Devices used to amplify weak microwave signals have improved dramatically during the last 30 years with the development of such low noise solid-state devices such as the HEMT (high electron mobility transistor). Researchers at Aalto University School of Science in Finland have now come up with an entirely new way of detecting and amplifying microwave signals that adds the minimum amount of noise required by quantum mechanics.
The amplification takes place in a "nanomechanical oscillator," a very small device the University said resembles a miniature guitar string. The oscillator, a thousand times thinner than a human hair, is cooled to near absolute zero—minus 273 centigrade. At this temperature, all of the atoms in the resonator oscillate are in pace in their shared quantum state.
Researchers at the Low Temperature Laboratory at Aalto University discovered the effect when probing the device with a microwave laser.
A news release from the University said, "The discovery was actually quite unexpected. We were aiming to cool the nanomechanical resonator down to its quantum ground state. The cooling should manifest as a weakening of a probing signal, which we observed. But when we slightly changed the frequency of the microwave laser, we saw the probing signal to strengthen enormously. We had created a nearly quantum limited microwave amplifier, according to Academy Research Fellow Mika Sillanpää, who planned the project and made the measurements."
Academy Research Fellow Tero Heikkila explained "the beauty of the amplifier is in its simplicity: it consists of two coupled oscillators. Therefore, the same method can be realized in basically any media. By using a different structure of the cavity, one could detect terahertz radiation which would also be a major application."
More research is needed to make the amplifier suitable for real-life applications. Initially it is likely to be used in basic research on the borderline region between the everyday world and the quantum realm.
The research is detailed in the Nature article Microwave amplification with nanomechanical resonators (opens in new tab). Although access to the full article is limited to subscribers, the preview portion indicates the device provided 25 dB of amplification with the addition of only 20 quanta of noise.
Doug Lung is one of America's foremost authorities on broadcast RF technology. He has been with NBC since 1985 and is currently vice president of broadcast technology for NBC/Telemundo stations.
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