Split-ring polariton condensate as a macroscopic two-level quantum system

Abstract

Superposition states of circular currents of exciton-polaritons mimic the superconducting flux qubits. The current states are formed by a macroscopic number of bosonic quasiparticles that compose a single quantum state of a many-body condensate. The essential difference between a polariton fluid and a supercurrent comes from the fact that polaritons are electrically neutral, and the magnetic field would not have a significant effect on a polariton current. Nevertheless, the phase of a polariton condensate must change by an integer number of $2\pi$, when going around the ring. If one introduces a $\pi$-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 $2\pi$. We show that such a $\pi$-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 coherent oscillations passing periodically through clockwise and anticlockwise current states. We predict that these oscillations should persist far beyond the coherence time of the polariton condensates. As a consequence the qubits based on split-ring polariton condensates are expected to be characterized by a very high figure of merit that makes them a valuable alternative to superconducting qubits.