Department of PhysicsJohn 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 2019-2020

Semester I

Semester II

* Note: Outside of regular schedule.

Advanced LIDAR Technologies

Fu Yang (Donghua University) 17th September 2019, 3pm, JA3.17

Prof Fu Yang will firstly present an overview of the research activities of the Physics Department at Donghua University, Shanghai. This includes activities in atmosphere plasma physics & applications, fusion plasma, micro-nano optoelectronic materials and devices, and photoelectric detection. She will then discuss her own research in advanced lidar technologies.

Lidar is the Abbreviation of light detection and ranging. Its original use is for range detection. From hundreds of kilometers away, lidar altimeters can give scientists a broad overview of the features of remotely detected objects. So whenever scientists launch a satellite to a new planet, the lidar altimeter will always be equipped to give scientists the three-dimension of the new planet, which is one of the most exciting features. All of the launched laser altimeter payloads adopt the traditional time of flight direct-detection method. The advantages of this method are mature technology and simple system structure. The disadvantage is the huge peak power resulting from the long detection range. Such drawback results in the problem of low pulse repetition frequency (PRF) because of the need to avoid risking damage to the laser. Many new detection methods have been proposed. I have studied three advanced lidar ranging technologies in detail by using narrow linewidth lasers. They are chirped amplitude modulation together with heterodyne detection, pseudorandom amplitude modulation together with single photon counting, and pseudorandom phase modulation together with heterodyne detection. Both simulation and experiment results will be introduced. In addition, I developed the pseudorandom phase modulation together with heterodyne detection technology to both range and velocity measurement. Through signal processing, this technology can be used for wind detection without blind zone. Finally high precision ranging using the femtosecond frequency comb and ocean lidar detection are also introduced. These two parts are simulation work.

Laser Cooled Neutral Plasmas: a Laboratory for the Study of Strongly Coupled Systems

Tom Killian (Rice University) 23rd September 2019, 3pm, JA5.07

Strong coupling arises when interaction energies are comparable to, or exceed, kinetic energies, and this occurs in diverse systems such as dense white dwarf stars, strongly correlated electron systems, and cold quantum gases. In all environments, strong coupling complicates theoretical description and gives rise to new, emergent phenomena. Ultracold neutral plasmas (UNPs), generated by photoionization of a laser-cooled gas, are a powerful platform for studying strong coupling in classical systems, and serve as an ideal laboratory model for other strongly coupled plasmas.

In this talk, I will present experimental studies of self-diffusion and thermal equilibration, and describe the role of strong coupling in these phenomena. I will also present results from the first application of laser-cooling to a neutral plasma, which increases the achievable coupling strength. Although the technique we use, optical molasses, is well established, the high collision rates and rapid hydrodynamic expansion of the plasma create a unique environment for laser cooling. Through laser-cooling we have created plasmas with ion temperatures as low as 50 mK and achieved a factor of 4 enhancement in the coupling strength, placing the laser-cooled UNP in the same coupling regime as white dwarf stars and allowing for experimental benchmarking of new models and molecular dynamics simulations of transport.

The Role of Diagnostics in Plasma Etch Reactors in Enabling the Information Age

Alex Paterson (Lam Research Corp, San Jose, CA), 3pm, 8th October 2019, Court Senate Suite

Over the last decade, semiconductor industry growth has been driven chiefly by the demand for consumer electronics and the advent of the data economy: the move to mobile smart devices such as phones and tablet PC’s and the proliferation of Artificial Intelligence. It is now common place for hand-held mobile devices to have 512 Gb of memory and processor speeds of over 2 GHz, a truly remarkable feat that would have been unthinkable 10 years ago. This capability has been enabled by the continuation of IC scaling to smaller and smaller features sizes with the present technology being mass produced by 14 nm node technology and smaller nodes down to 3 nm currently being developed by IC manufacturers. For example, the latest Apple® iPhone® 11 uses an A13 Bionic CPU with 8.5 billion transistors fabricated with 7nm technology. The limitations of lithography to keep up with the decrease in dimensions required for these smaller nodes has resulted in new challenges for plasma etch to enable patterning at these small feature sizes. Device performance requirements also drive critical dimension (CD) non-uniformity to less than one nanometre across the entire 300 mm wafer for sub-20 nm features and yield requirements extend this pattering region to within 1.5 mm of the wafer edge. Wafer fabrication production also relies on plasma etch solutions to be stable at these levels across long periods of time and capable of flexibility in multiple applications. The realization of all of these goals has been greatly facilitated by a much better understanding of the basic chemical, physical, and electromagnetic processes that occur during the plasma etch of semiconductor devices.

