Bell-state generation in circuit QED via Landau-Zener tunneling

Abstract

A qubit may undergo Landau-Zener transitions due to its coupling to one or several quantum harmonic oscillators. First we show that for a qubit coupled to one oscillator, Landau-Zener transitions can be used for single-photon generation and for the controllable creation of qubit-oscillator entanglement, with state-of-the-art circuit QED as a promising realization. Second, for a qubit coupled to two cavities, we show that Landau-Zener sweeps of the qubit are well suited for the robust creation of entangled cavity states, in particular symmetric Bell states, with the qubit acting as the entanglementmediator. Finally, for a qubit coupledto an environmentor bath we proposeto employ dissipative Landau-Zener sweeps of the qubit for the detection of bath properties. At the heart of our proposals lies the calculation of the exact Landau-Zener transition probability for the qubit, by summing all orders of the corresponding series in time-dependent perturbation theory.