Wednesday, 17 April

Wednesday, 17 April

Sneha Malde

Beautiful and Charming CP violation : Looking for cracks in the Standard Model

An unexpected discovery of CP violation in Kaon decays in 1964 led to the development and understanding of the quark mixing matrix. More than 50 years later the rare phenomenon of CP violation continues to hold great interest, particularly due to the capabilities and results coming from the LHCb experiment. I will discuss the importance of CP violation studies, the precision detectors built to observe it, and recent measurements on the topic, including the recent first observation of CP violation in charm decays. 

 

 

Wednesday, 20 March

Wednesday, 20 March

Christoph Englert

Particle Physics in the Higgs era

Our understanding of the weak force has been spectacularly verified with the discovery of the Higgs boson in 2012. But not all is well, and more importantly, where does particle physics go from here? I will review the major shortcomings of the Standard Model of Particle Physics and discuss how they motivate new precision investigations of the electroweak interactions at present and future colliders. These theoretical developments are joined by a rapid adoption and the development of machine learning techniques in the context of particle phenomenology, which will enable the most robust constraints on the presence of new interactions beyond the Standard Model or facilitate their discovery.

 

 

6 March 2019

6 March 2019

Susan Smith

Particle Accelerators at Daresbury Laboratory

This talk presents the evolution and revolution in particle accelerator activities at STFC’s Daresbury Laboratory. Having left Glasgow University to join the Accelerator Physics group at Daresbury Laboratory in 1985, I found myself at the heart of one of the UK’s largest accelerator driven facility. Through this talk, I show how the International Accelerator Laboratory that I joined in 1985 has grown and developed into a multifaceted Science and Innovation Campus. I present a portfolio of activities that illustrates the growth, diversity and excitement of accelerator science at Daresbury today. The CLARA Free Electron Laser test facility is still under construction, the rationale behind the facility is explained and the first results of beam exploitation for research applications are presented.

 

 

20 February 2019

20 February 2019

Sir Michael Berry

Nature’s optics and our understanding of light

Optical phenomena visible to everyone abundantly illustrate important ideas in science and mathematics. The phenomena considered include rainbows, sparkling reflections on water, green flashes, earthlight on the moon, glories, daylight, crystals, and the squint moon. The concepts include refraction, wave interference, numerical experiments, asymptotics, Regge poles, polarisation singularities, conical intersections, and visual illusions.

 

 

6 February 2019

6 February 2019

Vivien Kendon

Computational quantum walks

Random walks underpin some of the best known classical algorithms, such as Monte Carlo simulations.  There are quantum versions of random walks which provide a speed up for some of these algorithms -- when we have a quantum computer to run them on.  But what is the best way to build a quantum computer?  I will explain how quantum walk algorithms work, and how we can use physics to design quantum computer hardware that is optimised for quantum walks and related algorithms.  I will present recent work on search problems and spin glasses that illustrate the potential of this approach to quantum computing.

 

 

23 January 2019

23 January 2019

Ed Daw

Hunting axions with ADMX (Axion Dark Matter eXperiment)

Abstract

Axions are hypothesised ultra-light particles that, if shown to exist, might both solve the dark matter problem and explain the apparent CP (charge conjugation and parity) symmetry of quantum chromodynamics, the theory of quarks. With the ever-more-stringent limits on new physics at the electroweak scale, the search for axions and other hidden sector fields has seen a worldwide resurgence of interest, including here in the UK. I will describe the ADMX resonant cavity axion search and present its recent results. I will also address the issue of the search rate for QCD axions with Sikivie-type resonant detectors of which ADMX is the most sensitive to date. I will describe an idea to use resonant feedback circuits to induce artificial resonances which, if successful, may increase the search rate for such experiments by factors of order 100.
 

16 January 2019

16 January 2019

Sally Jordan

Demographic gaps in physics retention and attainment: Myth and reality

Abstract

Demographic gaps in retention and attainment mean that certain groups of students, e.g. those of particular gender, socio-economic group or ethnicity or with a disability, are considerably less likely to continue in their study of physics. This contributes to the “leaky pipeline” whereby the percentage of students and workers in particular demographic groups declines further and further. Various factors have been hypothesised as contributing to these discrepancies in attainment and the talk will start by outlining these factors, including the possibility that other “hidden variables” might be at play, the impact of a lack of self-confidence and an absence of appropriate role models, and the possibility that something in our teaching or assessment might favour particular demographic groups.

The talk will then focus on research at the Open University into variation between demographic groups (in particular gender) in engagement with different types of assessed tasks and features within the tasks (Dawkins et al., 2017; Hedgeland et al, 2018) as well as describing some recent findings into variation in decision-making behaviours.

