Quantum Fluids Laboratory

Fred M. Ellis - Director

Department of Physics, Wesleyan University, Middletown, CT 06459

Third Sound


Projects and Publications


Low Temperature Physics of Quantum Fluids

At a low enough temperature, the properties of any material become dominated by quantum mechanics. Especially dramatic effects occur in systems which remain fluid-like in this regime. Superconductivity of electrons and superfluidity of liquid helium are examples. In the case of liquid helium, there is much to be learned about the microscopic details of these effects. One reason why this system is particularly difficult to understand is the relatively large interparticle interaction -- a quantity usually assumed small in most theories of many particle systems. The validity of any one of these theoretical approaches can be checked through its predicted effect on macroscopically measurable properties such as heat capacity or viscosity.

I am especially interested in this connection between the macroscopic properties and the microscopic models when the helium is adsorbed on a surface as a thin film. In this case, the physics being probed can be two dimensional. Macroscopic hydrodynamic properties are studied through the velocity and attenuation of thickness oscillations propagating in the film called "third sound". The experimental apparatus consists of a closed box, with the film adsorbed on the inner surfaces, all mounted on a dilution refrigerator able to cool the film down to below 0.05K. The third sound resonances in the box are driven and detected electrostatically with amplitude oscillations observed as either steady state resonances or as free decays.

Several problems are currently being addressed. The attenuation of the sound modes is dominated by three mechanisms: thermal exchange with the substrate, caused by temperature oscillations travelling with the wave; wave induced dissipative motion of pinned vortices (microscopic singularities of rotational flow); and harmonic pumping, in which nonlinearities associated with high amplitude waves transfer energy out of the driven mode into higher order modes. The relative importance of these mechanisms has yet to be determined. The fundamental role of Bose-Einstien condensation in the film is the focus of an experiment attempting to demonstrate the acoustic analog of a laser. Finally, persistent currents and macroscopic quantization of flow are being studied through their mutual interaction with the modes observed in the resonator where effects such as quantum swirling have been identified.

I find that the unique mixture of classical and quantum mechanics makes the study of this system particularly interesting, and enjoy working with my students on these, and related problems.


      Fred M. Ellis, faculty,     fellis@wesleyan.edu

      Josh Eddinger GRAD-ABD,     jeddinger@wesleyan.edu

      Yudhiakto Pramudya, GRAD,     ypramudya@wesleyan.edu

      Joseph Schindler, '2012,     jschindler@wesleyan.edu

Past Students

The past and present members of the Quantum Fluids Laboratory gratefully acknowledge support from Wesleyan University, and the National Science Foundation DMR and REU program.

Go to the Wesleyan Physics Home Page for information on other physics at Wesleyan.

Last update: January 2012.  Send comments or problems with links to fellis@wesleyan.edu .