Vortices and solitons in finite-temperature Bose-Einstein condensates

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In recent years there has been a great deal of attention paid to the properties of ultracold gases. This interest has been prompted by experiments that, by using a combination of magnetic fields and lasers, have been able to confine and cool dilute gases down to temperatures billionths of a degree above absolute zero. At these temperatures strange situations can arise that are unfamilar to us in our everyday lives. For example, if the temperature is low enough the atoms can undergo a phenomenon called Bose-Einstein condensation, where all of the atoms tend to move together. This leads to some rather startling and fascinating behaviour, such as the ability of the gas to flow without resistance. This property, which is similar to the flow of an electric current through a superconductor, is known as superfluidity. A nice feature of ultracold atoms is that they can be easily controlled and imaged directly, and are relatively simple to treat theoretically, so are very good systems in which to study superfluid behaviour.The proposed research will theoretically study the properties of these superfluid ultracold gases. Of particular interest are vortices, which are a familiar feature in fluids where they sometimes appear as whirlpools or tornados. They appear in superfluids when they are rotated or forced to flow past an obstacle too quickly. The vortices can then interact with atoms that are not part of the superfluid, creating a frictional force and therefore a resistance to the flow. So, the vortices are an important component in the breakdown of superfluidity, and our research will be mainly concerned with studying these interactions. A strong motivation for research into this problem is that similar behaviour is found in other systems, such as liquid helium or inside neutron stars, but isn't fully understood theoretically. So by studying this system and comparing to experiments we expect that this will provide valuable insights into these other systems.