Department of Physics John Anderson Research Colloquia

Wednesday's at 3.00pm (unless otherwise stated) 

Colloquia will usually be held in JA3.14
John Anderson Building 
107 Rottenrow, Glasgow

Coffee and Tea served at 4.00 pm.

All Welcome

Coordinated with the Colloquia at the Department of Physics and Astronomy of the University of Glasgow. (They may have donuts but we have free chocolate covered biscuits and coffee!)

Colloquia Schedule 2016-2017

Semester I

Semester II

* Note: Outside of regular schedule.

Glassy Metal Fibres for measuring big G

Dr Riccardo DeSalvo (California State University, University of Sannio), 2nd September 2016, 2pm JA5.04

The measurements of the Universal Gravitational Constant “G” have been improving in precision and spread for 200 years Then starting 50 years ago, while the nominal precision of the experiments has shrunk to 10 ppm, or less, the spread between measurements has remained around 100 ppm. Clearly an uncontrolled physical mechanism is at work.

It has been proposed that the same Self Organized Critical behaviour that destabilise GAS filters and IPs at low frequency also acts on the Tungsten fibres and breaks down the F=kx restoring force at the base of all measurements. It is proposed to use glassy metal fibres, which being dislocation free cannot be subject to the suspected physical mechanism. If proven correct, the same materials can be used for low frequency seismic attenuations for the Einstein Telescope.

Harnessing the complexity of quantum many-body systems

Dr Luca Tagliacozzo, (Department of Physics, Strathclyde), 21st September 2016, 3pm, JA3.13

Quantum many-body systems underlie our understanding of Nature. For example, an electric current of one Ampere for one second consists of around 10^18 electrons, and a laser beam involves a huge number of photons. In these systems both photons and electrons interact weakly and thus can be described as "independent" particles enabling us to correctly describe their behaviour.

What happens when a large number of constituents interact strongly? In most cases we don't know exactly but have observed that the emergent behaviour can be extremely different from that of the individual constituents alone. To use the words of the Nobel Laureate Phil Anderson, "more is different".

In the quest to describe emergent phenomena, we have recently understood that entanglement can be used as a guiding principle to characterize collective behaviour. In particular, I will discuss how understanding the structure of entanglement allows us to obtain an effective description of many-body systems in terms of tensor networks. This gives the unprecedented ability to compute the emerging properties of many-body quantum systems from first principles. I will conclude by addressing the issue about the existence of entanglement in the real world, by presenting recent results about a strategy to measure entanglement in experiments.

Developing Semiconductor Nanowires for Future Optoelectronics

Dr Hannah Joyce (Cambridge), 12th October 2016

Semiconductor nanowires exhibit outstanding potential as nano-building blocks for the next generation of electronic devices, ranging from solar cells to nanoscale lasers. A variety of innovative fabrication techniques can be employed to "grow" these nanowires with tight control over the nanowire geometry and crystallographic properties. Electrical characterisation of these tiny nanowires can be achieved with high accuracy and high throughput without requiring any electrical contacts, using a contact-free technique known as terahertz conductivity spectroscopy. This talk will discuss how detailed nanowire growth studies together with terahertz conductivity spectroscopy are guiding the development of novel nanowire-based devices.

Cavity Quantum Electrodynamics in Superconducting Circuits

Dr Peter Leek (Oxford), 20th October 2016

The last decade has seen remarkable improvements in coherence and control of superconducting quantum circuits, such that they have become a leading candidate for the implementation of a quantum computer. One of the most important advances behind this progress is the realisation of circuit quantum electrodynamics (QED), in which superconducting qubits are coupled to electromagnetic resonators to realise the physics of cavity QED on an electronic chip. In this talk I will introduce this field and discuss how it can be used for microwave frequency quantum optics experiments, demonstrations of fundamental building blocks of quantum computing, as well as how it can be employed to investigate the physics of other quantum systems in solid state. I will touch on recent progress on realising new forms of circuit QED, motivated by the goal of building a practically useful quantum computer.

Frequency Comb Generation and Spontaneous Symmetry Breaking in Microresonators

Dr Pascal Del'Haye (NPL), 2nd November 2016

Microresonator-based frequency combs ("microcombs") have attracted a lot of attention for their potential applications in precision metrology, gas sensing, arbitrary optical waveform generation, telecommunication and integrated photonic circuits. Microcombs are generated in ultra-high-Q optical resonators that enable the confinement of extremely high optical power levels in tiny mode-volumes. The high optical power densities lead to the conversion of a continuous wave laser into a comb of equidistant optical modes that can be used like a ruler for optical frequency measurements. This talk presents new results in the field of microresonator-based frequency combs, which are a promising candidate to realize out-of-the-lab applications for this technology.

The second part of the talk presents new results on optically induced symmetry breaking between counter-propagating light in microresonators. This effect shows that microresonators can act as nonreciprocal devices that transmit light in one direction but not in the other. The symmetry breaking can be used for optical diodes, circulators and for the development of integrated optical gyroscopes.

