Quantum mirages formed by coherent projection of electronic structure

Image projection relies on classical wave mechanics and the use of natural or engineered structures such as lenses or resonant cavities. Well-known ex amples include the bending of light to create mirages in the atmosphere, an d the focusing of sound by whispering galleries. However, the observation o f analogous phenomena in condensed matter systems is a more recent developm ent(1), facilitated by advances in nanofabrication. Here we report the proj ection of the electronic structure surrounding a magnetic Co atom to a remo te location on the surface of a Cu crystal; electron partial waves scattere d from the real Co atom are coherently refocused to form a spectral image o r 'quantum mirage'. The focusing device is an elliptical quantum corral(2,3 ), assembled on the Cu surface. The corral acts as a quantum mechanical res onator, while the two-dimensional Cu surface-state electrons form the proje ction medium. When placed on the surface, Co atoms display a distinctive sp ectroscopic signature, known as the many-particle Kondo resonance(4-6), whi ch arises from their magnetic moment. By positioning a Co atom at one focus of the ellipse, we detect a strong Kondo signature not only at the atom, b ut also at the empty focus. This behaviour contrasts with the usual spatial ly-decreasing response of an electron gas to a localized perturbation(7).