Illustration of how the BEC torus is cut by a green laser. The laser is rotated about the axis of the torus such that the cut moves through the torus. (Courtesy: K C Wright et al. 2013 Phys. Rev. Lett.)

Physicists create SQUID-like Bose–Einstein condensate

Jan 18, 2013

Physicists in the US have developed an analogue of a superconducting quantum interference device (SQUID) that replaces the superconductor with a Bose–Einstein condensate and measures rotation rather than magnetic flux. They hope that the research will lead to the development of new, ultra-sensitive gyroscopes.

The SQUID is a well-established and extremely sensitive device for measuring magnetic fields that has found a range of commercial applications. At its heart is a loop of superconductor broken by one or two Josephson junctions. These are thin barriers of non-superconducting material that superconducting pairs of electrons are able to tunnel across. SQUIDs rely on the fact that superconducting electrons are all represented by the same wavefunction, which extends around the loop and includes the junctions. This means that the current that flows around the loop – and therefore the magnetic flux through the loop – is quantized at discrete values. If the magnetic flux in the loop increases or decreases, there is an oscillation in the voltage across the Josephson junctions every time the magnetic flux changes by one quanta. These quanta are very small and therefore an extremely small change in magnetic flux can be measured by counting the voltage oscillations.

A Bose–Einstein condensate (BEC) resembles a superconductor because it is a collection of ultracold atoms that is represented by the same wavefunction and flows as a superfluid without mechanical resistance. If a BEC is confined in a loop, the superfluid can flow around forever – at least in principle – and the angular momentum of the BEC is quantized much like current is quantized in a superconductor loop.

Read more: Physicists create SQUID-like Bose–Einstein condensate – physics world.

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