References

Dawkins, H., Hedgeland, H. & Jordan, S. (2017). The impact of scaffolding and question structure on the gender gap. Physical Review Physics Education Research, 13, 020117.

Hedgeland, H., Dawkins, H. & Jordan, S. (2018). Investigating male bias in multiple choice questions: Contrasting formative and summative settings. European Journal of Physics, 39(5), 055704.

Wednesday, 5 December

Wednesday, 5 December

Cristian Bonato

Quantum technology with single spins

Abstract

The capability to detect and control individual electronic and nuclear spins, for example those associated to single point defects in solids, has opened novel opportunities for quantum technology. A single spin is the smallest possible magnetic field sensor, enabling imaging of magnetic fields with nanoscale spatial resolution, at room temperature. In addition, due to the short-range of magnetic coupling, spins are well protected from environmental noise, resulting in record storage of quantum information.

This talk will consist of two parts. In the first one, I will tackle the question of how to efficiently extract information from a quantum sensor. In a sequence of measurements on a single spin, outcomes obtained by earlier measurements could be used to optimize the settings for later measurements. What kind of advantage can this provide? Is adaptive estimation advantageous also in the presence of noise and imperfect measurements?
In the second part of the talk, I will discuss recent results about spin control in silicon carbide. While most of the work in this field has been done with spins associated with the nitrogen-vacancy colour centre in diamond, I will show how silicon carbide can combine excellent spin properties and efficient spin-photons interfacing in a semiconductor that is widely used by the microelectronic industry.

21 November 2018

21 November 2018

Leo Molina-Luna

Electric field in situ TEM of functional materials: towards atomic-resolution operando nanoscopy

Abstract

Recent advances in microelectromechanical systems (MEMS) based chips for in situ transmission electron microscopy are opening exciting new avenues in nanoscale research. The capability to perform current-voltage measurements while simultaneously analyzing the corresponding structural, chemical or even electronic structure changes during device operation would be a major breakthrough in the field of nanoelectronics and beyond.  We aim to directly link the atomic structure to the physical properties under working or so called operando conditions. Shown in figure 1 is an electro-thermal chip sample carrier that allows the combined application of an electrical bias with a thermal gradient directly inside a transmission electron microscope [2]. With this setup, in situ atomic-resolution experiments on functional materials systems and electronic devices are possible. This talk will address the challenges, recent advances and possibilities of the field. Furthermore, I will present our efforts in systems that are relevant for random access memory devices (RRAM) [1], tunable microwave applications and nanomaterials with switchable polarization that are indispensable in memory devices, sensors, actuators, and transducers [2].

References

[1] A. Zintler et al., “FIB based fabrication of an operative Pt/HfO2/TiN device for resistive switching inside a transmission electron microscope,” Ultramicroscopy, vol. 181, no. Supplement C, pp. 144–149, Oct. 2017.

[2] L. Molina-Luna et al., “Enabling nanoscale flexoelectricity at extreme temperature by tuning cation diffusion,” Nature Commun., vol. 9, no. 1, Dec. 2018.

7 November 2018

7 November 2018

Ilja Gerhardt

Polarization entangled photon pairs from a single molecule

Abstract

Single molecules – the first ever detected single quantum emitter in the solid state – allow for the generation of single photons over the entire visible spectrum from 400 to 850 nm. Unlike as for other emitters the photon collection efficiency can approach unity [1]. Under cryogenic conditions their spectral linewidth can be truly Fourier limited. We observe more than 1.2 Mio raw single photon clicks per second on a silicon avalanche photo diode (APD). At the same time the emitted photons show a spectral linewidth of less than 20 MHz. In the past years, we have learned to utilize the spectral superposition of the molecule's emission with alkali atoms. This allowed us to observe slow light in a hot atomic vapor [2], to filter the emitted photons from background contributions, and to perform atomic spectroscopy with a stream of single photons [3]. The combination of an atomic filter with single molecule studies allows to achieve a pure single photon stream on the sodium D2 line. A next hybridization step aims towards a utilization of these photons in all-optical quantum operations, such as in all-optical gates. A first step to this goal is an efficient Hong-Ou-Mandel interference [4]. This is the basic building block of many linear optics quantum operations [5]. A Hong-Ou-Mandel visibility of 94% is observed. In a slightly modified Hong-Ou-Mandel experiment, we can prove the ideal Fourier limited nature of the emitted photons. A closely related experiment is the preparation of the incoming photons into orthogonal polarization states. This is known as Shih-Alley configuration [6]. It does not only allow for the implementation of a "quantum eraser", but also for the observation of a Hong-Ou-Mandel peak instead of the commonly observed dip [7]. Most importantly, this experiment allows for the generation of polarization entangled photons. Coincidence clicks on both sides of the beam splitter are entangled in the state: ψ-=2-1/2(|HV〉- |VH〉). We are able to disprove the locality-reality principle with a Bell-parameter of S = 2.26 ± 0.06. Unlike for many other emitters, the violation of Bell's inequality can also be observed with the raw coincidence clicks [8].

