Quantum dots are nanometer—sized semiconductor objects in which electrons are "trapped" in a very small volume, which makes their energy spectrum discrete, like that of atoms. This directly affects optics: a quantum dot can emit light of a strictly defined wavelength, and it can be "tuned" by the size of the structure itself.

According to scientists, promising semiconductor devices of the future require not just arrays of a large number of randomly located quantum dots, but complexes of a small number of such objects with a predetermined location. Of particular interest is the case of three points at the vertices of an equilateral triangle: in such geometry, the effects of charge distribution frustration and controlled quantum connections between qubits arise. This is important for quantum simulators, logical operations, and quantum information processing.

Until now, such structures have mainly been created by lithography, through the formation of electrodes over a two—dimensional electron gas that set the position of quantum dots. Simply put, they first "draw" a very thin pattern on the surface of the material, and then use electric gates to force electrons to gather in the right places, forming quantum dots.

The method is widely used, but it has limitations: a relatively weak quantum constraint (that is, electrons are not held as "rigidly" as we would like for ideal quantum effects), weak optical properties, and complex manufacturing technology.

In a new paper, researchers from the SFedU Laboratory of Epitaxial Technologies have proposed a different approach — epitaxial growth, in which quantum dots form and self-organize directly during crystal growth. At the same time, the predefined geometry of the surface "directs" their location, making it possible to obtain stable triple complexes.

According to the scientists, this approach provides high structural quality and pronounced quantum effects, and also opens the way to photonic applications, in particular, to sources of entangled photons for quantum technologies. The high selectivity of the formation of triple quantum dots is noted separately: up to 93% of quantum dots end up in target positions, which is important for scaling the method.

"In such works, it is important that for the first time it was possible to combine two usually conflicting approaches: the exact geometry specified by surface treatment technology and the subsequent self-organization of quantum dots during epitaxy. In fact, this is an attempt to get "semi—manual" control of the quantum architecture — when you don't cut out the structure with lithography, but set the conditions for it to assemble itself in the right way," said Sergey Balakirev, PhD, leading researcher at the Center for Advanced Technologies of Micro and Optoelectronics and the Institute of Epitaxial Technologies. Associate Professor of the Electronics Division at SFedU.

Why is this important for humanity? The ability to grow such triangular complexes opens up a new path to creating scalable quantum processors where qubits must interact in a strictly defined way. In addition, it allows the construction of quantum simulators for simulating complex molecules and materials, which can lead to important results in the development of new drugs, superconductors or efficient batteries. Finally, sources of entangled photons based on such structures are the basis of quantum cryptography and the future quantum Internet, where information will be protected by the laws of physics.

The study was supported by Russian Science Foundation Grant No. 23-79-10313 and published in Materials Science in Semiconductor Processing.

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AES SFedU has been operating since 2022, is among the TOP 6 in Russia and is one of the largest Schools in the country. Research is conducted on nanotechnology and nanomaterials, sonar, robotics, photonics, biotechnical systems and technologies, electronics, radio engineering and communication systems.

The advanced engineering school of the Southern Federal University takes into account the interests of industrial partners and contributes to the transformation of the engineering education system. The School was designed as a holding company: partner companies initiate the creation of divisions that are extensions of these companies.

The SFedU's medium–term goal is to ensure the leadership of the Russian Federation in technologies for creating autonomous RTK groups as the main unit of combat operations and the technological future of unmanned vehicles by 2028.