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Physics PhD Project Ideas

Physics PhD project ideas

Physics PhD project ideas

Physics PhD project ideas

We are looking for excellent PhD student candidates, who would like to explore project ideas with us. Examples of ideas in our pipeline are listed below.

These are open to self-funded students and those who want to apply to the DTP programme. We strongly recommend that you contact potential supervisor(s) in advance- contact details can be found within the individual project.

Biomedical physics

Supervisors: Dr Peter Petrov and Prof Peter Winlove (Department of Physics and Astronomy)

Toxins secreted by bacteria are major causes of disease. Usually, the interaction between the toxin and the cell plasma membrane is a complex, multistage process, which may ultimately lead to cell death. Whilst the biochemistry, molecular and cell biology of this process has been extensively studied, little is known about the role of the membrane physical properties in cell susceptibility to toxins. We have pioneered research revealing that electrical and mechanical properties of the cell plasma membrane could determine cell susceptibility to toxin. Membrane physical properties are also altered in disease, thereby influencing cellular susceptibility to toxin. This project will focus specifically on a class of toxins called pore-forming toxins. We shall investigate how membrane physical properties (viscoelasticity, electrical properties and their changes in disease) affect the three stages of toxin-membrane interactions (binding, aggregation and membrane insertion) leading to formation of pores in the membrane and, ultimately, cell lysis. We shall also investigate the effects of elevated oxidative stress, an ubiquitous condition in a number of diseases. This will be achieved through integrated cross-disciplinary approaches accounting for each aspect of toxin-membrane interactions and their interdependence.

This research will have an impact on the growing community of scientists working on the mechanisms of invasion of host cells by bacterial pathogens. It will inform the development of novel therapeutic approaches to combat bacterial infections in humans and domestic animals, major concerns for human health and for farming communities.

This is an exciting interdisciplinary project suitable for a student motivated to work at the boundary between physics and biology.

For more information, please contact Dr Peter Petrov or Prof Peter Winlove.

Supervisors: Dr Peter Petrov (Department of Physics and Astronomy) and Dr Stefano Pagliara (Living Systems Institute)

This project aims to optimise sorting of biological cells according to their mechanical properties by utilising novel microfluidic devices.

Various diseases lead to alteration in the physical properties of the cell plasma membrane such as membrane elasticity, viscosity and electrostatics. This could compromise biological functions hosted by the plasma membrane. Sorting of cells according to their physical properties is therefore an important step in understanding the effects of disease on membrane properties and cell function. This project will explore novel strategies for cell sorting based on their viscoelastic properties, using structured microfluidic devices with carefully controlled geometries. The concept will be validated on subpopulations of human red blood cells with different viscoelastic properties (membrane bending and shear moduli, membrane and cytoplasmic viscosity) and geometry (volume-to-area ratio), all of which are important for cell deformability. Later stages of the project will focus on designing and implementing adaptive microfluidic devices capable of optimising cell sorting depending on particular cell properties in the subpopulations. This is an exciting interdisciplinary project suitable for a student interested to work on the boundary between physics and biology.

Please contact Dr Peter Petrov and Dr Stefano Pagliara for more information.

Electromagnetic and acoustic materials (EMAG)

Supervisors: Dr Paul Keatley and Prof Rob Hicken (Department of Physics and Astronomy)

With the advent of Big Data and the Internet of Things, demand for data storage is growing exponentially, placing additional strain on the world’s energy resources. As scaling of existing technology, such as the hard disk drive, reaches its physical limits, there is an urgent need to develop new recording paradigms that are ultra-dense, ultrafast, and energy efficient. Switching of magnetic “bits” by ultrafast laser pulses is highly attractive for its potential speed, but the physical mechanisms needed to deliver the required density and energy efficiency are as yet unclear. All-optical “toggle switching” of ferrimagnetic materials has recently been demonstrated [1] but requires heating, full demagnetization, and a significant time for cooling. It has been proposed that switching may also be induced by non-thermal mechanisms that are potentially faster and more energy efficient [2]. Optically induced non-thermal switching will be explored in artificial ferrimagnetic trilayer materials, and van der Waals bonded semiconductor/magnetic bilayer materials, that allow the magnetic parameters of the material to be carefully tuned. The underlying aim is to promote transfer of electron spin angular momentum without significant absorption of energy. The project will make extensive use of the new EPSRC funded EXTREMAG facility.

