Department of PhysicsJohn Anderson Research Colloquia

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 2024-2025

* Note: Outside of regular schedule.

Dr Margarita Khokhlova (King’s College London) 16th October 2024, JA 314

Light has always been our natural tool to discover the world, from everyday naked-eye observations, through the progress of optical aids such as magnifying glasses to microscopes, followed by a drastic leap in man-made light sources, from candles to lasers. Laser pulses marked a new beginning, opening a platform to dive much deeper into the nature of matter.

The shortest light flashes of attosecond duration (Nobel Prize in Physics 2023) are the ideal tool to track electrons, on their natural attosecond timescale, in atoms, molecules and solids, and, even more, to control their ultrafast dynamics underlying the molecular machinery of life, the structure and properties of materials, and the currents of modern electronics technology.

The newest progress in ultrafast science refers to ultrafast chirality: when chiral molecules, which are mirror-image twins with sometimes vitally different properties linked to the foundation of life, can be revealed in the nonlinear interaction where a laser light structured in space and time touches the electronic cloud.

One of the examples of this ultrafast chiral interaction is the chiral steering of free-induction decay radiation. We propose an experiment, where preexcited chiral molecules shone at with tri-colour chiral light send the free-induction decay emission either ‘left’ or ‘right’, thereby unveiling the chirality of the molecule in hand from its twin one. This interaction is based at a deeper level on the chiral Stark shift that we introduce – a chiral cousin of the Stark shift of the electronic levels in a laser field. This scheme offers a new tool of chiral recognition based on strong dipole interactions.

Dr Sebastian Wood (National Physical Laboratory) 30th October 2024, JA 314
 
The National Physical Laboratory (NPL) is the UK’s National Metrology Institute and undertakes research in measurement technology to support national industry. Net Zero ambitions (in the UK and globally) require electrification of transport and growth in renewable energy generation. The adoption of new semiconductor materials will play an integral role in this journey by enabling more efficient generation, distribution, and use of electricity. This talk will focus on two classes of materials: wide bandgap compound semiconductors (SiC, GaN, and Ga2O3) for power electronics; and organic-inorganic hybrid perovskites for photovoltaics. In each case, successful commercialisation and adoption requires robust methods for quantitatively characterising the quality, performance, and reliability of devices. 
 
The European power electronics industry is leading the transition from silicon to wide bandgap compound semiconductors (SiC, GaN, and β-Ga2O3). These materials offer huge benefits in terms of performance, but the manufacturing yield and long-term reliability are affected by material defects, which are hard to identify and characterise at the fabrication facility with existing techniques. The ‘PowerElec’ project is a European Metrology Project developing new metrological methods for quality assurance and to support standards development that will support supply chain growth. The project has developed new high-throughput optical metrology techniques for rapid wafer-scale measurements, as well as novel forms of off-line nanoscale defect characterisation. Compressive sensing is a key component of this project, which provides a means of overcoming the traditional trade-off between measurement throughput and sensitivity. 
 
Hybrid organic-inorganic perovskites have emerged over the last decade as a promising material for photovoltaics with tuneable bandgaps and potential for scalable manufacture. The power conversion efficiencies of perovskite devices are approaching commercial viability but long-term operational stability remains challenging. The performance of perovskite devices is highly sensitive to the nanoscale composition and thin film structure. NPL has developed novel methods of electrical scanning probe microscopy to relate nanoscale morphology with local functional properties. This leads to insights into local charge carrier dynamics and mitigation of degradation pathways.

Dr Ahsan Nazir (University of Manchester), 13th November 2024, JA 314

Quantum systems are invariably open, evolving under surrounding influences rather than in isolation. Standard open quantum system methods eliminate all information on the environmental state to yield a tractable description of the system dynamics. By incorporating a collective coordinate of the environment into the system Hamiltonian, I shall explain how to circumvent this limitation [1]. The resulting theory provides straightforward access to important environmental properties that would otherwise be obscured, allowing quantification of the evolving system-environment correlations. As a direct result, I shall show that the generation of robust system-environment correlations that persist into equilibrium renders the canonical system steady state almost always incorrect. The resulting equilibrium states deviate markedly from those predicted by standard perturbative techniques and are instead fully characterized by thermal states of the mapped system-collective coordinate Hamiltonian. I shall also outline how noncanonical system states could be investigated experimentally to study deviations from canonical thermodynamics [2,3,4], with direct relevance to molecular and solid-state nanosystems.
 
