  Quantum interference is a natural consequence of wave-particle duality in
quantum mechanics, and is widely observed at the atomic scale. One interesting
manifestation of quantum interference is coherent population trapping (CPT),
first proposed in three-level driven atomic systems and observed in quantum
optical experiments. Here, we demonstrate CPT in a gate-defined semiconductor
double quantum dot (DQD), with some unique twists as compared to the atomic
systems. Specifically, we observe CPT in both driven and non-driven situations.
We further show that CPT in a driven DQD could be used to generate adiabatic
state transfer. Moreover, our experiment reveals a non-trivial modulation to
the CPT caused by the longitudinal driving field, yielding an odd-even effect
and a tunable CPT.
