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)

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

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

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, TBC