[1] J. Iles-Smith, N. Lambert, and A. Nazir, Phys. Rev. A 90, 032114 (2014)
[2] D. Newman, F. Mintert, and A. Nazir, Phys. Rev. E 95, 032139 (2017)
[3] H. Maguire, J. Iles-Smith, and A. Nazir, Phys. Rev. Lett. 123, 093601 (2019)
[4] O. Diba, H. J. D. Miller, J. Iles-Smith, and A. Nazir, Phys. Rev. Lett. 132, 190401 (2024)

James Millen (King’s College London) 27th November 2024, JA 314

Mesoscopic particles levitated in vacuum offer a unique insight into a range of physics. They are at the boundary of what is feasible to control at the quantum level, appreciably couple to gravity, and are of a size scale relevant to both biophysics and nanotechnology. The motional energy of a levitated microparticle is comparable to the energy of the thermal environment, making them a key testbed for stochastic thermodynamic processes. In this talk, I will introduce a new neuromorphic method for detecting and controlling levitated microparticles, and present our progress in synthesizing extreme and unusual thermodynamic scenarios.

James P. McGilligan (University of Strathclyde), 4th December 2024, JA 314

The separation of atomic energy levels provides a previously unobtainable accuracy and precision in metrology, with an SI traceable reference to frequency and wavelength [1]. This achievable performance is widely exploited in atomic sensors, built around platforms in both cold and thermal ensembles to manipulate atom-light interactions to the benefit of real-world applications in navigation, geological surveying, medicine, communication, and finance.

In recent years, our research team has focussed on the micro-fabrication of core components to aid the miniaturisation of atomic sensors to the chip-scale, where their mass producibility and portability enable deployment out of laboratory environments [2]. Our research has focussed on the realisation of a lab-on-a-chip platform, where we address measurements in length, time, rotation, and magnetic field as our primary sensor foundation.

This talk will highlight our recent work on chip-scale components that facilitate a new-generation of atomic sensors. This work includes an overview of our work in the research of chip-scale atomic clocks [3,4], tunable wavelength references [5], and portable magnetometers [6,7]. Additionally, we will discuss the novel fabrication approaches we have developed with an outlook to in-field deployment of quantum technology [8].

References

  1. Kitching, Chip-scale atomic devices, Appl. Phys. Rev. 5, 031302 (2018)
  2. McGilligan, et. al. Micro-fabricated components for cold-atom sensors, Rev. Sci. Instrum. 93, 091101 (2022)
  3. McGilligan, et. al., Laser cooling in a chip-scale platform, Appl. Phys. Lett. 117, 054001 (2020)
  4. Bregazzi, et. al. A simple imaging solution for chip-scale laser cooling, Appl. Phys. Lett. 119, 184002 (2021)
  5. Dyer, et. al. Chip-scale packages for a tunable wavelength reference and laser cooling platform, Phys. Rev. Appl. 19, 044015 (2023)
  6. Dyer et al. Nitrogen buffer gas pressure tuning in a micro-machined vapor cell, Appl. Phys. Lett. 123, 074001 (2023)
  7. Hunter, et al. Free-induction-decay magnetic field imaging with a microfabricated Cs vapor cell, Opt. Exp. 31, 33582-22595 (2023)
  8. Dyer, et. al. Micro-machined deep silicon atomic vapor cells, J. Appl. Phys. 132, 134401 (2022)

Ursula Keller (ETH Zurich), 15th January 2025, TIC Level 1 Auditorium

The optical frequency comb (OFC) revolution began in the late 1999, marked by three pivotal publications [1-3]. Since then, the field has been a major focus of research, continuously evolving with new innovations. A key advancement in OFC technology are dual-comb lasers, which employs a pair of combs distinguished by a small yet precise difference in their spacing. This allows for rapid pump-probe and spectroscopy measurements without any mechanical delay lines.

