Department of PhysicsJohn Anderson Research Colloquia

Swapan Chattopadhyay (University of Strathclyde) 22nd June 2022, 3pm, JA3.14 

Stochastic phase space cooling using microwave techniques in the GHz frequency range have been employed historically in particle colliders, leading to ground-breaking discoveries. ‘Cooling’ increases the likelihood of observing rare physics events.

The first important advance, conceptual and technological, in this area was stochastic cooling of anti-matter (e. g. ‘antiprotons’) invented by Simon van der Meer (Nobel Prize, 1984), which was instrumental in the discovery of the W and Z Bosons at CERN in 1983 and the ‘top’ quark at Fermilab years later.

Stochastic Cooling reduces the random motion of the beam particles through granular sampling and correction of the beams phase-space structure, thus resembling a ‘Maxwell's demon’. The extension of Stochastic Cooling from the microwave regime up to optical frequencies and bandwidths, samples and exploits a charged particle’s radiation reaction to affect its own phase space, leading to increases in the achievable cooling rates by three to four orders of magnitude.

I will report on the recent first experimental observation of this achievement in the IOTA ring by a Fermilab team.

Fabien Massabuau (University of Strathclyde) 20^th July 2022, 3pm, JA3.14

By 2070, the world population is predicted to reach 10.5B inhabitants, and manned space missions as well as settlements on Mars may be on Humanity’s agenda. These predictions forecast extreme pressures on water, food and waste resource management. These challenges are already tangible now, recognised by the United Nations’ Sustainable Development Goals and Net Zero targets.

Ultraviolet (UV) technologies can alleviate these pressures on our Society. The UV range of the electromagnetic spectrum is extremely important with applications including water and air purification, intensive agriculture, medical therapies, and electronics fabrication. Implemented in every household, UV light emission and its monitoring can achieve safe water at the tap, sanitise rooms, or extend shelf-life of food in fridges. Deployed for farming, these technologies can boost crop yields, enable underground farming, and allow reforestation of old farmlands to combat climate change. UV technologies have the potential for substantial impact on the United Nations’ Sustainable Development Goals.

With a bandgap of ca. 5 eV, gallium oxide (Ga₂O₃) is the leading contender wide bandgap semiconductor for future power electronics and UV sensing application. This compound is highly polymorphic, with the corundum α phase variant (α-Ga₂O₃) displaying several indisputable assets: (i) it exhibits the largest bandgap (5.3 eV) amongst all phases, (ii) is isostructural with several other semiconducting group-III or transition metal sesquioxides (e.g. In₂O₃, Ti₂O₃) and (iii) with the cheap and widely available sapphire (α-Al₂O₃) substrate.

This presentation will give an overview of the group’s activities on α-Ga₂O₃ growth, characterisation, bandgap engineering and applications for UV sensing.

Alessandro Rossi (University of Strathclyde) 27^th July 2022, 3pm, JA3.14

Quantum technologies for computing, sensing and communicating are developing at a relentless pace. However, a consensus has not been reached on what hardware platforms are the most promising to bridge the prototype-to-product gap and take these systems to commercial fruition. Several solid-state systems are currently under scrutiny, ranging from superconductors to topological insulators, as well as 2D and magnetic materials. Among these, semiconductors occupy a privileged position because they leverage the industrial infrastructure that has enabled modern mainstream electronics for decades. In particular, the prospect of employing well-established Complementary Metal Oxide Semiconductor (CMOS) manufacturing and design techniques could be key to realize large integrated quantum systems of practical use.

In this talk, I will provide an overview of my team’s research on three established semiconductors, namely silicon, germanium, and silicon carbide, which constitute the cornerstones of today’s digital, radio-frequency (rf) and power electronics, respectively. Our mission is to take these materials into the quantum realm and develop devices for quantum computing and quantum metrology applications by preserving full compatibility with the CMOS industrial protocols. To this end, I will show how a field-effect transistor can be turned into a device with quantum functions, namely a quantum dot (QD) with exquisite control of individual charges and spins.¹ I will highlight the versatility of this technology by showing that one can virtually use the same QD as either a spin-based information quantum² or an accurate source of quantised electric current³ for metrological applications. Furthermore, by virtue of ambipolar technology, one can operate such devices to control either conduction electrons or valence holes, each with their own merits for different target applications. Finally, I will argue that, in order to scale up QD-based systems, the interfacing of classical control electronics to the underlying quantum hardware will be one of the crucial challenges. I will discuss these challenges, and possible solutions accessible with the aid of existing CMOS architectures, such as Random Access Memory (RAM) integrated circuitry⁴ in tandem with rf dispersive readout techniques.^2,5

