Coupling a nano-trumpet with a quantum dot enables precise position determination

July 14, 2017
Trumpet-shaped nanowires with a length of about 10 micrometers are coupled to quantum dots located at their bases. The movement of the nanowire can be detected with a sensitivity of 100 femtometers by changing the wavelength of the light emitted by the quantum dots. The arrows are important for fabrication and help to locate the nanowires. Credit: Grenoble Alps University

Scientists from the Swiss Nanoscience Institute and the University of Basel have succeeded in coupling an extremely small quantum dot with 1,000 times larger trumpet-shaped nanowire. The movement of the nanowire can be detected with a sensitivity of 100 femtometers via the wavelength of the light emitted by the quantum dot. Conversely, the oscillation of the nanowire can be influenced by excitation of the quantum dot with a laser. Nature Communications published the results.

Professor Richard Warburton and Argovia Professor Martino Poggio's teams in the Department of Physics and the Swiss Nanoscience Institute at the University of Basel worked with colleagues from Grenoble Alps University and the Alternative Energies and Atomic Energy Commission (CEA) in Grenoble to couple a microscopic mechanical resonator with a nano-scale quantum dot. They used made of gallium arsenide that are about 10 micrometers long and have a diameter of a few micrometers at the top. The wires taper sharply downwards and therefore look like tiny trumpets arranged on the substrate. Near the base, which is only about 200 nanometers wide, the scientists placed a single quantum dot that can emit individual light particles (photons).

Excitations lead to strains

If the nanowire oscillates back and forth due to thermal or electrical excitation, the relatively large mass at the wide end of the nano-trumpet produces large strains in the wire that affect the quantum dot at the base. The quantum dots are squeezed together and pulled apart; as a result, the wavelength and thus the color of the photons emitted by the quantum dot change. Although the changes are not particularly large, sensitive microscopes with very stable lasers - specifically developed in Basel for such measurements - are capable of precise detection of the wavelength changes. The researchers can use the shifted wavelengths to detect the motion of the wire with a sensitivity of only 100 femtometers. They expect that by exciting the quantum dot with a laser, the oscillation of the nanowire can be increased or decreased as desired.

Potential uses in sensor and information technology

"We are particularly fascinated by the fact that a link between objects of such different sizes is possible," says Warburton. There are also various potential applications for this mutual coupling. "For example, we can use these coupled nanowires as sensitive sensors to analyze electrical or magnetic fields," explains Poggio, who is investigating the possible applications with his team. "It may also be possible to place several quantum dots on the nanowire, to use the motion to link them together and so pass on quantum information," adds Warburton, whose group focuses on the diverse use of quantum dots in photonics.

Artificial atoms with special properties

Quantum dots are nanocrystals, and are also known as artificial atoms because they behave similarly to atoms. With a typical extent of 10 to 100 nanometers, they are significantly larger than actual atoms. Their size and shape, as well as the number of electrons, can vary. The electrons' freedom of movement in the quantum dots is significantly restricted; the resulting effects give them very special optical, magnetic and electrical properties. For example, are able to emit individual light particles (photons) after excitation, which can then be detected using a tailor-made laser microscope.

Explore further: Researchers use quantum dots to manipulate light

More information: Mathieu Munsch, Andreas V. Kuhlmann, Davide Cadeddu, Jean-Michel, Gérard, Julien Claudon, Martino Poggio, and Richard J. Warburton, Resonant driving of a single photon emitter embedded in a mechanical oscillator, Nature Communications (2017) DOI: s41467-017-00097-3

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dnatwork
not rated yet Jul 14, 2017
So, could you set up an array of these things with interferometers to get even higher sensitivity, and could you replace LIGO with that or improve its sensitivity? Widespread gravity-wave based asstronomy is not going to happen if there's just one LIGO with two or three multi-billion dollar detectors.
eachus
not rated yet Jul 14, 2017
LIGO with that or improve its sensitivity? Widespread gravity-wave based astronomy is not going to happen if there's just one LIGO with two or three multi-billion dollar detectors.

Actually LIGO is now aLIGO, and a detector in Italy (Virgo) has just been upgraded to the point where it can take simultaneous observations with aLIGO. (GEO 600 in Germany has never reached that sensitivity.) The advantage to having three detectors running simultaneously is that the timing data can be used to determine the location of the observation.

The problem as I see it with LISA, the space based observatory, is that currently it is planned to be a "one off." It will be useful when the more sensitive LISA data can be combined with aLIGO to provide directional data, but most LISA observations are expected to be too faint to be detected by aLIGO. So the next move forward will be to provide two more LISA arrays. (Putting one outside the plane of the Solar System will be extra tricky.

dnatwork
not rated yet Jul 14, 2017
And they're going to build one in India.

The thing is, they have upgraded the existing faclities several times, and that's how they finally got detections last year. I think they will have trouble upgrading anything they put into space, so they will need to be able to build something small and cheap so they can just launch a new one when they come up with improvements.

So, starting from 100 femtometres initial sensitivity, could interferometry between these light sources get them down to the level needed for small and cheap gravity wave detection? Just wondering.

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