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Researchers have shown how to detect and amplify electromagnetic signals almost noiselessly using a guitar-string like mechanical vibrating wire. In the ideal case the method adds only the minimum amount of noise required by quantum mechanics.
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Physicists
in Low Temperature Laboratory of Aalto University have shown how a
nanomechanical oscillator can be used for detection and amplification of
feeble radio waves or microwaves.
A
measurement using such a tiny device, resembling a miniaturized guitar
string, can be performed with the least possible disturbance. The
results were recently published in the most prestigious scientific
arena, the British journal Nature.
The
researchers cooled the nanomechanical oscillator, thousand times
thinner than a human hair, down to a low temperature near the absolute
zero at -273 centigrade. Under such extreme conditions, even nearly
macroscopic sized objects follow the laws of quantum physics which often
contradict common sense. In the Low Temperature Laboratory experiments,
the nearly billion atoms comprising the nanomechanical resonator were
oscillating in pace in their shared quantum state.
The
scientists had fabricated the device in contact with a superconducting
cavity resonator, which exchanges energy with the nanomechanical
resonator. This allowed amplification of their resonant motion. This is
very similar to what happens in a guitar, where the string and the echo
chamber resonate at the same frequency. Instead of the musician playing
the guitar string, the energy source was provided by a microwave laser.
Microwaves get amplified by interaction of quantum oscillations
Researchers
from the Low Temperature Laboratory, Aalto University, have shown how
to detect and amplify electromagnetic signals almost noiselessly using a
guitar-string like mechanical vibrating wire. In the ideal case the
method adds only the minimum amount of noise required by quantum
mechanics.
The
presently used semiconductor transistor amplifiers are complicated and
noisy devices, and operate far away from a fundamental disturbance limit
set by quantum physics. The Low Temperature Laboratory scientists
showed that by taking advantage of the quantum resonant motion, injected
microwave radiation can be amplified with little disturbance. The
principle hence allows for detecting much weaker signals than usually.
Any
measurement method or device always adds some disturbance. Ideally, all
the noise is due vacuum fluctuations predicted by quantum mechanics. In
theory, our principle reaches this fundamental limit. In the
experiment, we got very close to this limit, says Dr. Francesco Massel.
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click to enlarge
Aluminium nanowire, whose vibrations are coupled to the superconducting cavity (on the right), enabling almost noiseless amplification of microwaves. |
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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, says Academy Research Fellow Mika Sillanpää who planned the project and made the measurements.
Certain
real-life applications will benefit from the better amplifier based on
the new Aalto method, but reaching this stage requires more research
effort. Most likely, the mechanical microwave amplifier will be first
applied in related basic research, which will further expand our
knowledge of the borderline between the everyday world and the quantum
realm.
According to Academy Research Fellow Tero Heikkilä,
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.
The
research was carried out in the Low Temperature Laboratory, which
belongs to the Aalto University School of Science, and is part of the
Centre of Excellence in Low Temperature Quantum Phenomena and Devices of
the Finnish Academy. The devices used in the measurements were
fabricated by VTT Nanotechnologies and microsystems. The research was
funded by the Finnish Academy, European Research Council ERC, and the
European Union.
Microwave amplification with nanomechanical resonators
SOURCE
