Quantum dynamical phase transition in a system with many-body interactions

Recent experiments, [G.A. Álvarez, E.P. Danieli, P.R. Levstein, H.M. Pastawski, J. Chem. Phys. 124 (2006) 194507], have reported the observation of a quantum dynamical phase transition in the dynamics of a spin swapping gate. In order to explain this result from a microscopic perspective, we introduce a Hamiltonian model of a two level system with many-body interactions with an environment whose excitation dynamics is fully solved within the Keldysh formalism. If a particle starts in one of the states of the isolated system, the return probability oscillates with the Rabi frequency ω 0 . For weak interactions with the environment 1 / τ SE < 2 ω 0 , we find a slower oscillation whose amplitude decays with a rate 1 / τ ϕ = 1 / ( 2 τ SE ) . However, beyond a finite critical interaction with the environment, 1 / τ SE > 2 ω 0 , the decay rate becomes 1 / τ ϕ ∝ ω 0 2 τ SE . The oscillation period diverges showing a quantum dynamical phase transition to a Quantum Zeno phase consistent with the experimental observations.