Members of Pavlos Lagoudakis’ team in the lab experimenting with polaritons.@ Skoltech
Skoltech physicists are developing light-based organic transistors that can be switched on and off by a single photon and unconventional computers capable of solving problems that are currently unsolvable using supercomputers. These two very different applications both exploit particle-like entities known as polaritons.
Polaritons are curious hybrids, being half light and half matter. They form when a photon combines with an electronic transition, a hydrogen-like atom produced when an electron pairs up with a positive hole. Polaritons thus combine the properties of light with those of matter. “Polaritons combine the best of both worlds — the speed of light with electrons’ ability to interact,” explains Professor Pavlos Lagoudakis, head of Skoltech’s Hybrid Photonics Laboratories at the Skoltech Photonics Center. “At high densities, polaritons come together to form micron-scale droplets of liquid light. We’re developing technologies based on these interacting droplets of liquid light.”
Transistors are the building blocks of modern electronics and computing. By using polaritons, Lagoudakis and his team have realized an organic transistor that operates 100–1,000 times faster than its electronic counterparts. “Since our transistor works with photons instead of electrons, it is much faster than electronic transistors,” he says. “In the future, by incorporating ultrafast optical processors in supercomputers, it will be possible to overcome computational bottlenecks that arise during parallel processing.”
Lagoudakis’ team recently demonstrated a polariton-based transistor that can be switched on and off by a photon — the smallest parcel of energy that can be practically used. This transistor could greatly reduce the energy costs involved in computing. “Computing accounts for a significant percentage of the global electricity consumption, and it’s increasing all the time,” says Lagoudakis. “So if you can make computing greener by using light in computer processors, it could have a large impact on reducing energy consumption.”
Professor Natalia Berloff is using polaritons for another computing application — a polariton simulator that can be used as an analogue computer. Berloff is a theorist, but when a theoretical paper her group wrote got rejected by three journals and a referee wrote the concept off as completely unrealizable, she set out to prove them wrong by demonstrating the idea in collaboration with Lagoudakis’ team.
The result was an analogue computer that can locate the lowest valleys in the landscapes that represent complex problems in fields as diverse as finance, genetics and physics. Conventional computers can solve problems that involve a small number of variables, but they require an inordinate amount of time to solve most real-life optimization problems, which have many variables. In contrast, the polariton simulator lends itself to such problems.
Interestingly, Berloff never set out to develop a computing system for real-life problem; she was initially just interested in a theoretical question. “We were surprised when we realized our system solves this hard, universal problem of optimization,” says Berloff. “This opened the door to addressing a range of interesting problems, since any other real-life problem can be mapped onto this universal problem. It’s an incredibly exciting time to be working in this area,” she adds.
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