Quantum sensors help BT boost the power of its 5G network a hundred fold

British telecoms giant BT is undertaking a trial of new antenna technology that may boost the range of 5G networks and reduce mobile network energy consumption. But the technology’s new, unconventional, and something that wouldn’t be out of place in a military lab because it relies on highly sensitive Rydberg sensors.

The receiver technology works by exploiting a quantum effect called "electromagnetically induced transparency" to form a highly sensitive electric field detector. According to BT, this could theoretically make it over 100 times more sensitive than traditional receivers, allowing it to detect weaker signals and thus extend the range of a mobile network deployment.

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Regular readers will no doubt have become twitchy at the mention of the word "quantum" so I asked BT if it could supply us with a simple explanation of how the new antenna technology works, and this is what they said:

“A conventional dipole antenna is a macroscopic solid conductor and subject to thermal noise as the billions of atoms jostle each other at room temperature. In a diffuse gas, the atoms interact much less, so thermal noise can be reduced and the signal-to-noise ratio is [increased] even for weak signals, especially in a narrow frequency band.”

BT also directs those with an interest in this technology to an article its researchers published in the Journal of Lightwave Technology. This mentions the use of Rydberg RF sensors to exploit the electromagnetically induced transparency effect in an atomic vapor.

This relies on Rydberg atoms that are highly excited, which means they have one or more electrons that are highly energetic and thus farther out from the nucleus of the atom. Rydberg atoms have a number of peculiar properties including an exaggerated response to electric and magnetic fields, or so we understand, and this is utilized in a Rydberg RF sensor.

This technology is not actually new, and the US National Institute of Standards and Technology (NIST) is recognized as a leader in developing and exploring Rydberg sensors for a variety of applications.

What is new in BT's trial is that the technology has been used for the first time to receive a digitally encoded transmission sent over a 3.6GHz carrier frequency, demonstrating that it is possible for Rydberg RF sensors to be deployed as part of a 5G network.

BT's ongoing work is now aimed at simplifying these very complex devices so that they can be deployed in the field, utilizing an economic laser source in the receiver.

In the abstract for its research article, the BT researchers explain: "We present a simple analytic model for the operation of a sensitive Rydberg RF receiver to predict the optical modulation in response to an RF signal... by detuning the coupling frequency to compensate for the RF detuning we demonstrate that the useful RF bandwidth of the receiver can be significantly extended... This convenient analytic approach will simplify the design and operation of Rydberg RF receivers as sensitive components in future 5G mobile communications, particularly for the power-limited uplink from mobile device to base-station."

The researchers at BT Labs in Martlesham are working to miniaturize the equipment and find the optimum RF modulation and signal processing for potential use in future generations of radio networks.

This is not likely to happen overnight, as BT Senior Manager for Network Physics Fraser Burton – one of the researchers – told me.

"A commercial product is at least three to five years out, so network deployment within the decade is possible," Burton said. And even though the technology might be later than hoped to the 5G party it might also end up playing a significant role in the roll out of 6G networks.

While the technology is still in the very early stages, it has the potential to provide greater sensitivity than conventional radio antennas, according to BT, with tuneable operation from very low frequencies, detection of analogue and digital modulation, and low energy consumption through reduced need for electronics.

BT said it has also been granted a number of patents relating to its implementation of the atomic RF receiver technology.