Past Colloquia
Speaker: Dr Sean Barrett (Macquarie University)
Date: 23rd October 2009
Building a quantum computer is one of the central challenges in modern
physics. One of the main obstacles to a practical realization is that
existing approaches to quantum computation seem to be rather fragile
to environmental noise and other imperfections. Only a small amount of
noise can render a quantum computer completely useless.
In the first part of the talk I will review the two most promising
approaches to overcoming the problem of noise in quantum computers:
one which might be dubbed a `software’ approach, utilizing quantum
error correcting codes, and a `hardware’ approach where physical
robustness is built into the system, e.g. by making use of a new class
of materials called topologically ordered systems.
Towards the end of the talk I will briefly describe some recent work
(performed by myself, Tom Stace and Andrew Doherty, see Phys. Rev.
Lett. 102, 200501) on the effect of qubit loss robust quantum
information processing schemes. Remarkably, we have found that robust
quantum storage is possible even if up to half the qubits are lost,
and furthermore our results indicate that fully fault tolerant quantum
computation is possible if up to 24% of the qubits are lost. I briefly
discuss the consequences for both software and hardware approaches to
noise tolerance.
October 23rd, 2009
Speaker: Professor Tadeusz Sarna (Jagiellonian University, Poland)
Date: 16th October 2009
In mammals, melanin is responsible for the pigmentation of the skin, eye and hair. Although it is believed that melanin is involved in photoprotection of the human skin and eye, the exact mechanism by which melanin protects pigmented cells against light-induced oxidative stress is not well understood. In this talk, a brief review of basic physicochemical properties of melanin pigments, particularly melanosomes from the human retinal pigment epithelium (RPE) will be given, and new results, illustrating the antioxidant ability of melanin in model systems will be discussed. An attempt will be made to identify in situ conditions that may lower antioxidant efficiency of melanin and stimulate its pro-oxidant action. A new-developed model of in vitro photoaging of retinal pigment epithelium (RPE) melanin to explain the observed changes in photoreactivity and antioxidant properties of human RPE melanosomes with aging will also be discussed.
October 16th, 2009
Speaker: Dr Michael Brown (Monash University)
Date: 25th September 2009
In cold dark matter (CDM) cosmologies, the most massive dark matter halos undergo rapid growth between a redshift of z=1 and z=0, corresponding to the past 7 billion years of cosmic time. There is thus an expectation that the stellar masses of the most massive galaxies will also rapidly grow via merging. While there are examples of massive merging galaxies at low redshift, recent observations show that the stellar masses of massive galaxies have grown by only 30% since z=1. While some claim this is contrary to the CDM paradigm, this is not necessarily the case. To determine why massive galaxies are not growing rapidly, we have used measurements of the evolving space density and spatial distribution of galaxies to constrain models of how galaxies populate dark matter halos. We find that the stellar masses of the largest galaxies are proportional to dark matter halo mass to the power of a third. In the most massive dark matter halos, we also find that the stellar mass is distributed mostly among satellite galaxies. As a consequence, the stellar masses of large galaxies are expected to increase relatively slowly, even though they reside within rapidly growing dark matter halos.
September 25th, 2009
Speaker: Professor Charles Lineweaver
Date: 18th September 2009
I will present a paper recently published in Physics of Life Reviews entitled “Life, gravity and the second law of thermodynamics” in which we (i) review the cosmic evolution of entropy and the gravitational origin of the free energy required by life and (ii) describe how all dissipative structures in the universe including all forms of life, owe their existence to the fact that the universe started at low entropy and has not yet reached equilibrium. The low initial entropy was due to the low gravitational entropy of the nearly homogeneously distributed matter and has, through gravitational collapse, evolved gradients in density, temperature, pressure and chemistry. These gradients, when steep enough, give rise to far from equilibrium dissipative structures (e.g. galaxies, stars, black holes, hurricanes and life) which emerge spontaneously to hasten the destruction of the gradients which spawned them. This represents a paradigm shift from “we eat food” to “food has produced us to eat it”.
September 18th, 2009
Speaker: Professor Cornelia Denz (Institut für Angewandte Physik and Center for Nonlinear Sciences,Westfaelische Wilhelms-Universität Münster, Germany)
Date: 11th September 2009
In live sciences, the observation and analysis of moving living cells, molecular motors or motion of micro- and nano-objects is an actual field of research. Especially in the field of system biology and nano-medicine, a complete in vivo analysis of the molecular dynamics of functional systems is one of the challenges of the near future. At the same time, micro fluidic innovations are needed for biological and medical applications on a micro- and nano-scale. Conventional microscopy techniques are reaching considerable, principle limits with respect to these issues.
