“Liquid light” was used for ultra-fast calculations

In the last decades of spintronics research — technologies that use the spin states of particles to store and process information are steadily moving towards new frontiers. A new study conducted by Chinese scientists reveals the possibility of realizing the coherent optical spin Hall effect (OSHE) at room temperature, which could fundamentally change our understanding of spintronic devices.

The scientific work was published in the journalNature Materials. Exciton polaritons — these are quantum objects (liquid light), which are a superposition of material quasiparticles, excitons (connected electrons and holes) and light quanta, photons placed in special semiconductor microresonators. These unique particles have spin properties, making them ideal candidates for transmitting spin currents over long distances.

Since its inception at the beginning of the 21st century, spintronics has attracted the attention of scientists due to its ability to potentially outperform traditional electronic technologies. However, due to the complex nature of spin interactions and fast spin relaxation, the implementation of spin computing devices proved to be difficult. Previous studies have shown that energy splittings associated with crystal symmetry prevent a stable flow of pure spin current.

If the spin carriers are polaritons, the strong effective magnetic field of polariton microresonators, which quickly rotates the spin of polaritons, which makes it difficult to use the spin current, should be taken into account when creating devices. However, the use of a superfluid polariton liquid formed in an organic-inorganic hybrid FAPbBr microcavity with an isotropic cubic crystal structure overcomes this problem, allowing highly coherent spin currents to be obtained. The spins in such a structure are carried by superfluid polariton flows, which allows solving the problem of rapid dissipation due to thermal fluctuations, allowing the spintronic device to operate at room temperature.

Scientists have also implemented two innovative spintronic devices: a logic NOT gate and a spin-polarized beam splitter. The logic gate is able to change the right circular polarization of the spin to the left and vice versa, and the beam splitter divides the linearly polarized light into two beams with opposite spins. These devices can operate on ultrafast picosecond timescales, far ahead of today's electrical devices that operate on nanosecond timescales. A nanosecond — it is one billionth of a second, and a picosecond is even a thousand times smaller. This means that such spintronic devices will be able to work a thousand times faster than modern electronic ones.

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Physicists performed both theoretical calculations and experimental studies. Theoretical calculations consisted of solving the two-component controlled-dissipative Schrödinger equation, which describes the motion of polaritons. Modeling included calculating the spin components of the wave function and studying the influence of a random potential on spin states. This contributed to a deeper understanding of the processes occurring in polariton flows and made it possible to predict how they could be used in spintronic devices.

The result of the simulation was the prediction that particles of liquid light can propagate ballistically while maintaining a coherent state. The experiment showed that at room temperature, polaritons can fly up to 60 micrometers without destroying their state, which is more than enough for use in spintronic devices as spin current carriers. This was confirmed by observing interference bands.

In addition, theoretical calculations predicted that the spin state of liquid light particles oscillates along the path of its propagation, which makes it possible to control it and invert the polarization using a magnetic field. The described effect was experimentally demonstrated with the help of laser excitation of a supercurrent flow of polaritons. When a linearly polarized laser beam excited a microresonator, the spin states of polaritons were formed depending on the direction of their angular moments. The observed effect allows you to effectively control the direction of spin currents and use them for calculations.

«All-optical logic circuits will be able to provide high data processing speed with low energy consumption, which is especially important in the era of big data and artificial intelligence. Thanks to this, we can expect not only an increase in the performance of modern computer systems, but also the emergence of new innovative applications in the field of quantum computing, information processing and data transmission. This can lead to the creation of more compact, powerful and resistant to external influences devices that can change the approach to the design and architecture of future computer systems.

This work is a significant step forward in the field of spintronics and polaritonics. Scientists have opened new horizons for the practical application of excitonic polaritons at room temperature, which could lead to revolutionary changes in the technologies we use every day.