Professor Andrew Briggs
Department of Materials
Tel: +44 1865 273725 (Room 195.30.05)
Tel: +44 1865 273700 (switchboard)
Fax: +44 1865 273730
Quantum Electronic Devices
Summary of Interests
Whenever a fundamental new principle of science is discovered, the chances are that sooner or later a way will be found to use it for a new technology. The quantum mechanical principles of superposition and entanglement, identified nearly a century ago, are now understood to offer spectacular potential for technological applications. Superposition describes how an object can be in two states at once, as it were "here" and "there" at the same time. Two or more objects in superposition states can be entangled, so that measurements on each of them are correlated in a way that goes beyond anything we would expect from everyday intuition. Exploiting these effects in practical devices would provide new capabilities for fields such as molecular light harvesting and for molecular quantum technologies such as sensors, simulators, and quantum computers.
Successful laboratory experiments have shown that molecules of various kinds can exhibit these crucial quantum properties. Molecules are composed of electrons and atomic cores or "nuclei". Both electrons and nuclei can have a property called spin associated with them that makes them behave like tiny bar magnets. We have confirmed that electron and nuclear spins can be put into superpositions or entangled, and they can last for a long time in that condition. Most of the experiments so far have been in small test tubes. The crucial step now is to implement the same effects in nanometre scale electrical devices, such as single electron transistors consisting of single sheets of carbon rolled up as nanotubes or flat as sheets of graphene. By making hybrid technologies that combine molecules with nanoelectronics, we will lay the foundation for scaling up to more complex systems.
At this very small size, different atoms or molecules in different places affect the behaviour of the device. A breakthrough in the past few years enables us to see the positions of individual atoms in the materials which we want to use in our devices. The technique is aberration-corrected electron microscopy, and provided the electrons are not too energetic it is possible to look at the structures which we have made without damaging them. In this way we shall be able to relate the device performance to the atomic resolution microscopy of the component materials. Individual components of this vision include the following.
- design the devices to build, based on a deep understanding of how to control their quantum states;
- produce the materials, such as molecules with suitable spin states with carbon nanotubes and graphene for electrical substrates;
- make nanoscale devices and examine them in a microscope to see where the individual atoms and molecules are;
- perform the experiments to develop the quantum control and measurement for the effects which we aim to exploit;
- undertake theoretical modelling to understand the electron behaviour and to design new materials systems for improved performance.
Prizes and Awards
- Holliday Prize, Institute of Materials, 1984
- Metrology award for World Class Manufacturing, 1999
- Honorary Fellow of Royal Microscopical Society, 2000
- "The Search for Evidence-based Reality" - Video presentation, Heidelberg, October 2012
- "Experimental Implementations of Quantum Paradoxes" - Video presentation, Chapman University, California, August 2012
Quantum Effects in Electronic Nanodevices
Professor G.A.D Briggs, Dr L. Bogani, Dr J. Mol, Professor H. Anderson, Professor C. Lambert
Electronic devices, when shrunk to the molecular scale, display prominent quantum effects. Within the QuEEN programme we shall develop the scientific understanding and technological know-how needed to exploit these quantum effects for reduced-energy computing, molecular recognition, universal memory and thermoelectric recovery of energy. Our research will concentrate on the underpinning science of stable and reproducible devices, consisting of single molecules connected to graphene electrodes, with the potential for scalable production. We aim to harness quantum interference in these devices by pursuing five complementary research challenges: 1. How can quantum interference in a molecule be controlled by an electrostatic gate? 2. Can spintronic effects provide superior molecular devices? 3. Can quantum interference be used to achieve high thermoelectric effects? 4. What are the performance limits for a single-molecule transistor? 5. Can we make single molecule devices that work in ambient conditions? The QuEEN programme combines chemical synthesis, nanofabrication, measurement, and theory, and integrates these different areas of expertise. QuEEN has a distinguished international Board and a range of industrial partners from local enterprises to established global firms.
1 public active projects
Publications since 2013 are listed below.
A two-step approach to the synthesis of N@C60 fullerene dimers for molecular qubits. Chem. Sci. 4, 2971-2975 (2013); doi:10.1039/c3sc50395j. S.R. Plant, M. Jevric, J.J.L. Morton, A. Ardavan, A.N. Khlobystov, G.A.D. Briggs and K. Porfyrakis.
Quantum sensors based on weak-value amplified cannot overcome decoherence. Phys. Rev. A 87 012115 (2013); doi:10.1103/PhysRevA.87.012115. G.C. Knee, G.A.D. Briggs, S.C. Benjamin and E.M. Gauger.