References:

• [1] Yang et al. Nature Communications 4, 2069 (2013)
• [2] West et al. Nature Nanotechnology 4, 2069 (2019)
• [3] Rossi et al. Nano Letters 14, 3405 (2014)
• [4] Schaal et al. Nature Electronics 2, 236 (2019)
• [5] Ahmed et al. Physical Review Applied 10, 014018 (2018)

Prof Michael Tobar (University of Western Australia) 2^nd August 2022, 3pm, JA3.14

The Quantum Technologies and Dark Matter research laboratory has a rich history of developing precision tools for both fundamental physics and industrial applications. This includes the development and application of novel low-loss and highly sensitive resonant photonic and phononic cavities, such as whispering gallery and re-entrant cavities, as well as photonic band gap and bulk acoustic wave structures. These cavities have been used in a range of applications, including highly stable low noise classical and atomic oscillators, low noise measurement systems, highly sensitivity displacement sensors, high precision electron spin resonance and spin-wave spectroscopy, high precision measurement of material properties and applications of low-loss quantum hybrid systems, which are strongly coupled to form polaritons or quasi-particles. Translational applications of our technology has included the realization of the lowest noise oscillators and systems for advance radar, the enabling of high accuracy atomic clocks and ultra-sensitive transducers for precision gravity measurements.

Meanwhile, there is currently a world-wide renascence to adapt precision and quantum measurement techniques to major unsolved problems in physics. This includes the effort to discover “Beyond Standard Model” physics, including the nature of Dark Matter, Dark Energy and the unification of Quantum Mechanics with General Relativity to discover the unified theory of everything. Thus, the aforementioned technology has been adapted to realize precision measurement tools and techniques to test some of these core aspects of fundamental physics, such as searches for Lorentz invariance violations in the photon, phonon and gravity sectors, possible variations in fundamental constants, searches for wave-like dark matter and test of quantum gravity. This work includes: 1) Our study and application of putative modified physical equations due to beyond standard model physics, to determine possible new experiments: 2) An overview of our current experimental program, including status and future directions. This includes experiments that take advantage of axion-photon coupling and axion spin coupling to search for axion dark matter. High acoustic Q phonon systems to search for Lorentz violations, high frequency gravity waves, scalar dark matter and tests of quantum gravity from the possible modification of the Heisenberg uncertainty principle.

Peter Kirton (University of Strathclyde) 3^rd August 2022, 3pm, JA3.14

Developing accurate simulations of quantum mechanical systems unavoidably involves taking into account coupling to the outside world. Understanding and predicting the behaviour of these open quantum systems provides a formidable theoretical challenge. Yet, such modelling is important for a wide range of physical systems, whose quantum properties are now routinely measured in the lab. These include arrays of superconducting qubits, cold atoms in optical cavities and semiconductor heterostructures. They provide us with carefully controlled devices, made to emulate the behaviour of particular quantum mechanical models, giving us an exciting new way to test our best theories. While the effect of dissipation is often detrimental to the production of interesting quantum states there are cases where the competition between coherent and incoherent processes to lead to the stabilisation of new phases.

In this talk I will outline our groups activities in developing techniques for understanding these phenomena. I will present some results which show the connections between (equilibrium) superradiance and (non-equilibrium) lasing in models of cold atoms coupled an optical mode [1,2]. I will also present a novel numerical technique, TEMPO [3], for accurately finding the dynamics of open systems strongly coupled to their environment. This allows us to relax many of the approximations commonly made to find the behaviour of more realistic models.

• [1] Kirton and Keeling PRL, 118, 123602 (2017) and NJP 20, 015009 (2018)
• [2] Werren et al. arXiv:2201.13368 (2022)
• [3] Strathearn et al. Nat. Commun. 9, 3322 (2018)

Masazumi Fujiwara (Okayama University) 7th September 2022, 3pm, JA3.14

Nanodiamond quantum sensors have attracted great interest to realize nanometre-scale magnetometers and thermometers with high sensitivity. The heart of this technology is measuring the electron spin states of nitrogen-vacancy color defect centres in diamond under the optical microscope observation. Exploring practical applications and system engineering of the spin-optical detection for some specific usages is at the forefront of this technology. In this talk, I will talk about our recent activities on this topic, including temperature sensing in biological samples [1,2] and engineering its on-chip devices [3,4].