Diagram to accompany project idea: All-optical magnetic switching for ultrafast data storage

Figure 1. Magnetic switching induced by circularly polarized light [3].

[1] T. A. Ostler et al., Nat. Commun. 3, 666 (2012)

[2] S. Mangin et al., Nat. Mater. 13, 291 (2014).

[3] C.D Stanciu et al., Phys. Rev. Lett. 99, 047601 (2007).

Supervisors: Dr Paul Keatley and Prof Rob Hicken (Department of Physics and Astronomy)

Spintronics seeks to exploit the spin angular momentum that is associated with every electron. A spin-polarized electric current can be used to exert a torque upon a magnet causing it to switch. This effect is already being exploited within magnetic random access memory (MRAM) cells, but the flow of electric current leads to energy dissipation and degradation of the most delicate components of the device. Instead, pure spin currents, in which spin flows without an associated transfer of charge, may be generated from an electric current by means of the spin Hall effect, but with limited efficiency. Following the prediction that spin current can be amplified within an antiferromagnet [1], we recently confirmed that the effect results from the superposition of evanescent antiferromagnetic spin waves [2]. In this project we will use time resolved optical and x-ray probes to explore the character of the underlying spin waves, and then determine the extent of the spin current amplification that may be achieved within a multilayered antiferromagnetic material. The generation of enhanced spin currents could play a vital role in the continued development of MRAM technology. The project will make extensive use of the new EPSRC funded EXTREMAG facility.

Please contact Dr Paul Keatley or Prof Rob Hicken for further information.

Diagram for project idea: Amplification of spin current within antiferromagnets

Figure 1. Schematic representation of time resolved x-ray detection of propagation of spin current s(t) through an antiferromagnetic NiO layer. A spin current is injected from the FeCo source layer and drives precession of the magnetization in the NiFe sink layer, which is detected by a short pulse of x-rays.

References

[1] R. Khymyn et al., Phys. Rev. B 93, 224421 (2016).

[2] M. Dabrowski et al. Phys. Rev. Lett. 124, 217201 (2020).

Supervisors: Prof V. V. Kruglyak and Dr A. V. Shytov (Department of Physics and Astronomy)

Our civilization is defined by the functionalities delivered by devices, ranging from smartphones to airplanes. These functionalities are however constrained by materials available to engineers, when constructing and indeed even conceiving a device. Radically new dynamical properties and advanced functionalities can be created by tailor-tuning the spectra of wave excitations in structured media – so-called metamaterials. Among other waves, ‘surface acoustic waves’ have been investigated for over one hundred years and currently used e.g. for a wide and diverse range of functions, e.g. analogue signal processing in mobile phones. Recently, the field of metamaterials research has expanded to acoustic waves. To date, however, there have been very few suggested ways of designing acoustic metamaterials that can be dynamically reconfigured and tuned. Integration with magnetic materials, well known for their ability to store information e.g. in magnetic hard disk drives, offers an exciting route for achieving non-volatile tuning of acoustic metamaterials. In this experimental project, you will explore a new class of magneto-acoustic metamaterials in which the role of their building blocks (“meta-atoms”) is played by magneto-acoustic resonators [1,2]. Such metamaterials will add magnetic field tunability to structures aimed to control the propagation of surface acoustic waves, opening intriguing opportunities both in fundamental science and technology. The memory phenomenon inherent to magnetism will enable significant energy savings in non-volatile magneto-acoustic data and signal processing devices. For instance, they would be instantly bootable and could be more easily integrated with the existing magnetic data storage devices. From the point of view of fundamental science, the magneto-acoustic metamaterials will serve as an excellent test bed for studying the physics of wave propagation in non-uniform and non-stationary media. This research is related to a larger, EPSRC-funded project, within which you will collaborate with researchers from the University of Sheffield.

For further information, please contact Prof V. V. Kruglyak or Dr A. V. Shytov.

