Nano-optical detection of novel phases in ultracold Fermi gases

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Frontier areas of physics operate at extreme conditions. Researchers routinely laser cool and trap neutral atoms at temperatures around a few billionths of a degree above absolute zero. The collective behaviour of atoms in this ultracold regime is surprising and very different from common everyday experiences. The atoms may e.g. flow with low shear viscosity in a superfluid phase. Researchers can nowadays tune the interactions in the ultracold quantum gas to become so strong that the detailed nature of the interaction potential is less important. In this unitary regime physicists are discovering that cold atoms have features in common with other strongly interacting systems such as condensed matter and even baryonic matter despite several tens of orders of magnitude difference in density. Specific areas of interest to both atomic and condensed matter physics are already identified with phenomena relating to superconductivity perhaps the best known example. There are increasingly clear hints of a connection to baryonic matter. For example, at temperatures of around 2 trillion Kelvin previously only reached moments after the Big Bang researchers find that the constituent quarks and gluons of baryonic matter make a transition to a plasma which also flows with low shear viscosity. At densities found in neutron stars quantum field theories predict that superfluid and superconducting phases of nuclear or even quark matter may exist. The connection between ultracold atoms at the unitary limit and other strongly interacting systems is intriguing and the rapid experimental cycle of cold atoms experiments could help elucidate phenomena in diverse areas of physics. In particular the nature of phase transitions in strongly interacting systems in general is still not well understood, and the tuneability of the atomic interactions makes this area an ideal candidate for further study. An intense effort is now underway to exploit the connection between cold atoms and condensed matter and there is growing interest to explore the connection to nuclear matter. Unfortunately, the standard detection techniques currently used in ultracold atoms experiments do not reveal details of exotic new quantum phases of interest. In this project we aim to construct an entirely new atom detector which will resolve this problem by detecting correlations in the cold gas at the single atom level. Achieving our goal requires us to work at another extreme; optics at the nanometre scale. We will make optical fibres with diameters less than the optical wavelength (a few hundred nanometres). Astonishingly, most of the light that is guided by such fibres propagates outside the fibre itself! This feature allows us to detect the presence of a single atom simply by observing whether the nanofibre photon has been absorbed by the nearby atom. The small mode size will ultimately result in an unprecedented optical resolution. In parallel we will create a trapped ultracold degenerate Fermi gas with resonant atomic collisions so that the gas becomes strongly interacting at unitarity. We plan to incorporate an array of nanofibre detectors in the experiment so that we can test how individual atoms released from the trap are correlated. We will be able to see pairwise correlated atoms relating to superconductivity in solids, but also signatures of quantum phases relating to nuclear matter and its constituents. At the end of the project we will be equipped with new tools to tackle questions of interest to both quantum field theorists and cold atom experimentalists. We will also try to further clarify the connection to quark matter.The future applicability of the nanofibre detector extends to quantum information science where controlled atom-photon interactions are important. The nanofibre can also become a sensitive detector of complex molecules and larger nanostructures. In the long term the detector may find applications in biosensing and nanotechnology.