Sudden death of entanglement induced by a minimal thermal environment

We study the dynamics of two interacting two-level systems (qubits) having one of them isolated and the other coupled to a single mode electromagnetic field in a thermal state. The field plays the role of a small environment, in contrast to the usual approach of modeling an environment via a thermal reservoir with many degrees of freedom. We find the analytical solution of the proposed model, which allows us to investigate the consequences of the coupling to the small environment on characteristic quantum features of the two-qubit system. We study the time evolution of quantum entanglement and coherence, verifying the dependence on the relevant coupling constants as well as the influence of the effective temperature of the environment. Interestingly, we find that both sudden death and sudden birth of entanglement may occur in such a simple system. We also discuss a different partition, in which the isolated qubit is considered to be coupled to a composite environment, constituted by the other qubit plus the field mode.Comment: References added; additional figures also included in this versio

Two coupled qubits under the influence of a minimal, phase-sensitive environment

In this work, we investigate the influence of a minimal, phase-sensitive environment on a system of two coupled qubits. The environment is constituted by a single-mode field initially prepared in a type of Schr\"odinger cat state, a quantum superposition of two squeezed coherent states. We present an analytical solution to the model and investigate the degradation of the quantum features of the system due to the action of the environment. In particular, we find that the time-averaged linear entropy for long times, $\bar{S}_T$, has approximately a linear dependence on Mandel's $Q$ parameter as well as on the variance of the $\hat{X}$ quadrature of the initial state of the environment.Comment: 14 pages, 13 figures. This version contains an additional section about the dynamics of quantum coherenc