  Recent advances in atomic manipulation techniques have provided a novel
bottom-up approach to investigating the unconventional properties and complex
phases of strongly correlated electron materials. By engineering artificial
condensed matter systems containing tens to thousands of atoms with tailored
electronic or magnetic properties, it has become possible to explore how
quantum many-body effects---whose existence lies at the heart of strongly
correlated materials---emerge as the size of a system is increased from the
nanoscale to the mesoscale. Here we investigate both theoretically and
experimentally the quantum engineering of nanoscopic Kondo lattices -- Kondo
droplets -- that exemplify nanoscopic replicas of heavy-fermion materials. We
demonstrate that by changing a droplet's real space geometry, it is possible to
not only create coherently coupled Kondo droplets whose properties
asymptotically approach those of a quantum-coherent Kondo lattice, but also to
markedly increase or decrease the droplet's Kondo temperature. Furthermore we
report on the discovery of a new quantum phenomenon -- the Kondo echo -- a
signature of droplets containing Kondo holes functioning as direct probes of
spatially extended, quantum-coherent Kondo cloud correlations.
