Researchers at Chalmers are first to show the
use of sound to communicate with an artificial atom. They can thereby
demonstrate phenomena from quantum physics with sound taking on the role of
light. The results are published by the journal Science.
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On the right, an artificial atom generates sound
waves consisting of ripples on the surface of a solid. The sound, known as a
surface acoustic wave (SAW) is picked up on the left by a
"microphone" composed of interlaced metal fingers. According to
theory, the sound consists of a stream of quantum particles, the weakest
whisper physically possible. The illustration is not to scale. Credit: Philip
Krantz, Krantz NanoArt. Source: chalmers.se
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The
experts, from Chalmers University of Technology in Gothenburg, were
investigating the relationship between sound and atoms in the hope of learning
more about quantum physics.
They
believe manipulating sound on the quantum level could lead to new developments
in computing - giving us faster and more efficient computers.
The
scientists started by placing the artificial atom on to a superconducting
material, designed to carry sound-waves efficiently.
After
guiding sound along the material and bouncing it off the atom, they were able
to record what came back - using a minute microphone.
What
they recorded was a D-note, around 20 octaves above the highest note on a piano
- which is much higher than the human ear can detect.
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The researchers believe manipulating sound on
the quantum level could lead to new developments in quantum computing (Photo source: Daily Mail)
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Per
Delsing, the physics professor who led the experimental research group, said:
'We have opened a new door into the quantum world by talking and listening to
atoms.
'Our
long term goal is to harness quantum physics so that we can benefit from its
laws, for example in extremely fast computers.'
The
study's co-author, Martin Gustafsson, added: 'According to the theory, the
sound from the atom is divided into quantum particles.
'Such
a particle is the weakest sound that can be detected'
Sound
has a short wavelength and travels 100,000 times slower than light, which means
it's much easier to control.
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The researchers by
the cryostat used for the measurements. From left to right: Per Delsing, Thomas
Aref, Göran Johansson, Martin Gustafsson, Maria Ekström, Anton Frisk Kockum. Photo: David Niepce. Source: chalmers.se
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The
report on the school’s website reports:
The
interaction between atoms and light is well known and has been studied
extensively in the field of quantum optics. However, to achieve the same kind
of interaction with sound waves has been a more challenging undertaking. The
Chalmers researchers have now succeeded in making acoustic waves couple to an
artificial atom. The study was done in collaboration between experimental and
theoretical physicists.
"We have opened a
new door into the quantum world by talking and listening to atoms", says
Per Delsing, head of the experimental research group. "Our long term goal
is to harness quantum physics so that we can benefit from its laws, for example
in extremely fast computers. We do this by making electrical circuits which
obey quantum laws, that we can control and study."
An artificial atom is an
example of such a quantum electrical circuit. Just like a regular atom, it can
be charged up with energy which it subsequently emits in the form of a
particle. This is usually a particle of light, but the atom in the Chalmers
experiment is instead designed to both emit and absorb energy in the form of
sound.
"According to the
theory, the sound from the atom is divided into quantum particles", says
Martin Gustafsson, the article's first author. "Such a particle is the
weakest sound that can be detected."
Since sound moves much
slower than light, the acoustic atom opens entire new possibilities for taking
control over quantum phenomena.
"Due to the slow
speed of sound, we will have time to control the quantum particles while they
travel" says Martin Gustafsson. "This is difficult to achieve with
light, which moves 100,000 times more quickly."
The low speed of sound
also implies that it has a short wavelength compared to light. An atom that
interacts with light waves is always much smaller than the wavelength. However,
compared to the wavelength of sound, the atom can be much larger, which means
that its properties can be better controlled. For example, one can design the
atom to couple only to certain acoustic frequencies or make the interaction
with the sound extremely strong.
The frequency used in the
experiment is 4.8 gigahertz, close to the microwave frequencies common in
modern wireless networks. In musical terms, this corresponds approximately to a
D28, about 20 octaves above the highest note on a grand piano.
At such high frequencies,
the wavelength of the sound becomes short enough that it can be guided along
the surface of a microchip. On the same chip, the researchers have placed an
artificial atom, which is 0.01 millimeters long and made of a superconducting
material.
The paper Propagating
phonons coupled to an artificial atom is published online by the journal
Science, at the Science Express web site.
Additional details about
the research:
The sample that the
researchers use is made on a substrate of gallium arsenide (GaAs) and contains
two important parts. The first one is the superconducting circuit that
constitutes the artificial atom. Circuits of this kind can also be used as
qubits, the building blocks of a quantum computer. The other essential
component is known as an interdigital transducer (IDT). The IDT converts
electrical microwaves to sound and vice versa. The sound used in the experiment
has the form of surface acoustic waves (SAWs) which appear as ripples on
the surface of a solid. The experiments are performed at very low temperatures,
near absolute zero (20 millikelvin), so that energy in the form of heat does
not disturb the atom.
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Microscope image: The
artificial atom, in grey-blue to the upper right, can emit and absorb sound
that moves across the surface of a microchip. The grey-blue structure to the
lower left is the combined loudspeaker/microphone used to communicate
acoustically with the atom. Credit: Martin Gustafsson and Maria Ekström. Source: chalmers.se
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The
theoretical research group, led by Göran Johansson, recently published a paper on how the
acoustic atom functions:
The research was funded by
the Swedish Research Council, the Knut and Alice Wallenberg Foundation, the
European Research Council and the Wenner-Gren Foundations.
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Microscope image:
Zoom-in of the artificial atom, with its integrated Superconducting Quantum
Interference Device (SQUID) in violet. The SQUID gives the atom its quantum
properties, and the fingers sticking up to the left provide the coupling to sound waves. Credit: Martin Gustafsson and Maria Ekström. Source: chalmers.se
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This report was prepared with materials from both Daily Mail and Chalmers school website.
