A quantum fluid is one where the properties of the fluid are strongly influenced by quantum mechanical behaviour. A classic case is liquid helium and in its superfluid phase, which forms at temperatures below 2.2 K, the quantum mechanical effects become particularly extreme.
Laser pump-probe data showing the periodic rotational motion of CO in helium clusters
For example, superfluid liquid helium shows a negligible viscosity, which allows objects to move freely through the medium without any resistance. However, the behaviour of individual molecules in superfluid helium is not well understood. Also, although superfluidity is usually viewed as a property of the bulk liquid, there is recent and remarkable evidence that even a few atoms of helium can behave like a superfluid at very low temperatures.
Femtosecond Laser at the ARTEMIS Facility
In a new project led by Klaus von Haeften (Department of Physics and Astronomy) with collaborating partners Russell Minns (University of Southampton) and Andrew Ellis (Department of Chemistry, Leicester), we are using ultra-fast laser techniques to study the rotation of molecules in small helium clusters. The idea is to use the rate of rotation of molecules as markers of viscosity, which in turn reveals the degree of superfluidity.
These experiments employ sophisticated ultra-fast laser apparatus such as that at the ARTEMIS facility at the Rutherford Appleton Laboratory in Oxfordshire.
Apparatus used for pump-probe measurements (drawn by Gediminas Galinis)
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