We have invented new shared-cavity methods to generate two optical combs with slightly different, adjustable pulse repetition rates. By generating both combs within the same cavity, the system is simplified, and the combs exhibit highly correlated noise properties. These single-cavity dual-comb lasers achieve low noise levels, making them suitable for practical dual-comb measurements. We pioneered two techniques based on polarization [4] and spatial [5] multiplexing. In 2017, the polarization multiplexing approach enabled dual-comb spectroscopy from a single free-running passively mode-locked laser cavity, a key milestone [6].

Since then, we have demonstrated low-noise performance using diode-pumped Yb-doped solid-state and vertical-emitting semiconductor lasers. To verify these low-noise properties, we developed a highly sensitive pulse timing jitter characterization tool [7]. We have demonstrated coherent averaging of dual-comb signals, enabling dual-comb spectroscopy applications with excellent signal-to-noise ratios from free-running dual-comb oscillators without additional stabilization [8]. Many application demonstrations have been done with these lasers, such as picosecond ultrasonics [9], lidar [10], time-domain THz spectroscopy [11], equivalent sampling of SESAM response [12], spectroscopy with adjustable delay intervals [13], 3D microscopy [14], OPO and mid-IR spectroscopy [15] and bio-medical applications [16].

This talk will provide an introduction to dual-comb lasers and highlight several specific application demonstrations.

  • [1] H. Telle et al., Appl. Phys. B 69, 327–332 (1999)
  • [2] A. Apolonski et al., Phys. Rev. Lett. 85, 740–743 (2000)
  • [3] D. J. Jones et al., Science 288, 635–639 (2000)
  • [4] S. M. Link et al., Optics Express 23 (5), 5521 (2015)
  • [5] J. Pupeikis et al., Optica 9 (7), 713 (2022)
  • [6] S. M. Link et al., Science, 356, 1164 (2017)
  • [7] S. L. Camenzind et al., Opt. Express 30 (4), 5075 (2022)
  • [8] C. R. Phillips et al., Opt. Express 31 (5), 7103 (2023)
  • [9] J. Pupeikis et al., Photoacoustics 29, 100439 (2023)
  • [10] S. L. Camenzind et al., Optics Express 30 (21), 37245 (2022)
  • [11] B. Willenberg et al., Applied Optics 63 (15), 4144 (2024)
  • [12] A. Nussbaum-Lapping et al., Applied Physics B 128, 24 (2022)
  • [13] F. Flöry et al., Ultrafast Science 3, 0027 (2023)
  • [14] W. Lu et al., Optics Letters 49 (7), 1766 (2024)
  • [15] C. P. Bauer et al., Nature Communications 15, 7211 (2024)
  • [16] B. Zhang et al., ACS Photonics 11 (10), 3972 (2024)

Dr Matthew Mears (University of Sheffield), 29th January 2025, JA 314

In this presentation, I will explore the theme of equality, diversity, and inclusion (EDI) in physics education through the lens of three distinct research projects, structured around the lifecycle of a student's academic journey.

Beginning with an investigation into pre-university exposure to coding, I will discuss the barriers and opportunities that different students face before entering university. Next, I will present the issue of gender bias in assessment tools within physics education, and how deeply rooted these biases may persist. Finally, I will show the impact of non-traditional modules, such as employability and soft skills courses, on students' academic outcomes and career readiness, delving into the balance between real-world skills and academic achievement.
 
By sharing these insights, I aim to shine a light on how the tools, experiences, and structures we use—no matter how well-intentioned—can have varied, unexpected, and sometimes conflicting impacts on different demographic groups. It’s crucial for us, as educators, to understand these nuances and rethink our approaches to foster truly inclusive and supportive learning environments.

Prof Elena Blokhina (University College Dublin), 12th February 2025, 3pm, JA314

Silicon-based spin qubits have been investigated extensively over the past years as a promising platform for scalable quantum computing. Silicon quantum computing leverages semiconductor manufacturing technologies that are well-established in terms of materials and wafers, process steps, and circuit design. Recent advancements have demonstrated high-fidelity single-qubit and two-qubit gates for Si qubits, reinforcing silicon’s viability as a qubit platform. Moreover, its compatibility with classical electronics makes it an attractive candidate for large-scale quantum processor integration.

