Resolved Sideband Cooling of a Micromechanical Oscillator

Micro- and nanoscale opto-mechanical systems provide radiation pressure coupling of optical and mechanical degree of freedom and are actively pursued for their ability to explore quantum mechanical phenomena of macroscopic objects. Many of these investigations require preparation of the mechanical system in or close to its quantum ground state. Remarkable progress in ground state cooling has been achieved for trapped ions and atoms confined in optical lattices. Imperative to this progress has been the technique of resolved sideband cooling, which allows overcoming the inherent temperature limit of Doppler cooling and necessitates a harmonic trapping frequency which exceeds the atomic species' transition rate. The recent advent of cavity back-action cooling of mechanical oscillators by radiation pressure has followed a similar path with Doppler-type cooling being demonstrated, but lacking inherently the ability to attain ground state cooling as recently predicted. Here we demonstrate for the first time resolved sideband cooling of a mechanical oscillator. By pumping the first lower sideband of an optical microcavity, whose decay rate is more than twenty times smaller than the eigen-frequency of the associated mechanical oscillator, cooling rates above 1.5 MHz are attained. Direct spectroscopy of the motional sidebands reveals 40-fold suppression of motional increasing processes, which could enable reaching phonon occupancies well below unity (<0.03). Elemental demonstration of resolved sideband cooling as reported here should find widespread use in opto-mechanical cooling experiments. Apart from ground state cooling, this regime allows realization of motion measurement with an accuracy exceeding the standard quantum limit.Comment: 13 pages, 5 figure

Minimization of phonon-tunneling dissipation in mechanical resonators

Micro- and nanoscale mechanical resonators have recently emerged as ubiquitous devices for use in advanced technological applications, for example in mobile communications and inertial sensors, and as novel tools for fundamental scientific endeavors. Their performance is in many cases limited by the deleterious effects of mechanical damping. Here, we report a significant advancement towards understanding and controlling support-induced losses in generic mechanical resonators. We begin by introducing an efficient numerical solver, based on the "phonon-tunneling" approach, capable of predicting the design-limited damping of high-quality mechanical resonators. Further, through careful device engineering, we isolate support-induced losses and perform the first rigorous experimental test of the strong geometric dependence of this loss mechanism. Our results are in excellent agreement with theory, demonstrating the predictive power of our approach. In combination with recent progress on complementary dissipation mechanisms, our phonon-tunneling solver represents a major step towards accurate prediction of the mechanical quality factor.Comment: 12 pages, 4 figure

Janus’ Voice: Religious Leaders, Framing, and Riots in Kano

This article analyses the role of religious leaders in collective violence in Kano, the major urban centre in northern Nigeria. It compares two episodes of collective action in the city—the violent ‘Plateau riots’ in 2004 and the non-violent ‘cartoon protests’ in 2006—to explore the role of religious leaders in the variation in violence between the two events. The core argument is that the ways in which Islamic and Christian preachers framed the triggering events for these cases facilitated different forms of mobilisation and enemy identification in response. In 2004, the interpretation of violence in Plateau State through the ‘Christians-versus-Muslims’ frame allowed for mobilisation within Kano’s Christian and Muslim communities as well as for the identification of local Christians as enemies. In 2006, in contrast, the infamous Danish cartoons were actively framed as part of the global struggle between faithful Nigerians and nonreligious Westerners, facilitating non-violent mobilisation across Christian-Muslim boundaries. Thus, the divergent discursive strategies employed by religious leaders are likely to have contributed to violent escalation in 2004 and to peaceful mobilisation in 2006. At the same time, however, the article emphasises the interaction of discursive framing with other factors, such as the role of security forces and the inextricable connections between religious and political authorities in Kano. The article is based on mixed-methods data collected in Kano between 2006 and 2012, including perceptions survey data, semi-structured interviews, and newspaper articles.Global Challenges (FGGA