A research team from Skoltech and the University of Wuppertal in Germany determined that an all-optical universal logic gate that was previously developed at Skoltech can operate at a speed of 240 GHz at room temperature. In an article published in the Physical Review B journal, the authors also examined what limits the time between successive polariton condensations by examining the effect of bimolecular quenching — it plays a key role in limiting the speed of transistors. The research was supported by the Russian Science Foundation grant No. 23-72-00059.

The Skoltech Laboratory of Hybrid Photonics, headed by Distinguished Professor Pavlos Lagoudakis, Senior Vice President for Fundamental Research at Skoltech and a laureate of the Vyzov Scientific Prize, continues its research project on how to speed up computing and computers with optics. To perform more tasks, computers need fast processors, but semiconductor electronics cannot handle this task — they heat up very quickly from high clock speeds. Alternatively, optical systems can operate a thousand times faster than electronic ones.

Previously, the scientists created a universal NOR logical element (from NOT — a negation operator and OR — a disjunction operator). It is based on polariton condensates, operates at room temperature, has multiple inputs, can work hundreds of times faster than electronic analogues, and is also completely optical — that is, it works without electric current. Such elements can be reproduced and connected in a circuit.

The speed of polariton transistors is determined by how quickly consecutive logic states can be executed. This process requires sufficiently depleting the residual polariton population from the previous “1” state to ensure a clear distinction between the “1” and “0” logic states. As operational frequency increases, the residual polaritons from the first pulse can unintentionally amplify the second pulse, thus creating a maximum amplification at some nonzero time delay between pulse sequences.

“Our new study has revealed that our logic gate can operate at 240 GHz. We also described the effect of bimolecular quenching, which is important to consider when calculating, since it limits the maximum clock frequency of a polariton device — delocalization of polaritons leads to additional losses,” said Mikhail Misko, the lead author of the study, a PhD student of the Physics program at Skoltech.

The authors concluded that their observations reinforce theoretical predictions. The researchers proposed a model that considers k-dependent losses in order to successfully compare experimental data from various trials. The study outlines that for optimal performance, the duration of pump pulses must be shorter than the characteristic times of relevant processes in order to effectively manage polariton dynamics and enhance the functionality of optical logic devices.

The results of the study were another important step towards the creation of optical computers that can work hundreds of times faster than traditional computers.