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ESCQUMA Report Summary

Project ID: 335266
Funded under: FP7-IDEAS-ERC
Country: United Kingdom

Mid-Term Report Summary - ESCQUMA (Exploring Strongly Correlated Quantum Matter with Cold Excited Atoms)

The research project ESCQUMA is designed to deliver a comprehensive and interdisciplinary theoretical study of strongly correlated quantum matter. The platform of choice are atomic gases excited to high-lying Rydberg states in which particles strongly interact. This system offers strong and long-ranged interactions that compete with coherent laser excitation and controllable noise. It is therefore ideally suited to study dynamical and static properties of correlated states of matter. The work of ESCQUMA has for objectives which are set out to characterise ground state phases (O1), dynamical properties of Rydberg gases (O2 and O3) as well as to identify potential technological applications of ESCQUMA’s research findings (O4).
Towards achieving O1 we have investigated the physics of correlated many-body states formed in Rydberg gases with specifically tailored interactions. For example, we have shown that a so-called double dressing approach permits the creation interaction potentials with attractive short range and repulsive long range parts which results in a plethora of interesting crystalline states. We have moreover highlighted that gases in which multiple Rydberg states are excited simultaneously display interesting frustration effects.
In our efforts towards achieving O2 we could reveal an interesting and novel connection between the physics of Rydberg gases in the presence of noise and glassy systems, typically studied in the context of soft-matter physics. We have shown that in some limit the dynamics of a Rydberg gas is mapped onto that of an effective spin system with so-called kinetic constraints. This means that the relaxation pathways in these systems are opened or closed depending on specific local configurations. Precisely such mechanism is successfully used in the soft condensed matter community to formulate idealised models glass forming substances. Rydberg gases now allow to explore this in detail and in principle allow also to understand the role of quantum effects in glassy relaxation.
In pursuing O3 we have characterised the stationary states of Rydberg gases which is formed by the competition between strong interactions, laser excitation and noise. We have clarified that the stationary universal properties of Rydberg gases in their simplest manifestation are described by a classical Ising model. This allowed us to interpret non-linear effects that are currently observed in several Rydberg experiments in terms of the emergence of metastable states. This led us to a general theory describing metastabilility in open quantum systems. We have furthermore shown that Rydberg gases feature so-called absorbing state phase transitions the character of which strongly depends on the relative strength of coherent driving and noise. To the best of our knowledge this is the first time such question was addressed in a cold atomic setting.
In our work towards O4 we have characterised quantum switches and transistors that are central ingredients for an envisioned quantum computation architecture that is solely based on photons. Here interactions between photons are mediated via the interactions of Rydberg states. Moreover, we have uncovered a rather surprising link connecting the dynamics of open Rydberg ensembles with that of interacting electron-nuclear spin systems. Understanding the latter is important in the context of so-called hyperpolarisation methods that use out-of-equilibrium effects for enhancing the signal of nuclear magnetic resonance imaging. We could develop a theoretical approach that allowed for the first time the numerical simulations of ensembles formed by thousands of nuclei. This has shed light on the microscopic dynamics with which polarisation is built up which is important for devising new and highly optimised approaches to magnetic resonance imaging.
ESCQUMA so far has resulted to date in 35 publications a number of which have been conducted together with experimentalists. The funds of the project have been used to hire scientific personal and to further scientific exchange via the invitation of external guest as well as the co-organisation of workshops and summer schools.

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United Kingdom
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