  Recent years have seen the development of several experimental systems
capable of tuning local parameters of quantum Hamiltonians. Examples include
ultracold atoms, trapped ions, superconducting circuits, and photonic crystals.
By design, these systems possess negligible disorder, granting them a high
level of tunability. Conversely, electrons in conventional condensed matter
systems exist inside an imperfect host material, subjecting them to
uncontrollable, random disorder, which often destroys delicate correlated
phases and precludes local tunability. The realization of a condensed matter
system that is disorder-free and locally-tunable thus remains an outstanding
challenge. Here, we demonstrate a new technique for deterministic creation of
locally-tunable, ultra-low-disorder electron systems in carbon nanotubes
suspended over circuits of unprecedented complexity. Using transport
experiments we show that electrons can be localized at any position along the
nanotube and that the confinement potential can be smoothly moved from location
to location. Nearly perfect mirror symmetry of transport characteristics about
the centre of the nanotube establishes the negligible effects of electronic
disorder, thus allowing experiments in precision engineered one-dimensional
potentials. We further demonstrate the ability to position multiple nanotubes
at chosen separations, generalizing these devices to coupled one-dimensional
systems. These new capabilities open the door to a broad spectrum of new
experiments on electronics, mechanics, and spins in one dimension.