• [1] Fujiwara et al., Sci. Adv. 6, eaba9636 (2020).
• [2] Yukawa et al., Nanoscale Adv. 2, 1859 (2020).
• [3] Fujiwara et al., Nanotechnology 32, 482002 (2021).
• [4] Oshimi et al., Lab Chip 22, 2519 (2022).

Dr Kali Wilson (University of Strathclyde), 3PM, JA3.14

In complex, macroscopic systems, unexpected behaviour emerges which depends crucially on the interactions between individual constituent particles. Such collective behaviour is observed in biological systems, e.g., flocks of birds and schools of fish, and also in the formation of quantum materials such as superfluid helium or superconductors. In quantum systems the collective behaviour can result in the emergence of useful bulk properties such as superfluidity and superconductivity. 

Quantum mixtures formed of ultracold atoms provide an extremely clean and well-controlled system for studies of the cooperative behaviour inherent in superfluidity, with exquisite control over interactions, geometry, and rotation (vorticity). In particular, experimental control of interspecies interactions has enabled recent demonstrations of beyond-mean-field phenomena such as quantum droplets and Lee-Huang-Yang gases. Here the net mean-field interactions are significantly reduced such that quantum fluctuations play a dominate role in governing the behaviour of the system. Quantised vortices, topologically-protected defects, are ideal probes of the quantum-many-body state, as their nucleation, internal structure, and dynamics depend directly on the microscopic physics at play. Furthermore, vortices play an integral role in the dissipation of energy in these systems.  

I will discuss how vortices may be used to probe binary superfluids and quantum-fluctuation-enhanced regimes, and how this will be implemented experimentally using the ultracold atom apparatus that I am currently developing here at Strathclyde.

John Maddocks (Swiss Federal Institute of Technology Lausanne) 9th November 2022, 3PM, JA 3.14

It is now widely believed that the sequence of DNA not only encodes genes, but also controls how double stranded (or ds) DNA functions in the cell, through modulations in its precise intrinsic shape and stiffness along the famous double helix. I will describe a Gaussian coarse-grain model that captures such sequence-dependent effects in an equilibrium statistical mechanics sense, to within the accuracy of underlying Molecular Dynamics (MD) simulations, but which allows much greater variations in sequence space to be studied, and at longer length scales than is accessible to direct MD simulation. Millions of base pairs forming entire chromosomes can be scanned for their mechanical properties. The model now has associated parameter sets describing dsDNA in both standard and epigenetically modified alphabets, as well as dsRNA, and RNA/DNA hybrid helices. Another application of the cgNA+ model is to compute sequence-dependent dsDNA minicircle shapes.

• https://lcvmwww.epfl.ch/research/cgDNA
• https://cgdnaweb.epfl.ch

  

Konstantinos Lagoudakis (University of Strathclyde)  - 23rd November 2022, 3pm, JA 3.14

Spin qubits in semiconductor quantum dots have been hailed as a potential system for the creation of on-chip quantum information processing platforms [1]-[3]. Despite the technological challenges for the creation of scalable systems, several growth techniques have been developed for the growth of deterministically positioned quantum dots [3]. In this talk I will give an overview of related research activities and experimental capabilities in the recently founded Experimental Quantum Nanoscience Lab here at Strathclyde University. In particular, I will present out recent investigations of the behavior of spins in self assembled quantum dots under magnetic fields in several configurations and the resulting level structure by means of magnetospectroscopy studies and optical pumping. Employing the spin system as optically addressable spin qubits, we demonstrate all optical coherent control. Finally, we show preliminary investigations of spin pumping and control in deterministically positioned quantum dots [4].

References

• [1] D.P. DiVincenzo arXiv:quant-ph/0002077 (2000).
• [2] D. Press et al. Nature 456, 218–221 (2008).
• [3] S. M. Clark et al. Phys Rev Lett. 99 040501 (2007)
• [4] G. Juska et al. Nat. Phot 7, 527 (2011).

Prof Graham Machin (Senior Fellow, NPL)  - 8th February 2023, 3pm, JA 3.14

In May 2019 the International System of Units (the SI) underwent what was its biggest change since its introduction when the definition of four of the seven SI base units were changed to be based on defined values of fundamental physical constants. Since the change, the kelvin is now defined in terms of the Boltzmann constant, the ampere on the electron charge, the kilogram on the Planck constant and the mole on the Avogadro constant.

The redefinition of the kelvin has opened several new possibilities for traceable thermometry direct to the kelvin definition. These could include using primary thermometry to calibrate sensors at National Measurement Institutes (NMIs) and, in the medium term, in calibration laboratories dispensing with traceability to the defined scales (ITS-90, PLTS-2000) and so disseminating thermodynamic temperature. In the longer term these changes could lead to the rise in potential, paradigm changing, approaches to temperature sensing such as traceability at the point of measurement both through self-validating thermometers and more radically by the deployment of practical primary thermometry based on fundamental physics and where temperature sensor itself will, unlike today, no longer need calibrating to provide traceability.

