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ColDSIM Report Summary

Project ID: 307688
Funded under: FP7-IDEAS-ERC
Country: France

Final Report Summary - COLDSIM (Cold gases with long-range interactions: Non-equilibrium dynamics and complex simulations)

Cold gases of electronically excited Rydberg atoms and groundstate polar molecules have generated considerable interest in cold matter physics, by introducing for the first time many-body systems with interactions that are both long-range and tunable with external fields. The overall objective of ColDSIM was “.. the development of theoretical ideas and tools for the understanding and control of non-equilibrium dynamics in these diverse systems and in their mixtures and to analyse emerging many-body phenomena in the classical and quantum regimes of strong interactions”. Within the project duration we have invented new techniques for interaction engineering, some of which have been already realized in experiments, as well as investigated several novel basic phenonema of nature.

Work within ColDSIM has generated new proposals for interaction engineering between atoms and molecules that utilize the outstanding flexibility in design and strength of Rydberg-excited atomic interactions as a tool. For example, exotic Rydberg molecular states can be utilized to generate so-called optical Feshbach resonances with unusually favorable properties for tuning the interactions of cold atoms prepared in their internal groundstate; laser-induced interactions between cold atoms and “warm” molecules may be utilized for dissipative cooling of the latter from the milliKelvin down to the microKelvin regimes, a considerable problem for non-bialkali molecules.

In a series of interdisciplinary works, we have investigated the static and dynamic properties of ensembles of quantum and classical particles that interact via soft-core potentials of the kind obtainable by dressing Rydberg atoms using laser light. These works have led to the predictions of several new phenomena. For example, we have demonstrated that Rydberg atoms trapped in an optical lattice in one dimension realize critical quantum liquids with qualitatively new features with respect to the Tomonaga-Luttinger liquid paradigm [Phys. Rev. Lett. 111, 165302 (2013)]. In these liquids, the relevant degrees of freedom at low energy are not individual particles, rather highly unusual self-assembled clusters of particles and holes, opening up a simple avenue to design exotic quantum many-body phases with basic two-particle interactions. In [Nature Comm. 5, 3235 (2014)] we demonstrated for the first time a model system where so-called “defect-induced supersolidity” (or “Andreev-Lifshitz” scenario for supersolidity) can occur in free space. Supersolidity is a long-sought-for phenomenon in condensed matter physics, corresponding to the coexistence of solid and non-viscous (superfluid) behaviour in a same system. In [Phys. Rev. Lett. 118, 067001 (2017)] we demonstrated a mechanism for structural glass formation for a simple two-dimensional monodisperse ensemble of particles interacting via isotropic, repulsive, ultrasoft particles, in the absence of any disordered substrates. This is surprising as those conditions are usually associated with minimal frustration. Due to the generality of the underlying mechanism, these results may find applications in fields as diverse as classical colloidal physics and vortex matter in so-called “type-1.5 superconductors. In [Phys. Rev. Lett. 116, 135303 (2016)] we have shown that glassiness can coexist with superfluidity for ultrasoft Rydberg dressed particles trapped in optical lattices, forming an exotic “superglass” phase.
In a series of works, we aimed at elucidating basic properties of many-body systems with long-range couplings, such as power-law interactions and particle hopping. For example, we have introduced an exactly solvable “Kitaev-type” model [Phys. Rev. Lett. 113, 156402 (2014)] for one-dimensional fermions with long-range pairing and have used it to demonstrate and clarify analytically for the first time new phenomena of relevance to Rydberg atoms, ions, or polar molecules, as well as solid-state setups such as, e.g., magnetic impurities coupled to certain superconductors.

Some exciting results of ColDSIM opened new research directions. For example, we discovered that charge [Nature Mat. 14, 1123 (2015) in collaboration with the experimental groups of Ebbesen and Samori in Strasbourg; Phys. Rev. Lett. 199, 223601 (2017)] and exciton (e.g., Rydberg excitations) [Phys. Rev. Lett. 114, 196403 (2015)] transport in disordered media can be enhanced by coupling intra-molecular / intra-atomic transitions to the bosonic field of a cavity or of a plasmonic structure prepared in its vacuum state. These results may have interesting technological applications, e.g., in designing novel diodes or vertical transistors [News and Views, “Organic electronics: Something out of nothing”, Nature Mat. 14, 1077 (2015)].

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