The following results have been achieved so far:
A) The transition between classical and quantum dynamics in Rydberg gases out of equilibrium has been clarified [1]. This study has confirmed that the behaviour in the classical limit (see Ref. [2]) remains qualitative unchanged even for relatively high levels of 'quantumness'. This addresses the major goal of Objective 1.
B) The dynamics of multi-level Rydberg gases has been thoroughly explored for the first time [3]. The time evolution of these systems, which is characterised by several typical length scales, has been related to those of mixtures of glass-forming liquids. As in such glassy systems, we find metastable behaviour (features that persist for very long times before eventually disappearing) arising from complex interaction patterns. These results address the main goal of Objective 2.
C) The existence of collective effects in a Rydberg gas of rubidium atoms has been studied in a collaboration led by the Researcher between theorists at Nottingham and experimentalists at the University of Pisa [4]. For the first time, a non-equilibrium phase transition (i.e. a situation similar to a change of state of aggregation when a system is not in thermodynamic equilibrium, but rather driven externally) has been experimentally observed in a quantum system. This fulfilled the second point of Objective 3 above.
D) A quantum version of a well-known classical spreading model based on Rydberg atoms has been proposed and analysed [5]. The model undergoes a non-equilibrium phase transition equivalent to that of old model in the classical limit, but behaves in a completely different way (showing a sequence of discontinuous transitions) in the quantum limit. This work, which originated from discussions while working on (C), addresses a new facet of Objective 1.
E) A study of the dynamics of dissipative Rydberg gases under a quench (i.e. a sudden change of parameters) [6]. The quench dynamics is described by an extension of the classical model for the description of the kinetics of phase transformations (i.e. how a liquid becomes a solid when the system is moved below the melting point). We verify numerically our predictions for the classical and the quantum regimes. This work originates from previous work by the Researcher on stable glasses [7], and falls within Objective 1.
Since the beginning of the project, these and related results have been orally presented at three conferences and scientific meetings to an overall audience of over 200 researchers.
Some of this work was actually carried out before the starting date of the project, as the Researcher had the opportunity to be funded by the host organisation before becoming a Marie Sklodowska-Curie fellow. As a result, (A) and (B) were published before the starting date of the project, while (C), (D) and (E) were carried out during the 11 months of the fellowship. Two ongoing projects will help us make further progress towards the achievement of Objective 2.
[1] Levi, E., Gutiérrez, R., & Lesanovsky, I. J. Phys. B, 49, 184003 (2016).
[2] Gutiérrez, R., Garrahan, J. P., & Lesanovsky, I. Phys. Rev. E, 92, 062144 (2015).
[3] Gutiérrez, R., Garrahan, J. P., & Lesanovsky, I. New J. Phys., 18, 093054 (2016).
[4] Gutiérrez, R. et al. Phys. Rev. A, 96, 041602(R) (2017).
[5] Pérez-Espigares, C., Marcuzzi, M., Gutiérrez, R. and Lesanovsky, I. Phys. Rev. Lett. 119, 140401 (2017).
[6] Gribben, D., Lesanovsky, I., & Gutiérrez, R. arXiv:1709.10383 (2017).
[7] Gutiérrez, R., & Garrahan, J. P. J. Stat. Mech. Theor. Exp., 2016, 074005 (2016).
