School Research Seminars
School of Mathematics & Physics Highlighted Seminars
Wednesday 21 April 2021 at 5.30 pm
Online Larmor Lecture followed by private Question and Answer Session
With the invention of lasers, the intensity of a light wave was increased by orders of magnitude over what had been achieved with a light bulb or sunlight. This much higher intensity led to new phenomena being observed, such as violet light coming out when red light went into the material. After Gérard Mourou and I developed chirped pulse amplification, also known as CPA, the intensity again increased by more than a factor of 1,000 and it once again made new types of interactions possible between light and matter. We developed a laser that could deliver short pulses of light that knocked the electrons off their atoms. This new understanding of laser-matter interactions, led to the development of new machining techniques that are used in laser eye surgery or micromachining of glass used in cell phones.
‘Quantum Reality: Unperformed experiments have no results and unobserved results can affect future experiments’
Date: 4th November 2020 from 12:00 - 15:30
The 2020 John Bell Day Lecture will take place on Wednesday 4th November: we have an exceptional speaker this year in Professor Vlatko Vedral, Professor of Quantum Science at the University of Oxford. The title of this year’s lecture will be ‘Quantum Reality: Unperformed experiments have no results and unobserved results can affect future experiments’.
Professor Vedral has kindly agreed to an additional “unplugged” session for students - ‘Quantum Physics, Life and the Universe: In Conversation with Professor Vlatko Vedral’, where he will speak about his career and anything quantum physics-related that he can answer! This session will be hosted by Professor Mauro Paternostro, Head of School of Maths and Physics, and will take place from 12.00-12.45pm on Wednesday 4th November.
Once registered a link will be sent out via email so you can join the conversations.
We are delighted to invite you to Queen’s University Belfast's third online independently-organised TEDx conference, in association with the Faculty of Engineering and Physical Sciences, taking place on Thursday 24 June from 12.30pm to approximately 2pm.
TEDxQueensUniversityBelfast 'Engineering our Sustainable Future' will showcase our community - our staff, students and alumni; offering a glimpse of the innovation, discovery and creativity taking place in the Faculty of Engineering and Physical Sciences.
The programme highlights just a few exciting projects and ideas, involving technology, design, people and natural resources, that may help to engineer a more sustainable future for all.
The Gender Justice and Society Network at QUB invites you to an online event 'Tackling Sexual Violence in Universities' on Wednesday 16th June from 12-2 pm (on Zoom).
Students should have a university experience free from harm and abuse. Far from being very isolated incidents, most research suggests rape and sexual assault involving students is a feature across University campuses. With the combination of academics, students, and organisations dedicated to the improvement of safety from sexual violence on campus, join us for a discussion about how prevalent this issue still is, and what can be done to tackle the issue.
Our fantastic speakers will share their reflections on experiences within Irish universities and the challenges faced in making a transformative change:
- Prof. Louise Crawley (University College Cork), Executive member of Bystander intervention at UCC https://www.ucc.ie/en/bystander/meet-the-team/
- Dr Pádraig MacNeela (NUI Galway), Active consent programme co-lead.
- Discussant: Meghan Hoyt(QUB), PhD candidate, Addressing Misogyny: The Law, Hate Crime and New Feminist Approaches” (TBC)
- Chair: Sarah Kay (QUB), activist lawyer, Steering Committee member of the Gender Justice Society Network
The event will be introduced by Megan Stith (QUB), Steering Committee member of the Gender Justice and Society Network
There will be plenty of time for Q&A following the presentations by the speakers.
Towards a detailed understanding of strong light-matter coupling effects
Date and Time: Friday June 11, 2021; 2:00-3:30 PM
In the last decade a host of seminal experimental results have demonstrated that properties and dynamics of molecules and solids can be modified and controlled by coupling strongly to the electromagentic field of a photonic environment, e.g. an optical cavity. However, many of the observed effects are not well understood and the common models of strong light-matter coupling lead to contradictory conclusions. It therefore becomes desirable to have first-principles approaches to strong light-matter coupling in order to obtain a so far elusive detailed understanding of photon-modified matter properties.
