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Seminar Speakers (2017/18)

Upcoming Seminars:

Seminar 8: All-optical coherent control of diamond-based quantum bits

Dr Jonas Becker
University of Oxford

Time: 14:00 - 15:00
Wednesday 28th February
Venue: MAS 2.06

Full coherent control of individual quantum systems is a key prerequisite to build a quantum information processing (QIP) system. Oftentimes, coherent control of the internal state of a quantum bit (qubit) is achieved utilizing radio frequency- or microwave-based control schemes. These techniques, however, only allow for a relatively slow manipulation on the nanosecond to microsecond time scale, a significant disadvantage in the presence of fast decoherence processes, as they are for example common in solid state environments. In contrast, suitable quantum systems provided, all-optical control techniques allow for a spatially resolved and potentially ultrafast coherent control of a quantum system. 
In this talk, I am first going to review efforts in optically controlling solid state qubits, with a particular focus on the well-known nitrogen vacancy centre (NV) in diamond. I will then introduce the silicon vacancy centre (SiV) in diamond as a more recent and highly interesting candidate for all-optical coherent control. I will discuss our own experiments of coherently controlling both individual SiVs as well as dense SiV ensembles and highlight a number of potential QIP applications for this colour centre. To conclude, I will discuss how the results obtained for the NV and SiV can now be used to perform a targeted search for novel colour centres in diamond with optimized properties for QIP and I will briefly highlight a number of candidates that have already been identified.

Students Allocated: Tom Weaver (Podcast), Andrew Kirkpatrick (Podcast), Martin Lee (Podcast), William Leigh (News & Views)

Recent Seminars:

Seminar 7: Short pulse laser fabrication in transparent materials- applications in diamond

Dr Patrick Salter
University of Oxford

Time: 14:00 - 15:00
Wednesday 14th February
Venue: MAS 2.06

Using ultrafast lasers with a pulse duration below a picosecond, it is possible to fabricate inside a wide range of transparent materials. The fabrication is highly non-linear, such that the material modification is confined to the focal volume of the laser, enabling three dimensional internal processing. In this talk, I will discuss some basics related to the laser fabrication process and then how it may be related to the structuring of diamond. We will look at the various forms of laser induced structural modifications achievable in diamond, both in the bulk and on the surface. These can then be used to create functional components in 3D, including graphitic wires, defects, waveguides and other optical structures.

Students Allocated: Ben Woodward (Podcast), Andrew Kirkpatrick (News & Views), Martin Lee (News & Views)

Seminar 10b: Probing the viscoelasticity of biological tissue on a microscale with Brillouin spectroscopy

Dr Francesca Palombo
University of Exeter

Time: 14:00 - 15:00
Monday 12th February
Venue: MAS 2.06

The biomechanics of living tissues are critical to normal tissue function and disturbances in these properties are widely implicated in aging and disease. Protein fibres of the extracellular matrix (collagen and elastin) are the fundamental mechanical structures in connective tissues such as bone, cartilage and vasculature. We applied Brillouin light scattering (BLS) spectroscopy and quasistatic stress-strain testing to the study of the mechanics and structure of collagen and elastin fibres purified from connective tissues. BLS probes mechanical properties on a microscopic scale in biological tissues and thereby providing insights into structure–function relationships under normal and pathological conditions. The sensitivity of BLS measurements to fibre structure and hydration was investigated using samples mounted onto reflective substrates. We obtained a complete characterization of the mechanical tensor and elastic moduli which could be compared with complementary data from quasistatic stress-strain measurements at different hydration levels, hence giving the full description of fibre viscoelasticity. BLS micro-spectroscopy applied to epithelial tissue provides the heterogeneous distribution in mechanical properties in correspondence of molecular composition probed by Raman scattering.

Students Allocated: Ryan Corbyn (Podcast)

Seminar 6: Diamond Electronics – Fact or Fiction?

Prof Richard Jackman
University College London

Time: 14:00 - 15:00
Wednesday 31st January
Venue: MAS 2.06

Beyond diamond’s high optical refractive index, few realise it is an exceptional electronic material. With a wide band gap (5.5eV) it can be doped with boron to display p-type character, perhaps doped to be n-type as well, and can display very high carrier mobilities and electric breakdown field strength. When allied to its extreme thermal conductivity and resilience to radiation many applications can be envisaged for diamond electronics. Throughout the 1990s’ many spoke of ‘diamond as the new silicon’, but we know that this transition never took place. Why? Poor diamond material? Difficulty in processing diamond into electronic devices and doping? Market resistance? Lack of prototypes? Perhaps all of these. This seminar will look into whether diamond electronic devices are now, or ever will be, a fact, or a fiction.

We will start by reviewing the basic structure and operating principles of the two main classes of currently used transistors, the Metal Oxide Semiconductor Field Effect Transistor (MOSFET) and the Bipolar Junction Transistor (BJT). We will discuss differing materials merits for these devices, and look directly at how diamond may perform in an ideal case. We will move onto the issues hindering diamonds’ use in this context and the prospects for their resolution.

Next, we will consider different device designs that may take advantage of diamonds character and lead to a new generation, or even a new paradigm, for electronics. Both power device and computational device prospects will be discussed.

Finally, niche device applications, where Si and other ‘conventional’ materials cannot perform will be discussed.

This presentation will be accessible to all, not just those with and Electronics background, the only criteria requested for attendance is a keen interest in the future prospects for the useful use of diamond beyond the gem trade!

