Category: Seminars

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Seminars

Dr AnnMarie Oien

Evolution of a Physicist’s career: an example

1pm Tuesday 13th August 2024, Room G400, Science III

Dr AnnMarie Oien, 1996 graduate from Otago Physics, will cover her career arc and how a PhD in Atomic and Laser Physics eventually led her to retiring in the USA as a Technical Fellow in Agile Systems Engineering in the aerospace industry. However deeply our interests start in the world of physics, opportunities and adjacent curiosities crop up leading to new jobs and fields, all enabled by the meta-skills we first acquired in our physics degree.

About the speaker:

Dr AnnMarie Oien now lives in Colorado with husband Mark Phillips, and is a proud tennis captain, expert skier, occasional singer and pianist, and poor golfer.

Dr Oien is a good friend of the Department of Physics and a great supporter of the University of Otago, having served as the vice-president of the Alumni of University of Otago in America, Inc. She created the Oien Prizes in Physics and Energy, which are our most prestigious prizes for senior undergraduates.

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Seminars

How Much Does Sea Ice Affect Arctic Precipitation?

Professor Xiahong Feng

Dartmouth College

Global climate is influenced by the Arctic hydrologic cycle, which is, in part, regulated by sea ice through its control on evaporation and precipitation. However, the quantitative link between precipitation and sea ice extent is poorly constrained. This talk presents observational evidence for the response of precipitation to sea ice reduction and assesses the sensitivity of the response. Changes in the proportion of moisture sourced from the Arctic with sea ice change in the Canadian Arctic and Greenland Sea regions over the past two decades are inferred from annually averaged deuterium excess (d-excess) measurements from six sites. Other influences on the Arctic hydrologic cycle, such as the strength of meridional transport, are assessed using the North Atlantic Oscillation index. We find that the independent, direct effect of sea ice on the increase of the percentage of Arctic sourced moisture (or Arctic moisture proportion, AMP) is 18.2 ± 4.6% and 10.8 ± 3.6%/100,000 km2 sea ice lost for each region, respectively, corresponding to increases of 10.9 ± 2.8% and 2.7 ± 1.1%/1 °C of warming in the vapor source regions. The moisture source changes likely result in increases of precipitation and changes in energy balance, creating significant uncertainty for climate predictions.

Wednesday 8 May 2024, 12.00pm
Room 314, Science III Building
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Seminars

Concepts of quantum machine learning

Associate Professor Christopher Gies

Institut für Theoretische Physik, Universitat Bremen

The seminar will give a glimpse into the vibrant field of quantum machine learning (QML)— its underlying quantum- mechanical principles, hardware implementations, and potential advantages over classical systems. QML has gained substantial interest as a quantum technology application capable of taking advantage of the noisy intermediate scale quantum (NISQ) devices of the current era, i.e. systems operating with tens to hundreds of imperfect qubits.

A particular focus will be on reservoir computing, which utilizes physical systems as artificial (quantum) neural networks to process information. Like in conventional machine learning, an input u(t) undergoes processing within the network to yield an output y(t). Only by training the output weights W, even small quantum systems can approximate non-linear functions of the input data due to the exponentially large Hilbert space dimension.

WEDNESDAY 1 May, 12:00PM, Room 314, Science III Building, University of Otago
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Waves in a Plasma Ocean: Wave-Particle Interactions Throughout the Solar System

Associate Professor Allison Jaynes

University of Iowa

All planetary and smaller bodies in our solar system are embedded in a sea of plasma, like boulders in a terrestrial ocean. Their surfaces or magnetic fields run into this ocean of space plasma, generated primarily by our Sun, and create a whole range of fascinating effects as a result.

The American Physical Society’s Katherine E. Weimer Award winner talks about the plasma ocean of our solar system, from aurora and “killer electrons” to the furthest reaches of space exploration.

This talk will be accessible to all backgrounds, knowledge of Physics not required.

WEDNESDAY 17 April, 5:00PM, Archway 3, University of Otago

 

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Photonic Crystal Ring Resonators for Tailored Optical Microcombs

Dr Ewan Lucas

Research Fellow, Laboratoire Interdisciplinaire Carnot de Bourgogne

Nonlinear-wave mixing in optical microresonators offers a promising avenue for compact optical-frequency microcomb generation [1]. These microcombs have rapidly found applications across diverse fields, including optical frequency synthesis and high-capacity data communication systems. A fundamental characteristic of microcombs is their spectral profile, which is principally determined by the resonator’s dispersion. An illustrative example is the sech2 spectrum of dissipative Kerr solitons that emerges under anomalous group-velocity dispersion.