References:

1. O. S. Latcham, et al, “Controlling acoustic waves using magneto-elastic Fano resonances”, Appl. Phys. Lett. 115, 082403 (2019).

2. O. S. Latcham, et al, “Hybrid magnetoacoustic metamaterials for ultrasound control”, Appl. Phys. Lett. 117, 102402 (2020).

Supervisors: Prof. V. V. Kruglyak and Dr. A. V. Shytov (Department of Physics and Astronomy)

Spin waves (elementary excitations of magnetically ordered materials) may be excited by electromagnetic waves at frequencies from a few to hundreds of GHz. This is however not easy, due to a huge mismatch between the wavelength (and therefore momentum) of electromagnetic and spin waves at the same frequency. You will tackle this challenge by exploring spin wave excitation and control in media with translational symmetry broken by compositional, geometrical or micromagnetic non-uniformities, which may either naturally exist (they are ubiquitous, in fact) or be artificially created. The interaction (‘coupling’) between propagating waves (spin or electromagnetic) and localised non-uniformities is often enhanced at specific discrete frequencies [1,2], giving rise to a rich variety of phenomena often referred to as ‘Fano resonances’ or ‘Fano physics’. You will explore such Fano resonances as a platform for creation of novel spin-wave devices and metamaterials with unseen functionalities, such as re-programmability and non-reciprocity, and use them to address new physics that is inaccessible for other waves.

For further information, please contact Prof. V. V. Kruglyak or Dr. A. V. Shytov.

References:

1. Y. Au, et al, “Resonant microwave-to-spin-wave transducer”, Appl. Phys. Lett. 100, 182404 (2012).

2. Y. Au, et al, “Nanoscale spin wave valve and phase shifter”, Appl. Phys. Lett. 100, 172408 (2012).

Supervisor: Prof V. V. Kruglyak (Department of Physics and Astronomy)

In this theoretical (computational, actually) project, you will study wave excitations of the magnetic order - so called spin waves, quanta of which are called magnons. Spin waves have a dispersion relation like no other kind of waves: it is nonlinear, anisotropic and often non-reciprocal. In addition, the spin wave dispersion is very sensitive to the sample’s magnetic properties and micromagnetic configuration, so that spin waves are rarely observed to propagate in uniform media. Using hints from other, more traditional areas of wave physics, you will explore the excitation, propagation and control of spin waves in media with continuously varying properties, i.e. media with a ‘graded magnonic index’ [1,2]. Not only this research is full of exciting fundamental physics questions, but also a new, spin wave based technology for data and signal processing is out there to be grabbed by those who dare to face the challenges!

For further information, please contact Prof V. V. Kruglyak.

References

1. N. J. Whitehead, et al, “A Luneburg lens for spin waves”, Appl. Phys. Lett. 113, 212404 (2018).

2. N. J. Whitehead, et al, “Graded index lenses for spin wave steering”, Phys. Rev. B 100, 094404 (2019).

Supervisors: Dr Paul Keatley and Prof Rob Hicken (Department of Physics and Astronomy)

Information is processed within the human brain through the mutual synchronization of a vast 3 dimensional network of neurons that oscillate at a frequency of order 40 Hz. In contrast, spin transfer oscillators (STOs) are nanoscale non-linear oscillators with frequencies that can be tuned within the GHz frequency range. Synchronization of a chain of 4 STOs has been used for recognition of human vowel sounds [1], while mutual synchronization of 8 x 8 arrays of STOs has recently been demonstrated [2]. Exploiting the high frequency and small footprint of STOs, arrays of STOs can be connected together to form powerful devices for high-speed pattern recognition. This project addresses a critical gap in present understanding of STO synchronization, namely the relative phase of oscillation in adjacent STOs. Time resolved scanning Kerr microscopy will be used to directly resolve the GHz oscillations of each STO device so that its relative phase can be determined. Spatial resolution of down to 50 nm will be achieved through the optimization of a plasmonic antenna mounted on the tip of an atomic force microscope [3]. The project will make extensive use of the new EPSRC funded EXTREMAG facility.

For further information, please contact Dr Paul Keatley or Prof Rob Hicken.

