  We consider a classic two-state switching diffusion model from a
single-particle tracking perspective. The mean and the variance of the
time-averaged mean square displacement (TAMSD) are computed exactly. When the
measurement time (i.e., the trajectory duration) is comparable to or smaller
than the mean residence times in each state, the ergodicity breaking parameter
is shown to take arbitrarily large values, suggesting an apparent weak
ergodicity breaking for this ergodic model. In this regime, individual random
trajectories are not representative while the related TAMSD curves exhibit a
broad spread, in agreement with experimental observations in living cells and
complex fluids. Switching diffusions can thus present, in some cases, an
ergodic alternative to commonly used and inherently non-ergodic continuous-time
random walks that capture similar features.
