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Experiments on ultra-cold quantum gases
Efimov physics with ultra-cold atoms: Universality of the few-body Efimov parameter
Physics governing few-body bound states has attracted the attention of physicists for a long time. In 1970, Vitaly Efimov predicted an infinite series of trimer states with universal geometric scaling for a system of three identical bosons with resonant two-body interaction. Counterintuitively, these trimer states can exist even in the absence of corresponding two-body bound states. This exotic phenomena predicted for a variety of systems ranging from nuclear to atomic and molecular physics eluded observation for 36 years till it was observed in ultra-cold Cs atoms and thereafter for a variety of atomic species.
In our experiment on few-body physics with ultra-cold atoms, we have demonstrated for the first time the universality of the three-body Efimov parameter for narrow Feshbach resonances, the critical scattering length for the appearance of the first trimer state, for narrow Feshbach resonances. We took measurements for both intermediate and narrow resonances, where the three-body parameter was predicted to be non-universal. In contrast, our observed ratio of the three-body parameter with the Van der Waals radius is the same universal ratio as for broader resonances. The universality of the three-body parameter suggests that few-body phenomena in a wide range of physical systems with varying length and energy scales can be understood well using ultra-cold atomic systems.
Publication:
“ Test of the universality of the three-body Efimov parameter at narrow Feshbach resonances”, Sanjukta Roy, Manuele Landini, Andreas Trenkwalder, Giulia Semeghini, Giacomo Spagnolli, Andrea Simoni, Marco Fattori, Massimo Inguscio and Giovanni Modugno, Phys. Rev. Lett. 111, 053202 (2013) (Selected as Editor’s suggestion letter and highlighted in Physical Review Letters))
Highlighted in Physics: New Atomic Trios Follow The Rules
Study of 3D Anderson localisation with Bose-Einstein condensates in disordered potentials
Anderson localisation is an ubiquitous phenomenon occurring in a variety of physicalsystems where propagation of waves occur in a random media such as electrons in solids, light waves, microwaves and sound waves. Anderson localisation was predicted in 1958 in a seminal work by P. W. Anderson. Anderson localisation happens when multiple scattering from random obstacles results in a destructive interference of the waves which leads to suppression of the propagation of the waves resulting in exponentially localised eigenstates. This is in sharp contrast to the Drude-Boltzmann theory of classical transport which predicts that incoherent scattering induces diffusion of particles. In condensed matter physics, Anderson localisation is considered a fundamental phenomenon underlying the physics of certain metal-insulator transitions.
In our experiment, we employ ultra-cold atoms with controlled inter-particle interactions in disordered optical potentials to study 3D Anderson localisation. In 3D, Anderson localisation is particularly interesting to study because of the phase transition from localised to extended states which takes place at the critical energy Ec called the mobility edge. Despite being an important issue in the study of disordered systems, the mobility edge and its dependence on the strength of the disorder have never been precisely measured so far. In this work, we developed novel methods to precisely control the energy of the ultra-cold atomic system in 3D disordered potential and used them to precisely measure the mobility edge and its dependence on the strength of the disorder.
Publication:
“Measurement of the mobility edge for 3D Anderson localization”, G. Semeghini, M. Landini, P. Castilho, S. Roy, A. Trenkwalder, G. Spagnolli, M. Fattori, M. Inguscio and G. Modugno, Nature Physics 11, 554 (2015). (Highlighted in Nature Physics: News and Views).
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