Calculate faster with quasiparticles

Majorana particles are very particular members of the family of elementary particles. Planned for the first time in 1937 by the Italian physicist Ettore Majorana, these particles belong to the group of so-called fermions, a group that also includes electrons, neutrons and protons. Majorana fermions are electrically neutral and also have their own antiparticles. These exotic particles can, for example, emerge as quasi-particles in topological superconductors and constitute ideal building blocks for topological quantum computers.

Go to two dimensions

On the road to such quantum quantum computers based on Majorana quasiparticles, physicists from the University of Würzburg and colleagues from Harvard University (USA) have reached an important milestone: whereas previous experiences in this area were mainly focused on one-dimensional systems. Würzburg and Harvard teams managed to switch to two-dimensional systems.

In this collaboration, the groups of Ewelina Hankiewicz (Theoretische Physik IV) and Laurens Molenkamp (Experimental Physik III) of the University of Würzburg have joined the groups of Amir Yacoby and Bertrand Halperin of Harvard University. Their results are presented in the current issue of the scientific journal Nature.

Two superconductors can simplify things

"Making Majorana fermions is one of the most studied topics in condensed matter physics," says Ewelina Hankiewicz. According to her, previous achievements generally focused on one-dimensional systems such as nanowires. She explains that a manipulation of Majorana fermions is very difficult in these configurations. It would therefore be necessary to make considerable efforts to make the Majorana fermions in these configurations finally applicable to quantum computing.

In order to avoid some of these difficulties, the researchers studied Majorana fermions in a two-dimensional system with strong spin-orbit coupling. "The system we are studying is a phase controlled Josephson junction, that is, two superconductors separated by a normal region," explains Laurens Molenkamp. The superconducting phase difference between the two superconductors provides an additional button, which renders unnecessary a complex fine-tuning of the other parameters of the system.

Important step towards improved control

In the material studied, mercury tellurium quantum well coupled to thin-film superconducting aluminum, physicists observed for the first time a topological phase transition involving the appearance of Majorana fermions in controlled Josephson junctions phase.

The experimental setup here is a versatile platform for the creation, manipulation and control of Majorana fermions, which offers several advantages over previous one-dimensional platforms. According to Hankiewicz, "this is an important step in the direction of better control of the Majorana fermions". The proof of concept of a topological superconductor based on a two-dimensional Josephson junction opens up new possibilities for research on Majorana fermions in condensed matter physics. In particular, several constraints of the previous achievements of Majorana fermions can be avoided.

Potential revolution in computer science

At the same time, better control of Majorana fermions represents an important step towards topological quantum computing. Theoretically, such computers can be considerably more powerful than conventional computers. They have the potential to revolutionize computer technology.

Next, the researchers plan to improve Josephson junctions and advance to junctions with narrower normal regions. Here, more localized Majorana fermions are expected. They are also studying other possibilities of handling Majorana fermions, for example, using other semiconductors.