In this paper we will discuss the crucial role diagnostics play in achieving this understanding and in the development of state-of-the-art plasma etch chamber technology that allow the continuation of Moore’s Law. Diagnostics are essential not only to understand etch mechanisms and chamber characteristics but to also accelerate hardware development in order to meet customer time critical needs. We will review the different types of diagnostics commonly used in plasma etch chamber development with reference to findings from literature and augment this with diagnostic work undertaken at Lam Research. Finally, we will discuss the suitability of diagnostics in main stream production and give some thoughts on future diagnostics that may be required for production enhancement and angstrom level etching.

Generation and characterisation of high-dimensional discrete cluster states on chip

Lucia Caspani (University of Strathclyde) 9th October 2019, JA3.14

The generation of quantum states of light featuring entanglement over many photons and multiple modes allows to access larger Hilbert spaces, thus increasing the resources for applications in, e.g. quantum metrology, communications and computing. In this context, cluster states are of particular importance as the primary resource for the so-called one-way quantum computation. Among the different approaches for the generation of these complex quantum states, hyperentanglement increases the number of modes combining independent variables, such as polarisation and optical path, or orbital angular momentum. However, such degrees of freedom are either limited in dimensionality (polarisation) or quite difficult to achieve and manipulate.

We proposed an innovative scheme for the generation of hyperentangled states by properly combining the temporal and frequency degrees of freedom readily accessible in an integrated microring resonator. Furthermore, we developed a deterministic phase gate based on a frequency-to-time mapping scheme allowing us to manipulate these variables independently for generating high-dimensional discrete cluster states on-chip. The characterisation of these multipartite, high-dimensional states is, however, quite challenging. We developed a universal technique to derive experimentally-friendly entanglement witnesses for high-dimensional cluster states. This allowed us to characterise our d-level multipartite cluster state with fewer measurements compared to the full density matrix reconstruction. Finally, we demonstrated proof principle one-way quantum computing operations with our system.

Physics, we need to talk about... Resilience & Wellbeing

Sara Shinton (University of Edinburgh) 23rd October 2019, JA3.17

The event will feature a keynote talk from Dr. Sara Shinton (Head of Researcher Development, University of Edinburgh), followed by a panel discussion focussed on topics relating to resilience & wellbeing in academia.

Near-threshold self-pulsing in Fabry-Perot lasers

Luigi Lugiato (Universita' dell’ Insubria, Como, Italy) 4th November 2019, JA3.14

We analyse multimode instabilities in a Fabry-Perot laser. It is well known that in the case of a ring cavity the multimode instability can arise only when the pump parameter is several times above lasing threshold. We focus on the parametric conditions that allow for the adiabatic elimination of the atomic polarization only. Under such conditions no multimode instability is possible in the ring configuration. By investigating the stability of the stationary solutions in a fully analytical manner, we demonstrate that, on the contrary, in the Fabry-Perot case a multimode instability can arise very close to lasing threshold and is governed by a remarkably simple formula. Numerical solutions of the dynamical equations confirm this scenario and describe the self-pulsations generated by this instability.

The work is done in collaboration with Dr. Franco Prati.

Boosting fluorescence in high-resolution imaging by tunable nano-coatings and optoplasmonics

Katrin Heinze (Rudolf Virchow Center, Research Center for Experimental  Biomedicine, University of Würzburg) 6th November 2019, 3pm, JA3.14

