  Electrostatic gating is essential for defining and control of semiconducting
devices. However, nano-fabrication processes required for depositing gates
inevitably degrade the pristine quality of the material of interest. Examples
of materials that suffer from such degradation include ultra-high mobility
GaAs/AlGaAs two-dimensional electron gases (2DEGs), graphene, topological
insulators, and nanowires. To preserve the pristine material properties, we
have developed a flip-chip setup where gates are separated from the material by
a vacuum, which allows nanoscale electrostatic gating of the material without
exposing it to invasive nano-processing. An additional benefit is the vacuum
between gates and material, which, unlike gate dielectrics, is free from charge
traps. We demonstrate the operation and feasibility of the flip-chip setup by
achieving quantum interference at integer quantum Hall states in a
Fabry-P\'erot interferometer based on a GaAs/AlGaAs 2DEG. Our results pave the
way for the study of exotic phenomena including fragile fractional quantum Hall
states by preserving the high quality of the material.