Quest for Higher Sensitivity in Fluorescence Based Detection. From Ultrasensitive Biomedical Assays to Super-resolution Imaging

Prof Zygmunt (Karol) Gryczynski (Texas Christian University, Fort Worth & Center for Fluorescence Technologies and Nanomedicine, UNTHSC, Fort Worth), 2nd November 2016, 11am, JA5.05

Background is a fundamental problem restricting sensitivity of biomedical assays and imaging. The limiting factors are sample autofluorescence (fluorescence of inherent components of cells, tissue, and fixatives) and scattering of excitation that can produce secondary unwanted excitations or may simply leak into the detector. Bright probes emitting in the red and NIR range significantly improved detection limit. Since background emission is dominated by short-lived components long-lifetime probes offer additional possibility for enhancing signal-to-background ratio by applying time-gated detection. Also, we recently realised that detection can be highly improved when using multi-pulse pumping excitation technology. Implementation of multi-pulse pumping and use of time-gated detection allows for high (few orders of magnitude) enhancement of the fluorescence signal of the probe over the autofluorescence. We will discuss applications of our new pumping technology in combination with time-gating and total internal reflection fluorescence (TIRF) to increase sensitivity of biomedical assays while decreasing the sample volume. We will present assays ranging from DNA detection, traumatic brain injuries (TBI), to possible Zika detection.

The possibility to highly enhance signal from an object by simple electronic pulse sequence manipulation opens a new way for obtaining subwavelength resolution images. Just changing from single pulse excitation to multiple-pulse excitation within one excitation trace will instantaneously increase (many-fold) the intensity of a subwavelength size object labelled with a long-lived probe, allowing for its quick localisation. In such a way we can highly increase imaging speed as compared to stochastic methods allowing for dynamic imaging of physiological processes. I will present imaging with 50 nm resolution and applications to biological systems.

Temporal Localized Structures and Light Bullets in Passively Mode-Locked Lasers

Dr Julien Javaloyes, Departament de Fisica, Universitat de les Illes Baleares, Mallorca, Spain, 16th November 2016, 3pm, JA3.14

Localised structures (LS) are nonlinear states of dissipative extended systems characterised by a correlation range much shorter than the size of the system, thus allowing for individual addressing. They appear ubiquitously in nature and they are very appealing in optical systems for applications to information processing, especially in semiconductor lasers which are fast, scalable and cheap devices.

We present experimental and theoretical evidences [1] regarding how the mode-locked pulses in the output intensity of a laser coupled to a saturable absorber transform into temporal lasing LS, allowing for individual addressing and arbitrary low repetition rates. These results form the basis of the recent prediction [2] of three dimensional light bullets in a similar experimental configuration. These results would pave an experimental path toward full spatio-temporal localisation, which has been so far elusive in nonlinear science.

[1] Marconi, Mathias, et al. "How lasing localized structures evolve out of passive mode locking." Physical review letters 112.22 (2014): 223901.
[2] Javaloyes, J. "Cavity light bullets in passively mode-locked semiconductor lasers." Physical review letters 116.4 (2016): 043901.

Laser source development at the Fraunhofer Centre for Applied Photonics

Loyd McKnight, Fraunhofer CAP, University of Strathclyde, 30th November 2016, 3pm, JA3.14

The Fraunhofer Centre for Applied Photonics (CAP), based in Strathclyde University’s Technology and Innovation Centre, is a leading applied research and technology organisation in the field of laser source development and laser-based applications. Fraunhofer CAP provide professional R&D services to industry, increasing the technology readiness to allow for commercialisation and uptake of new technology by industry.

This talk will present an overview of the organisation and the laser source development activities that are ongoing. These sources and systems have been developed with industry partners to target specific applications and market sectors. A few projects will be discussed in detail including the technical challenges involved in the development of compact laser sources for biological imaging, Doppler lidar, remote explosive detection and quantum technologies.

Protein Design as a Physical Sciences approach for Biological Function

Max Ryadnov, National Physical Laboratory, 18th January 2017, 3pm, JA3.14

Protein design is a physical sciences approach that exploits mechanistic aspects of biology. It strives to provide design constraints for supramolecular self-assembling systems that are functional at biologically relevant length and time scales. A challenge remains in replicating native assemblies synthetically, that is at will, and differentially, that is for a specific function at a given length scale. Recent examples emulating biology include virus-like capsules for gene delivery [1], fibrillar matrices for tissue repair [2], and autonomously responsive antimicrobial agents [3], while mechanistic designs enable structures with properties advanced [4] and unknown [5].

