  Electronic transport through a quantum dot chain embodied in an Aharonov-Bohm
interferometer is theoretically investigated. In such a system, it is found
that only for the configurations with the same-numbered quantum dots
side-coupled to the quantum dots in the arms of the interferometer, some
molecular states of the quantum dot chain decouple from the leads. Namely, in
the absence of magnetic flux all odd molecular states decouple from the leads,
but all even molecular states decouple from the leads when an appropriate
magnetic flux is introduced. Interestingly, the antiresonance position in the
electron transport spectrum is independent of the change of the decoupled
molecular states. In addition, when considering the many-body effect within the
second-order approximation, we show that the emergence of decoupling gives rise
to the apparent destruction of electron-hole symmetry. By adjusting the
magnetic flux through either subring, some molecular states decouple from one
lead but still couple to the other, and then some new antiresonances occur.
