Physicists at the RUB, working in collaboration with researchers from Grenoble and Tokyo, have succeeded in taking a decisive step towards the development of more powerful computers. They were able to define two little quantum dots (QDs), occupied with electrons, in a semiconductor and to select a single electron from one of them using a sound wave, and then to transport it to the neighbouring QD.
3 D diagram: the electrons are yellow; the waves in the crystal are presented in red
A single electron “surfs” thus from one quantum dot to the next like a fish on a wave. Such manipulation of a single electron will in the future also enable the combination of considerably more complex quantum bits instead of classical bits (“0” and “1” states). The researchers have reported their results in “Nature”, one of the highest-impact-factor international scientific journals.
Semiconductor physics: a fisherman’s dream
Electrons can move as freely as fish in water in electric conductors (metals) and semiconductors such as silicon (Si) or gallium arsenide (GaAs), albeit not “swimming” of their own but moving owing to differences in voltage. Inside a metal, they are present as a huge number of fish that fill nearly the entire volume of water. In semiconductors, this “fish density” is not as high and so the distance between the electrons (fish) is much larger. The electrons can be concentrated in a thin layer near the surface by the application of an external voltage. The new method that the international team of researchers has developed now fulfils this “fisherman’s dream” for semiconductor physicists. The electron “fish” are all in one layer close to the surface and easily, individually accessible from the surface.
Fishing one from the quantum dot
Prof. Andreas Wieck, physicist at the RUB, points out that there are, however no, “big fish,” all electrons being similar and even always identical, undistinguishable objects. The method that the researchers from Germany, France and Japan used, nevertheless enables the “emission” of individual electrons from the QD, moving them over a specific distance and then detecting them at the neighbouring QD. A distance of four micrometres (μm) was used in the experiment – this is twenty times larger than a highly integrated transistor. Targeted transport of individual electrons is possible in the following way: First, a QD is defined between the tips of four electrodes to form this zero-dimensional object, containing some hundred electrons. The scientists subsequently send a sound wave along the semiconductor surface using interdigital (like two combs fitted together without touching each other) electrodes to which they apply a radio frequency voltage. This method functions in the opposite way as the electrical discharge of a piezo ignition system in which a crystal is deformed to attain a voltage. The researchers applied voltage to the crystal and thus deform it, and the alternating voltage leads to the formation of a sound wave.
The fish surfs on the wave
In a sample, this wave moves, for example, from left to right through the quantum dot at the velocity of sound – inside the crystal at three kilometres per second. Its height is adjusted so that it extracts exactly one “fish” from it. The latter subsequently surfs on the wave in a one-dimensional channel. The “fish” arrives at the neighbouring quantum dot 4 μm to the right thereof. The researchers were able to attain good statistics by repetition of the waves and measurements and thus capable of determining the reliability of the method. During the first experiments, the probability of emission and detection of a single electron with the wave was 96 and 92%, respectively.
The innovation: aligning the fish
It is not possible to differentiate between the electrons “fish”, but they can be differently aligned because they rotate like little spinning tops. This is called the “spin” of the electron. For example one can align a fish with “its head upwards,” let it be transported with the wave, and then detect it again at the target quantum dot still having “its head upwards.” The time for the spin to change is longer than the surfing time on the wave, so the probability of this occurring is very high. The quantum bits of the future will also consist of such spin-polarized electrons. The researchers attained their results with samples prepared by so-called molecular beam epitaxy at the chair of Applied Solid State Physics at the Ruhr University Bochum. They were structured in Tokyo and subsequently measured in Grenoble. But not only the samples, also a further development of this concept originates from Bochum: Prof. Wieck already published his vision of an electron directional coupler with two parallel one-dimensional channels, in which the electrons can skip from one to the other channel, 21 years ago. The research team has in the meantime realized this vision based on the results presented here. A further publication is therefore to follow shortly.
Sylvain Hermelin, Shintaro Takada, Michihisa Yamamoto, Seigo Tarucha, Andreas D. Wieck, Laurent Saminadayar, Christopher Bäuerle and Tristan Meunier: Electrons surfing on a sound wave as a platform for quantum optics with flying electrons. DOI: 10.1038/nature10416
Further InformationProf. Dr. Andreas Wieck, Angewandte Festkörperphysik, Fakultät für Physik und Astronomie der RUB, Tel. +49 234 32 26726, E-Mail: email@example.com
Editor: Jens Wylkop
Dr. Josef König | idw
Quantum optics allows us to abandon expensive lasers in spectroscopy
22.11.2017 | Lomonosov Moscow State University
Nano-watch has steady hands
22.11.2017 | University of Vienna
The WHO reports an estimated 429,000 malaria deaths each year. The disease mostly affects tropical and subtropical regions and in particular the African continent. The Fraunhofer Institute for Silicate Research ISC teamed up with the Fraunhofer Institute for Molecular Biology and Applied Ecology IME and the Institute of Tropical Medicine at the University of Tübingen for a new test method to detect malaria parasites in blood. The idea of the research project “NanoFRET” is to develop a highly sensitive and reliable rapid diagnostic test so that patient treatment can begin as early as possible.
Malaria is caused by parasites transmitted by mosquito bite. The most dangerous form of malaria is malaria tropica. Left untreated, it is fatal in most cases....
The formation of stars in distant galaxies is still largely unexplored. For the first time, astron-omers at the University of Geneva have now been able to closely observe a star system six billion light-years away. In doing so, they are confirming earlier simulations made by the University of Zurich. One special effect is made possible by the multiple reflections of images that run through the cosmos like a snake.
Today, astronomers have a pretty accurate idea of how stars were formed in the recent cosmic past. But do these laws also apply to older galaxies? For around a...
Just because someone is smart and well-motivated doesn't mean he or she can learn the visual skills needed to excel at tasks like matching fingerprints, interpreting medical X-rays, keeping track of aircraft on radar displays or forensic face matching.
That is the implication of a new study which shows for the first time that there is a broad range of differences in people's visual ability and that these...
Computer Tomography (CT) is a standard procedure in hospitals, but so far, the technology has not been suitable for imaging extremely small objects. In PNAS, a team from the Technical University of Munich (TUM) describes a Nano-CT device that creates three-dimensional x-ray images at resolutions up to 100 nanometers. The first test application: Together with colleagues from the University of Kassel and Helmholtz-Zentrum Geesthacht the researchers analyzed the locomotory system of a velvet worm.
During a CT analysis, the object under investigation is x-rayed and a detector measures the respective amount of radiation absorbed from various angles....
The quantum world is fragile; error correction codes are needed to protect the information stored in a quantum object from the deteriorating effects of noise. Quantum physicists in Innsbruck have developed a protocol to pass quantum information between differently encoded building blocks of a future quantum computer, such as processors and memories. Scientists may use this protocol in the future to build a data bus for quantum computers. The researchers have published their work in the journal Nature Communications.
Future quantum computers will be able to solve problems where conventional computers fail today. We are still far away from any large-scale implementation,...
15.11.2017 | Event News
15.11.2017 | Event News
30.10.2017 | Event News
22.11.2017 | Business and Finance
22.11.2017 | Physics and Astronomy
22.11.2017 | Physics and Astronomy