In this talk I will discuss the fundamental setting for such ab-initio methods, the Pauli-Fierz quantum field theory in Coulomb gauge , highlight subtle yet important issues, e.g., the significance of the bare masses of the particles, and introduce a hierachy of approximations in first-principles approaches to light-matter coupled systems [2,3]. I will then show how the recently developed quantum-electrodynamical density-functional theory [4,5] is able to treat all these levels of approximations, and demonstrate how a detailed understanding of strong light-matter coupling becomes accessible by ab-initio simulations. Among others I will highlight how decoherence and dissipation are naturally included in such simulations [1,5,6], that common models of light-matter interactions become less accurate if applied naively to vibrational excitations  and that collective coupling effects imply local strong coupling between light and matter . This last finding is especially important, since it provides a so far elusive basic understanding of photon-modified chemistry .
 Spohn, Herbert. Dynamics of charged particles and their radiation field. Cambridge university press, 2004.
 Ruggenthaler, Michael, et al. "From a quantum-electrodynamical light–matter description to novel spectroscopies." Nature Reviews Chemistry 2.3 (2018): 1-16.
 Ruggenthaler, Michael, et al. "Quantum-electrodynamical density-functional theory: Bridging quantum optics and electronic-structure theory." Physical Review A 90.1 (2014): 012508.
 Ruggenthaler, Michael. "Ground-state quantum-electrodynamical density-functional theory." arXiv preprint arXiv:1509.01417 (2015).
 Jestädt, René, et al. "Light-matter interactions within the Ehrenfest–Maxwell–Pauli–Kohn–Sham framework: fundamentals, implementation, and nano-optical applications." Advances in Physics 68.4 (2019): 225-333.
 Flick, Johannes, et al. "Light–matter response in nonrelativistic quantum electrodynamics." ACS photonics 6.11 (2019): 2757-2778.
 Sidler, Dominik, et al. "Chemistry in Quantum Cavities: Exact Results, the Impact of Thermal Velocities, and Modified Dissociation." J. Phys. Chem. Lett. 11 (2020): 7525-7530
 Sidler, Dominik, et al. "Polaritonic Chemistry: Collective Strong Coupling Implies Strong Local Modification of Chemical Properties." J. Phys. Chem. Lett. 12 (2020): 508-516
 Schäfer, Christian, et al. "Shining Light on the Microscopic Resonant Mechanism Responsible for Cavity-Mediated Chemical Reactivity." arXiv preprint (2021)
Wednesday 2nd June 2021 at 2pm
The iconic spiral arms that decorate the disks of massive galaxies (like our own Milky Way) have been studied since they were first recorded (Rosse 1843), nevertheless the details of their nature remains elusive. I will review what is known observationally about spiral arms, including recent results from Galaxy Zoo crowdsourced morphologies and data from the spatially resolved (IFS) survey, MaNGA. I will discuss how these observational data are constraining some of the different physical models which have been proposed.
Maths and Physics Gender Equality Annual Lecture
Gender and Information and Communication Technologies: results from PISA 2018
Tuesday 18th May at 12pm
ICT literacy has become an important key driver regarding the competence for the adults, but even more for young people. As it was pointed out in 2003, ICT literacy is defined as “the interest, attitude, and ability of individuals to appropriately use digital technology and communication tools to access, manage, integrate, and evaluate information, construct new knowledge, and communicate with others in order to participate effectively in society” (Lennon et al., 2003). Using data from 2018 Programme for International Student assessment (PISA), this work will show the gender differences in ICT literacy and will explore the relationships in ICT literacy with literacy in mathematics, reading and science.
Lennon, M., Kirsch, I., von Davier, M., Wagner, M., & Yamamoto, K. (2003). Feasibility study for the PISA ICT Literacy Assessment, Report to Network A. Retrieved from http://eric.ed.gov/PDFS/ED504154.pdf.
High-resolution wave activity in the lower solar atmosphere
Wednesday 5th May 2021 at 2pm
Waves and oscillations have been proposed as one of the prime candidates for the transport of energy and momentum to the upper solar atmosphere whose heating has been a much-debated topic in solar physics over the past few decades. In this talk, we will briefly review our recent observations of waves in the lower solar atmosphere at high resolution. In particular, we will first present properties of magnetohydrodynamic wave dynamics in various small-scale magnetic structures in the lower solar atmosphere, at high-spatial resolution, from observations with the SUNRISE balloon-borne solar observatory. Our analysis reveals the prevalence of kink and sausage mode waves in the magnetic structures, propagating at similar high frequencies. The estimated energy flux carried by the observed waves is marginally enough to heat the upper solar atmosphere. We will further present advances on such wave signatures from the Atacama Large Millimeter/submillimeter Array (ALMA) which started regular observations of the solar chromosphere at millimeter wavelengths in December 2016. These provide us with new insights into the nature of various wave phenomena in the solar chromosphere, thus, their role in heating the upper solar atmosphere.
