Manipulation of the Electron Spins Without Information Loss

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Physicists have developed a new technique to control the electron spin with electrical voltages on a chip. With the newly developed method, the decay of the spin can be suppressed, the information contained can be obtained and transmitted over comparatively large distances. This is demonstrated by a team from the Department of Physics at the University of Basel and the Swiss Nanoscience Institute in a publication in Physical Review X.

Electrons rotate on their way through the chip in a spiral pattern. By changing the voltage, the wavelength of this pattern changes and the orientation of the spin can thus be influenced. At a specific location (gray box), the electron spin has a different orientation depending on the voltage. (Image: University of Basel, Department of Physics)

For some years now, the world has been studying how the spin of the electron can be used to store and transmit information. The spin of each electron is always coupled to its motion, ie its path in the chip. This spin-orbit coupling allows the targeted manipulation of the electron probe by an external electric field, but also causes the decay of the orientation of the spin, which would lead to a loss of information.

In an international collaboration with colleagues from the USA and Brazil, scientists from Professor Dominik Zumbühl of the Department of Physics and the Swiss Nanoscience Institute of the University of Basel have now developed a new method that allows targeted spin manipulation without suffering such a disintegration.

Transmission of the spins over long distances

The scientists have developed a chip on which an electron rotates uniformly on its path through the material without a decrease in the rotation, the orientation of the spin following a spiral pattern - similar to a helix. If the voltages applied by two gate electrodes are changed, this affects the wavelength of the helix. The orientation of the spin can thus be influenced by a voltage change.

It is mainly the so-called Rashba and Dresselhaus fields, which determine the circular movement of the spins. In the above experiment, the Dresselhaus and the Rashba field can be kept at the same level, while at the same time the overall strength of the two fields can be controlled. In this way the decay of the spins can be suppressed.

Thus, the researchers can adjust the orientation of the spins over voltages of more than 20 micrometers. On a chip are the very long distances corresponding to many revolutions of the spins. Thus, for example, spin information could be transmitted between different quantum bits.

Adjust the fields with electrical voltages

This method is only possible by experimentally demonstrating for the first time that not only the Rashba-field, but also the Dresselhaus field can be adjusted with electrical voltages. Although this was predicted more than 20 years ago in a theoretical work, it could only now be demonstrated by a newly developed measurement method based on quantum interfering effects at low temperatures near absolute zero. It is, however, expected that the control of the helix with voltages will also function at higher temperatures and even at room temperature.

Basis for further development

"With this method, we can not only influence the spin orientation in situ but also control the transfer of electron spins over longer distances without losses," notes Dominik Zumbühl. The excellent collaboration with colleagues from Universidade de Sao Paulo, the University of California and the University of Chicago is the basis for a whole new generation of devices that build on spin-based electronics and creates prospects for further experimental work.