Diagram for project idea: Synchronizing spin transfer oscillators for neuromorphic computing

Figure 1. Schematic of an array of nanoscale spin transfer oscillators [2].

References:

[1] M. Romera et al., Nature 563, 230 (2018).

[2] M. Zahedinejad et al., Nature Nanotechnology 15,  47 (2020).

[3] P. S. Keatley et al., Rev. Sci. Instrum. 88, 123708 (2017).

Supervisors: Prof V. V. Kruglyak and Dr P. S. Keatley (Department of Physics and Astronomy)

A stone thrown into water creates waves that propagate in form of circles. An intense and tightly focused ultrashort optical pulse incident on a thin solid film of a magnetic material also launches waves – so called spin waves as well as more familiar acoustic waves. By studying the shape of the excited wave fronts, one can obtain vital information about the waves’ properties, which are in turn inherently related to the interatomic and magnetic interactions in the studied films. These phenomena can be studied using the time-resolved optically pumped scanning optical microscopy (TROPSOM), a unique technique pioneered in Exeter [1] and now to be set up within the EPSRC funded Exeter Time-Resolved Magnetism Facility (ExTReMag). In this experimental project, you will contribute to setting up of the TROPSOM experiment at ExTReMag and then use it to explore magnonic and acoustic metasurfaces. Disentangling optically excited dynamics of their electron, lattice and spin sub-systems is a challenging and exciting task. Yet, a bunch of radically novel functionalities arising from interplay between surface acoustic and spin waves is a prize for those who solve it! When the primary goal of in-depth understanding of the observed dynamics is achieved, you will proceed to exploration of lithographically shaped, optically driven magnonic and acoustic sources that will enable control of the excited waves.

References:

1. Y. Au, et al, “Direct excitation of propagating spin waves by focused ultrashort optical pulses”, Phys. Rev. Lett. 110, 097201 (2013).

Quantum systems and nanomaterials (QSN)

Supervisor: Dr Luis A. Correa

No quantum system exists in isolation—they all interact with their surrounding environment, which can largely affect their dynamics [1]. Treating the full combined problem of ‘system + environment’ is, in most cases, unworkable. Luckily, an effective theory—the theory of open systems—has been developed to approximately solve such problems. This is able to drastically reduce complexity, albeit at the expense of a number of heavy approximations and perturbation theory. Traditionally, very weak linear dissipation into a linear reservoir is assumed. While much work has been done recently to relax some of these assumptions, considering, e.g., strong dissipation into structured environments [2], the dogma of ‘linear dissipation’ has hardly been questioned. Yet, nearly any real physical open quantum system of interest is highly non-linear. Problems such as energy transport in molecular complexes within biological systems [3], or diffusion of impurities in atomic condensates [4] cannot be fully understood until a new theory of non-linear open quantum systems is put forward. The aim of this project is to develop it and explore its physical consequences.

In this project we will primarily work with continuous-variable open quantum systems connected to non-linear environments through possibly non-linear couplings. In particular, we will explore limits of practical interest, such as weak non-linear dissipation; and the strong but weakly-non linear regime. To do so, we will combine perturbative methods, Markovian embedding techniques [3], quantum master equations [5] and Langevin equations [2,5]. We will then apply our newly developed tools to transport problems, the problem of temperature estimation in atomic condensates [4], or to understand the thermodynamics of quantum systems in the nonlinear regime [1].

Please check out the Exeter Open Quantum Systems group page.

For more information, please contact Dr Luis A. Correa

References:

[1] Alicki and Kosloff, “Introduction to quantum thermodynamics: history and prospects”. In: Binder, Correa, Gogolin, Anders, and Adesso (eds) “Thermodynamics in the quantum regime”, Fund. Theor. Phys. 195, Springer (2018).

[2] Correa et al., Phys. Rev. A 96, 062103 (2017).

[3] Garg, Onuchic and Ambegaokar, J. Chem. Phys. 83, 4491 (1985).

[4] Mehboudi et al., Phys. Rev. Lett. 122, 030403 (2019).

[5] González et al., Open Syst. Inf. Dyn. 24, 1740010 (2017).