Students Allocated: Teena Rajan (News & Views), Ryan Corbyn (News & Views)

Seminar 10a: Electrochemical gas sensors- saving lives and helping our planet breathe

Dr John Saffell

Time: 14:30 - 15:30
Thursday 18th January
Venue: MOAC Seminar Room (top floor, Senate House)

Students Allocated: Teena Rajan (Podcast), Ben Woodward (News & Views)

Seminar 5: The laser processing of diamond and cubic boron nitride materials for industrial applications

Dr Paul Butler-Smith
Nottingham University

This presentation looks at the ablation mechanisms of diamond and cubic boron nitride materials and evaluates the structural integrity of these laser processed materials using FIB/SEM preparation and TEM/EELS/EDX and STEM investigatory techniques. The laser processing of diamond and cubic boron nitride structures for ordered abrasive and defined edge rotary tools are presented along with performance comparisons of these tools over those produced using traditional techniques.

Time: 14:00 - 15:00
Wednesday 6th December
Materials and Analytical Sciences (MAS 2.06)

Students Allocated: James Brixey (News & Views), William Leigh (Podcast)

Seminar 4: Multiscale and multiphysics diamond defects

Dr Ben Hourahine
University of Strathclyde

Point and extended defects in diamond display a rich and varied range of physical effects and properties. In this seminar I'll discuss a collection of models and theories for three classes of behaviour that occur in diamond related to nitrogen-vacancy (NV) defects:

1. Starting with quantum-chemistry-like methods, the ground and excited properties of different charge and spin states of NV. This leads to a sensitive nanoscale probe of local strain, electric and magnetic fields. Here I'll briefly review ground and excited state density-based methods, in particular Density Functional Based Tight Binding (DFTB), before discussing some problems the negative NV singlet state poses for this type of theory.

2. One interesting possible application of NV- is as a single photon source, so next some discussion of the quantum optics of radiating sources in nano-structured environments. The local density of optical states (LDOS) directly influences the lifetime and coupling between mater and light, so can be used to produce states where the quantum state of the defect is strongly mixed with the surrounding light field (strong coupling limit). Here I'll discuss some recent work on finding the contributions to the LDOS from different optical modes of nano-structures.

3. The collective spin properties of of NV centres have recently been used to forms 'time crystals' - non equilibrium systems that spontaneously break continuous time symmetry. Here I will introduce this type of symmetry breaking and briefly talk about non-equilibrium kinetic models and some on-going work about multi-scale behaviour of lattice spin modes.

Finally, and time allowing, the final topic to be discussed is a new joint experimental-theoretical activity at Strathclyde using energy filtered scanning electron microscopy to measure and understand dislocations in materials like diamond, where the low atomic weight strongly limits the spatial resolution of channelling microscopy.

Time: 12:30 - 13:30
Wednesday 22nd November
Materials and Analytical Sciences (MAS 2.06)

Students Allocated: James Brixey (Podcast), Daniel Field (News & Views)

Seminar 3: Coherent few-spin systems in diamond nanocrystals for quantum sensing

Dr Helena Knowles
Cavendish Laboratory, University of Cambridge

Single isolated spins in solids can act as a unit of a quantum network or as an individual magnetic or electric field sensor. Such a unit can be expanded by using coherently interacting spin clusters, which provide a performance enhancement for quantum technologies.

In this talk, I will show how we investigate hybrid spin systems composed of the Nitrogen Vacancy centre (NV) in diamond coupled to dark spins, i.e. spins that are not directly optically accessible. Both electronic and nuclear dark spins offer distinct advantages: Nuclear spins provide a robust memory for quantum states and electronic spins allow for fast dipole-mediated interactions[1, 2].

The access to nuclear spins in diamond nanocrystals has so far remained elusive but, as we demonstrate, can provide important sensitivity enhancements for NV centre-based sensing, as NVs in nanodiamond typically have short coherence times (~μs) compared with their bulk counterparts (~ms)2. We also make use of a proximal nitrogen (N) impurity cluster to perform environment-assisted sensing: An entangled state of the NV and N spins is used to detect an external magnetic field and we observe a double-frequency component in the interferometer signal, corresponding to the contribution of at least two electronic spins, in contrast to the NV spin only.

[1] Knowles et al. PRL 117 100802 (2016),

[2] Knowles et al. PRB 96 115206 (2017)

Time: 14:00 - 15:00
Wednesday 8th November
Materials and Analytical Sciences (MAS 2.06)

Students Allocated: Lewis Mills (Podcast), Jennifer Orme (Podcast), Rajesh Patel (News & Views)

Seminar 2: Electron microscopy: atomic resolution images and what we can do with them

Dr Richard Beanland
University of Warwick

The interaction between high energy electrons and matter is strong and produces a myriad of effects that can be used to investigate materials. This lecture will describe some of the technical advances that have allowed atomic resolution imaging and spectroscopy in transmission electron microscopy, with some examples from semiconductors, oxides and metals. Future possibilities, for new kinds of information that may be obtained by computer control of the microscope (particularly using electron diffraction) will also be described.

Time: 14:00 - 15:00
Wednesday 25th October
Materials and Analytical Sciences (MAS 2.06)

Students Allocated: Daniel Field (Podcast), Rajesh Patel (Podcast), Tom Weaver (News & Views)

Seminar 1: The growth of doped diamond by chemical vapour deposition

Dr Shannon Nicley
Hasselt University

In this seminar I will begin by reviewing methods of diamond growth, focussing on chemical vapour deposition. I will describe both n- and p-type doping of diamond, and discuss the challenges in achieving high quality doped diamond. I will describe various characterisation methods, and conclude with a summary of strategies for achieving high quality doped single crystal diamond, focussing on substrate preparation and substrate temperature during deposition.

Time: 14:00 - 15:00
Thursday 26th October
Materials and Analytical Sciences (MAS 2.06)

Students Allocated: Lewis Mills (News & Views), Jennifer Orme (News & Views)