Physicists grew microdiamonds with tin for quantum computers

Physicists grew microdiamonds with tin for quantum computers

For the first time in the world, scientists have grown diamonds with an admixture of tin several micrometers in size in microwave plasma. Such crystals are able to absorb and re-emit visible light, which can potentially be used to transmit information between elements of quantum computers. The results of the study, supported by a grant from the Presidential Program of the Russian Science Foundation (RNF), were published in the journal Philosophical Transactions of the Royal Society A.

Quantum computers allow solving some tasks – for example, modeling molecular systems – much faster than the most powerful “classical” supercomputers. They work on the basis of qubits — quantum computing elements that are an alternative to bits in ordinary computers and are capable of performing more complex operations, thereby increasing the speed of calculations.

The role of qubits can be played by impurity coloring centers of tin, germanium or silicon in diamonds. The inclusion of these elements in crystal lattices leads to the appearance of new spin states, which can be used to encode information. The difficulty lies in the fact that such states occur only at extremely low temperatures. In the case of silicon and germanium centers we are talking about temperatures below 1 Kelvin (or -272°C), while tin centers have an operating temperature slightly above 2-5 Kelvin (from -271°C to -268°C). This means that it will be easier and cheaper to develop quantum devices on tin centers. However, there is still no reliable method for the synthesis of large, high-quality diamonds with tin inclusions. The crystals created today are either significantly smaller than the required size, or have insufficiently good optical properties.

Scientists from the A. M. Prokhorov Institute of General Physics of the Russian Academy of Sciences (Moscow) and their colleagues created, for the first time in the world, diamond microparticles with single color centers made of tin in microwave plasma. The authors grew diamonds in a reactor filled with methane and hydrogen. The researchers placed seed crystals of diamond and particles of tin oxide in the installation and heated them with microwave radiation (microwave plasma) to temperatures of about 1000°C. At the same time, methane served as a source of carbon atoms – the “building blocks” for diamond, and hydrogen extracted individual tin atoms from the particles, which first entered the gaseous environment, and then settled on the surface of the diamond and were included in its crystal lattice.

The authors studied the structure of the obtained crystals using a scanning electron microscope. The particles had a size of 2-4 micrometers (which can be compared with the average size of bacteria) and the shape of cubooctahedrons – polyhedra with alternating triangular and rectangular faces – characteristic of high-quality diamonds.

Schematic of the synthesis of diamonds with color centers made of tin. Source: Vadym Sedov

In addition, the researchers evaluated the optical properties of the crystals by studying the luminescence spectra of the samples. The obtained results confirmed that tin particles were indeed embedded in the crystal lattices of some diamonds, but most of the samples turned out to be ordinary diamonds without coloring centers. This emphasizes that it is quite difficult to incorporate tin atoms into diamonds, but the method proposed by the authors allows it to be done.

“Our work proved that it is quite possible to produce high-quality diamonds with tin. Diamonds obtained by our proposed method will be useful in the field of optical temperature sensors, quantum optics, as well as for storing and transmitting quantum information. In the future, we plan to improve the methodology for the synthesis of high-quality films with tin inclusions on macroscopic diamond crystals with a size of several millimeters,” said the head of the project supported by a grant from the Russian Academy of Sciences, Vadym Syedov, Candidate of Physical and Mathematical Sciences, senior researcher of the Laboratory of Diamond Materials of the Russian Academy of Sciences.

Employees of the P.N. Lebedev Institute of Physics of the Russian Academy of Sciences (Moscow), MIREA – Russian University of Technology (Moscow), Moscow Pedagogical State University (Moscow) and the School of Physics and Astronomy of Cardiff University (Great Britain) also participated in the research.

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