The 'Resolution Revolution' in fluorescence microscopy over the last decade has given rise to a variety of techniques that allow imaging beyond the diffraction limit with resolution up to the nanometer range. One particularly powerful technique is direct stochastic optical reconstruction microscopy (dSTORM), a widely-used type of single molecule localization microscopy (SMLM), which is based on the temporal separation of the emission of individual fluorophores and subsequent localization analysis. This eventually allows to reconstruct a super-resolved image revealing details down to typically 20 nm in a cellular setting. The key point here is the achievable localization precision, which mainly depends on the image contrast generated by the individual fluorophore’s emission. We found that reflective metal-dielectric nano-coatings represent a tunable nano-mirror that can do both quenching and boosting fluorescence for high-contrast imaging on the nanoscale. The resolution improvement achieved with such mirror-enhanced STORM (meSTORM) is both spectrally and spatially tunable and thus allows for dual-color approaches on the one hand, and selectively highlighting region above the cover glass on the other hand. Even if the resulting resolution boost is based on a near-field effect and thus restricted to imaging near surfaces, most membrane fluorescence applications benefit. Beyond SMLM this also includes live-cell methods such as Fluorescence Correlation Spectroscopy and Fluorescence Resonance Energy Transfer.

Mirror-enhanced fluorescence is very different from other surface techniques based on total internal reflection microscopy or optoplasmonics. While surface-plasmon supported fluorescence method provide much higher enhancement factors, mirror-enhanced approaches are more versatile and thus highly suitable for modern bio-imaging.

Alternative quantum facts: testing local observer independence

Alessandro Fedrizzi (Heriot-Watt University) 20th November 2019, 3pm, JA3.14 (CANCELLED)

The scientific method relies on facts, established through repeated measurements and agreed upon universally, independently of who observed them. In quantum mechanics the role of the observer has always be somewhat troublesome—it is for example not entirely clear where to draw the line between system and observer. This issue is at the heart of the famous measurement problem and its consequences are exposed by a thought experiment first suggested by Eugene Wigner in the 60s. A quantum system is observed by an observer—Wigner’s friend—in an enclosed box, which is itself observed from the outside by Wigner. From Wigner’s perspective, system and friend are in an entangled state, which can be verified by measurement. The friend on the inside though will be convinced to have observed a definite measurement outcomes in each experimental trial. So the two observers seem to experience subjective realities.

The question whether the two narratives can be reconciled has only recently been made accessible to empirical investigation, through recent no-go theorems that construct an extended Wigner’s friend scenario with four observers. I will introduce this background and then present results from a recent six-photon experiment in which we realised this extended Wigner’s friend scenario and experimentally violated the so-called Bell-Wigner inequality by five standard deviations. If one holds fast to the assumptions of locality and free choice, this result implies that quantum theory should be interpreted in an observer-dependent way.

Women in Leadership: An overview of the global leadership initiative Homeward Bound & my personal experience as participant

Dr Jana K Schniete (University of Strathclyde) 22nd January 2020, 3pm, JA3.17

Despite continuous efforts for gender equality, there is still a big gender gap in STEMM fields, this is particularly pronounced at senior level. In this seminar, I will talk about Homeward Bound, which is a global leadership initiative with the aim to equip 1000 women in STEMM with leadership skills to enable them to join the leadership tables around the world.

The initiative has created a year-long program to significantly improve women in STEMM’s clarity, confidence, shared vision and strategic capability for authentic leadership to proactively contribute to a sustainable world, both individually and collectively.

In doing this, Homeward Bound aims to create a new way of leading that is better suited to the world we are now living in, with a greater focus on the concept of a ‘global home’ – led with integrity, a drive for results, an ability to motivate others, a deep care for relationships and the will to collaborate towards this shared ambition.

I will also talk about my personal experience as a participant and my learnings and how these have influenced me and how these can be useful in a day to day context and how by taking little adjustments we can all contribute to a cultural change which in the end will lead to greater inclusion and diversity at all levels.

Next Generation Biophysics to study DNA: in vitro, in silico and in the living cell

Mark Leake (University of York) 29th January 2020, 3pm, JA3.14

The biological functions of DNA rely not just on its raw nucleotide sequence but also on a suite of proteins which interact with DNA. Many of these interactions have a significant influence on the topology of DNA and its subsequent role inside living cells: several basic, essential processes such as DNA replication, transcription and gene regulation are all dependent in highly sensitive ways upon these often complex and heterogeneous binding and dissociation events. Here I will discuss some of our insights in this area, which have all stemmed from the development and application of in vitro, in silico and in vivo methods, that could, perhaps, be thought of as emerging from the growing toolkit of ‘next generation biophysics’. This powerful combinatorial approach has enabled us to shed some light into the role of shape of DNA in regards to its biological function at the level of single, functional molecules.

