06.12.2017 change 06.12.2017

Wrocław physicists are investigating how to protect spins from the environment

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Data storage in electron spins is one of the quantum computer methods considered by scientists - but it is very sensitive to external factors. Physicists from Wrocław are working on ways to protect the spins and data stored in them.

We are still far from quantum computers that would have the functionality of traditional computers. "However, we are getting closer to identifying an appropriate quantum system in laboratory demonstrations" - told PAP Prof. Paweł Machnikowski from the Faculty of Fundamental Problems of Technology, Wrocław University of Technology.

Spintronics is often mentioned as a field the development of which may contribute to the implementation of the quantum computer vision. This technique of coding and processing information is an alternative to today\'s electronics. While in traditional electronics electron charge is used for data storage, spintronics uses another fundamental property of the electron, namely its spin.

Prof. Machnikowski explained that spin can be imagined as an arrow attached to an electron. "Spin is different from the classic bit, which can be either 0 or 1, because this arrow can be rotated in any direction - the number of possible states is much higher" - he described. However, to use these states in computers, advanced methods of switching them need to be developed.

"The next step after recording the information in the spins is finding a way to operate these spins at the quantum level" - said the PAP interviewee. "The goal is to control a single particle: isolate it from the environment and control its state. If we were able to write a bit of data in memory based on a single spin - it would be the physical limit of the information storage density, it would no longer be possible to generate a denser data storage".

Prof. Machnikowski\'s research concerns structures called quantum dots. "This term refers to small semiconductor structures in which carriers of charges, or electrons can be captured" - said the physicist. This, in turn, opens the possibility of manipulating various properties of the captured electron, such as its spin.

There are different ways to control particle spins. In his research, Prof. Machnikowski wants to use optical methods. This means that the tested structures will be illuminated with laser light in such a way that their quantum properties manifest themselves. "In the future, it may help us reach the development of usable quantum computing" - said Prof. Machnikowski. He explained that optical methods are very fast by definition: light pulses can have durations of about a picosecond (one billionth of a second), which allows to quickly switch spin states. "If it can be done quantum coherently, then it will be possible to realize a quantum computer on such systems" - added the scientist.

But if we know so much about them, why don\'t we have quantum computers on our desks yet? "The main difficulty stems from the fact that a single quantum system is very delicate and sensitive to the influence of the environment" - the researcher explained. "It may even be disturbed by other spins in its vicinity, such as the spins of atomic nuclei in a semiconductor. The result may be an interaction that causes the spins to reverse each other - which will destroy the information stored in them".

The exact nature of the processes through which the environment affects the spins is not known yet. "We know roughly what these factors are, but the dynamics of these processes is not well researched yet. That\'s what we want to focus on: study the interactions of spins with the environment and how they can be protected from external influences" - the researcher told PAP.

As part of the project, Polish scientists cooperate with physicists from the Schottky Institute at the Munich University of Technology. "They can create structures in which exactly one electron can be placed. They can also initiate a spin with laser light - that is, put it in a defined initial state - as well as read its state" - explained Prof. Machnikowski.

Polish physicists will work on the theoretical part of the project. Experiments will be carried out at the Schottky Institute. According to Prof. Machnikowski, the German research group is one of the few groups in the world capable of conducting experiments on a single quantum dot as well as on a pair of coupled dots, the state of which can be controlled both optically and by precise application of electric fields.

The project "Spin qubits in artificial molecules" is being implemented as part of the Polish-German Beethoven grant, from the Polish side financed by the National Science Centre.

PAP - Science in Poland

author: Katarzyna Florencka

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