A promising approach for this challenge is nonlinear dynamic phase contrast microscopy. It is an alternative full field approach based on nonlinear refractive index changes that allows to detect motion as well as phase changes of living unstained micro-objects in real-time, thereby being marker free, without contact and non destructive, i.e. biocompatible. The generality of this system allows it to be combined with several other microscope techniques as well as with optical tweezers or optical manipulation. In this talk I will present the nonlinear optics basics of the dynamic phase contrast technique and its applications in analysis of microorganismic dynamics, micro-flow velocimetry and micro-mixing analysis. Moreover, combinative approaches of nonlinear refractive index changes techniques with optical multifocus-tweezers are presented.
September 11th, 2009
Speaker: Dr Ben Powell (University of Queensland)
Date: 4th September 2009
Condensed matter provides a rich variety of playgrounds for studying the quantum mechanics of large numbers of strongly interacting particles. Yet in condensed matter systems materials issues, such as disorder and the inherent complexity of materials science, often mask the richness of the physics. Therefore an important task for condensed matter physicists is to identify and understand universal properties of matter, i.e. properties are the same in broad classes of materials. This approach has led to many deep insights into quantum many-body physics. I will discuss the history of universal ratios in condensed matter physics and how they have helped us understand the quantum many-body problem. I will then introduce a new ratio, which compares the temperature dependence of a metal’s resistivity to that of its heat capacity, that takes the same (predicted) value in a wide range of strongly correlated metals - despite the numerator and denominator varying by ten orders of magnitude. Finally, I will discuss what we learn about strong correlated electrons from this result.
September 4th, 2009
Speaker: Professor Paul Burn (University of Queensland)
Date: 28th August 2009
The application of conjugated ‘organic’ (plastic) materials in opto-electronic devices is one of the fastest growing fields in chemistry and condensed matter physics. The importance of the field was recognized in 2000 by the award of the Nobel Prize to Shirakawa, McDairmid, and Heeger (a chemistry and physics team) who were the pioneers of work on ‘conducting’ polymers, that is polymers that had conductivity similar to metals. However, the ‘semiconducting’ properties of conjugated ‘organic’ materials have proved more fruitful with such compounds being applied as the active layers in devices such as organic light-emitting diodes (OLEDs), solar cells, plastic electronics (field effect transistors), and sensors. Of these applications the use of OLEDs in displays and lighting is the most advanced. For all these applications the photonic and electronic properties, e.g., photoluminescence quantum yields and charge mobility respectively, are dependent on how each (macro)molecule interacts with its neighbours. These interactions are turn is dependent on the shape of each (macro)molecule. In this seminar we will explore how the shape of the ‘organic’ semiconductors affect their performance in a range of device applications.
August 28th, 2009
Speaker: Professor David Jamieson (University of Melbourne)
Date: 21st August 2009
The year 2009 has been declared the international year of astronomy to commemorate and celebrate the 400th anniversary of the first time Galileo turned his newly invented telescope to the heavens. This lecture looks at Galileo’s technological breakthrough with the invention of his astronomical telescope and investigates the avalanche of new discoveries and knowledge that it produced. Some of these discoveries are well known like the discovery of the moons of Jupiter and the lunar landscape. But there is a surprise drawn from the pages of Galileo’s logbooks of 1612 and 1613. He notes the position of a “fixed star” that does not exist in any star chart because it is the planet Neptune which Galileo observed 234 years before its official discovery. Did he know this “fixed star” was a planet? His notes suggest he saw Neptune move and computer simulations show the precision of his observations. This lecture will review the evidence.
August 21st, 2009
Speaker: A/Professor Kae Nemoto (National Institute of Informatics, Japan)
Date: 14th August 2009
Quantum mechanics is one of the most successful formalism in physics in the last century and has already been more than a hundred years of history. Yet, quantum mechanics remains difficult to understand by following our natural scientific sense. In the last decade, quantum physics has been most intensively investigated. Behind the sudden heat in the quantum physics research, there is the integration of concepts of physics and computer/information sciences. This development allowed us to enter a new regime where we have never been able to reach before. In this talk, I will introduce the basics of quantum information processing as well as most recent results and explain why this approach leads us to a new adventure in the quantum world.
August 14th, 2009
Speaker: Dr Austin Lund (Griffith University)
Date: 7th August 2009
Since the publication of Knill, Laflamme and Milburn [Nature 409, 46 (2001)] on how to perform a quantum computation using linear optical elements and photo-detection efficiently, there has been a huge flurry of activity in optical quantum computing. The large resource consumption of this scheme has been a concern of many and there have been new proposals which have fundamentally redesigned this scheme to address this problem (e.g. cluster state quantum computing). In this talk I will present a scheme based on coherent states which I worked on during my PhD studies at UQ. This coherent state scheme achieves scalable linear optical quantum computing by increasing the amplitudes of the coherent states and not the number of resources required. I will show how this scheme naturally fits into the world of quantum error correction and compare its performance to other schemes. There may also be some semi-humorous photos of cats.
August 7th, 2009
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Physics Colloquia are held on Friday afternoons in Room 222, Parnell Building, from 4-5pm. All are welcome to attend! Refreshments are served before the talk, from 3:30pm.
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