to today’s technology. This is an instance where pure scientific discovery will ultimately make an enormous difference in how we use everyday technologies.

Note: The chart with images showing the outer electron orbit in a Rydberg atom is taken from F. Barry Dunning, "Rydberg atoms and atomic engineering," Open Access Government, November 16, 2022.