Search

We study quantum (T = 0) phases of strongly-correlated matter, and their possible implementation in a quantum simulator. We focus on the non-perturbative regimes of 1D spin-boson models. As a reference physical system we consider trapped-ion chains. We realize complex many-body states, such as a ground state exhibiting magnetic frustration, a lattice gauge theory, and a topological insulator. The exquisite control over these phases offered by a quantum simulator opens up exciting possibilities for exploring the exotic phenomena emerging in these systems, such as enhanced fluctuations and correlations. We address the non-perturbative regimes of the phase diagrams by means of mean-field theories and the numerical algorithm DMRG. We have established the universality class of the continuous transition in the spin-boson chain, the existence of a first order phase transition when the system is endowed with a gauge symmetry, and the possibility of probing topological states of matter in these systems. Our results show that some of the most exotic phases of quantum matter can be readily realized in trapped-ion quantum simulators. This offers the possibility of exploring these physical models beyond their original realm of applicability, which may provide us with new insights on both theoretical and applied fields of physics, ranging from high-energy processes to low-energy cooperative phenomena.

This PhD thesis focused on identifying the effect of elevated CO2 on: 1) patterns of fine root growth; and 2) the role of water and nutrient availability as regulators of such effects. Fine root responses were studied quantitatively - assessing changes in biomass, production and turnover rates (Chapters 2 and 3) - and qualitatively, examining shifts in fine root morphological and chemical traits (Chapters 3, 4 and 5). This comprehensive approach allowed me to explore the linkages between these fine root adaptations and many of the diverse ecosystem processes driving C and nutrient cycling, including the transfer of C, N and P to the soil from fine root turnover (Chapter 3), the activity of microbial communities in the rhizosphere (Chapters 4 and 5), the uptake and use of nutrients by plants (Chapter 4and 5), and rates of CO2 exchange (Chapter 4). In all the experiments conducted, either in the field or the glasshouse, I addressed these questions using P-limited soils characteristic of vast areas from South East Australia (Peñuelas et al. 2013). The scarce information about the role of P-limitation on ecosystem responses to rising [CO2] adds further novelty to my work, addressing an important knowledge gap in climate change research. In addition, glasshouse experiments were designed to provide mechanistic insight into the potential for changes in fine root structure and function to overcome soil P-limitation under future climate change scenarios. Taken together, the information generated in this project can then be integrated in Earth System Models to predict potential feedbacks of terrestrial ecosystems on C cycling under eCO2 while accounting for the widespread phenomenon of P-limitation (Norby et al. 2016).