报告人：Alexey Kavokin教授   

主持人：孙政研究员   

时间：2021年11月05日（周五）上午10：00-12：00   

地点：光学大楼B325，zoom会议id：6108034229，密码：111111   

报告人简介：

Alexey V. Kavokin is a Russian and French theoretical physicist and writer. He is an expert in solid state optics and semiconductor physics. He graduated from the Saint Petersburg Polytechnical University in 1991. He was a member of staff of the Ioffe Physico-Technical institute (1992 – 2000). He graduated from the Ioffe Physico-Technical institute in 1993, with a PhD in physics and mathematics. He was a Professor at the Blaise Pascal University (Clermont-Ferrand, France, 1998 – 2005). He was a Professor at the University of Southampton (Southampton, United Kingdom, 2005 – present). In July 2010, he co-founded the Mediterranean Institute of Fundamental Physics with the support of Dr. Giuseppe Eramo and was appointed scientific director. Since 2011, he was the head of the Spin Optics Laboratory at the University of Saint Petersburg. Since 2014 he was a Head of the Quantum Polaritonics group at the Russian Quantum Center. In 2018, he joined the Westlake University (Hangzhou, China) as a Chair Professor and Director of the International Center for Polaritonics.

报告内容：

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. We argue that a valuable alternative to superconducting flux qubits may be offered by qubits based on superfluid currents of quasiparticles of liquid light: exciton-polaritons, propagating in plane of semiconductor microcavities. 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. We argue that qubits based on split-ring polariton condensates may be characterized by a very high figure of merit due to the topological protection of superfluid circular currents. Moreover, as the Bose-Einstein condensation and superfluidity of exciton-polaritons were observed at the room temperature, quantum networks based on polariton qubits would not require cryogenic operation temperatures. This makes them a valuable alternative to superconducting qubits.