Theory of ultracold atoms: from fundamentals of quantum mechanics to applications

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Techniques such as laser cooling can now cool gases of atoms to temperatures as low as a few billionths of one degree above absolute zero (nK). These "ultracold" atoms behave in a very quantum mechanical way because their de Broglie wavelengths are so large (~µm, i.e., 5 orders of magnitude larger than at room temperature). Ultracold atoms have already been used to make new states of matter such as Bose-Einstein condensates (BECs) in which every atom in the gas has the same quantum wave function. However, the scientific potential of ultracold atoms is not just confined to fundamental quantum mechanics; their motional state can be controlled to such an unprecedented degree that they are also beginning to play an important role in precision measurements of nature's forces and constants. My research concerns the theory behind both of these aspects.Firstly, I propose to continue my studies of BECs in which the atoms interact via dipole-dipole interactions. This is of particular relevance to polar molecules. The idea is to investigate how these long-range and anisotropic interactions affect properties such as superfluidity. Secondly, I want to initiate Canadian studies of ultracold atoms trapped inside optical microcavities. This marriage of cavity quantum electrodynamics with the quantum motion of atoms combines two of our best controlled physical systems and so promises to be a natural arena for quantum information processing as well as precision measurement of forces at short distances. Thirdly, I plan to investigate how macroscopic superpositions of ultracold atoms suffer from decoherence, e.g. in Josephson junctions. This is closely tied in to the second topic above and is relevant to a number of ultracold atom experiments currently being carried out in Canada.