In this talk, I will provide an overview of the basic principles of spin qubits in silicon, including electrostatically defined quantum dots, charge sensors for spin qubits, basic quantum gates, and qubit benchmarking. I will present our recent results on fully depleted silicon-on-insulator quantum dots implemented using a commercial fabrication process. This commercial approach presents new opportunities for scalable quantum systems. Our results include transport studies, charge stability analysis, and the realization of tunable tunnel-coupled quantum dot arrays, providing insights into the feasibility of this technology for silicon-based spin qubits. Additionally, I will present selected results on SiGe qubits as an example of an established spin qubit platform, including their benchmarking at elevated temperatures.

Prof Daniel J Blumenthal (University of California Santa Barbara), 25th February 2025, 3pm, TIC Level 1 auditorium

Visible-light to short-wave IR (SWIR) integrated lasers and integrated photonics will enable compact, reliable quantum and atomic experiments. Integration also has the potential to realize improved performance and scalability as well as new functionality for quantum sensing, computation, clocks, and metrology. We discuss progress in ultra-low-loss silicon nitride integration for precision lasers, modulators, and other atomic and quantum related photonics and quantum and atomic, molecular, and optical (AMO) physics functions. We also discuss progress towards integration of experiments and applications with cold neutral atoms and trapped ions.

Prof Livio Gianfrani (Università degli studi della Campania "Luigi Vanvitelli"), 26th February 2025, 11-12noon, TL455

Mercury is a quite interesting atom for fundamental tests and measurements. It is a good candidate for the development of a primary frequency reference in the optical domain. The intercombination transition, which is typical of a two-electron atom, can be used to search for an electric dipole moment in the electronic ground state of the 199Hg atom. In addition, this line is a highly sensitive probe of possible long-term variations of the fine-structure constant. Its seven isotopes, five of which have a zero nuclear spin, make it an ideal system for isotope shift spectroscopy, looking for a possible King-plot nonlinearity as a signature of a new physics, beyond the Standard Model. An ongoing experiment in Caserta employs the Hg intercombination line at 253.7 nm for temperature metrology, by using comb-calibrated Doppler width spectrometry.

I will report on recent efforts and results concerning Doppler broadening thermometry and, more generally, precision measurements on mercury isotopes, including isotope shift determinations, as well as the first results of a double resonance experiment in an open three-level ladder scheme.

Dr Gillian Butcher (University of Leicester), 12th March 2025, Room TBA

Dr Gillian Butcher graduated from Strathclyde University in 1987 with a degree in Applied Physics. Thus armed and with an enthusiasm for all things involving photons, she embarked on a career which has encompassed designing airfield lighting, researching the use of lasers in molecular orientation studies and designing, building and testing instruments for space. After briefly discussing her career and the various Earth observation, planetary and astronomical missions she has worked on, Gillian will talk about space science in general and more specifically about what she and her Space Projects and Instrumentation colleagues do at Space Park Leicester.

Prof Louise Hirst (University of Cambridge), 26th March 2025, 3pm, JA314

The space sector has seen rapid expansion in recent years with increasing commercialisation and reduction in the cost of launch. For many decades spacecraft payloads have been powered by photovoltaic systems; however, emerging applications including next generation satellite networks, space based solar power and science in space missions have a unique combination of design criteria including extended radiation resilience for longer missions in more hostile environments; high specific power for further launch cost reduction with high power payloads; deployable form factors for efficient launch packing; and lower fabrication costs. These new demands are driving innovation in the sector.
 
Ultra-thin photovoltaics (~100 nm active region) offer inherent tolerance to particle radiation induced damage while the use of integrated photonic structures enables selective scattering of incident photons into laterally propagating modes for full solar absorption in the ultra-thin film. This platform also offers a lightweight flexible form factor and pathway to lower cost fabrication. In this talk our approach to system design and fabrication will be discussed along with characterisation of particle radiation damage in these materials using cathodoluminescence and how these advancements can impact on mission capabilities and the provision of space-based services.

Prof. Dr. Maria Dienerowitz, Deutsches Optisches Museum
TL423 for Friday from 14.00 – 15.00
The Deutsches Optisches Museum (D.O.M.) is currently being developed as the national flagship museum for optics and photonics, offering approximately 3000 m² of publicly accessible exhibition space. The exhibition concept places a strong focus on three core elements: (1) interactive stations that allow visitors to explore physical laws and optical phenomena through hands-on edutainment, (2) demonstrations of how these principles are implemented in technical instruments and applied in both everyday life and scientific practice, and (3) a dedicated space showcasing cutting-edge research in optics and photonics. This talk offers insights into the design and development process. A key emphasis is placed on accessibility - across different levels of prior knowledge and age groups. The museum thus becomes a space for active learning, engagement, and an inspiring exploration of optics and photonics. 

