A sharp step-like structure, which is seen in the current-voltage characteristic of a laterally confined AlGaAs/GaAs resonant tunnelling structure, is a novel manifestation of a quantum effect arising when one-dimensional wires feed electrons into a zero-dimensional quantum box. The authors can analyse the data to deduce a tunnelling time, an inelastic scattering time and the transmission probability for electrons in this system. The height of the current steps, Delta I, gives the electron tunnelling time, tau_e, via Delta I=e/2 tau_e, while the differential conductance gives the peak transmission probability, T₀, via G approximately (e²/h)T₀. The authors must invoke inelastic scattering to explain the low value of T₀ approximately 9% obtained from the data, and so they find that tunnelling in their structure is sequential.