As the atoms flow

Samuel Häusler and his colleagues in the Esslinger group have now implemented in their setup an analogue of a method known in semiconductor electronics as scanning-gate microscopy⁵. Using this method the team, led by Jean-Philippe Brantut (now at the École polytechnique fédérale de Lausanne), observed currents that originate mainly from quantum tunneling — a regime that is out of reach for its electronic counterpart.

In scanning-gate microscopy, a sharp obstacle is placed in a channel and subsequently its effect of the current is recorded. As the obstacle is moved, spatial dependencies of transport properties can be determined. The method has been introduced for studying electronic transport in semiconductor nanostructures, where electrically conductive tips are used as probes. In the experiments of the ETH physicists, in contrast, neutral atoms are transported through structures defined by light fields and a tightly focused laser beam serves as the obstacle (shown above in cyan).

With their novel method, Häusler et al. achieved spatial resolutions comparable to the extent of the atomic wave function in the transport channel. Depending on the strength of the tip, the atoms were observed to either flow over or tunnel through it.

The team expects that their flexible scanning-gate microscope for neutral atoms will extent the capabilities of their quantum simulators. In the future, the approach could provide both fresh fundamental insights — for instance into disorder in materials — and a scalable route towards controlling transport at the quantum level in mesoscopic ‘atomtronic’ devices.