Continue reading “Photonic Crystal Ring Resonators for Tailored Optical Microcombs”
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2023 Dan Walls Medal Public Lecture: Maths powers black holes, the Universe and everything

Prof. David Wiltshire

University of Canterbury

Sixty years ago New Zealander Roy Kerr helped revolutionize physics, achieving what had eluded scientists for 47 years. He discovered the solution to Einstein’s equations defining space around a rotating star or black hole. He combined advanced mathematics with one key simplifying insight: All bodies collapsing under their own gravity inevitably rotate faster.

The Kerr solution became the basis for revolutions first in fundamental physics in the 1960s, in astronomy in the 1970–80s, and in cosmology in the 1990s and beyond. The discoveries of gravitational waves from colliding black holes, first in 2015, and then from colliding neutron stars in 2017, mean that decades of further scientific revolutions are just beginning.

Continue reading “2023 Dan Walls Medal Public Lecture: Maths powers black holes, the Universe and everything”
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Seminars

History of the Master Equation

Crispin Gardiner

Honorary Professor, University of Otago

Master equations, both classical and quantum, have been in use since at least 1910 as the basis for the description of random events in physics, and my career in Quantum Optics since the 1970s has been built on the foundation of the master equation description of quantum optics.

But why is it called the master equation, and who is responsible for its development into one of the major tools in the physics of randomness?  And how far can we trust the master equation?

I will track back the origin of the idea, and its importance in physics to the very beginning, with some unexpected results. I will cover kinetic theory, quantum optics, and the mathematics of stochastic processes, both quantum and classical up to the end of the 20th century.  At the same time, I will give some particular attention to the conditions necessary for the validity of the Master Equation.

Wednesday 8 November, 3.00pm
Room 314, Science III Building

 

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Seminars

An introduction to the physics of magnetic confinement fusion

Dr Toby Adkins

Post Doctoral Fellow, University of Otago

The ultimate goal of the global fusion programme is to harness a self-sustained nuclear fusion reaction as a commercially viable source of clean energy. At the high pressures required for nuclear fusion, the fuel becomes a plasma – an electromagnetically interacting gas of charged electrons and ions – which is unable to be contained by normal materials. Magnetic-confinement fusion proposes to use large external electromagnetic coils to generate a series of nested magnetic field “surfaces” that wrap around the device and help confine the plasma. In this talk, I will introduce the general concepts underlying magnetic-confinement fusion and review some of the fundamental physics challenges it faces, including magnetohydrodynamical stability, Neoclassical transport, and microscale turbulence. Within the latter strand, I show that the scaling of the turbulent heat flux with parameters of the plasma equilibrium can be constrained by an underlying symmetry (scale invariance) of the governing equations, a prediction that is borne out by numerical simulations. Finally, I will discuss the outlook of the global nuclear fusion programme in an effort to convince you that fusion is much closer than “thirty vears away”. This talk is appropriate for anyone with a basic physics background.

Friday 13th October, 12.00pm,
Room 314, Science III Building

 

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Seminars

Ocean and atmosphere effects on sea ice in McMurdo Sound

Dr Maren Richter

Department of Physics University of Otago

Each winter the ocean in McMurdo Sound, Antarctica freezes to form sea ice. I will present results from my PhD studying the effect of atmosphere and ocean on the thickness of landfast sea-ice. Measurements were taken between 1986–2022 which provided a baseline against which I examined the variation in landfast sea-ice thickness between years. I will highlight the atmosphere and ocean properties most likely to influence landfast sea-ice thickness in McMurdo Sound. There is no main driver of fast-ice thickness in McMurdo Sound, but I found that in years when the air is colder, (southerly) wind speed is higher, and there are less southerly storms, the landfast sea ice is thicker. There remains a need for a future event-based analysis, especially around extreme storm events driving winter landfast sea- ice break up and persistence. The talk will give a general overview of Antarctic sea ice and McMurdo Sound in particular, as well as fieldwork undertaken during my PhD.

12.00pm, Wednesday 23 August 2023
Room 314, Science III Building

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Seminars

The Levitated Dipole Reactor: An introduction to a new concept for commercial fusion energy

Dr Ratu Mataira

OpenStar Technologies Wellington

Fusion energy is a hot topic at the moment and does not need any introduction. Useful fusion energy has been 30 years away for the past 80 years, and although recent achievements have been advertised as “breakthroughs”, the reality is that there are still a lot of technical challenges to overcome with the current fusion devices before we are likely to see them providing electricity to the grid.

Inspired by the dipole plasma observed around Jupiter, a joint MIT-Columbia experiment was born in the early 2000’s to test a concept known as the levitated dipole reactor (LDR). The LDR boasts a wide range of plasma performance improvements over the conventional approaches to fusion and represents the first commercially relevant fusion concept that can be achieved with current technology.

OpenStar Technologies is a Wellington-based start-up developing a levitated dipole fusion reactor. In this seminar we will introduce the physics of LDRs and why a fusion company has started in New Zealand, of all places.

12.00pm Monday 29 May 2023 
Room 314, Science III Building