  We study a multi-functional device for cold atoms consisting of a
three-terminal ring circuit pierced by a synthetic magnetic flux, where the
ring can be continuous or discretized. The flux controls the atomic current
through the ring via the Aharonov-Bohm effect. Our device shows a flux-induced
transition of reflections from an Andreev-like negative density to positive
density. Further, the flux can direct the atomic current into specific output
ports, realizing a flexible non-reciprocal switch to connect multiple atomic
systems or sense rotations. By changing the flux linearly in time, we convert
constant matter wave currents into an AC modulated current. This effect can be
used to realize an atomic frequency generator and study fundamental problems
related to the Aharonov-Bohm effect. We experimentally demonstrate
Bose-Einstein condensation into the light-shaped optical potential of the
three-terminal ring. Our work opens up the possibility of novel atomtronic
devices for practical applications in quantum technologies.