References

[1] G. K. Lee et al., A planar dielectric antenna for directional single-photon emission and near-unity collection eciency, Nature Photonics, 5, 166-169, (2011)

[2] P. Siyushev et al., Molecular photons interfaced with alkali atoms, Nature, 509, 66-70, (2014)

[3] W. Kiefer et al., An atomic spectrum recorded with a single molecule light source, Applied Physics B, 122, 1-12, (2016)

[4] C. K. Hong et al., Measurement of subpicosecond time intervals between two photons by interference, Phys. Rev. Lett., 59, 2044-2046, (1987)

[5] E. Knill et al., A scheme for efficient quantum computation with linear optics, Nature, 409, 46-52, (2001)

[6] Y. H. Shih and Alley, New Type of Einstein-Podolsky-Rosen-Bohm Experiment Using Pairs of Light Quanta Produced by Optical Parametric Down Conversion, Phys. Rev. Lett., 61, 2921-2924, (1988)

[7] M. Rezai et al., Coherence properties of molecular single photons for quantum networks, Phys. Rev. X, 8, 031026, (2018)

[8] M. Rezai et al., Polarization Entangled Photon Pairs from a Single Molecule, under review, (2018)

24 October

24 October

Laura Nuttall

How data quality affects the search for gravitational waves and the resulting astrophysical implications

Abstract

Interferometric gravitational-wave detectors are some of the most complex instruments ever built; understanding their output is a huge challenge. Detector performance will change on a daily basis due to environmental, hardware and software issues. As such, data from the Laser Interferometer Gravitational-wave Observatory (LIGO) are typically non-stationary, and contain many long and short duration artefacts. Modelled and un-modelled transient gravitational-wave searches are most sensitive to short duration noise events or ‘glitches’ which can mask or mimic a true gravitational-wave signal. These glitches can not only limit the detection of gravitational waves from the merger of black holes and neutron stars, but can also affect the ability to estimate the source parameters accurately. This talk will discuss the recent challenges of characterising the LIGO detectors in both the first and second observing runs, how glitches have affected the search for gravitational-waves from compact binary coalescences, and preparation for the third observing run, due to start next year.

10 October

10 October

World Mental Health Day

Daniel J. Smith

Mental health research using large-scale population data

Abstract

Psychiatric disorders like schizophrenia, bipolar disorder and major depression are common and highly morbid. In 2017, the World Health Organisation announced that depression is now the single leading cause of disability worldwide. The causes of mental illness are not yet fully understood but they probably occur as a result of a complex and dynamic interplay between genetic and environmental risk factors. This talk will focus on how the UK Biobank cohort of over half an million individuals is helping to drive forward large-scale collaborative research efforts in mental health. Three areas will be highlighted:

a) understanding the overlap between mental and physical health;

b) discovering genes for neuroticism and depression; and

c) investigating relationships between sleep and circadian rhythms and mental illness.

26 September

26 September

Steve Barnett

Vacuum friction and related puzzles

Abstract

The interaction between a single atom with light is the most fundamental component of quantum and atom optics. Although much studied it still has the capacity to surprise. In this presentation I shall introduce and, I hope, explain three such subtleties:

(i) The existence of a friction force experienced by a radiating atom moving in otherwise free space.

(ii) The dipole force that leads to the suggestion that a laser pulse tuned below an absorption resonance might suck an atom towards it even though the radiation pressure points in the opposite direction!

(iii) An atom has a sufficiently low mass that it recoils when absorbing a photon.  Given this, is it the initial velocity, the final velocity or something else that should be used in the Doppler shift?  

19 September

19 September

Daniele Faccio

Viewing the world with quantum eyes

The recent development of photon counting cameras has provided us with new opportunities for imaging. These quantum “eyes” allow wonderful applications such as imaging light in flight, imaging behind walls or imaging inside opaque materials. I will discuss the (very) brief history of this technology, the motivation for wanting to see e.g. inside opaque materials and some recent results that we have obtained in our labs. I will then conclude with a few examples of quantum-inspired imaging results that, although not based on the same technology, are too cool to not be shown.