  Dissipation can serve as a powerful resource for controlling the behavior of
open quantum systems.Recently there has been a surge of interest in the
influence of dissipative coupling on large quantum systems and, more
specifically, how these processes can influence band topology and phenomena
like many-body localization. Here, we explore the engineering of local, tunable
dissipation in so-called synthetic lattices, arrays of quantum states that are
parametrically coupled in a fashion analogous to quantum tunneling. Considering
the specific case of momentum-state lattices, we investigate two distinct
mechanisms for engineering controlled loss: one relying on an explicit form of
dissipation by spontaneous emission, and another relying on reversible coupling
to a large reservoir of unoccupied states. We experimentally implement the
latter and demonstrate the ability to tune the local loss rate over a large
range. The introduction of controlled loss to the synthetic lattice toolbox
promises to pave the way for studying the interplay of dissipation with
topology, disorder, and interactions.
