Novel precision control techniques in a trapped Yb+ ion implementation

Precise control of quantum systems is vital to scientific and technological progress, including the realisation of quantum computation and simulation, record-breaking timekeeping and positioning applications. Control of quantum systems is hampered by the effects of random environmental or hardware noise, which leads to unknown deviations from the system's desired evolution. This thesis presents a set of interaction-focussed methods for improving precision control, tailored to the problems of quantum error suppression and stabilisation of oscillators, which share a common basic structure. These methods are based on a theoretical framework called the filter-transfer function formalism, which expresses the convolution of user-applied control and random noise in the language of spectral filtering. This powerful and accessible approach is experimentally verified in this thesis, and is used to formulate novel control techniques and improve on existing ones. This thesis experimentally demonstrates the effectiveness of novel composite pulse schemes for suppressing error in quantum bits. Furthermore, the thesis derives and demonstrates a novel predictive technique for stabilising oscillators by means of combining multiple frequency measurements against a quantum reference. The thesis therefore advances the theoretical understanding of a frequency-domain formalism for noise-affected quantum systems, on which basis it presents and demonstrates novel and improved techniques for mitigating the effects of such noise on the user's precision control over the system

The Precarious Past: Historical Practices in Indic Java

Java is a major Southeast Asian culture that was strongly influenced by Indic cultural forms between the fifth and fifteenth centuries CE. The Indic Javanese practised history. Their texts are crucial sources for the region’s past. In some ways, these texts satisfy our expectations of how history ought to be done, but in other ways, they defy them. There is a serious gap in our understanding of why the Indic Javanese practised history as they did. This thesis addresses that gap. It puts forward and justifies an original theory of historical practice, by applying historical and philological methods to the inscriptions and manuscripts of Indic Java. The thesis presents extensive empirical evidence for Indic Javanese historical practices, furnished with new translations and interpretations of a wide range of textual sources. The key theoretical finding of the thesis is that historical practices are fundamentally shaped by the conditions in which texts are created, preserved, and transmitted. The thesis explains how textual forms, textual modes, and the materiality of texts played decisive roles in the practice of history. At the centre of this theory is the realisation that, for the Indic Javanese, the past was precarious. This precarity was due to the difficulty of preserving and accessing original written sources, which in turn generated contradictions within the historical tradition. The findings of the thesis have significant implications. By understanding why the Indic Javanese practised history as they did, we can better interpret their texts and thereby improve our knowledge of Java’s history. These implications go beyond the Javanese case, because many other premodern societies pose similar challenges to our understanding of historical practice. The thesis thus makes innovative contributions to historical theory and methodology in general