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The Quantum Matter group covers several interrelated themes ranging from superfluids and superconductivity in condensed matter systems and ultracold atoms, to quantum optics, to extreme quantum matter such as the physics of neutron stars. Our work encompasses a range of methods including theoretical and numerical modelling, experiments, and observations. Our primary research falls into four main areas described below.
Quantum Fluids
Research in quantum fluids focuses on understanding the properties of superfluids such as superfluid Helium and ultracold atomic Bose-Einstein condensates. Specifically, we are interested in their out-of-equilibrium properties and nonlinear dynamics as would arise in the scenarios of non-equilibrium quantum phase transitions, and turbulence. A common focus of our work is on understanding the role of topological defects and their interplay with wave excitations. In the simplest systems, these defects correspond to quantum vortices. In spinor Bose-Einstein condensates, where the quantum-mechanical spin degree of freedom leads to complex internal symmetries, more exotic topological excitations arise including monopoles, and skyrmions which have close analogues in other systems from liquid crystals to cosmology. They can also give rise to non-Abelian vortices which requires methods from topology and group theory to characterise their dynamical properties.
Faculty working in this area: Magnus Borgh, Davide Proment, Hayder Salman
Quantum Optics
Quantum optics is the study of the quantum nature of light and interaction between light and matter on the atomic scale. The group has expertise in photonics using methods from both quantum and semiclassical optics with a particular emphasis on molecular and chemical systems. Topics studied span a broad spectrum of areas including nano-optics, structured light, optical manipulation, quantum chemistry, nonlinear optics, optical activity and chiral light-matter interactions, and molecular quantum electrodynamics. Research in this area focuses on how quantum-optical methods can be applied to molecules to understand excited state dynamics, light-molecule interactions, quantum dynamical models of ultrafast ultrabroadband 2D electronic spectroscopy, and open quantum systems. Research is also centred around characterising ultrafast chemical physics of isolated molecules and probing their structure and photo-induced dynamics with ultrafast (femtosecond to nanosecond duration) laser pulses. Applications range from characterising the efficiency of photoswitchable molecules used in technological applications such as light-driven molecular machines, understanding the core units in photoactive proteins, and understanding the lifecycles and why certain molecules are observed in space.
Faculty working in this area: Magnus Borgh, James Bull, Kayn Forbes, Garth Jones
Extreme Quantum Matter
Research in this area aims to understand properties of neutron stars, the highly dense, rapidly rotating remnants of massive stellar collapse, and the emergence of novel states of matter (e.g. superconductivity) at very low temperatures. The core of a neutron star is composed of electron, neutron and proton fluids, with the possibility of more exotic particle species in the deep core. The high densities result in correspondingly high critical temperatures for Cooper-pairing, and thus a mature neutron star hosts a neutron superfluid and a superconducting proton fluid in its core, as well as neutron superfluid permeating the inner crust. Progress on the properties of neutron stars continues to be made through the observation of pulsars. They are proven to be effective probes into the nature of exotic nuclear matter that comprise their interiors, as well as the evolution of their extreme magnetospheric activity. This continues to be achieved through pulsar timing, a highly precise tool for characterising their rotational evolution. Specifically, young pulsars typically experience two principal types of spin irregularities: glitches and timing noise. These can be directly connected to our understanding of the neutron star interior and magnetic field. Research on observations of pulsars compliments another major focus of our research that is concerned with the theoretical modelling of how superconductivity affects the star's magnetic field structure and evolution. In addition, we have interests in experimental studies carried at ultra-high applied pressures and very low temperatures to tune material properties in the vicinity of quantum phase transitions and/or quantum critical points. These measurements help discover novel phases of matter, such as superconductivity, and potential functionalities of interest to the many materials limited problems including energy storage, low power electronics and lossless power transmission.
Faculty working in this area: Robert Ferdman, Seb Haines, Samuel Lander
Quantum Computing and Quantum Information
Research in this area is centred on the development of novel computational methods for modelling spin systems, such as the Ising, XY and Heisenberg Hamiltonians, and for simulating Hamiltonians describing models in quantum chemistry. Many optimization problems can be formulated as a solution of the ground state of a corresponding spin Hamiltonian that can subsequently be solved using a quantum computer or a quantum annealer. Our research focuses on contrasting the use of these emergent quantum technologies against semiclassical platforms (e.g. coherent Ising machines) that are being developed as alternative physics-based optimizers. Research on chemical systems focuses on developing non-Markovian open quantum system models for the purpose of linking quantum information dynamics to experimental observables, such as two-dimensional optical spectroscopies, and quantum optical measurements, such as photon-photon correlation functions.
Faculty working in this area: Garth Jones, Hayder Salman
Group Head: Hayder Salman
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