Quantum Anharmonicity in solids with the Stochastic Self-Consistent Harmonic Approximation.
Friday, April 23, 2021 Time: 2:00 PM - 3:30 PM
The treatment of non perturbative quantum anharmonicity is a challenge for state-of-the-art first-principles electronic structure calculations. The quantum anharmonic effects are particularly relevant (i) in proximity of a second order phase transition where the harmonic phonon frequency becomes imaginary and perturbation theory breaks down, (ii) in the case of light atoms, as the ionic displacement is substantial and a large portion of the potential is sampled.
In the last years our group developed the Stothastic Self-Consistent Harmonic Approximation  (SSCHA) a technique that rigorously describes the full thermodyamics of crystals accounting for nuclear quantum and thermal anharmonic fluctuations. The approach requires the evaluation of the Born-Oppenheimer energy, as well as its derivatives with respect to ionic positions (forces) and cell parameters (stress tensor) in supercells, which can be provided, for instance, by first principles density-functional-theory codes. The method performs crystal geometry relaxation on the quantum free energy landscape, optimizing the free energy with respect to all degrees of freedom of the crystal structure. It can be used to determine the phase diagram of any crystal at finite temperature. It enables the calculation of phase boundaries for both first-order and second-order phase transitions from the Hessian of the free energy. Finally, the code can also compute the anharmonic phonon spectra, including the phonon linewidths, as well as phonon spectral functions.
In this talk, after a brief introduction to the (SSCHA), I will present its application to several systems of interest, ranging from transition metal dichalcogenides [2,3] to high pressure hydrogen.
 www.sscha.eu and references therein.
 Theory of the thickness dependence of the charge density wave transition in 1 T-TiTe2 JS Zhou, R Bianco, L Monacelli, I Errea, F Mauri, M Calandra 2D Materials 7 (4), 045032 (2020)
 Anharmonicity and Doping Melt the Charge Density Wave in Single-Layer TiSe2 JS Zhou, L Monacelli, R Bianco, I Errea, F Mauri, M Calandra Nano Letters 20 (7), 4809 (2020)
 Black metal hydrogen above 360 GPa driven by proton quantum fluctuations L Monacelli, I Errea, M Calandra, F Mauri Nature Physics 17, 63 (2021)
Searching for Bumps in the Night: A Data-driven Revolution for Time Domain Astrophysics
Wednesday 21st April 2021 at 2pm
The eruptions, collisions and explosions of stars drive the universe’s chemical and dynamical evolution. The upcoming Large Synoptic Survey Telescope will drastically increase the discovery rate of these transient phenomena, bringing time-domain astrophysics into the realm of “big data.” With this transition comes the important question: how do we classify transient events and separate the interesting “needles” from the “haystack” of objects? In this talk, I will discuss efforts to discover and classify unexpected phenomena using semi-supervised machine learning techniques.
Wednesday 14 April, 3pm
Adding dissipation channels to quantum simulation devices can achieve two important goals. On the one hand, dissipation can cool the simulator to a low-energy state that can be used subsequently in further simulations . On the other hand, adding dissipation to a quantum simulator allows to realize novel classes of dynamical systems with intriguing properties. I will focus on the investigation of a quantum version of an elementary cellular automaton, which results in extremely complex dynamics whose statistical properties can only be
predicted by actually running the simulation. Remarkably, it is possible for this complex dynamics to coexist with quantum entanglement. Finally, I will comment on the realization of such cellular automata on current quantum simulation devices based on ultracold Rydberg atoms, by using a variational principle for open quantum systems  to engineer the required many-body interactions.
 M. Raghunandan, F. Wolf, C. Ospelkaus, P. O. Schmidt, H. Weimer, Science Adv. 6, eaaw9268 (2020).
 H. Weimer, PRL 114, 040402 (2015).
Wednesday 14th April at 2pm
What are the observable effects induced by substellar ingestion? Do we have any hope of unambiguously detecting such signatures? In this talk, I address these open questions, describing my efforts to unveil stellar hosts that have ingested their substellar companions within open cluster environments. These stars offer invaluable constraints to test stellar evolutionary models. Moreover, they offer a rare opportunity to directly measure the bulk composition of substellar companions. I describe several promising ingestion-derived tracers, emphasizing a need for targeted photometric and spectroscopic to unambiguously detect such sources.
