01.09.2017 change 01.09.2017

New important step towards the topological quantum computer

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Physicists from Warsaw institutes have taken an important step towards the creation of a new, scalable semiconductor platform for quantum computing.

The research was carried out by a group of scientists from the Institute of Physics of the Polish Academy of Sciences and the Research Foundation MagTop (International Centre for Interfacing Magnetism and Superconductivity with Topological Matter). The research was led by Prof. Tomasz Wojtowicz and Grzegorz Karczewski, in collaboration with American scientists at Purdue University in West Lafeyette (Prof. Leonid Rohkinson and Yuli Lyanda-Geller). Researchers from the Institute of Physics informed about the research in a release sent to PAP.

Quantum computers are calculating machines that would use the law of quantum mechanics to compute. Scientists hope that such devices will be much faster and more powerful than currently used computers. One of the greatest challenges the designers of such devices are facing is the problem of decoherence. Systems that allow quantum computing are susceptible to interference and "loss" of information.

These systems are "quantum" objects such as atomic nuclei, semiconducting quantum dots, superconducting tunnel connectors, Bose-Einstein condensates, etc., proposed as "quantum" memory cells that store qubits and quantum gates.

Dekoherence, or information "loss" is related to both quantum fluctuations and the unavoidable influence of small disturbances related to the quantum objects\' contact with the outside world. In practice, the problem of decoherence means that a quantum computer will make calculation errors after a fraction of a second.

Of the many proposed solutions to the problem of decoherence, alongside more or less complex error correction schemes, the most promising seems to be the use of so-called topological invariants, that is, the physical properties associated with deep symmetries that remain unchanged by the small local disturbances of the system. For years, researchers have been searching for systems and physical objects that on the one hand would enable the construction of the basic "blocks" of quantum computers, memory qubits and quantum gates, and on the other would have the required topological attributes.

One of the possible implementations of a scalable and technologically interesting system in which topological excitation can be stimulated has been presented by a team of American and Polish Physicists in the latest issue of Physical Review Letters (https://journals.aps.org/prl/abstract/10.1103/PhysRevLett. 119.046803).

The authors have proposed and demonstrated experimentally that a single domain wall can be generated in a controlled way in a quantum Hall ferromagnetic material using local electrostatic gates. Quantum Hall ferromagnetic material is formed in two-dimensional electron gas when two energy levels of electrons with opposite spins intersect in the presence of a strong magnetic field in the quantum Hall effect.

The results of the Polish-American group of scientists are an important step towards the creation of a universal semiconductor platform for quantum computing, based on a modifiable network of one-dimensional helical channels, in which quantum operations will be realized by simply applying voltage to gates.

Detailed information is available on the Institute of Physics PAS website http://press.ifpan.edu.pl/news/17/08/IFPAN170816.html

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