We investigate hyperfine induced electron spin and entanglement dynamics in a
system of two quantum dot spin qubits. We focus on the situation of zero
external magnetic field and concentrate on approximation-free theoretical
methods. We give an exact solution of the model for homogeneous hyperfine
coupling constants (with all coupling coefficients being equal) and varying
exchange coupling, and we derive the dynamics therefrom. After describing and
explaining the basic dynamical properties, the decoherence time is calculated
from the results of a detailed investigation of the short time electron spin
dynamics. The result turns out to be in good agreement with experimental data.Comment: 10 pages, 8 figure
