Krzysztof Jachymski

Quantum theory of reactive collisions for 1/r(n) potentials.

We develop a general quantum theory for reactive collisions involving power-law potentials (-1/r(n)) valid from the ultracold up to the high-temperature limit. Our quantum defect framework extends the conventional capture models to include the nonuniversal case when the short-range reaction probability P(re)<1. We present explicit analytical formulas as well as numerical studies for the van der Waals (n=6) and polarization (n=4) potentials. Our model agrees well with recent merged beam experiments on Penning ionization, spanning collision energies from 10 mK to 30 K [Henson et al., Science 338, 234 (2012)].

Broad universal Feshbach resonances in the chaotic spectrum of dysprosium atoms

We report on the observation of weakly bound dimers of bosonic dysprosium with a strong universal

Analytical model of overlapping Feshbach resonances

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Three-Body Interaction of Rydberg Slow-Light Polaritons.

-wave halo character, associated with broad magnetic Feshbach resonances. These states surprisingly decouple from the chaotic background of narrow resonances, persisting across many such narrow resonances. In addition they show the highest reported magnetic moment

Communication: Importance of rotationally inelastic processes in low-energy Penning ionization of CHF3

\ensuremath{\mu}\ensuremath{\simeq}20{\ensuremath{\mu}}_{\mathrm{B}}

Quantum-defect model of a reactive collision at finite temperature

of any ultracold molecule. We analyze our findings using a coupled-channel theory taking into account the short range van der Waals interaction and a correction due to the strong dipole moment of dysprosium. We are able to extract the scattering length as a function of magnetic field associated with these resonances and obtain a background scattering length

Light scattering from ultracold gases in disordered optical lattices

{a}_{\mathrm{bg}}=91(16)\phantom{\rule{0.16em}{0ex}}{a}_{0}

Single-Atom Transistor as a Precise Magnetic Field Sensor

. These results offer prospects of a tunability of the interactions in dysprosium, which we illustrate by observing the saturation of three-body losses.

Experimental and Theoretical Studies of Low-Energy Penning Ionization of NH3, CH3F, and CHF3

Feshbach resonances in ultracold collisions often result from an interplay between many collision channels. Simple two-channel models can be introduced to capture the basic features, but cannot fully reproduce the situation when several resonances from different closed channels contribute to the scattering process. Using the formalism of multichannel quantum defect theory we develop an analytical model of overlapping Feshbach resonances. We find a general formula for the variation of the scattering length with magnetic field in the vicinity of an arbitrary number of resonances, characterized by simple parameters. Our formula is in excellent agreement with numerical coupled channels calculations for several cases of overlapping resonances in the collisions of two

Ultracold atoms in quasi-one-dimensional traps: A step beyond the Lieb-Liniger model

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