Dr Edward Laird
Department of Materials
Tel: +44 1865 273769 (office)
Quantum mechanics is not only fascinating in its own right, but also offers the possibility of revolutionary applications. I create electronic devices that exploit quantum behaviours of superposition and entanglement. I aim both to develop new technology and to explore fundamental science in quantum engineered devices. I use techniques of nanofabrication, quantum transport, and spin resonance.
For an up-to-date list of publications, see http://users.ox.ac.uk/~oums0769/index.htm
*Efficient quantum device tuning using machine learning
Edward Laird, Natalia Ares, Andrew Briggs, Simon Benjamin
Fault-tolerant quantum computers will require hundreds to millions of physical qubits to be operated with high fidelity. Inevitable hardware imperfections must be tuned away through iterative interplay of characterization, simulation, and parameter refinement, with each data point informing the decision of what to measure next. The technology is only scalable if this task can be efficiently automated. In the language of computer science, this is a Bayesian optimization problem. Recent progress in machine learning, currently one of the most rapidly developing fields of computing, makes it possible to automate the entire process. This project will apply these new techniques experimentally, working with leaders in machine learning. This is primarily an experimental project, but with substantial theoretical and computational elements. We seek candidates with a strong physics background, but with good knowledge of programming.
The focus will be electron spin qubits in gate-defined GaAs quantum dots. These are an ideal testbed because the physics is known and the dot potential and tunnel barriers are conveniently optimized by tuning gate voltages. Nonetheless, tuning a simple device by hand takes days to weeks, which is clearly not scalable.
The goal of this project is to develop a machine to automatically tune a singlet-triplet qubit in a double quantum dot. The machine will use electrical measurements of the quantum dot to deduce device parameters in the most efficient way, and then adjust gate voltages to optimise them. Inevitably, device imperfections lead to trade-offs in how it is tuned, and we will use simulations of small qubit clusters to identify how to optimise these to make spin qubits useful even in the presence of errors. This project makes use of new equipment in Oxford, including a facility for hardware-in-the-loop testing of quantum technology, and the NQIT computing facility. The applications of this approach will, we hope, ultimately extend to many areas of experimental science.
Candidates are considered in the January 2017 admissions cycle which has an application deadline of 20 January 2017.
The NQIT Hub is funded by an award to a consortium of nine universities and is supported by a number of commercial and governmental partners, including the EPSRC. This 3-year studentship will provide full fees and maintenance for a student as home fee status (this includes an EU student who has spent the previous three years (or more) in the UK undertaking undergraduate study). The stipend will be £14,296 per year. Other EU students should read the guidance at http://www.materials.ox.ac.uk/admissions/postgraduate/eu.html for further information about eligibility.
Any questions concerning the project can be addressed to Dr Edward Laird (firstname.lastname@example.org). General enquiries on how to apply can be made by e mail to email@example.com. You must complete the standard Oxford University Application for Graduate Studies. Further information and an electronic copy of the application form can be found at http://www.ox.ac.uk/admissions/postgraduate_courses/apply/index.html.
Chip-based atomic clocks
Dr E. A. Laird / Professor G. A. D. Briggs
Atomic clocks are among the most precise scientific instruments ever made, and are key to advanced navigation, secure communication, and radar technology. We are pursuing a new approach to create a clock that will fit on a chip. Instead of atomic vapours, we will use electron and nuclear spins in endohedral fullerene molecules, whose energy levels offer an exquisitely stable frequency reference. To make this novel approach work, we must overcome a range of physics and engineering challenges, including detecting spin resonance from a small number of spins, identifying the energy levels involved, and miniaturizing the control electronics and magnet. The reward will be a completely new technology with a wide range of civilian and military uses. We are looking for a candidate who has a strong interest in applying quantum physics in new technology, and is motivated to develop the new and demanding electronic measurement techniques that will be necessary.
Putting the mechanics into quantum mechanics: creating superpositions of motion using vibrating carbon nanotubes
Dr E. A. Laird / Dr N. Ares / Professor G. A . D. Briggs
The quantum mechanics of microscopic objects such as atoms and spins is well established. But what about larger objects? Can we verify true quantum behaviour for these?
As a first step to answering this question, we plan to create and measure quantum superpositions of nanoscale mechanical devices. Although tiny by everyday standards, even the smallest fabricated device contains thousands of atoms. We will make use of suspended vibrating carbon nanotubes. These possess many attractive features for creating mechanical quantum superpositions, including low mass, large quantum level spacing, and comparatively large zero-point motion. Our goal is to carry out a foundational test of quantum mechanics – the Leggett-Garg test – that falsifies the hypothesis of classical behaviour in this device. This project will focus on creating and probing so-called “macroscopically distinct” superpositions, such as a superposition of zero and ten phonons in the same device. These challenging experiments on tiny devices are the first step on a long road to discovering whether quantum mechanics applies to macroscopic objects.
