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 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.

Testing dark energy models with atom interferometry

Clare Burrage (University of Nottingham) 4th December 2019, 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.