Internal Seminar: Konstantinov Unit and Wolf Unit

Join us for September's Internal Seminar Series, from 17:00 to 18:00 in B250, central building.
This month's seminars feature the Quantum Dynamics Unit (Denis Konstantinov) and the Molecular Cryo-Electron Microscopy Unit (Matthias Wolf).

Quantum Dynamics Unit (Denis Konstantinov)

Speaker : Denis Konstantinov

Title : Spectroscopy of superfluid helium-4: probing roton excitations with millimeter-waves

Abstract : Superfluidity, that is ability of a fluid to flow without friction, is one of the remarkable examples of a quantum phenomenon observed at the macroscopic scale. It is believed that onset of the superfluidity coincides with the Bose-Einstein Condensation of helium atoms, that is accumulation of a macroscopic number of atoms in the state of the lowest energy, while the superfluidity is destroyed by thermal excitation of some collective motions of the atoms. The spectrum of these collective motional modes, the elementary excitations, was predicted in a brilliant 1941 paper by L. Landau [1]. He divided them into two categories: sound quanta, the phonons, which correspond to ordinary compression/rarefaction waves in the liquid and much less intuitive motional modes, rotons, which have a non-zero energy minimum, the roton gap. It followed that all properties of superfluid helium at non-zero temperatures could be derived from the presence of thermally excited rotons, thus providing nearly complete theory of superfluidity (L. Landau, 1962 Nobel Prize in Physics). Nevertheless, in spite of a few theoretical attempts to understand the microscopic structure of rotons (e.g. R. Feynman, 1954), the nature of these excitations remains mysterious. Recent experiments by A. Rybalko in Kharkov revealed an astonishing fact: the superfluid helium-4 absorbs and emits electromagnetic radiation at a frequency of about 180 GHz (millimeter wavelength) corresponding exactly to energy of the roton gap [2]. This naturally suggests an analogy between the roton and a quantum two-level system coupled to the microwave photon. Here at OIST we are making experiments to study this hypothesis and shed more light on the long-standing puzzle of rotons.

[1] L. D. Landau, Phys. Rev. 60, 356 (1941).

[2] A. Rybalko et al., Phys. Rev. B 76, 140503R (2007).

Molecular Cryo-Electron Microscopy Unit (Matthias Wolf)

Speaker : Matthias Wolf

Title : A High Throughput Pipeline for Cryo-EM

Abstract : TBA