Speech Title: Qubits based on Split-Ring Condensates of Exciton Polaritons
Abstract: Superconducting flux qubits are based on a superposition of clock-wise and anti-clockwise currents formed by millions of Cooper pairs. In order to excite the system in a superposition state, the half-quantum flux of magnetic field is passed through the superconducting circuit containing one or several Josephson junctions. The system is forced to generate a circular current to either reduce the magnetic flux to zero or to build it up to a full-quantum flux. Circular currents of exciton-polaritons mimic the superconducting flux qubits being composed by a large number of bosonic quasiparticles that compose a single quantum state of a many-body condensate. The essential difference comes from the fact that polaritons are electrically neutral, and the magnetic field would not have a significant effect on a polariton current. We note however, that the phase of a polariton condensate must change by an integer number of 2π, when going around the ring. If one introduces a π-phase delay line in the ring, the system is obliged to propagate a clockwise or anticlockwise circular current to reduce the total phase gained over one round-trip to zero or to build it up to 2π. We show that such a π-delay line can be provided by a dark-soliton embedded into a ring condensate and pinned to a potential well created by the C-shape non-resonant pump-spot. The physics of resulting split-ring polariton condensates is essentially similar to the physics of flux qubits. In particular, they exhibit pronounced Bloch oscillations passing periodically through clockwise and anticlockwise current states as Figure 1 shows. We argue that qubits based on split-ring polariton condensates may be characterized by a high figure of merit that makes them a valuable alternative to superconducting qubits. (details)
Biography: Professor Alexey Kavokin has received his PhD in Physics from the Ioffe Institute of Russian Academy of Sciences in 1993. In 1998 he has become a Professor of the Blaise Pascal University, Clermont-Ferrand, France. In 2005 he has joined the University of Southampton, United Kingdom, as a Chair of Nanophysics and Photonics. In 2018 he has moved to China where he now works as a Chair Professor and Director of the International Center for Polaritonics at the Westlake university, Hangzhou. The track record of Prof. Kavokin includes over 400 publications mostly devoted to the physics of strongly coupled light-matter systems. He authored the monographs “Cavity polaritons” (Elsevier, 2003) and “Microcavities” (Oxford University Press, 2007, 2013). His awards include the Marie Curie Chair of Excellence in Rome (2006), the Megagrant of the Government of Russian Federation (2011) and the Established Career Fellowship of the EPSRC (United Kingdom, 2013). Main research achievements include the theory of Polariton lasing, the predictions of Optical Spin Hall and Spin Meissner effect and the series of works toward observation of the Light Induced Superconductivity.