Large Molecules in Space: The Hunt for Fullerenes in the Diffuse Interstellar Medium
Wednesday 24th March 2021 at 2pm
The 'soccer ball' molecule buckminsterfullerene (C60) was first identified by Kroto et al. (1985) during a series of experiments attempting to synthesize long carbon chain molecules in the laboratory. The unusual molecular properties of fullerenes, including their size, strength, electrical conductivity and stability make them uniquely attractive for a range of practical uses, including high-tech medical applications, aerospace and advanced sporting equipment. The icosahedral symmetry of C60 renders its molecular structure extremely stable, and Kroto realized that this stability would allow it to persist in harsh astrophysical environments, including the strongly-irradiated diffuse interstellar medium where less-stable molecules are easily destroyed. This realization led to the suggestion of C60+ and, more specifically, its electrically charged counterpart (C60+), as possible carriers of (some of) the unidentified diffuse interstellar bands (ubiquitously observed absorption features in the spectra of stars residing behind interstellar clouds). In this talk, I will summarize our knowledge of cosmic fullerenes and present new results obtained using an unorthodox observing mode of the Hubble Space Telescope, producing unprecedented sensitivity in the near-infrared part of the spectrum, and confirming the presence of C60+ in the diffuse interstellar medium.
Wednesday 3rd March 2021 at 2pm
The theoretical description of stars is plagued by severe scale problems: the many physical processes at play act on vastly different spatial and temporal scales. The classical approach to deal with this problem has been to formulate the underlying equations assuming spherical symmetry and hydrostatic equilibrium thus allowing for (numerical) solutions that explain the main phases of stellar evolution and reproduce many observables. This success, however, came at a price: casting inherently multidimensional physical processes in a one-dimensional framework required strong parametrization and sometimes even tinkering with the underlying physics. This diminishes the predictive power of stellar models and improvements are required to interpret and guide current and future observations. The next generation of stellar models has to be build on multidimensional simulations. Are current (super-)computational resources sufficient to meet this challenge? What numerical techniques are required to enable simulations of challenging multi-physics, multi-scale stellar models? I will discuss three examples where a one-dimensional treatment fails: convection in stellar interiors, stellar explosions, and common envelope phases in binary stellar evolution. With special numerical techniques, these phenomena are accessible to three-dimensional hydrodynamic simulations that pave the way to a better understanding of stellar evolution.
Semi-empirical models of spicule from inversion of Ca II 8542 Å line.
Wednesday 3rd February 2021 at 2pm
We study a solar spicule using high-resolution imaging spectroscopy in the Ca II 8542 Å line obtained with the CRisp Imaging SpectroPolarimeter on the Swedish 1-m Solar Telescope. Using a new version of the non-LTE code NICOLE specifically developed for this problem we invert the spicule line profiles. This new version considers off-limb geometry and computes atomic populations by solving the 1D radiative transfer. We show that the double-component model of a spicule, with uniform temperature and exponential decrease of density, reproduce the line profiles at all spicule segments. This is the first spectral diagnostics of the physical parameters of a spicule through line profile fitting with a non-LTE inversion code. In this talk, I will outline our method, approach to inversions and present the resulted semi-empirical spicule models.
Wednesday 27th January 2021 at 2pm
Comets are some of the most pristine relics of planetary formation and their nuclei preserve invaluable clues about the conditions prevailing in the protoplanetary disk at the time of their formation. They are thus incredible tools to study the history of planetary systems. Cometary science has made huge progresses in the past decades, especially thanks to the Rosetta mission. However, numerous questions are still left to answer. One of those is: how does the composition of comets reflect their place of formation in the protoplanetary disk?
I will discuss how this question can be answered using ground-based observations of comets: by comparing the composition of large number of comets coming from different reservoirs, which may have formed at different distances in the protoplanetary disk; by measuring isotopic ratios in the atmosphere of comets; and by studying the composition interstellar comets formed in very different environments.
Wednesday 28th October 2020 at 2pm
When we observe the first terrestrial exoplanet atmospheres, we expect to find planets around a wide range of stellar types, UV environments, and geological conditions. Since the first exoplanets available for characterization will be likely for M dwarf host stars, understanding the UV environment of these cool stars is a vital step in understanding the atmospheres of these planets. Additionally the atmospheres of these planets will not been fixed in time. Earth itself offers many possible atmospheric states of a planet. We set out to examine how an Earth-like planet at different geological epochs might look around other star types Additionally, we examine the plausibility of detecting prebiotically interesting molecules, such as HCN, NH3, CH4, and C2H6 in an early-Earth type atmosphere around stars with very different UV environments, an M dwarf and a solar analogue.