Microwaves subtly shift the atoms’ state, and lasers translate those shifts into a readable signal. The result is a receiver that can detect extremely weak signals without adding its own interference.

The modern world is saturated with radio and microwave signals, from Wi-Fi and Bluetooth to car radars and satellite communications. Conventional receivers rely on antennas and layers of electronics to amplify and process these waves.

While this works well for phones and routers, the electronics themselves emit microwaves and noise. In environments where extremely faint signals must be measured — for example, near quantum computers or in radio astronomy, a standard receiver can become more of a hindrance than a help.

The Warsaw scientists took a different approach. “A properly prepared atom can act as a single, extremely sensitive antenna,” the researchers said. Unlike conventional radios, it does not transmit information via electrical currents. Instead, it subtly alters the way it transmits light, allowing the receiver to “listen” without adding interference.

Their work, published in Nature Communications, focuses on Rydberg atoms - atoms in which a single electron is ejected into a distant orbit around the nucleus. These atoms are “like huge, delicate spheres, hundreds of times larger than a typical atom,” the researchers say, making them highly sensitive to electric fields, including microwaves. Even a weak microwave signal can shift their state noticeably.

Rubidium vapour is placed in a glass cell and illuminated by several lasers. Some beams prepare the atoms in a state close to the Rydberg level. A narrow probe beam passes through the vapour. When microwaves reach the atoms, the transmittance of the beam changes and its intensity and phase increase or decrease. These subtle shifts encode information about the microwave signal, much like a conventional radio reads modulation.

Ordinary receivers require an oscillator - a relatively strong microwave source of known frequency - to mix with the incoming wave and extract information. The Warsaw team removed the need for this additional source.

Lasers serve as the reference, positioning the atoms in the correct state and ensuring they respond to microwaves in a controlled, predictable way.

Laser instability, however, presents another challenge. Small fluctuations in frequency create noise that can overwhelm weak signals. To counter this, part of the laser light is routed into an additional optical path containing a nonlinear crystal.

Two beams combine to create a third, highly sensitive to laser fluctuations. This output provides a real-time map of laser noise, which is digitally subtracted from the atom-cell signal, leaving the cleanest possible record of external microwaves.

The resulting receiver can detect microwaves far weaker than those accessible with conventional communication systems. Importantly, it can process real data.

“The researchers demonstrate that their system receives normally encoded signals, for example, a signal with modulation similar to that used in modern telecommunications networks,” the study says. This confirms that the device is not just a scientific curiosity, but a prototype of a practical, functional receiver.

Potential applications are wide-ranging. Atom-based radios could measure signals without introducing interference in quantum computing laboratories, test high-speed electronics, power miniature radars for autonomous vehicles, and perhaps one day contribute to radio astronomy, where detecting the faintest cosmic signals is essential.

(PAP)

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