An international group of scientists based at Aalto University has developed a new ultra-thin material with which they have been able to reproduce the elusive quantum states – Majorana fermions. It is believed that these hypothetical particles could form the basis of a quantum computer with topological qubits. The main feature of these particles is that they are not found in nature. All Majorana fermions created so far are man-made, and each researcher has his own approach.

As you know, a quantum computer is based on a qubit, which is used for high-speed computing. The most widely represented are cryogenic qubits, when the system is cooled to temperatures close to absolute zero. Cooling and shielding reduce the likelihood of qubits interacting with external “stimuli” – thermal, electromagnetic, and other noises that introduce errors into quantum calculations. But even severe isolation does not allow qubits to be in a consistent (coherent) state for a long time (seconds) in order to perform calculations and take the result. Topological qubits are a different matter.

The idea of a quantum computer based on topological qubits was presented by the Soviet, Russian, and later American scientist Alexei Kitaev. The qubit is named topological for the reason that it is extremely stable in its state. It can remain stable for an arbitrarily long time under normal conditions while maintaining the necessary parameters of the environment or the conditions for its formation. For example, it is not destroyed during the measurement, like a “normal” qubit. Needless to say, Microsoft first grabbed the topological qubit and then Intel, not to mention others?

Kitaev proposed to use Majorana fermions as a topological qubit. The point is that this hypothetical particle is simultaneously its antiparticle. As a result, its electric charge tends to zero, and this is indifference to everything in the world, including “irritants”. Just the top of stability and constant demonstration of superposition. But Majorana fermions have not been discovered by anyone, so scientists represent this particle in the form of a quasiparticle, for example, in the form of collective interaction of electrons. And it is this kind of collective interaction of electrons that scientists at Aalto University have modeled.

To create a Majorana zero energy modes (MZM) fermion, very thin 2D materials (two-dimensional) are required. They can be used to create a one-dimensional zero-energy Majorana fermion (1D MZM) or a topological superconductor, also predicted by Kitaev. It is the 1D MZM that Kitaev presented as a possible basis for a topological qubit.

Topological superconductivity arises at the interface between two 2D materials and makes it possible to create traps for Majorana fermions – groups of electrons in our case. It is at the boundary that a one-dimensional space is created, which makes possible the appearance of a qubit in the form of a 1D MZM. One of the materials is a magnetic electrical insulator and the other is a superconductor. The magnetic field of the insulator is relatively weak, so it does not violate superconductivity in the attached superconductor.

In the study under discussion, a topological superconductor consists of a layer of chromium bromide, a material that remains magnetic even at a thickness of only one atom. The team grew islands of chromium bromide one atom thick on the surface of a superconducting niobium diselenide crystal and measured their electrical properties with a scanning tunneling microscope. After a series of simulations, it was concluded that the measured electrical properties of the phenomenon can be confidently represented as a one-dimensional Majorana fermion with zero energy, and not something else.

The researchers believe they have learned how to create one-dimensional MZM from two-dimensional materials, and the next step will be to try to turn them into topological qubits. We add, an article about the study was published the other day in the journal Nature. Quantum computers are one step closer.

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