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The Rydberg sensor is a technology rooted in the fundamental structure of nature on the smallest scales that points to a complete revolution in the detection of radio waves. And it may be coming soon to that cell phone in your hand.

The current cell phone radio frequency network is an engineering marvel that most of us never think twice (or even once) about except when a call gets dropped and we find ourselves talking into dead air. The engineers who designed and operate the cellular network work very hard to maintain it, but lets take a look at this new technology and how it may change cell service forever.

Switching Heavy Traffic

As outlined by UCSB, a cellular handset (aka your phone) contains a compact, low-powered two-way radio, with sufficient range to connect to a nearby base station mounted on a cellular tower. The base station, in turn, uses higher-powered long-range equipment to connect to broader regional and global networks.

The whole point of this system is to enable users to move around freely, including moving from one base stations reception area to anothers. According to Dr. Sid Ghosh of Northrop Grumman, the normal sequence of operations when making a phone call on the move is as follows:

All of this works impressively well, says Ghosh, and a call being dropped during handoff is quite rare. But mobility does put challenging demands on cell phone radio frequency technology. When you are driving or on a train, explains Ghosh, the handovers tend to get tricky since the user may not be optimally located for cell tower coverage.

Even if dropped calls are rare, multiply the basic technology challenge by the number of calls being made, and the problem of dropped calls and generally poor cell phone reception becomes serious especially when its your call that gets dropped or garbled.

The Antenna Fiddling Challenge

A key component of any radio frequency detector is the antenna that picks up the signal. This is, in principle, simply a length of wire. If the wire is the right length and oriented in the right direction, the electric field of passing radio waves will trigger an electric current in the wire, which can be detected and amplified.

This has been the principle of every standard radio receiver since, as noted by the AAAS, Heinrich Hertz first demonstrated and reported on the existence of radio waves in 1889. But it is not ideal for rapid and frequent handoffs from one cell phone radio frequency base station to the next. The thing about antennas is that their ability to pick up a signal depends on the antennas physical size and geometry, which need to be adjusted to pick up a signal well.

Anyone whos moved a radio around to improve reception or fiddled with old-fashioned TV rabbit ears will appreciate that this can be tricky. But as Ghosh explains, quantum physics now provides an entirely different way of detecting radio waves that can revolutionize cell phone reception.

Giant Atoms and a Tiny Detector

Under the right circumstances and hit with the right frequency of laser light, atoms of rare alkaline metals, such as cesium and rubidium, can swell up enormously to a diameter of about 1/25,000 of an inch still submicroscopic but about 10,000 times the size of ordinary atoms.

This atomic bloat is an effect of quantum mechanics. The atomic nucleus is unchanged, but the orbits of its outermost electrons are pumped up by the laser and pushed outward to the atoms far outer envelope, where they are only tenuously bound to the nucleus. This loose binding makes these outer electrons extremely sensitive to electric fields, such as those produced by radio waves.

In effect, the radio signals fluctuating signal jiggles the loosely bound outer electrons, producing changes in the optical spectrum of the Rydberg atoms, and an optical sensor can detect these spectrum changes. It adds up to a nifty physics bank shot: radio waves jiggle the outer electrons of Rydberg atoms, producing spectrum changes in the (vastly shorter wavelength) optical band.

Moving Beyond the Antenna

What makes this one weird physics trick so important to radio technology is that unlike any conventional radio antenna Rydberg atoms do not need to be arranged in a particular length or pointing in a particular direction to pick up a signal. The only thing that needs to be adjusted is the frequency of laser light used to pump up the Rydberg atoms. This property drew the particular interest of the Defense Advanced Research Projects Agency (DARPA), most famous for having developed the internet.

Changing a laser frequency is a much faster and simpler process than physically adjusting the size and orientation of an antenna, particularly when the receiver is on the move and must continually switch frequency as it passes from base station to base station. Size also matters when it comes to mobile radio devices. Conventional antennas need to be proportionate in size to the radio waves they are intended to detect a major constraint on the available radio frequency spectrum when it comes to devices, like cell phones, that must be physically compact.

In contrast, explains Ghosh, Rydberg atoms can act as electrically small antennas and detect the modulation of a carrier wave. They can detect and demodulate AM, FM and phase modulation over a broad range of carrier frequencies, making them a promising platform for advanced communication receivers.

Moreover, he adds, the Rydberg receiver is frequency agnostic over a wide range of operating frequencies, and thus, the size of a Rydberg receiver does not need to scale with operating frequency to maintain optimal performance. The current standard for Rydberg sensor elements, notes Ghosh, is that the sensor must fit inside one cubic centimeter. This is far more compact than most conventional antennas.

The Future of Rydberg Sensors

The Rydberg sensor technology is currently still in its research and development stage in the Quantum Apertures program. But as Ghosh outlines, the gas cell technology for producing Rydberg atoms is maturing rapidly, while similar rapid development is taking place in adjacent peripheral technology development in the commercial optical communication domain thats helping move the concept of a Rydberg receiver toward a viable product that can operate over a wide range of frequencies in various application scenarios.

As reported by EE Times, the wide scope of capabilities offered by Rydberg sensor technology has drawn the interest of NASA as well as DARPA, pointing toward space-based as well as ground-based applications. The possible range of applications is enormous, but few are more ubiquitous than the cell phone network, which makes it likely that people will soon be holding Rydberg sensor technology in their hands. But with improved reliability and performance, theyll probably spend even less time thinking about the technological marvel theyre holding than they do now.

Are you interested in all things related to technology? We are, too. Learn more about life at Northrop Grumman, and check out our career opportunities to see how you can participate in this fascinating time of discovery in science, technology and engineering.

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Transforming Cell Phone Radio Frequency With Quantum Apertures - Now. Powered by Northrop Grumman.