Prof. Emmanuel Saridakis (SUPA Distinguished Visitor Professor; IAASARS, National Observatory of Athens), 4th June 2025, 3pm, TL455

The whole history of science is a history of tensions between theoretical predictions and observations. We construct theories that can successfully explain physical phenomena, until new and more precise observational data appear, revealing tensions with our theories, which forces us to modify or replace them. The remarkable progress made in astrophysics and cosmology in the 21st century brings significant tensions, providing strong indications that we may be close to a scientific revolution.

Dr Carlo Sias (European Laboratory for Nonlinear Spectroscopy (LENS) Sesto Fiorentino, Italy), 2nd July 2025, 3pm, TL455
Trapped ions form, at a sufficient low temperature, spatially ordered Coulomb crystals, the configuration of which depends from the shape of the confining potential. In my talk, I will present our recent studies on the formation and changes of configurations of two-dimensional Coulomb crystals. In particular, I will discuss how this system exhibits bistability, i.e. two distinct metastable configurations can coexist, and transitions between them may be driven by thermal fluctuations [1].

We investigated bistability in two-dimensional Coulomb crystals composed of Ba+ ions by using an innovative Paul trap in which the aspect ratio of the confining potential can be continuously changed from a one dimensional “tube” to a two-dimensional “pancake” [2]. Using Monte Carlo simulations, we calculate the energies of different crystal configurations and reveal a parameter range in which a double-well structure emerges [3], where the relative depth of each well — each corresponding to a metastable configuration — can be tuned by adjusting the trap aspect ratio.

Experimentally, we realize a crystal of six ions and identify a bistable regime in which the ions arrange either in a hexagonal, “benzene-like” configuration or in a pentagonal configuration with one ion at the center the trap. We observe bistability through photon scattering and measure the probability of occupying the different configurations depending on the energy imbalance between the two energy wells.

Furthermore, by quenching the trap aspect ratio, we can populate a highly excited metastable configuration and witness its relaxation dynamics with a fast detection scheme.

Our study establishes a new platform to emulate molecule isomerization, and to explore quantum superpositions of crystalline configurations. To this end, we plan to place the Coulomb crystal at the crossing of a bow-tie optical cavity, and use this for creating a deep optical potential for a micromotion-free confinement of the ions [4].

  • [1] H. Oike et al., Nature Phys. 12, 62 (2016).
  • [2] L. Duca et al. Phys. Rev. Lett. 131, 083602 (2023)
  • [3] P. Haenggi, P. Talkner, and M. Borkovec, Rev. Mod. Phys. 62, 251 (1990).
  • [4] E. Perego et al. Appl. Sci. 10, 2222 (2020)

Prof Kavan Modi (Singapore University of Technology and Design), 10th September 2025, 3pm, JA314

Chaotic systems are highly sensitive to a small perturbation, and are ubiquitous throughout biological sciences, physical sciences and even social sciences. Taking this as the underlying principle, we construct an operational notion for quantum chaos. Namely, we demand that the future state of a many-body, isolated quantum system is sensitive to past multitime operations on a small subpart of that system. By 'sensitive', we mean that the resultant states from two different perturbations cannot easily be transformed into each other. That is, the pertinent quantity is the complexity of the effect of the perturbation within the final state. From this intuitive metric, which we call the Butterfly Flutter Fidelity, we use the language of multitime quantum processes to identify a series of operational conditions on chaos, particularly the scaling of the spatiotemporal entanglement. Our criteria already contain routine notions and well-known diagnostics for quantum chaos. We then extend the criteria to include projected process ensembles, motivated by studies on deep thermalisation. Our results account for previous attempts to make sense of quantum chaos, such as the Peres-Loschmidt Echo, Dynamical Entropy, Tripartite Mutual Information, and Local-Operator Entanglement. Finally, we will present numerical results using the XXZ model and discuss how chaos leads to equilibration, Markovianisation, and thermalisation.
Reference: N Dowling, K Modi, PRX Quantum 5, 010314 (2024)