Fast Amplification and Rephasing of Entangled Cat States in a Qubit-Oscillator System

In this work [1], we study a qubit-oscillator system described by the quantum Rabi model with a time-dependent coupling coefficient. and present two schemes. We propose a scheme for the fast generation of entangled Schrödinger-cat states. We propose another scheme for protecting the cat states against dephasing caused by the nonlinearity in the system. We focus on the case where the qubit frequency is small compared to the oscillator frequency. We first present the exact quantum state evolution in the limit of infinitesimal qubit frequency, and then analyze the first-order effect of the nonzero qubit frequency. Our scheme works for systems with wide range of coupling strength, including the ultra-strong and deep-strong coupling regimes [2-5].
[1] Z. Xiao, T. Fuse, et al., arXiv: 1807.04927. [2] T. Niemczyk, et al., Nature Phys. 6, 772 (2010). [3] P. Forn-Diaz, et al., Phys. Rev. Lett. 105, 237001 (2010). [4] P. Forn-Diaz, et al., Nature Phys. 13, 39 (2017). [5] F. Yoshihara, T. Fuse, et al., Nature Phys. 13, 44 (2017).