WHY THIS MATTERS IN BRIEF
On the battlefield electronic communications are almost the key to the battle, but new quantum technologies are making it easier – and harder – to spy on the enemy so militaries around the world are ramping their investments and research.
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US Army researchers are developing a quantum sensor capable of detecting electromagnetic emissions across frequency bands and at far greater ranges than traditional receivers and are considering demonstrating the capability with soldiers later this year.
The technologists at the Army’s Command, Control, Communications, Computers, Cyber, Intelligence, Surveillance and Reconnaissance (C5ISR) Center envision a shoebox-sized device capable of detecting signals across bands such as long band, short band and conventional band, which are often shortened to L-, S- and C-bands. The device might also pick up signals at far greater distances.
James Tucker Swindell, chief of the C5ISR Center’s Radio Frequency Communications Division, indicates that it is difficult to pinpoint exactly how much farther away a quantum sensor could detect signals because the distance would vary from one band to the other.
“I’d say it’s a bit early for any particular information because what you can estimate at HF [high frequency] might be different than what you can estimate at K-band. However, in general, I would expect there to be something along the lines of a hundredfold improvement,” he says, adding a caveat. “Now, this is science and technology, so let me preface this. If I get a hundredfold in the lab, it doesn’t mean that I get a hundredfold in the field, but it sure does help me get closer.”
The technology is a kind of sensor known as a Rydberg sensor, which takes advantage of the ability of so-called Rydberg atoms to react in different ways when exposed to varying kinds of electromagnetic fields.
“These atoms operate when excited in such a way that we can determine what electric field is around those atoms. The sensitivity of that is so strong that we actually believe that quantum phenomenology can be utilized to act as a receiver,” Swindell explains. “Instead of having – you name it – your whip antenna for everything from an HF area antenna to a 3-foot, 5-foot, 10-foot whip antenna sticking off your vehicle, we think we can get away with something more shoebox-sized.”
The C5ISR Center may soon demonstrate a quantum sensing capability.
“There are some possible demonstrations within the year for some of the Rydberg systems; however, we are going to remain cautiously optimistic as we continue to invest in this technology to get it to an eventual tactical form factor.”
It is too early, however, for Swindell to provide any details about the potential demonstrations. “Right now, we don’t have anything solid. We’re always looking to demonstrate capabilities for the soldiers. Whenever we have a technology we believe is far enough along to bring out to soldiers and have them touch and play, turn it on and utilize it, we try to,” he says.
If the demonstrations take place, they will come on the heels of an Army Research Laboratory demonstration that took place early last year. The lab, commonly referred to as ARL, used a Rydberg sensor to analyze “the full spectrum of radio frequency and real-world signals, unleashing new potential for soldier communications, spectrum awareness and electronic warfare,” according to an Army announcement.
The ARL’s quantum sensor samples the radio-frequency spectrum – from zero frequency up to 20GHz – and detects AM (amplitude modulation) and FM (frequency modulation) radio, Bluetooth, Wi-Fi and other communication signals. The system uses laser beams to create highly excited Rydberg atoms directly above a microwave circuit to boost and home in on the portion of the spectrum measured. The Rydberg atoms are sensitive to the circuit’s voltage, enabling the device to be used as a sensitive probe for the wide range of signals in the radio frequency spectrum.
“All previous demonstrations of Rydberg atomic sensors have only been able to sense small and specific regions of the RF spectrum, but our sensor now operates continuously over a wide frequency range for the first time,” explains Kevin Cox, a researcher at ARL, which falls under the U.S. Army Combat Capabilities Development Command (DEVCOM), in the press release. “This is a really important step toward proving that quantum sensors can provide a new and dominant set of capabilities for our soldiers, who are operating in an increasingly complex electromagnetic battlespace.”
The Rydberg spectrum analyzer has the potential to surpass fundamental limitations of traditional electronics in sensitivity, bandwidth and frequency range. Because of this, the lab’s Rydberg spectrum analyzer and other quantum sensors have the potential to unlock a new frontier of Army sensors for spectrum awareness, electronic warfare, sensing and communications—part of the Army’s modernization strategy, the release adds.
Swindell’s team at the C5ISR Center is not directly involved in the ARL’s Rydberg sensor research, but the two organizations do share information and sometimes resources. “ARL is a large proponent of quantum computing, as well as quantum communications. They are aware of our efforts. We are tracking theirs,” he says, adding that there may be an opportunity for the C⁵ISR Center to transition ARL’s work from the realm of basic research to applied or advanced research or advanced technology development.
The C5ISR Center also cooperates with the Office of the Undersecretary of Defense, research labs from the other services and with the Defense Advanced Research Projects Agency, better known as DARPA. DARPA’s Quantum Apertures program also works with Rydberg sensors. The program’s goal is to develop portable and directional radio frequency receivers useful for future Defense Department missions with greater sensitivity, bandwidth and dynamic range than classical receivers, according to a DARPA website.
Additionally, the agency announced in September that eight teams will work on its Science of Atomic Vapors for New Technologies (SAVaNT) program, which aims to overcome the need to use complex laser cooling capabilities to make quantum technology work. The SAVaNT program will focus on three approaches: Rydberg electrometry, vector magnetometry and vapor quantum electrodynamics, the program’s website explains.
Swindell notes that extreme cooling of quantum systems is not practical on the battlefield.
“We’re looking for things that operate at room temperature or near room temperature. To be fair, the Army does have systems that are cryo-cooled; however, that is not our first choice. Systems like the Rydberg do not require cryo-cooling,” he states.
Size also is an important factor, but for now it remains a challenge for many quantum systems. “We certainly don’t want to develop a capability that requires our soldiers to bring an 18-wheeler with them. That’s not going to float,” he declares. “We don’t want to show up with something the size of a college mini-fridge that can’t fit but on one vehicle because that doesn’t help us. But we do have to make some realistic expectations in terms of what we’re going to need for a system to be tactically relevant.”
In their pursuit of a shoebox-sized quantum sensor, the C5ISR team literally pulled out the tape measures. “In looking at some of the systems that are currently on our platforms, some of the guys and I have gone out with our tape measures and measured off different components of our ground vehicles as well as some of our aircraft. We believe that something around a shoebox size would be palatable in terms of a capability that we could bring to bear that would absolutely advance our current receive technologies but also be something that our soldiers can reasonably incorporate into their existing systems,” he reports.
Swindell says quantum sensors offer other benefits both as a receiver for radios or as a spectrum detector. “The use of quantum physics in terms of the communications we’re engaged in really has to do with finding a way to detect really, really faint signals so that perhaps you can detect an enemy from a greater distance,” he elaborates. “You can detect the blue (friendly) forces that might be using these systems from a greater distance. Perhaps they can even power down and not have to be so loud in order for me to detect them as long as we know what we’re looking for.”
The C5ISR Center’s research primarily focuses on signal reception, but quantum technology may ultimately prove beneficial for signal transmission as well. “At this juncture, I would say that our quantum sensor efforts are purely based in the receive realm; however, we are absolutely investigating what we can do on the transmit side to enable enhanced communications on the next step toward the future,” Swindell offers.