糖心TV

Speaker: Anne-Marie Broomhall

Helioseismology uses the Sun's natural acoustic oscillations to study the Sun's interior. Asteroseismology applies similar principles and techniques to use a star's natural resonant oscillations to characterise that star. Here I consider the asteroseismology of solar-like stars, whose oscillations are excited by turbulent outer convective regions. I will draw comparisons between helioseismic and asteroseismic data. In particular I will discuss the impact of solar and stellar magnetic fields on the properties of helio- and asteroseismic data. The Sun's magnetic activity cycle is particularly topical at the moment as it has recently been behaving unexpectedly: The solar activity minimum, observed between 2006 and 2010, lasted significantly longer than expected. The strength of the Sun's magnetic field has now, once again, increased and we are currently at or close to the maximum of solar cycle 24. However, even this cycle is unusual for recent times as its peak is smaller than any cycle observed since the early 1900s. I will show that the helioseismic data indicate that the solar interior displayed unusual behaviour well before the recent minimum. It is well known that violent eruptions associated with the Sun's magnetic activity cycle can impact life on Earth in the form of space weather. Asteroseismic studies of stellar activity are vital both for putting the Sun's activity cycle in a broader, stellar context, and for determining the habitability of any exoplanets.

Speaker: Tom Blake

I will discuss how unlikely decays of B mesons can be used to look for new particles with masses in the range 100GeV - 10TeV. To set the scene I will briefly touch on the concept of virtual particles in quantum mechanics and what they have already told us about the structure of the Standard Model. I will introduce so-called “penguin" decays and explain why they are of particular interest. Finally, I will conclude by discussing recent results from the LHCb detector at CERN.

Speaker: Dimitri Veras

The University of 糖心TV's Department of Physics will play a major role in the development of two areas of astrophysical science: (1) old, dying stars and (2) transiting extrasolar planets. Theoretical modelling of old stars which harbour planetary systems is in its infancy, as is preparatory modelling for transiting exoplanet programmes in which the Department is heavily invested, such as the recently-funded PLATO mission. As a theorist with unique experience in both subject areas, I will fill a void and ensure that future research endeavours of both groups contain predictive and explanatory theoretical components.

Speaker: Chris Brady

The next generation of high-power lasers requires a step change in how laser-plasmas are modelled. Rather than being a fundamentally classical science based on Maxwell's equations and Newton's laws of motion, additional QED processes must be included. The most important process for impending laser systems (such as the EU funded Extreme Light Infrastructure (ELI) project) is inverse Compton scattering. The interaction of this effect with classical plasma physics leads to an interesting, novel type of plasma called a QED-plasma. This has properties different from both classical plasma physics and the simple single particle models conventional to QED studies. In this talk a background and motivation to the field is presented followed by an overview of the modelling techniques employed. Finally a few of the first results showing the interesting new properties of the QED-plasma regime will be presented.

Computational materials design and discovery is critical to reduce the time to market of new technologies. Especially in the United States, database methods are emerging as a fruitful way to find and predict the structure and properties of new materials. This is an important first step, but current databases are limited to only a few hundred thousand structures. Ab initio random structure searching (AIRSS) is proposed as a way to generate many more new structures. AIRSS has been shown to be successful for predicting many phases relevant to high-pressure physics and astronomy. I show how AIRSS can be used for technologically relevant materials such as lithium ion batteries and highlight our recent successes. My vision for the future of structure prediction is discussed and show how this combined approach will be made available to experimentalists and industry. I explain why my group would thrive at the University of 糖心TV and outline possible future funding strategies.

Speaker: Nicholas Hine, Cavendish Laboratory, University of Cambridge

Electronic structure methods based on density functional theory (DFT) have been highly successful in recent years at predicting the properties of bulk materials. However, as the complexity and size of the system being studied is increased, traditional DFT methods inevitably hit a 'scaling wall' in terms of computational effort required, which rises as the cube of the number of atoms.

This would seem to preclude useful contact with experiment in the study of many nanomaterials, including nanocrystals, interfaces, proteins, and disordered molecular crystals, which require accurate calculations on systems comprising many thousands of atoms, beyond the scaling wall.

However, alternative methodologies exist, based on the density matrix rather than eigenstates, which can exploit real-space localisation to achieve linear-scaling with system size and make such calculations feasible and highly parallel. The ONETEP Linear-Scaling DFT code [1], of which I am an author, combines the benefits of linear-scaling, efficient parallelisation, and variational convergence akin to plane-wave approaches, together with a wide-ranging set of features. I will present an overview of the method and discuss a number of recent applications, including semiconductor nanorods, pigment-protein complexes, defects in metal oxides, and candidate organic photovoltaic materials.

[1]

Speaker: Animesh Datta

Quantum correlated probes have the potential of delivering enhanced precision in estimating individual parameters. Obtaining quantum enhancements in scenarios of wider appeal such as imaging require an understanding of the quantum limits of estimating several parameters across multiple modes simultaneously. The problem is made theoretically and practically interesting and non-trivial by the possible non-commutativity of the optimal measurements needed to attain the quantum limits for estimating the parameters. We will discuss the attainability of such bounds for simultaneous multiple phase estimation and the trade-offs involved in the simultaneous estimation of phase and loss, and phase and dephasing. We will also study how practical limitations such as efficiencies affect the demonstration of quantum enhancements in sensing and imaging. We will discuss the importance of these developments on the quantum theory of estimating multiple parameters -- arising from both unitary dynamics as well as decoherence -- simultaneously in a few scenarios, and their ramifications in the quantum-enhanced imaging of real-world samples.

Speaker: Pier-Emmanuel Tremblay (Hubble Fellow, Space Telescope Science Institute, Baltimore)

Most stars become white dwarfs at the end of the stellar life cycle.
The study of these old degenerate remnants in clusters and the
galactic halo provides essential information about the first stellar
populations in our galaxy. We have recently computed the first grid
of 3D model atmospheres for hydrogen-atmosphere white dwarfs.
These time-resolved radiation-hydrodynamics simulations, unlike the
commonly used 1D calculations, do not rely on the mixing-length theory
for the treatment of convection. The derived stellar masses using
these models are in much better agreement with our understanding
of stellar evolution. In the future, 3D model atmospheres will be
computed for all types of white dwarfs, and these simulations will
be connected to structure models. These theoretical tools will be
essential for the study of the upcoming Gaia satellite data set,
and will provide a much more precise picture of how stars and
their planetary systems evolve in the Milky Way.

Speaker: Jianming Cai

Color centers are atomic defects in diamond that possess electronic and nuclear spins, which are excellent candidates for the realization of various quantum applications. I will present my works on diamond-based quantum sensing technology, including a hybrid diamond quantum sensor for the very sensitive measurement of different physical quantities; the techniques for diamond-based quantum nuclear magnetic resonance spectroscopy, and a diamond-based quantum simulation for the study of intriguing many-body physics. I will also present an outlook for the furture development along this research direction.