Researchers at ITMO have shown that individual atoms can be transformed into polaritons — quantum particles that are a mixture between matter and light, which are transmitted via optical fibers. The research may have applications in quantum computing in the form of quantum memory. The researchers previously used techniques that subject matter to high-intensity light beams; the most common method uses optical resonators that let light in but don’t let the photons out easily. The photons are repeatedly reflected from the inner walls of the resonator, constantly interacting with the atoms inside. After being bombarded with photons, the atoms form bonds with them, facilitating the creation of the quasiparticles. “One of the limitations of this method is that polaritons can only form with the source of light constantly present. It means that when we turn off the light, all the newly acquired properties will return to their initial states. Additionally, more than one atom can fit inside a resonator, which negatively affects the result,” said Ivan Iorsh, a professor in ITMO’s physics and engineering department. The researchers instead turned to an optical waveguide that allows them to provide stronger communication between light and matter, and to subject a whole array of atoms to light. The main principle of the optical resonator method still holds, but the coupling is strong enough that the desired effect can be achieved even without external lighting. The method partially solves the instability problem of quantum memory. “Quantum memory ensures high security of stored information, but it remains relatively fragile. When you attempt to read the data secured in this way, there is a possibility you will lose it. Polaritons are interesting because photons make them perfect for storing units of information called qubits, while atoms ensure they can bond with other quasiparticles and give us more opportunities to control them. Thus, by acquiring long-living quasiparticles, we can increase the resilience of the quantum system as a whole,” Iorsh said. The research was published in Physical Review Letters (www.doi.org/10.1103/PhysRevLett.125.183601).