ITMO University Researchers Predict New Quantum Phase Of Matter In Chains Of Oscillating Atoms

The results of this research can be used to control the properties of light and matter and to create quantum memory.

Contemporary physics offers us many opportunities to control the properties of matter. By changing a substance’s composition or external conditions, such as pressure, temperature, or acidity, we can significantly influence the properties of this material.

Similar transformations can be done with the help of light. Both by simply subjecting the matter to high-intensity light beams and by applying a slightly more complicated method – using the so-called ultrastrong coupling of an atom and a photon. As a result of this ultrastrong interaction, a polariton is created. It is a particle that has the properties of both light and matter.

Light and matter
To produce a polariton, we need to create the conditions necessary for a sufficiently intensive interaction between atoms of a substance and photons. To achieve that, we would generally have to put the atoms into an optical resonator, which lets the light in but doesn’t let the photons out easily. They are repeatedly reflected from the inner walls of the resonator, constantly interacting with the atoms inside.

This limitation of polaritons possessing the same energy as photons give or take a specific amount is very important. As this difference depends on the strength of interaction between the light and the substance, when the interaction is strong enough the energy of lower polariton can be lower than the ground state, in which there is no photon in the resonator. It means that the material reaches its lowest energy state not in the ground state of an atom but in a polariton, a particle that is both light and matter. This is what allows us to change the properties of matter, control its conductivity, its magnetic and other properties.

However, placing atoms in optical resonators is not the only way to acquire polaritons. It was previously theoretically predicted that such particles can form from a group of atoms placed above a waveguide – an optical channel with photons streaming inside. ITMO University researchers have proven this as part of a project supported by the Russian Science Foundation.

Using this state we can control the light, prompting its non-classic states. For instance, we can produce single or coupled photons and not a large stream of them as found in a typical laser.