Bench-top experimental tests of gravitation in quantum systems
Dr N. Ares / Dr E. A. Laird / Professor G. A. D. Briggs
The territory where quantum mechanics has to be reconciled with gravitation is still experimentally unexplored. Gravitational effects in quantum systems are typically small, making laboratory-scale experiments extremely challenging. Advances in mechanical resonators at the micro-scale and cryogenic temperatures are beginning to bring such experiments within reach. We plan to evaluate the feasibility of bench-top experiments based on two micromechanical oscillators to explore the effect of gravity in quantum systems.
Heating of mechanical resonators is expected from gravitational decoherence. To determine whether this heating effect can be measured, we will build the world’s most sensitive calorimeter based on an optomechanical system at cryogenic temperatures. The optomechanical system will consist of two mechanical oscillators inside a 3D microwave cavity, whose interaction will allow for measurement of the mechanical oscillators’ temperature. The microwave cavity will be fabricated in an aluminium block and the mechanical resonators will be commercially available silicon nitride membranes with excellent mechanical properties.
This is an ambitious project with the goal of elucidating whether quantum gravitational effects can arise in table-top experiments, opening up the possibility for a whole new direction for the quest of quantum gravitational effects.
Carbon-based quantum devices characterised electrically and by imaging
Dr E. A. Laird, Dr J. H. Warner and Professor G. A. D. Briggs
Carbon nanomaterials are attractive materials for electronic devices, especially for quantum computers using the spin of single electrons. One challenge in realising these applications is that the detailed device structure cannot be fully controlled during fabrication. The aim of this project is to characterize the same devices both through electrical measurements and by high-resolution electron microscopy, with the aim of understanding the electronic properties in terms of the atomic structure.
The goal of project will be to determine how the bandstructure and spin-orbit coupling of carbon nanotubes depend on the atomic structure – in particular on the chirality, which describes how the carbon atoms are aligned. Through aberration-corrected high-resolution transmission electron microscopy (AC-HRTEM), it is possible to measure the chiral indices of individual nanotubes, but so far this has not been performed on nanotubes integrated into electronic devices. You will combine these two kinds of measurement by incorporating a TEM window into existing fabrication technology for ultra-low-disorder nanotubes. You will then make electrical measurements of selected devices in a dilution refrigerator, with the aim of correlating the measured spin-orbit coupling to the previously determined chirality and comparing with existing theoretical predictions.
Microwave to optical conversion using molecular magnetic emitters
Dr L. Bogani /Dr E. A. Laird / Professor J. M. Smith / Professor G. A. D. Briggs
Future quantum systems will likely use several elements conceived with different strategies. These elements, such as photonic networks or superconducting circuits, typically operate at extremely different frequencies, and making them communicate is fundamental for integrated quantum devices. Even techniques to coherently connect remotely-located superconducting nodes would necessitate optical signals and is yet to be developed. This project will develop a coherent microwave-to-optical interface within hybrid quantum architectures for large scale distributed quantum computing. The platform will allow interfacing devices consisting of superconducting microwave resonators by coupling them to emitting spin centres. The resulting scheme will thus allow converting quantum information between two completely different regimes, GHz and optical, that are of crucial relevance for networking. The work will comprise the fabrication of nanodevices with superconducting and magnetic properties and their characterization at low temperatures. The thesis is strongly multidisciplinary and candidates from materials, chemistry and physics will be welcome. The work is developed in the context of an international collaboration, so different aspects can be privileged depending on the interests and attitude of the candidate. The candidate will join an active and lively laboratory with an international atmosphere. He will be assisted in developing a personal vision and an autonomous scientific profile, as well as possible industrial links and scientific collaborations. Please refer directly to Dr. Lapo Bogani, Dr. Edward Laird, Prof. Jason Smith or Prof. Andrew Briggs for details.
Nanomaterials for quantum technologies
Professor G. A. D. Briggs, Professor K. Porfyrakis, Professor J. H. Warner and Dr E. A. Laird
Quantum information processing offers one of the most exciting challenges in the study and development of nanomaterials. It is at the cutting edge of quantum nanoelectronics, and Oxford is part of the world-wide endeavour to develop scalable quantum computers. Instead of classical bits of information, these will work with qubits (quantum bits). We need materials with quantum states that can be individually controlled and measured, and yet which are sufficiently robust against decoherence that they can sustain a sequence of quantum manipulations and interactions. We lead the world in using the new family of fullerene materials (popularly known as Bucky balls), which can be used to contain atomic species inside a cage that separates them from the environment. We can store the quantum information in an electron or nuclear spin, and exchange it between the two. We can manipulate and characterize the spin states by electron paramagnetic resonance and also optically. By creating entanglement between several spins, it is possible to develop sensors that exceed the standard quantum limit. A core thrust of our research is to incorporate molecular materials in working devices for practical quantum technologies. There will be several projects with these nanomaterials, ranging from synthesis and microscopy to experimental implementation of candidate schemes for quantum computing. The research is highly interdisciplinary, and there is scope for a range of skills and interests from materials science and chemistry to experimental quantum physics. There may be possibilities for industrial support and for international travel and collaboration.
Also see a full listing of New projects available within the Department of Materials.