Supervisor: Dr C. A. Downing (Department of Physics and Astronomy)

In recent years, chirality has been shown to have profound implications in nanophotonics and nanoplasmonics. This asymmetry has given the freedom for phenomena not previously thought possible to be realized, including the unprecedented directionality of emissions in microresonators and photonic crystals. In order to understand the wealth of physics which chirality allows for beyond standard quantum optics, the emerging field of chiral quantum optics has been developed. Recent successes of the field include the discovery of novel quantum many-body states and potential quantum entanglement protocols. Meanwhile, topology continues to play a decisive role in the development of novel phenomena in metamaterials, particularly those with strong light-matter coupling.

In this theoretical project, we will encounter new effects arising from the interplay of chirality, topology and nonlinearities. In particular, we will study how many-body interactions lead to a new paradigm for topological photonics, and how multi-excitation effects lead to much rich chiral phenomena, which can be exploited for quantum transport at the nanoscale. The results of this research will both be important for the fundamental understanding of topological phases and chirality beyond the single particle limit, and will find future applications in quantum technology, which is currently undergoing an unprecedented revolution.

For further information, please contact Dr C. A. Downing.

 

Figure 1: Evolution of the eigenvalues of a topologically nontrivial many-body system, where
the topological states are displayed in red.

In recent years, chirality has been shown to have profound implications in nanophotonics and nanoplasmonics. This asymmetry has given the freedom for phenomena not previously thought possible to be realized, including the unprecedented directionality of emissions in microresonators and photonic crystals. In order to understand the wealth of physics which chirality allows for beyond standard quantum optics, the emerging field of chiral quantum optics has been developed. Recent successes of the field include the discovery of novel quantum many-body states and potential quantum entanglement protocols. Meanwhile, topology continues to play a decisive role in the development of novel phenomena in metamaterials, particularly those with strong light-matter coupling. In this theoretical project, we will encounter new effects arising from the interplay of chirality, topology and nonlinearities. In particular, we will study how many-body interactions lead to a new paradigm for topological photonics, and how multi-excitation effects lead to much rich chiral phenomena, which can be exploited for quantum transport at the nanoscale. The results of this research will both be important for the fundamental understanding of topological phases and chirality beyond the single particle limit, and will find future applications in quantum technology, which is currently undergoing an unprecedented revolution. Please contact me at C.A.Downing@exeter.ac.uk for further details of the project.

Supervisors: Prof Janet Anders, Dr Simon Horsley and Dr Marco Berritta (Department of Physics and Astronomy)

 

This is a theoretical physics PhD project at the University of Exeter to start in Autumn 2021.


Quantum thermodynamics is a new research field, where thermodynamics is studied in the small-system size limit where fluctuations become non-negligible, weak coupling between system and environment cannot be assumed, and a fully quantum mechanical description may be needed [1]. This project is concerned with the application of theoretical tools from the fields of quantum thermodynamics and open quantum systems to the problem of modelling the dynamics, the equilibrium state, and the timescale of equilibration, of a collection of interacting spins that are strongly coupled to their environment. The aim of this project is to find analytical equations that describe the spin dynamics when they are driven by a changing magnetic field and exposed to a heated environment (with potentially multiple temperatures). These will then be used to quantify the importance of quantum mechanical and strong coupling effects in the magnetization dynamics and in the long-time steady state of the spins.


The critical components of magnetic hard drives have been continually scaled down in size. Magnetic grains, which store information, are pushing below 8nm and further miniaturization faces new challenges. Magnetically hard materials are required to ensure thermal stability of the information encoded in these small bits. But the magnetic write-fields in recording heads are no longer strong enough to switch them. Heat-assisted magnetic recording (HAMR) has been proposed as a candidate technology that would enable the switching of grains by providing additional energy in form of heat delivered by a laser diode in the recording head. The effective inclusion of such laser diodes in the recording head is actively developed by industry and first prototypes are now available [2].


It is anticipated that this new technology will soon reach the regime where the standard theoretical tools used to model the spin dynamics are insufficient and require a rethink of the theory used. The commonly used phenomenological Langevin equation, the Landau-LifschitzGilbert (LLG) equation, valid for large spin-grains will not describe the dynamics accurately at small sizes [3]. Alternative quantum Langevin equations describing the spin dynamics when undriven and in contact with a heat bath at a fixed temperature T has been derived by Prof Anders’ and her team [4].


