<p>The coherent manipulation of a quantum wave is at the core of quantum sensing. For instance, atom interferometers require splitting and recombination processes to map the accumulated phase shift into a measurable population signal. Although Bose-Einstein condensates (BECs) are the archetype of coherent matter waves, their manipulation in double-well potentials has been limited by the strong interparticle collisions dominating over the tunneling energy. Here, we overcome this problem by using BECs with tunable interactions trapped in an innovative array of double-well potentials and exploiting quantum tunneling to realize coherent beam splitting. We operate several Mach-Zehnder interferometers in parallel, canceling common-mode potential instabilities by a differential analysis, thus demonstrating a trapped-atom gradiometer. Furthermore, by applying a spin-echo protocol, we suppress additional decoherence sources and approach unprecedented coherence times of one second. Our interferometer will find applications in precision measurements of forces with a sub-micron spatial resolution and in linear manipulation of quantum entangled states for sensing with sub-shot-noise sensitivity.</p>