Opening up three quantum boxes causes classically undetectable wavefunction collapse. Proc. Natl. Acad. Sci. USA 110, 3777-3781 (2013); doi:10.1073/pnas.1208374110. R.E. George, L. Robledo, O.J.E. Maroney, M. Blok, H. Bernien, M.L. Markham, D.J. Twitchen, J.J.L. Morton, G.A.D. Briggs and R. Hanson.
Ultrasonic force and related microscopies. In Advances in Acoustic Microscopy and High Resolution Imaging (ed R.G. Maev), Weinheim: Wiley-VCH (2013). G.A.D. Briggs and O.V. Kolosov.
Alignment of N@C60 derivatives in a liquid crystal matrix. J. Phys. Chem. B 117, 5925-5931 (2013); doi: 10.1021/jp401582j. G.Q. Liu, M.D. Gimenez-Lopez, M. Jevric, A.N. Khlobystov, G.A.D. Briggs and K. Porfyrakis.
The Oxford Questions on the foundations of quantum physics. Proc. R. Soc. A 469, 20130299 (2013); doi:10.1098/rspa.2013.0299. G.A.D. Briggs, J.N. Butterfield and A. Zeilinger.
Experimental implementations of quantum paradoxes. In Quantum Theory: A Two-Time Success Story: Yakir Aharonov Festschrift (eds D.C. Struppe, J.M. Tollaksen), Springer Verlag Italia, Milan (2014); doi:10.1007/978-88-470-5217-8_24. G.A.D. Briggs.
Method versus Madness? The Way of Science: Finding Truth and Meaning in a Scientific Worldview By Dennis R. Trumble. Times Higher Education 2125, 50 (31 October 2013); http://www.timeshighereducation.co.uk/books/the-way-of-science-finding-truth-and-meaning-in-a-scientific-worldview-by-dennis-r-trumble/2008468.article. G.A.D. Briggs. §
Optically enhanced charge transfer between C60 and single-wall carbon nanotubes in hybrid electronic devices. Nanoscale 6, 572-580 (2014); doi:10.1039/C3NR04314B. C.S. Allen, G.Q. Liu, Y.B. Chen, A.W. Robertson, K. He, K. Porfyrakis, J. Zhang, G.A.D. Briggs and J.H. Warner.
The Search for Evidence-Based Reality. In The science and religion dialogue: past and future (ed Michael Welker), Peter Lang GmbH, Frankfurt am Main (2014); doi:10.3726/978-3-653-04874-2. G.A.D. Briggs. §
Nanoscale control of graphene electrodes, Phys. Chem. Chem. Phys. 16, 20398-20401 (2014); doi: 10.1039/c4cp03257h http://xlink.rsc.org/?doi=C4CP03257H. C.S. Lau, J.A. Mol, J.H. Warner and G.A.D. Briggs.
Electrically driven spin resonance in a bent disordered carbon nanotube. Phys. Rev. B 90, 195440 (2014); doi: 10.1103/PhysRevB.90.195440. Y. Li, S.C. Benjamin, G.A.D. Briggs and E.A. Laird.
Synthesis of the first completely spin-compatible N@C60 cyclopropane derivatives by carefully tuning the DBU base catalyst. Chem. Commun. 51, 7096-7099 (2015); doi:10.1039/c5cc01459j. S. Zhou, I. Rašovi?, G.A.D. Briggs and K. Porfyrakis.
Shear alignment of fullerenes in nanotubular supramolecular complexes. Polymer 56, 516–522 (2015); doi:10.1016/j.polymer.2014.11.058 http://www.sciencedirect.com/science/article/pii/S0032386114010957. M.R. Kincera, R. Choudhury, M. Srinivasarao, H.W. Beckham, G.A.D. Briggs, K. Porfyrakis and D.G. Bucknall.
Conductance enhancement in pico-scale electro-burnt graphene nano junctions. Proc. Natl. Acad. Sci. USA 112, 2658–2663 (2015); doi:10.1073/pnas.1418632112. H. Sadeghi, J.A. Mol, C.S. Lau, G.A.D. Briggs and C.J. Lambert.
Graphene-porphyrin single-molecule transistors. Nanoscale 7, 13181-13185 (2015); doi:10.1039/C5NR03294F. J.A. Mol, C.S. Lau, W.J.M. Lewis, H. Sadeghi, C. Roche, A. Cnossen, J.H. Warner, C.J. Lambert, H.L. Anderson and G.A.D. Briggs.
Three-terminal graphene single-electron transistor fabricated using feedback-controlled electroburning. Appl. Phys. Lett. 107, 133105. P. Puczkarski, P. Gehring, C.S. Lau, J. Liu, A. Ardavan, J.H. Warner, G.A.D. Briggs and J.A. Mol.
Redox-dependent Franck-Condon blockade and avalanche transport in a graphene-fullerene nanoelectromechanical oscillator. Nano Letters. DOI: 10.1021/acs.nanolett.5b03434. C.S. Lau, H. Sadeghi, G. Rogers, S. Sangtarash, P. Dallas, K. Porfyrakis, J.H. Warner, C.J. Lambert, G.A.D. Briggs and J.A. Mol.