You will begin your study with rederiving the standard LLG equation from a microscopic quantum Hamiltonian with the help of your supervisors, and assessing natural modifications of the LLG that include coloured noise rather than the standard flat Gaussian noise commonly assumed in the LLG equation [4]. In addition to quantum effects that arise because of the quantisation of the environmental modes, you will identify quantum effects that arise because of the quantisation of the spins themselves, including any dynamic features caused by quantum coherences and quantum correlations/entanglement. Beyond environments that have a fixed temperature T, you will explore how varying the temperature of the environmental modes, i.e. “heating”, as well as changing the magnetic field affects the spin dynamics. Taking the long-time or steady state limit of the dynamics, you will aim to establish how the spin dynamics becomes equilibrated, on what timescales and assess if the steady state may include strong coupling terms described by a Hamiltonian of mean force [5]. You will identify parameter ranges where any deviations from the standard LLG model could be evident and interact with a modelling group (York) who solve the dynamics numerically, and experimental groups (Exeter) who may be able to test the new predictions.
The derived theory will help clarify how to optimally heat and drive the spin dynamics, and assess when quantum effects become important for the optimisation of the HAMR technology. The research outcomes are potentially world leading, for the first time applying fundamental physics from the emerging theory of quantum thermodynamics to solve a practical problem in magnetic materials research.

For further information, please contact Prof Janet Anders, Dr Simon Horsley or Dr Marco Berritta.

References:
[1] S. Vinjanampathy, J. Anders, Contemporary Physics 57, 545 (2016).
[2] Mark Re, https://blog.seagate.com/craftsman-ship/hamr-next-leap-forward-now/ (2018)
[3] R. F. L. Evans, W. J. Fan, O. Chureemart, T. A. Ostler, M. O. A. Ellis and R. W. Chantrell, J. Phys. Cond. Mat. 26 103202 (2013).
[4] S. Horsley, C. Sait, J. Anders, "Versatile three-dimensional quantum spin dynamics equation with guaranteed fluctuation-dissipation" (2020).
[5] H. Miller, J. Anders, Nat. Comm. 9, 2203 (2018).

References:

[1] S. Vinjanampathy, J. Anders, Contemporary Physics 57, 545 (2016).

[2] Seagate blog https://blog.seagate.com/craftsman-ship/hamr-next-leap-forward-now/ (2018)

[3] R. F. L. Evans, W. J. Fan, O. Chureemart, T. A. Ostler, M. O. A. Ellis and R. W. Chantrell, J. Phys. Cond. Mat. 26 103202 (2013).

[4] S. Horsley, C. Sait, J. Anders, arxiv 2009.00600 (2020).

[5] H. Miller, J. Anders, Nat. Comm. 9, 2203 (2018).

Supervisors: Prof Janet Anders (Department of Physics and Astronomy, University of Exeter) and Dr Federico Cerisola (Department of Materials, University of Oxford)

External collaborators: Dr Natalia Ares (experimentalist) (Department of Materials, University of Oxford); Prof Juan Parrondo, (Department of Structure of Matter, Thermal Physics and Electronics, Madrid University); Prof Alexia Auffeves, (Department of Quantum Engineering, Grenoble University) and Dr Owen Maroney (Faculty of Philosophy, University of Oxford).

This is a theoretical physics PhD project based at the University of Exeter to start in Autumn 2021.

Landauer showed that information processing tasks are not thermodynamically neutral, quite the contrary: erasure of bits of information when in an environment at temperature T requires thermodynamic work, and this energy is dissipated as heat in the erasure process [1]. The fundamental realization that information is linked to physical laws, such as the laws of thermodynamics, was the starting point for the development of quantum information theory. However, the link between quantum information processing tasks and thermodynamics is only now being fully made. Quantum thermodynamics is a new research field where thermodynamics is studied in the small-system size limit where fluctuations become non-negligible, weak coupling between system and environment cannot be assumed, and a fully quantum mechanical description may be needed [2].

