  We study the transient dynamics subject to quantum coherence effects of two
interacting parallel quantum dots weakly coupled to macroscopic leads. The
stationary particle current of this quantum system is sensitive to
perturbations much smaller than any other energy scale, specifically compared
to the system-lead coupling and the temperature. We show that this is due to
the presence of a parity-like symmetry in the dynamics, as a consequence of
which, two distinct stationary states arise. In the presence of small
perturbations breaking this symmetry, the system exhibits metastability with
two metastable phases that can be approximated by a combination of states
corresponding to stationary states in the unperturbed limit. Furthermore, the
long-time dynamics can be described as classical dynamics between those phases,
leading to a unique stationary state. In particular, the competition of those
two metastable phases explains the sensitive behavior of the stationary current
towards small perturbations. We show that this behavior bears the potential of
utilizing the parallel dots as a charge sensor which makes use of quantum
coherence effects to achieve a signal to noise ratio that is not limited by the
temperature. As a consequence, the parallel dots outperform an analogous
single-dot charge sensor for a wide range of temperatures.
