Single-atom transistors are a novel approach opening intriguing perspectives for quantum electronics and logics at room temperature. They are based on the stable and reproducible operation of atomic-scale switches, which allow us to open and close an electrical circuit by the controlled reconfiguration of silver atoms within an atomic-scale junction. We demonstrate the operation of such atomic quantum switches, and discuss in more detail the process during which these switches are formed by repeated electrochemical deposition and dissolution. Only after repeated deposition/dissolution cycles, a bistable contact is formed on the atomic scale, which allows to switch between a configuration where the contact is closed, the conducting state or “on”-state, and a configuration where the contact is open, the nonconducting state or “off”-state. The controlled fabrication of these well-ordered atomic-scale metallic contacts is of great interest: it is expected that the experimentally observed high percentage of point contacts with a conductance at noninteger multiples of the conductance quantum
( ≈ 1 ∕ 12. 9 kΩ) in conventional experiments with simple metals is correlated with defects resulting from the fabrication process. Our combined electrochemical deposition and annealing method allows the controlled fabrication of point contacts with preselectable
quantum conductance. The resulting conductance measurements on silver point contacts are compared with tight-binding-like conductance calculations of modeled idealized junction geometries between two silver crystals with a predefined number of contact atoms.