This project is concerned with building theoretical models and predictions to quantify the thermodynamic work needed to perform certain quantum information processing tasks, such as Landauer erasure [1] and work extraction from coherences [3]. The aim of this project is to develop the theoretical understanding of work extraction from coherence for new experimental platforms on which these predictions can be tested, and answering if and when thermodynamic cycles could benefit from making use of coherences. A particular experimental platform that we will focus on is a new nanomechanics experiment that is being built by Dr Natalia Ares’ group [4]. Regular visits of the Exeter theory PhD student to the experimental group in Oxford, as well as visits to the other team members in Grenoble/Madrid, will be part of the PhD project.

The experimental platform being set up in Oxford, see Figure, combines the mechanical motion of a suspended carbon nanotube (indicated with the updown arrow) with the quantum states of an electron in a quantum dot (indicated by the blue circle). The pillars over which the carbon nanotube is suspended are electron reservoirs which act as heat baths at different temperatures. The up-down motion of the tube is strongly coupled to the quantum dot state, as recently demonstrated [4]. This setup provides a new, highly controlled platform that is suited to reveal the thermodynamic value of information in the quantum regime for the first time. The mechanical motion can act as a direct probe of the work done on the quantum dot, i.e. work extracted from the quantum dot can be stored in the mechanics and then reused (depicted by the wheel).

You will begin with revisiting Landauer’s erasure protocol and deriving protocols for work extraction from coherence [3]. You will gain understanding of key issues such as “where did the work go” and “what entropy should one use” to assess information changes and energetic exchanges in the quantum regime. With the help of your supervisors, you will learn how to theoretically model the nanomechanical platform, see Figure, and adapt Landauer erasure and coherence work extraction protocols for this twolevel system. We will work closely with the experimental group in Oxford to discuss progress and measurement results, as well as the philosophical implications of our findings. It is expected that these first experimental tests of work associated with quantum states/coherences can bring up entirely new perspectives on the thermodynamic cost of quantum information processing, which we hope to explore. We may also explore alternative platforms for the work-from-coherence protocol, including continuous-variable Bose-Einstein condensates that allow highly coherent manipulation and superconducting qubits where coherent interaction between qubit and cavity has been demonstrated [5].

For further information, please contact Prof Janet Anders or Dr Federico Cerisola.


References:
[1] Landauer, R. “Dissipation and heat generation in the computing process”, IBM J. Res. Dev. 5, 148 (1961).
[2] S. Vinjanampathy, J. Anders, “Quantum Thermodynamics”, Contemporary Physics 57, 545 (2016).
[3] P. Kammerlander, J. Anders, “Coherence and measurement in quantum thermodynamics”, Scientific Reports 6, 22174 (2016).
[4] Y. Wen, N. Ares , F.J. Schupp, T. Pei, G.A.D. Briggs, E.A. Laird, “A coherent nanomechanical oscillator driven by single-electron tunnelling’’, Nature Physics (2019).
[5] N. Cottet, et al., “Observing a Quantum Maxwell Demon at Work”, Proc. Nat. Aca. Sci. 114, 7561 (2017).

Reciprocity in the animal kingdom gave rise to the evolution of reciprocal altruism: “you scratch my back, and I will scratch yours”. Aside from mere grooming, the consequences of reciprocity for the sharing of food, medicine and knowledge are profound. However, the breakdown of reciprocity, perhaps fueled by a lack of affinity or obligation, can also lead to certain benefits for the non-reciprocator, who can profit from the nonreciprocal interaction. Introducing the concept of nonreciprocity into metamaterials research also allows one to profit from nonreciprocal interactions, with immediate technological applications. Non reciprocal devices, such as optical circulators and isolators,rely on the directional transfer of energy and information at the nanoscale. Furthermore, the realization of nonreciprocal waveguides will lead to extraordinary propagation lengths, being immune to backscattering. In this project, we will construct theoretical models inducing nonreciprocity in metamaterials, for example those built from nanoscopic lattices of meta-atoms. We will consider how topology, dissipation and various symmetries can be employed to create a new class of nonreciprocal metamaterials with extraordinary transport and directional properties. Our work will be done in close collaboration with the leading experimentalists at the CMRI, where the novel phenomena that we discover can be simulated by, for example, acoustic waves or microwaves. The results of this project should guarantee future applications in wave physics, metamaterials and nanotechnology, particularly via the exploitation of the unidirectional flow of excitations.