Putting the mechanics into quantum mechanics: creating superpositions of motion using vibrating carbon nanotubes
E A Laird / N Ares / GAD 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.
Quantum interference in single-molecule devices
Dr J. A. Mol, Professor G. A. D. Briggs and Professor H. L. Anderson*
Quantum interference offers a rich resource which could be exploited in molecular devices. If there are multiple pathways for energy transport through a molecule, or if electrical transport is subject to resonances within a molecule, then these effects could be exploited for practical technologies. For example, it may be possible to make transistors with much lower power consumption than current silicon CMOS, and it may be possible to develop improvement of thermovoltaic materials for scavenging heat that would otherwise be wasted. Understanding such phenomena may also shed light on postulated quantum coherent processes in biology, ranging from photosynthesis to bird navigation.
The project will require nanofabrication of carbon-based devices into which individual molecules can be inserted. The current through the molecules will be measured with a view to discovering mechanisms of quantum interference. A major challenge will be to devise and fabricate geometries with additional gates to control the quantum interference. The project will involve nanofabrication, chemical attachment of the molecules, and electrical measurements over a range of temperatures and frequencies, with especial regard to discovering the conditions under which quantum coherence can be found. A successful outcome will be to find regimes in which quantum coherence gives enhanced device performance.
* Department of Chemistry
Putting spins into carbon nanostructures
L Bogani/ G A D Briggs
Conducting carbon nanostructures have already been integrated in functioning electronic nanodevices and could soon constitute the fundamental elements of new era in electronics. Some of the most interesting representatives of this class of materials are probably graphene and carbon nanotubes. At the same time research in the field of spintronics has become a leading part of today’s science and technology. In this DPhil project you will make one more step ahead and connect the two fields of carbon nanostructures and spintronics, establishing a new field: molecular spintronics. The work will comprise the fabrication of carbon nanodevices with magnetic properties and their characterization of conducting nanostructures. The thesis is strongly multidisciplinary and candidates from materials, chemistry and physics will be welcome. The work is developed in the context of national and European collaborations, so different aspects can be privileged depending on the interests and attitude of the candidate. Visits and learning periods to international laboratories can also be arranged. 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 or Prof. Andrew Briggs for details.
DNA sequencing using graphene nanoelectrodes
Dr J. A. Mol and Professor G. A. D. Briggs
Single strand DNA sequencing is a rapidly developing field of research on the cutting edge of physics, biology and chemistry. Solid state nanopores are currently being researched by Oxford Nanopore Technologies to form the basis for next-generation DNA sequencing tools. This includes the evaluation of graphene as a membrane for DNA sequencing applications. There is great need to develop methods for fabricating holes and gaps in graphene membranes that are scalable enough to be part of a production process. We are looking for a DPhil student who will develop suspended graphene devices that have the potential to meet the requirements for solid state nano-pores, and will:
1. Optimise the nanogap size for analyte molecules of interest.
2. Incorporate our suspended graphene nanogaps into the kind of instrumentation which Oxford Nanopores already uses.
3. Characterise the signals which we can measure from a range of analytes.
4. Seek to improve the geometry in order to optimise the nanogap/nanopore structures for commercial applications.
5. Develop recognition tunnelling as an electronic single-molecule sequencing method for DNA.
The goal is to develop arrays of 10s to 100s of nanopore/nanogap sensing elements integrated with an ASIC for single molecule detection. Following an initial proof of concept, the DPhil student will be working closely with Oxford Nanopore Technologies’ team to manufacture the device at scale and increase the array density to 1000s of channels.
Bench-top experimental tests of gravitation in quantum systems
N Ares / E A Laird / GAD 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.
Chip-based atomic clocks
E A Laird / 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.
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.
Silicon quantum electronics
Dr J. A. Mol and Professor G. A. D. Briggs
Quantum information embodied in spins in silicon can be manipulated very precisely, and can persist for over three hours. Quantum computers made from silicon materials would benefit from the great industrial development of silicon processing and nanofabrication. Much of previous research in silicon for quantum computing has used donor impurities in bulk crystals. The great challenges now are to learn how to measure the states and control the interactions of a small numbers of spins in silicon. This project will seek to develop control techniques that will be sufficiently precise to allow fault-tolerant error-correction in silicon devices with small numbers of spins. Scalable quantum technologies will need to meet and surpass certain accuracy thresholds to demonstrate quantum error correction. The goal of the project will be to exceed these thresholds using impurity and quantum dot spins in silicon devices. For this you will investigate magnetic resonance in both many-spin and single-spin regimes. You will need to have, or to acquire early in the project, good knowledge of physics, magnetic resonance, quantum information, and semiconductor materials.