Testing dark energy models with atom interferometry

Clare Burrage (University of Nottingham) 4th March 2020, 3pm, JA3.14

The accelerated expansion of the universe motivates a wide class of scalar field theories that modify gravity on large scales. In regions where the General Relativity has been confirmed by experiment, such theories need a screening mechanism to suppress the new force. I will describe how theories with screening mechanisms can be tested in the laboratory, in particular with atom-interferometry experiments.

I will describe the results of a recent experiment in which we measured the acceleration of an atom toward a macroscopic test mass inside a high vacuum chamber, where the new force is unscreened in some theories. Our measurement shows that the attraction between atoms and the test mass does not differ appreciably from Newtonian gravity. This result places stringent limits on the free parameters in chameleon and symmetron theories of modified gravity.


Which way is North? Science and applications of geomagnetism: from the outer core to the Sun

Dr Ciaran Beggan (The British Geological Survey) 11 March 2020 3pm JA3.14

After temperature, high-quality magnetic field measurements are the longest geophysical record we have, stretching back to the age of sail  from around 1500 CE onward. While temperature tells us primarily about the surface processes, magnetic fields come from multiple sources, probing all the way from the outer core to the Sun. As any single measurement is the sum of these processes in varying proportions, it is impossible to disentangle the individual contributions. However, making multiple measurements across the world taken from surface to space over hundreds of years gives us a way to reveal the different sources and their behaviours. The crustal field changes over millions of years, the core field varies slowly over years to decades while the ionospheric and magnetospheric fields can change in seconds. On sub-second scales, lightning and pulsations are detectable. 

This rich environment of sources allows geophysicists to explore the Earth and Sun in ways complementary to seismology or astronomy. Practically, people have been making use of the magnetic field for applications such as navigation or mineral exploration for centuries. In this talk I will touch on the history of geomagnetism, recent science advances and applications. I will also note the opportunity that better instrumentation offers for new science and applications.

 Caption: Sketch of the various magnetic field sources detectable at or above the Earth’s surface

Olsen, Nils & Hulot, G. & Sabaka, T. (2010). Measuring the Earth’s Magnetic Field from Space: Concepts of Past, Present and Future Missions. Space Science Reviews. 155, 65-93, doi: 10.1007/s11214-010-9676-5


Two-dimensional moiré heterostructures

Brian D. Gerardot (Institute for Photonics and Quantum Sciences, SUPA, Heriot-Watt University) 18th March 2020, 3pm, JA3.14

The unique physical properties of two-dimensional materials, combined with the ability to stack unlimited combinations of atomic layers with arbitrary crystal angle, has unlocked a new paradigm in designer quantum materials. For example, when two different monolayers are brought into contact to form a heterobilayer, the electronic interaction between the two layers results in a spatially periodic potential-energy landscape: the moiré superlattice. Single particle wavepackets can be trapped in the periodic potential pockets with three-fold symmetry to form an intrinsic ‘quantum dot’ lattice. Here I will discuss the properties of such quantum emitter arrays and discuss their prospects as a spin-photon interface or the potential of strong interactions within the excitonic superlattice which can lead to superradiance, topological moiré minibands, or the realization of a tunable Mott-Hubbard Hamiltonian.




Efficiency in the interaction of light and matter:from nano-quantum optics to nanobiophotonics

Vahid Sandoghdar (Max Planck Institute for the Science of Light, Staudtstr) 9th June 2020, 3pm, JA3.14

Light-matter interaction at the nanometer scale lies at the heart of elementary optical processes such as absorption, emission or scattering. Over the past two decades, we have realized a series of experiments to investigate the interaction of single photons, single molecules and single nanoparticles. In this presentation, I will report on recent studies, where we reach unity efficiency in the coupling of single photons to single molecules and describe our efforts to exploit this for the realization of polaritonic states involving a controlled number of molecules and photons. Furthermore, I will show how the underlying mechanisms that play a central role in quantum optics, help image and track single biological nanoparticles such as viruses and small proteins with high spatial and temporal resolutions.