Supervisor: Dr Luis A. Correa (Department of Physics and Astronomy)

The lowest temperatures in the universe—of just a few nanokelvins—are nowadays within reach in many labs [1]. Ultracold gases loaded in optical lattices stand out as an ideal platform for quantum simulation, which could help to crack long standing condensed-matter physics problems, and assist in the design of new metamaterials or drugs. Precise temperature control is indispensable to run reliable simulations and yet, measuring extreme temperatures with high accuracy still remains a formidable open challenge [2]. Thermometry with atomic impurities immersed in Bose–Einstein condensates is a promising route to sense such extreme tem- peratures in practice [1]. However, up to now, the interpretation of measurement results has relied on the “classical” assumption that impurities thermalise with the condensate. Modelling the problem from first principles within the theory of open quantum systems, however, tell us otherwise—while this assumption works perfectly well at temperatures ~100 μK, it breaks down in the ~1 nK range. There, quantum correlations start to build up between probe and sample, which may radically change the way data should be interpreted [3,4]. A better theoretical understanding of this quantum-thermodynamic problem is, therefore, indispensable.

The newly-developed field of quantum thermometry aims to upgrade current technologies for high-precision low-temperature measurements [2]. To do so, it combines the toolbox of quantum metrology with that of the theory of open quantum systems. The most common theoretical open-system models rely on crude simplifying assumptions (weak and linear dissipation) that become inappropriate to model thermometric setups in the ultracold regime. There, the effects of strong, structured, and/or non-linear dissipation and the build-up of quantum correlations are likely to play a major role [3,4]. In this PhD project, we will develop and apply new methods to model quantum dissipative systems under strong, structured, and/or non-linear dissipation beyond the current state of the art. We will also devise new computationally efficient techniques in quantum metrology, to help us design novel data-analysis and measurement protocols that can maximise the sensitivity of quantum thermometers at ultra-low temperatures.

Check out Exeter Open Quantum Systems group page.

For more information and other available projects, contact Dr Luis A. Correa.

References:
[1] Olf et al., Nat. Phys. 11, 720 (2015).
[2] Mehboudi, Sanpera, Correa, J. Phys. A 52, 303001 (2019).
[3] Correa et al., Phys. Rev. A 96, 062103 (2017).
[4] Mehboudi et al., PRL 122, 030403 (2019).

References:

[1] Olf et al., Nat. Phys. 11, 720 (2015).

[2] Mehboudi, Sanpera, Correa, J. Phys. A 52, 303001 (2019).

[3] Correa et al., Phys. Rev. A 96, 062103 (2017).

[4] Mehboudi et al., PRL 122, 030403 (2019).

Supervisor: Dr C. A. Downing (Department of Physics and Astronomy)


While the eigenvalues of a Hermitian Hamiltonian are always real, the Hermicity condition is more stringent than is strictly necessary. In fact, it was shown by Bender in 1998 that Hamiltonians that obey parity-time (PT) symmetry can both admit real eigenvalues and describe physical systems. The condition of combined space (P) and time (T) reflection symmetry has immediate utility in open quantum systems, where there is balanced loss into and gain from the surrounding environment. The application of the concept of PT symmetry into both classical and quantum physics has led to some remarkable advances and unconventional phenomena, which cannot be captured with standard Hermitian Hamiltonians. Typically, unusual physics occurs near to exceptional points, where the PT symmetry transitions from its broken to unbroken phase. In this theoretical project, we will exploit the rich physics of PT symmetry in order to propose quantum systems which can transport energy and information highly efficiently, combating the pernicious effects of dissipation. We will utilize synthetic magnetic fields to induce chiral currents, and will investigate the effects of ultrastrong light-coupling and strong photon correlations. The results of this research should benefit future photonic technologies, where the unidirectional flow of excitations can be exploited in novel devices.


For further information, please contact Dr C. A. Downing.