Structuring atoms with structured light : optomechanical pattern dynamics and transport in cold atomic gases

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Awarding institution
  • University of Strathclyde
Date of award
  • 2022
Thesis identifier
  • T16178
Person Identifier (Local)
  • 201751136
Qualification Level
Qualification Name
Department, School or Faculty
  • The spontaneous appearance of highly organized states characterized by a decrease in entropy is a universal feature distinguishing the physics of systems with drive and dissipation from those at thermodynamic equilibrium [1]. Pursuant to such a universality, spatially and temporally ordered structures known as patterns can occur in a variety of contexts involving, e.g., biological and chemical systems, hydrodynamic convection, optical systems etc. [2]. All such systems share the same underlying mechanism, namely, the balance between the effect of nonlinearity as a source of inhomogeneity, and a linear spatial coupling among separated parts of the system, acting as an opposing, re-distributive tendency. Concurrently, such order in the system emerges due to the wider balance between gain and losses, inherent to systems exposed to drive and dissipation in the interaction with the external environment [3]. Among the most relevant contexts for pattern formation, coupled light-matter systems have provided excellent platforms for the observation of spatial pattern formation, after the pioneering works of Lugiato and Lefever in 1987 [4], and Firth and D’Alessandro in 1990-92 [5–7], showing that spatial dissipative structures can spontaneously emerge in the transverse profile of a passive optical resonator or optical feedback configuration, where the nonlinearity is provided by the optical medium itself and the spatial coupling by optical diffraction. The study of transverse optical patterns later became a burgeoning research topic throughout the 1990’s and 2000’s and detailed review papers can be found in Refs. [8, 9]. Along with the major developments in the field of nonlinear optics, formidable progress in the experimental control of light-atom interaction enabled the possibility of cooling a gas of neutral atoms to sub-Kelvin temperatures [10–12]. The basic principles of laser cooling, introduced in the next chapter, are based on the well-known mechanical action exerted by electromagnetic (e.m.) radiation onto atoms, i.e., so-called optomechanical forces. Such concepts, together with the achievement of kinetic temperatures well below the mK regime, were crucial to the observation and corresponding theoretical e orts in understanding the physics of Bose-Einstein condensation [13]. This paved the way to the era of cold/ultracold atoms, where the manipulation of coherence and quantum correlations at a many-particle level enable technological applications in quantum information processing and communication, with profound impact on future technologies [14, 15]. A common feature in all the systems considered so far is that the laser-cooled atoms can be also trapped into arrays or spatial geometries that are fixed, i.e., chosen at will for a specific target. The issue of static vs. dynamical potentials/fields allows to draw a connection between cold atom physics and the concept of self-organization and, as such, it represents one among the key topics in modern quantum simulation [16, 17]. As discussed below, when the optical field is spatially confined by a cavity or other diffractive feedback configurations, the emerging potential for dispersively coupled atoms can create a modulated density profile, maximizing a certain scattering condition and leading to optomechanical self-structured states [18]. For the case of ultracold atoms (namely, for temperatures below the Doppler limit), such a collectively generated dynamics has been of fundamental importance in the experimental realizations of the Dicke-model phase transitions [19], supersolidity with breaking of continuous symmetries [20–23], tunable range interactions [24], and structural phase transitions among different crystalline configurations [25]. [From Introduction. References in thesis]
Advisor / supervisor
  • Oppo, G.-L. (Gian-Luca)
  • Yao, Alison M.
  • Robb, Gordon R. M.
Resource Type