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A memory effect that is crucial in electronics has been seen for the first time in a cloud of ultracold atoms. The phenomenon represents a milestone in the emerging field of ‘atomtronics’, which seeks to create a whole new class of devices that use the flow of atoms, rather than electrons, in a circuit.

In atomtronics, clouds of atoms are super-cooled to form a collective quantum state known as a Bose-Einstein condensate (BEC). So far, physicists have used these atoms in analogues of basic electrical components such as transistors1 and capacitors2. Such condensates can also become a superfluid — meaning atoms can flow past obstacles without friction — and be set in motion, circulating inside a ring-shaped trap.

Atomtronics has so far been largely theoretical, but it holds potential for developing entirely new quantum devices, says Gretchen Campbell, a physicist at the University of Maryland in College Park. Publishing today in Nature3, her team is the first to directly see an effect known as hysteresis in an atomtronic circuit. Hysteresis is the dependence of a system not just on its current state, but also on its history. A thermostat, for example, might turn a heating system off as the temperature rises to 21 °C, but will not turn it on again until it falls below 18 °C. This prevents small disturbances from causing big changes.

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