Prof Vahid Sandoghdar (Max Planck Institute for the Science of Light)
Exploring and exploiting light-matter interaction at the nanometer scale: from quantum optics to biophysics
Friday 18 October 2024
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 in a microcavity and exploit this system for the realization of complex hybrid 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 detect, image, characterize, and track single biological nanoparticles such as viruses and small proteins with high spatial and temporal resolutions and in a label-free fashion.
Prof Amanda Wright (University of Nottingham)
Optical imaging deep into biological samples
Friday 1 November 2024
Aberrations, or wavefront distortions, present in optical microscopy systems degrade image quality and resolution. This problem is particularly apparent when imaging at depth in biological samples where changes in the local refractive index and structure of the sample can distort the beam producing a poor-quality focus and eventually making it impossible to image. Many techniques have been developed over the years to determine the aberrations present in a system and then subsequently correct for these aberrations by shaping the wavefront of the input beam with the equal but opposite distortion. Most of these approaches have been iterative, searching the wavefront space to optimise on a property of the image and determine the wavefront correction required. Such approaches typically require hundreds if not thousands of iterations to improve the quality of the image. This makes the correction processes slow; live, delicate, samples are exposed to an excessive amount of photons risking photo damage and it becomes impractical to make more than one correction across a field of view. I will present some of our recent work in the field of aberration correction, or wavefront shaping, for deep optical imaging, concentrating on approaches that are iteration free. The first method uses analytical approaches and more recently we have been employing AI and developing deep networks able to predict the aberrations present in an imaging system.
Prof David Alexander (Durham University)
I'm a quasar get me out of here
Friday 15 November 2024
Are quasars, the sites of the most rapidly growing black holes, buried in shrouds of dust? A quasar is the observed manifestation of a rapidly growing super-massive black hole. The majority of quasars discovered to date are blue in colour due to us having a direct view of the mass accretion onto the black hole. However, a minority of quasars are found to be optically red, almost always due to the presence of obscuring dust along the line of sight. The standard model postulates that these red quasars are more inclined towards our line of sight than blue quasars such that the accreting black holes are partially hidden from us. On the basis of this model red quasars would have essentially the same basic properties (on average) as blue quasars, when the effects of obscuration and orientation are taken into account.
I will report on a series of systematic and controlled multi-wavelength experiments where we identify fundamental differences between red and blue quasars, particularly in the radio waveband. I will show that these results suggest a connection between opacity and the production of radio emission, potentially due to shocks from winds and/or jets as the quasar tries to break free of a dusty shroud. These results appear in conflict with the standard model and I argue that they point towards red quasars representing a distinct phase in the evolution of quasars.
I will finish with our latest research which extends these results to even fully obscured quasars, where we also identify differences in the host galaxy and large scale properties. I will discuss plans to extend these results with our upcoming 4MOST survey and discuss our results in the context of the latest discoveries by the JWST telescope.
Dr Shuqiu Wang (University of Bristol)
Visualizing Intrinsic Topological Superconductivity
Friday 29 November 2024
Topological order represents a revolutionary framework in condensed matter physics that describes quantum states through their robust mathematical properties. This has led to the discovery of exotic quantum phases such as topological superconductivity and quantum spin liquids, with profound implications for new quantum matter physics and future technologies. A macroscopic quantum state emerges from the collective behaviour of electrons and spins. In correlated electronic systems, electrons or spins dance independently but follow identical patterns. In topological orders, electrons or spins interact through local quantum rules, creating coherent global patterns characterized by long-range entanglement. Intertwining electronic correlations and topology now stands at the frontier of modern quantum matter research. One of its most profound consequences is the intrinsic topological superconductivity (ITS), a unique and quite extraordinary type of macroscopic quantum matter. ITS promise both cutting-edge science and revolutionary quantum technology, such as quantum computing. Key signatures for an ITS include the existence of spin-triplet pairing, topological surface bands and persistent surface currents. None of these characteristics has ever been detected due to the lack of visualization techniques. I will present our quest to discover and visualize intrinsic topological superconductivity, starting with fundamental concepts and historical context. Using innovative scanning tunnelling microscopy (STM) imaging [1], we achieved a sequence of breakthroughs in the spin-triplet superconductor UTe2 [1], identifying key ITS signatures including distinctive surface bands and non-chiral pairing. These findings represent the first detection of three-dimensional ITS characteristics, which is an unprecedented quantum state.
[1] Gu, Carroll, Wang et al., Nature 618, 921 (2023).
[2] Gu, Wang, Carroll, Zhussupbekov et al., Science (2024).
Prof Sir Michael Berry (University of Bristol)
Four geometrical-optics illusions
Friday 13 December
Centuries after the laws of geometrical optics were established, they still have nontrivial and varied applications. Illustrating this are some illusions:
Mirages, and Raman’s error. Understanding why he denied the applicability of geometrical optics requires careful exploration of the continuum limit of a discretely-stratified medium, to reveal its nonuniform convergence.
Oriental magic mirrors and the Laplacian image. The optics of these several-millenniaold objects involves the unfamiliar regime of pre-focal brightening. The transmission analogue (‘Magic windows’) raises a challenge for freeform optics.
The squint moon and the witch ball. The moon sometimes appears to point the wrong way because we perceive the sphere of directions as a distorted ‘skyview’, on which geodesics appear curved. This can be conveniently viewed and analysed by viewing the sky in a reflecting sphere.
Distorted and topologically disrupted reflections in curved mirrors. Mirror-reflected rays from each point of a continuous object form caustic surfaces in the air. Images are organised by those points whose caustics intersect our eyes, and can be systematically understood in terms of the elementary catastrophes of singularity theory.
Professor Sir Michael Berry's abstract can also be found here.