In this talk an introduction to the kelvin redefinition and to the mise en pratique for the definition of the kelvin (MeP-K) will be given. How traceable temperatures are attained will be discussed, both presently, through the defined scales and how, in the medium and long term, this is likely to change; with thermodynamic temperature approaches becoming increasingly prevalent. The talk will end by introducing novel approaches to temperature traceability including provision of NMI like uncertainty thermodynamic temperatures in calibration laboratories and the rise of in-situ/in-process traceability and the implications, particularly in the context of digitalisation and the need for “points-of-truth” in for example autonomous sensor networks.

Dr Margherita Mazzera (Institute of Photonics and Quantum Sciences, Heriot-Watt University)  - 8th March 2023, 3pm, JA 3.14

The coherent interaction between photons and atoms lays the bases of quantum information science, whose purpose is to open new possibilities for the transmission and the processing of information. It is crucial, e.g., for the realisation of quantum networks. Solid-state systems have emerged as promising platforms; more specifically rare earth ion doped crystals are one of the most interesting candidates. The implementation of quantum memory protocols in waveguide has the potential of opening further avenues towards scalable quantum information protocols using complex quantum photonic circuits on chip.

 Our approach is based on fs-laser written waveguides (LWW) fabricated in an insulating crystal which has proven outstanding performances as interface between single photons and single atomic or spin excitations, i.e. Pr:YSO [1]. The new writing regime adopted gave, with respect to previous demonstration in the same material, sensibly smaller guiding modes, with diameter compatible with the core of telecom fibres, but lower insertion and bending losses. Given the simplicity and versatility of the fabrication, its unique 3D capability and the outstanding storage performance, the demonstration represented a change of paradigm in the quest for integrated quantum memories. We demonstrated that this integrated platform for the storage of quantum states of light [2], also enabled the storage of more than 100 spectro-temporal modes [3] and the storage of photonic entanglement in a fibre-integrated device [4]. However, much has to be demonstrated yet with this platform, e.g., the on-demand storage of single photons. One major problem is that the integrated storage devices might prove more prone to photonic noise due to light confinement, as the single photon inputs travel in the same spatial mode as the high intensity pulses used for on-demand storage and retrieval. We propose here two alternative routes to overcome this problem and perform on-demand storage in waveguides.

• [1] A. Seri et al, Phys. Rev. X 7, 021028 (2017); K. Kutluer et al, Phys. Rev. Lett.  118, 210502 (2017).
• [2] A. Seri et al, Optica 5(8) (2018) 934
• [3] A. Seri et al, Phys. Rev. Lett. 123 (2019) 080502
• [4] J. V. Rakonjac et al, Science Advances 8, eabn3919 (2022)

Prof K Long (Physics, ICL) and Prof A Giaccia (Oncology, Oxford) - cancelled till further notice

Cancer is the second most common cause of death globally. In 2018, 18.1 million new cancer cases were diagnosed, 9.6 million people died of cancer-related disease, and 43.8 million people were living with cancer.  Radiotherapy (RT) is used in 50% of cancer patients and is involved in 40% of cancer cures.  It is estimated that 26.9 million life-years could be saved in low- and middle-income countries if capacity could be scaled up. 

The beam characteristics that can be exploited in proton- and ion-beam therapy (IBT) facilities today are restricted to low dose rates, a small number of temporal schemes, and a small number of spatial distributions.  The use of novel beams with strikingly different characteristics has led to exciting evidence of enhanced therapeutic benefit.  This evidence, together with developments in our understanding of personalised medicine based on the biology of individual tumours, now provides the impetus for a radical transformation of IBT.

The ‘Laser-hybrid Accelerator for Radiobiological Applications’, LhARA, is conceived as a novel, uniquely flexible facility dedicated to the study of radiobiology.  The technologies that will be demonstrated in LhARA have the potential to allow particle-beam therapy to be delivered in a completely new regime, combining a variety of ion species in a single treatment fraction and exploiting ultra-high dose rates.  The laser-hybrid approach will allow the exploration of the vast “terra incognita” of the mechanisms by which the biological response is modulated by the physical characteristics of the beam.  We will describe the motivation for LhARA, present the status of its development and summarise the programme upon which the LhARA consortium has embarked to drive a step-change in clinical capability.