A trapped single ion inside a Bose-Einstein condensate

Improved control of the motional and internal quantum states of ultracold neutral atoms and ions has opened intriguing possibilities for quantum simulation and quantum computation. Many-body effects have been explored with hundreds of thousands of quantum-degenerate neutral atoms and coherent light-matter interfaces have been built. Systems of single or a few trapped ions have been used to demonstrate universal quantum computing algorithms and to detect variations of fundamental constants in precision atomic clocks. Until now, atomic quantum gases and single trapped ions have been treated separately in experiments. Here we investigate whether they can be advantageously combined into one hybrid system, by exploring the immersion of a single trapped ion into a Bose-Einstein condensate of neutral atoms. We demonstrate independent control over the two components within the hybrid system, study the fundamental interaction processes and observe sympathetic cooling of the single ion by the condensate. Our experiment calls for further research into the possibility of using this technique for the continuous cooling of quantum computers. We also anticipate that it will lead to explorations of entanglement in hybrid quantum systems and to fundamental studies of the decoherence of a single, locally controlled impurity particle coupled to a quantum environment

Undoing traceable beginnings: citizenship and belonging among former Burundian refugees in Tanzania

This article examines the sense of insecurity experienced by former Burundian refugees following their acquisition of legal citizenship in Tanzania. Using the concept of ontological security, it explores the strategies devised by the new citizens and their former refugee selves to negotiate a normative and stable identity in Tanzania, a country with a postcolonial history of contested citizenship and depoliticized ethnicity. Our argument is that the fluidity of identity, when associated with mobility, is vilified by policy-makers and given insufficient attention in the literatures on ethnicity and refugees in Africa, yet is important for generating a sense of belonging and a meaningful life away from a troubled and violent past. This fluidity of identity offers a significant mechanism for belonging even after the acquisition of formal citizenship