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.
A carbon nanotube quantum computer
Dr E. A. Laird and Professor G. A. D. Briggs
A computer based on the quantum states of single electrons has the potential to be exponentially more powerful for some tasks than existing classical computers. Creating such a computer is an extremely difficult challenge, because quantum states usually decohere rapidly due to interactions with their environment. One leading approach is to use the spin states of an electron in a semiconductor. Carbon nanotubes are a particularly attractive material for this purpose, because nuclear spins, which cause decoherence in some other semiconductors, can be virtually eliminated. In this project, you will create a proof-of-principle two-bit quantum computer in an isotopically purified carbon nanotube. Very recently, a single-qubit gate was demonstrated in a nanotube quantum dot. You will extend this work by using a radio-frequency measurement setup for high-fidelity qubit readout and implementing a two-qubit gate in a pair of quantum dots. The goal is to demonstrate simple quantum algorithms in a carbon nanotube device. This project will involve training in nanofabrication, as well as low- and high-frequency electronics at millikelvin temperatures.
Also see homepages: Andrew Briggs
Coupling valley-spin qubits in nanotubes by superconducting cavities
Professor G. A. D. Briggs, Dr E. A. Laird and Dr P. J. Leek*
Carbon-based quantum technologies will use electron spin states in nanotubes as a fundamental resource. A single electron in a confined region (sometimes referred to as a quantum dot) in a nanotube can form a valley-spin qubit, through the interaction between the valleys in the band structure and the spin of the electron. The spin-orbit coupling provides a means of linking the qubit to an external system via an electric dipole.
Quantum technologies will demand the ability to transfer quantum information from one device to another. The magnetic dipole moment of a single electron spin is too weak for this purpose, but by converting it to an electric dipole moment the coupling can be significantly increased. Superconducting cavities, fabricated either in the form of on-chip resonators or as a 3-D box, provide the means to couple two nanotube quantum devices together, or to couple a nanotube device to collective spin states as a quantum information register. The goal of this project will be to learn how to couple a valley-spin qubit to a superconducting cavity, and then to show how that will useful for scalable quantum technologies.
* Department of Physics
Also see homepages: Andrew Briggs
Coupling molecular spins to valley-spin qubits in carbon nanotubes
Professor G. A. D. Briggs, Professor J. H. Warner, Professor K. Porfyrakis and Dr E. A. Laird
Carbon-based quantum technologies require the ability to transfer quantum information from one form to another. Valley-spin qubits (so called because of the hybridisation between electron spin states and the valleys in the band structure of the nanotube) enable single states to be manipulated and measured in electron dipole spin resonance, but the coherence times are not long enough for scaleable quantum computing. Molecular qubits are known from ensemble experiments to have useful quantum coherence times, but to exploit these in useful devices we must have ways to measure them individually. By attaching molecules to the nanotube, and transferring quantum states between the nanotube and the molecule, it should be possible to exploit the best of each. The storage time can be increased a further thousandfold by using molecular nuclear spins as a further resource.
Successful development of this scheme will require nanofabrication of the devices, attachment of the spin-bearing molecules, microscopy of the resulting structures, and magnetic resonance at cryogenic temperatures. This project will involve training in nanofabrication, together with electron microscopy and low-temperature electronic measurements. Aspects of the project will be undertaken in collaboration with other members of the laboratory. The goal will be to show that quantum information can be effectively transferred between the nanotube device and the spin states of the attached molecules. This will be achieved by entangling quantum mechanically the molecular spin with an electron spin on the nanotube, and measuring the molecular spin state through its effect on the electron.
Quantum read-out of spin resonance in a silicon transistor
Dr J. A. Mol, and Professor G. A. D. Briggs
If quantum computers could be made using silicon materials, they would benefit from the vast investment that has been made in the purification of the materials and the nanofabrication of devices. Recent work in collaboration with Oxford has shown that the quantum coherence time of spin qubits can be more than three hours. The great challenges now are to learn how to control the interactions and measure the states of a small numbers of spins in silicon. This project will seek to detect electron spin resonance in a nanoscale silicon transistor through the resulting change in current.
The project will study electrically detected magnetic resonance (EDMR) in state-of-the-art silicon transistors. The size and geometry of these devices allows for the detection of spin states down to level of a single donor atom. The project will combine device fabrication and measurement with cavity-based electron and nuclear magnetic resonance. This will open the way to exploring phenomena usually associated with atomic physics for quantum information processing. The project will demand good knowledge of physics and/or electrical engineering as well as a deep understanding of semiconductor materials, and will benefit from new facilities currently being established at Oxford for experiments on quantum devices.
Also see homepages: Andrew Briggs
Also see a full listing of New projects available within the Department of Materials.