Public exhibit for demonstrating the quantum of electrical conductance

We present a robust setup that demonstrates the quantum of electrical conductance for a general audience. The setup is continuously available in a public space and allows users to manually thin a gold wire of several atoms in diameter while monitoring its conductance in real time. During the experiment, a characteristic step-like decrease in the conductance due to rearrangements of atoms in the cross-section of the wire is observed. Just before the wire breaks, a contact consisting of a single atom with a characteristic conductance close to the quantum of conductance can be maintained for up to several seconds. The setup is permanently available, needs little maintenance and can be used on different educational levels.