A transistor. Try making one with laser beams (Image: Glow Images/Getty)

Transistors are at the heart of the electronic circuits that make modern computers possible. Now a transistor that controls the flow of atoms, rather than electrons, could be used as a model to probe the mysterious electrical property of superconductivity.

“We can test concepts for quantum electronics,” says Tilman Esslinger at the Institute for Quantum Electronics in Zurich, Switzerland, who has created the transistor-like object from flowing atoms and light.

Thanks to quantum-mechanical effects, below a certain critical temperature some materials become superconducting: electrons flow through them unhindered by the usual electrical resistance. Because of this, superconductors potentially have many novel applications, such as energy-efficient data centres. But how best to design them for such applications is not known.


One way to gain a better understanding is to build a model using an analogous process called superfluidity. Rather like electrons flowing without electrical resistance, at temperatures close to absolute zero, some atoms turn superfluid, flowing with no friction or physical resistance.

Cigar channel

Esslinger and his colleagues wondered if they could observe the transition from non-superfluid to superfluid, and use this as a model for studying the onset of superconductivity. In doing so, they inadvertently created a device that was the atomic equivalent of a transistor.

Electrical transistors consist of a source and a drain, connected by a semiconducting channel. A voltage applied via a gate sitting above the channel changes the channel’s resistance, either impeding or allowing current to flow. Without meaning to, Esslinger’s team created what amounts to an atomic analogue of this using optical trapping, in which criss-crossing laser beams are used to corral ultracold atoms.

By strategically placing laser beams between a source of gaseous lithium atoms cooled to just 500 nano-degrees above absolute zero, and a reservoir that they could drain into, they created a cigar-shaped channel between the two. Made entirely of light, the channel was 200 micrometres long and 20 wide at its widest point.

Atomic current

As a superfluid, atoms could flow down this channel, from the source to the drain. But the researchers were able to switch the flow off using several more lasers. One was shone at the centre of the cigar, the equivalent of physically pinching the flow of atoms. A second laser, the gate beam, then controlled how tightly this first laser pinched, effectively closing the channel.

When closed, the ultracold lithium gas built up and lost its superfluid properties – but when the channel was opened again, the lithium rapidly recovered superfluid, resistance-free flow. This atomic “current” resembled the switchable electric current in a conventional transistor.

The device is unlikely to show up in a computer anytime soon. Instead, the team hopes to use their transistor-like system to simulate superconducting devices of the future. As atoms are much larger than electrons, they are much easier to observe.

Journal reference: Nature, DOI: 10.1038/nature11613