Characterising colliding atom clouds
Bose–Einstein condensates (BECs) are unique forms of matter, a fifth phase after solid, liquid, gas and high-energy plasma. These artificial ultracold atom clouds are the coldest thing known to exist in the Universe. They are formed when separate atoms cooled to near absolute zero coalesce into a quantum mechanical entity. They then behave as a single coherent matter wave with remarkable properties. Einstein predicted the existence of such forms of matter in 1924, based on formulations of the Indian scientist Bose. However, it was not until 1995 that the first BEC was realised, leading to a Nobel Prize in Physics in 2001 for the scientists responsible. During the last 20 years, research into behaviours of BECs has expanded tremendously, leading to potential applications in imaging, quantum memory and highly-sensitive measurement instrumentation. However, few studies have systematically varied a broad range of parameters in a variety of situations to generate detailed knowledge of the dynamical behaviour of BECs. The EU-funded project 'Characterisation of the basic elements of BEC dynamics beyond mean-field' (QUANTUMDYNAMICS) has opened the door to new lines of research with extensive and detailed descriptions and methods. Scientists focused on the atoms scattered out of the condensate to obtain a source of quantum correlated and entangled massive particles. They evaluated situations such as collisions of BECs and interactions with obstacles and vortices. Researchers successfully obtained quantitative maps of behaviour as a function of basic parameters-of-interest with important consequences for the design of new experiments. In addition, scientists developed novel numerical simulation methods. Some of these were employed in the ongoing experiment on metastable helium, demonstrating strongly non-classical correlations in atom pairs scattered from BEC collisions. The results extend the landmark quantum optics experiments from several decades ago on non-classical light fields and photons to massive atoms. BEC experiments and applications are flourishing. The methods and results developed within the scope of QUANTUMDYNAMICS advance the field in their own right and increase the discovery power in the condensed matter physics community.
