Scientists Harness 'Liquid Light' to Induce Electric Current in Superconductors

Scientists at HSE MIEM have induced a superconducting current using 'liquid light,' or excitonic polaritons, which are hybrid particles formed by interaction between light and matter and possess the properties of both light and material particles. The ability to manipulate an electrical system through an optical one can be valuable in the development of technologies such as quantum computers. The study has been published in Physical Review B.

When designing a quantum computer, conflicting requirements are imposed on its various components. For instance, a quantum processor should operate fast, whereas quantum memory must acquire and retain information slowly over an extended period, preserving it in a quantum format to prevent damage from environmental factors. Managing the interaction between these two systems poses a challenge that numerous physicists engaged in quantum technologies must confront today.

Researchers at HSE University have investigated the drag effect between superconducting and/or superfluid systems (the Andreev–Bashkin effect) in an unconventional hybrid system comprising two subsystems: a thin superconducting film and an exciton-polariton condensate.

Excitonic polaritons (also referred to as 'liquid light') represent an exotic state of light and matter (a thin semiconductor) trapped between two mirrors. In such a system, light alternates between existing as an exciton (a pair of electrons bound by the Coulomb force and a hole within a semiconductor) and running between the mirrors, which is how a polariton operates. An exciton-polariton liquid exhibits superfluidity, enabling it to 'flow' without energy loss due to friction.

Russian researchers have previously considered a model in which a superconductor sandwiched between mirrors and a semiconductor interacted with excitonic polaritons. A team of researchers led by Yurii Lozovik, professor at HSE University, hypothesised that, beyond the typical interaction, the mutual entrainment effect between a superconductor and excitonic polaritons might also be possible. Positioning a semiconductor between mirrors enables the generation of a superfluid liquid from excitonic polaritons, and its flow can induce an electron current in a superconductor. The authors of the paper computed the potential strength of this effect using realistic parameters for modern semiconductor and superconducting materials.

Each of the subsystems exhibits quantum effects, but electrons in the superconductor move at a slow pace, whereas excitonic polaritons travel very fast. The moving electrons carry an electric charge, while the flow of excitonic polaritons is neutral. Yet, these two very different systems can be connected through mutual entrainment.

Alexey Sokolik
Co-author of the paper, Senior Research Fellow, Laboratory of Mathematical Methods in Natural Science, HSE University

The phenomenon of entrainment can be characterised, for instance, by examining the magnitude of the electric current that will emerge in a superconductor when electrons are entrained. With realistic parameters of the modelled system, the current might be in the range of nanoamps, and this can be experimentally measured.

Azat Aminov
First author of the paper, Doctoral Student, Joint Department of Quantum Optics and Nanophotonics with the RAS Institute for Spectroscopy, Faculty of Physics, HSE University 

According to the researchers, enhancing the effect of mutual entrainment between excitonic polaritons and superconducting electrons holds promise for advancing quantum technologies.
IQ

February 27