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PhD Projects

This page outlines the PhD projects for which we are recruiting in 2017/18. The awards will include the payment of academic fees at the Home/EU rate and a maintenance grant in line with the UK Research Council stipend. Applicants must have obtained or be expected to obtain at least an upper second class honours degree (or equivalent) from a recognised institution of higher education before 31 July 2018.

If you are interested in one or more of the projects please contact Mark Newton (m.e.newton@warwick.ac.uk) and Gavin Morley (gavin.morley@warwick.ac.uk).

Rotation of a levitating nanodiamond containing a spin qubit

Single nitrogen-vacancy (NV-) centres in diamond have isolated electronic and nuclear spins which can store quantum information at room temperature for over one second. We have built an exciting new experiment to study nanodiamonds that are levitated by a focused laser beam. Our theoretical proposals (together with the groups of Sougato Bose and Peter Barker in UCL and Myungshik Kim at Imperial College) suggest that we could put these diamonds into a quantum superposition in which they try out being in two places at once [1-3]. This could permit tests of quantum mechanics and may lead to future quantum sensors.

We had found that our nanodiamonds heat up to destruction when we pump out the air that was taking away the energy absorbed from the trapping laser [4]. However, we have solved this problem with nanodiamonds that are 1000 times purer, so absorb less of the trapping light [5]. Our lab in Warwick also benefits from several other NV- experiments for quantum technology focused on nanoscale and bulk magnetometry both at room temperature and in helium cryostats. The goal of this project is to adapt our levitated nanodiamond experiment for detecting rotational oscillations of the nanodiamond. To achieve this you will begin by setting
up optical detectors which can see the higher rotational vibration frequency of around 1 MHz instead of our current work with the 100 kHz translational motion. High vacuum is required to increase the quality factor of these vibrations, and to reach this you will implement a “feedback cooling” scheme that has been used in several labs worldwide. You will add in a small homogeneous magnetic field so that the rotational motion of the nanodiamond couples to the electron spin of the NV- [6]. You will then have the chance to explore whether the diamond’s rotational state can be in a quantum superposition of clockwise and counterclockwise.
This would be significant for our understanding of quantum mechanics as the diamond would be the most massive object that has ever been put into a superposition state by several orders of magnitude.

Full funding is available from the Royal Society for 4 years at standard research council rates (stipend plus fees). You would start on your project in the lab from day one without doing an initial Masters course. For informal enquiries, please contact Gavin Morley (gavin.morley@warwick.ac.uk).

[1] M. Scala et al., Physical Review Letters 111, 180403 (2013).
[2] C. Wan et al., Physical Review Letters 117, 143003 (2016).
[3] S. Bose et al., Physical Review Letters, 119, 240401 (2017).
[4] A. T. M. A. Rahman et al., Scientific Reports 6, 21633 (2016).
[5] A. C. Frangeskou et al., arXiv:1608.04724 (2016).
[6] Y. Ma et al., Physical Review A 96, 023827 (2017).

A Study of the Relaxation Dynamics of Local Vibrational Modes Associated with Hydrogen in Diamond

Hydrogen is abundant in the source gases for the growth of diamond by chemical vapour deposition (CVD). Hydrogen is of considerable experimental and theoretical interest because of its ability to interact with virtually any lattice defect, including impurities, intrinsic defects, surfaces, and interfaces, thus possibly changing both the electronic and optical properties of the material. Until now, all spectroscopic studies of hydrogen-related in diamond have been carried out in the frequency domain, which probes the time-averaged optical response of the modes. Consequently, very little is known about the dynamics of the modes, i.e., the time scales and mechanisms for population and relaxation upon excitation. Such information is crucial since excited vibrational states may be involved in the dissociation of the bond between hydrogen and the lattice and in optical absorption at frequencies well above that of the fundamental vibration. In silicon, the degradation of some electronic devices is believed to be caused by the dissociation of vibrationally excited Si-H bonds. To understand such processes in diamond, it is necessary to know the time scale on which excited vibrational states decay. Such measurements are now possible with highspeed pump-probe laser systems. In silicon the Si-H vibration lifetimes are found to be extremely dependent on the defect structure, varying by more than two orders of magnitude, and the same is expected for diamond.

Knowledge of excited state lifetimes would be terrifically useful. For example we are currently unable to relate the strength of a C-H local vibrational mode to the concentration of the defect in diamond, for all except one defect where charge transfer has allowed calibration. The radiative lifetime relates the strength of the absorption to the concentration of the defect. Thus the lifetime information is vitally important for determining the amount of hydrogen incorporated in different defects in diamond. Furthermore, we know little about the mechanism(s) for the diffusion of hydrogen in diamond. Control of impurity diffusion is an important element in materials processing and device fabrication technologies. Thermal annealing is unselective and unwanted diffusion of a specific species may be stimulated while endeavouring to activate diffusion of another. It would be highly desirable to diffuse a specific species only (selective diffusion). It may be possible by irradiation with the resonant frequency could cause excitation of a C-H local vibrational mode to selectively enhance the diffusion of hydrogen in diamond. Since the optical excitation time should be short compared to the relaxation time knowledge of later would be terrifically useful. This PhD project combines time resolved pump-probe techniques, to measure the excited state lifetimes of a number of local vibrational modes, with a range of other spectroscopic measurements to investigate some of the outstanding hydrogen related defect identification, quantification and interaction issues in diamond. The project will involve working with a number of collaborators, both academic and industrial, and making use of strong existing links with theoretical researchers investing defect dynamics.
Contact: Mark Newton (m.e.newton@warwick.ac.uk)