  Labouvie \etal (\prl {\bf 115}, 050601, (20015)) recently demonstrated
negative differential conductivity (NDC) in a multi-well Bose-Einstein
condensate. They stated "we demonstrate that NDC originates from a nonlinear,
atom number dependent tunneling coupling in combination with fast collisional
decoherence." We show theoretically how the essential feature of NDC, a
reduction in atomic current caused by an increase in chemical potential, is
present in unitary dynamics through the well-known mechanism of macroscopic
self-trapping (MST), and that the collisional decoherence merely serves as a
quantitative modification of this.
