Robust coherent preparation of entangled states of two coupled flux qubits via dynamic control of the transition frequencies

Abstract

Coherent control and the creation of entangled states are discussed in a system of two superconducting flux qubits interacting with each other through their mutual inductance and identically coupling to a reservoir of harmonic oscillators. We present different schemes using continuous-wave control fields or Stark-chirped rapid adiabatic passages, both of which rely on a dynamic control of the qubit transition frequencies via the external bias flux in order to maximize the fidelity of the target states. For comparison, also special area pulse schemes are discussed. The qubits are operated around the optimum point, and decoherence is modeled via a bath of harmonic oscillators. As our main result, a coherent control scheme is presented which is robust against imperfections in the driving fields, and that enables one to prepare different Bell states consisting of the collective ground and excited states of the two-qubit system.