1. Noble, J. E., et al. A de novo virus-like topology for synthetic virions. J Am Chem Soc (2016), 138, 12202-12210.
2. Faruqui, N., et al. Differentially instructive extracellular protein micro-nets. J Am Chem Soc (2014), 136, 7889–7898
3. Rakowska, P. D., et al. Nanoscale imaging reveals laterally expanding antimicrobial pores in lipid bilayers. Proc. Natl. Acad. Sci. USA (2013), 110, 8918-8923
4. Pyne, A., et al. Structurally plastic peptide capsules for synthetic antimicrobial viruses. Chem. Sci. (2016), 7, 1707-1711.
5. Castelletto, V., et al. Structurally plastic peptide capsules for synthetic antimicrobial viruses. Chem. Sci. (2017), 10.1039/C6SC02925F

Quantum Communication: How quantum signals help to maintain privacy and speeds things up

Norbert Lütkenhaus, Institute for Quamtum Computing, University of Waterloo, 8th February 2017, 3pm, JA3.14

In Communication Protocols such as comparison of data and scheduling appointments, there are typically two important questions: how much bandwidth do I need to complete the task, and how much information about my local data do I leak out to my partners during the protocol? After all, when comparing data it is only important to find out whether they agree or not, but not what the data are. Same for scheduling: we want to find a joint open time-slot, but don’t want to reveal all our busy times. Quantum communication allows us to improve over classical communication in both aspects: it can use less signal to accomplish the task, and it can leak just enough information about the local data to the partners to accomplish the task, but not more.

Quantum communication protocols are usually formulated in rather abstract way, thought of more as a theoretical curiosity than a practical idea. We will see that there are ways to achieve some of the goals with rather simple tools from optical communication, just run in the quantum regime. I will review our theoretical and experimental progress for the comparison of data (quantum finger-printing) and give an outlook to the scheduling problem.

Super-resolution microscopy: Challenges, potentials and applications in biomedical research

Christian Eggeling, Professor of Molecular Immunology, MRC Human Immunology Unit & Scientific Director, Wolfson Imaging Centre Oxford

Understanding the complex interactions of molecular processes underlying the efficient functioning of the human body is one of the main objectives of biomedical research. Scientifically, it is important that the applied observation methods do not influence the biological system during observation. The most suitable tool that can cover all of this is optical far-field fluorescence microscopy. Yet, biomedical applications often demand coverage of a large range of spatial and temporal scales, and/or long acquisition times, which can so far not all be covered by a single microscope and puts some challenges on microscope infrastructure. Taking immune cell responses and plasma membrane organization as examples, we outline these challenges but also give new insights into possible solutions and the potentials of these advanced microscopy techniques, e.g. for solving long-standing questions such as of lipid membrane rafts.

Multiscale materials measurements and modelling

Benjamin Hourahine, (Department of Physics, Strathclyde), 15th March 2017, 3pm, JA3.14

Measuring the properties of materials across a range of scales is challenging – most methods can only be applied over a narrow range of lengths, and often require destructive sample preparation before they can be applied. Channelling and diffraction-based measurements in the scanning electron microscope can be very useful here: as well as being non-destructive, they give a wide field of view (~10s of μm), but are capable of resolving features on a lateral scale of ≲50 nm. However, applying these techniques to materials made from lighter atoms can be challenging, as the spatial resolution decreases proportional to the atomic number. The existing measurement methods also leave open a range of questions about what is actually being observed – its unclear for example at what depth into the sample most of the measured signal is coming from (this is estimated to be <100 nm for materials like GaN).

To improve the available quantitative information when measuring samples, and our understanding of the channelling process itself, we will be developing new approaches for energy filtered measurement of channelling. This is in concert with modelling of the elastic and inelastic channelling process and the nano-structure of these materials. Finally, image analysis using recent ideas from machine learning and image processing will be applied to speed up analysis the resulting images. Our aim is to be able to robustly characterize more challenging semiconductors, such as AlN, SiC and diamond, and we hope to be able to extend reliable measurements to two dimensional materials like graphene and BN.

Unravelling the soft X-ray emission from the Sun

Giulio Del-Zanna  (Senior Research Associate, DAMTP, University of Cambridge) , 29 March 2017, 3pm JA3.14

False-colour composite image of the Sun combining soft X-ray and EUV images.

False-colour composite image of the Sun combining soft X-ray and EUV images.

Solar and stellar coronae produce soft X-rays (5-15 nm), dominated by emission lines, mostly from Iron, formed between 1 and 15 MK. Until recently, the soft X-rays were largely unknown, compared to the other regions of the electromagnetic spectrum.

I will describe how I unravelled some of the mysteries in this spectral region using a combination of solar and laboratory observations together with state-of-the-art atomic physics calculations carried out within the UK APAP network, a collaboration between the Universities of Strathclyde, Cambridge and University College London.

Since 2010, we have for the first time continuous monitoring of the solar corona in two soft X-ray bands. In one of them, several spectral lines were unknown. The first identifications of Iron lines were carried out in the 1930's by Edlen, who became famous because they were then used to identify the visible forbidden lines, and the discovery that the solar corona has a temperature of a few million degrees.

Continuing Edlen's work required running large-scale electron-ion scattering calculations for all the coronal iron ions, which produced a number of surprising results.