(with Joe Bhaseen, Gareth Conduit, Martin Hohenadler, Jonathan Keeling, and Alex Silver)
|
In recent years, advances in atomic laser cooling, trapping, and
manipulation have allowed dilute alkali gases to be cooled below their
degeneracy temperature. These developments have inspired new directions
in quantum many-body physics, providing a platform to control and
explore strong interaction phenomena in and out of equilibrium. As such,
ultracold atom physics presents a new arena for solid state condensed matter
theorists to engage in cross-disciplinary research. Over the past few years
the group has addressed several topics within this area. In particular, we
have explored the dynamics of condensate formation in two-component Fermi
gases in the regime of BEC-BCS crossover,
|
|
resonance superfluidity in the regime of population and mass imbalance,
novel ground states of mutli-component Bose-Hubbard systems, and light-matter
interaction in Bose-Hubbard mixtures -- the atomic realisation of cavity QED.
Current research activities embrace a range of topics from dynamical quantum
phase transitions and superradiance phenomena in Bose-Einstein condensates
coupled to optical cavities, itinerant ferromagentism and quantum criticality
in resonant Fermi systems, and manifestations of phase coherence effects in
disordered atomic gases.
(with Joe Bhaseen, Hannah Price)
|
The multiple scattering of waves in weakly disordered or random media leads to the accumulation of interference effects that can strongly influence dynamics. As well as weak and strong localization phenomena, the interplay of disorder and symmetry can lead to novel phase behaviour such as the integer quantum Hall effect and topological insulators. Such mesoscopic effects impact on a wide variety of fields, from semiconductor physics to quantum chaos, wireless communication, random matrix methods, and number theory. From a theoretical perspective, the manifestations of phase coherence effects on the spectra and transport properties of disordered quantum systems can be developed through a field theory of nonlinear sigma model type. Resolving the properties of this theory, and developing its generalization to irregular ballistic quantum systems has been a subject of abiding interest to the group. As well as on-going research into disordered-generated phenomena in ultracold atomic physics, we are currently exploring two related projects. The first concerns the problem of lasing: In contrast to a conventional laser, a random laser involves a feedback mechanism based on disorder-induced light scattering. As lasing relies upon an active (or nonlinear) media in which the multiple scattering of light influences the effective random potential, one may expect optimal fluctuations to play a key role in controlling the pattern of lasing at threshold. By combining Keldysh techniques with the nonlinear sigma model approach, we are developing a field theory of the random laser. At the same time, we are exploiting a ballistic generalization of the nonlinear sigma model method to explore the influence of optimal fluctuations in chaotic quantum systems in relation to the phenomenon of wavefunction "scarring". |
|
(with Allon Klein, Gen Zhang, John Biggins)
|
In adult, many tissues undergo routine and constant turnover. Even in tissues that don't, many are able to regenerate rapidly on injury. It is widely believed that cellular maintenance and repair depends upon stem cells. In both adult and the developing embryo, stem cells may be characterised by their ability to self-renew and differentiate into more specialised cell types. However, in contrast to embryonic stem cells, tissue stem cells must maintain a perfect balance between differentiation and self-renewal. Resolving the mechanisms that control this balance represent one of the defining questions of tissue stem cell biology. Most studies focus on the identification of molecular regulatory markers. But such markers are rare and unspecific. Instead, we have exploited concepts from statistical physics and population dynamics to resolve simple and ubiquitous patterns of progenitor and stem cell fate. By addressing clonal fate data derived from the inducible genetic labelling of transgenic mice, we have shown that interfollicular epidermis is maintained by a single progenitor cell population in which cells follow a pattern of balanced stochastic fate -- a critical Galton-Watson type process -- overturning a paradigm long-held in the literature. Inspired by this discovery, we have successfully addressed clonal evolution in other mammalian tissue types from the germ line to the intestinal crypt. As well as providing a functional classification of stem and progenitor cell types, these studies suggest that stochastic cell fate choice and equipotency represent ubiquitous features of adult tissue maintenance. Currently, we are collaborating with a range of experimental groups to resolve the conserved molecular regulatory mechanism that underpin stochastic cell fate choice, and to extend these concepts to other adult tissue types. Current collaborations include studies of:
|
|
|
While many tissues, such as skin and gut, show persistent turnover throughout adult life, others, such as the hair follicle in mammalian epidermis, undergo periods of regression and regeneration. In such quasi-homeostasic systems, the features that constrain persistent tissue turnover continue to apply but on time scales in excess of the cycle time. Currently, we are involved in two collaborations to exploit clonal fate data to resolve the factors that regulate stem cell behaviour in quasi-homeostatic tissues, including studies of:
|
|
(with Allon Klein)
|
The identification of simple, robust, and conserved mechanisms of stem and progenitor cell fate in adult tissues provides a platform to explore factors responsible for disease, aging, and tumour initiation. Already, we have shown that the stochastic fate pathways that characterise normal tissue maintenance are conserved in UVB-induced p53 mutations in mouse and human epidermis. To develop this programme, we have established two complementary experimental collaborations to explore mechanisms of tumour initiation in adult tissues:
|
|
|
The restricted patterns of cell fate that characterise adult tissue maintenance can be traced to the severe constraints imposed by tissue homeostasis. The relaxation of these constraints in development make the identification of cell fate mechanisms potentially more challenging. However, the late stage development of tissues in the growing embyro still demands the cooperative dynamics of many cellular components. Moreover, it would be surprising if the stochastic cell fate mechanisms seen in adult do not emerge at an earlier stage of development. To develop this programme of research, we have established collaborations with two experimental groups to explore the pattern of cell fate in developing tissues including studies of:
|
