Observation of quantized conductance in neutral matter

In transport experiments, the quantum nature of matter becomes directly evident when changes in conductance occur only in discrete steps1, with a size determined solely by Planck's constant h. Observations of quantized steps in electrical conductance2,3 have provided important insights into the physics of mesoscopic systems4 and have allowed the development of quantum electronic devices5.Eventhough quantized conductance should not rely on the presence of electric charges, it has never been observed for neutral,massive particles6. In itsmost fundamental form, it requires a quantum-degenerate Fermi gas, a ballistic and adiabatic transport channel, and a constrictionwithdimensions comparable to the Fermi wavelength. Here we report the observation of quantized conductance in the transport of neutral atoms driven by a chemical potential bias. The atoms are in an ultraballistic regime, where their mean free path exceeds not only the size of the transport channel, but also the size of the entire system, including the atom reservoirs.We use high-resolution lithography to shape light potentials that realize either a quantumpoint contact or a quantumwire for atoms. These constrictions are imprinted on a quasi-twodimensional ballistic channel connecting the reservoirs7. By varying either a gate potential or the transverse confinement of the constrictions, we observe distinct plateaux in the atom conductance. The conductance in the first plateau is found to be equal to the universal conductance quantum, 1/h.We use Landauer's formula tomodel our results and find good agreement for low gate potentials, with all parameters determined a priori. Our experiment lets us investigate quantum conductors with wide control not only over the channel geometry, but also over the reservoir properties, such as interaction strength, size and thermalization rate. © 2015 Macmillan Publishers Limited.