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George Briggs

Professor Andrew Briggs
Professor of Nanomaterials

Department of Materials
University of Oxford
16 Parks Road
Oxford OX1 3PH
UK

Tel: +44 1865 283336 (Kippi Rai-Spraggon PA)
Tel: +44 1865 273725 (Room 195.30.05)
Tel: +44 1865 273777 (reception)
Fax: +44 1865 273730


QuEEN Programme
Quantum Electronic Devices
Personal Page

Summary of Interests

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.

  1. design the devices to build, based on a deep understanding of how to control their quantum states;
  2. produce the materials, such as molecules with suitable spin states with carbon nanotubes and graphene for electrical substrates;
  3. make nanoscale devices and examine them in a microscope to see where the individual atoms and molecules are;
  4. perform the experiments to develop the quantum control and measurement for the effects which we aim to exploit;
  5. 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

Recent Lectures

Current Research Projects

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

Research Publications

Published:

  • Our Paper Distance Measurement of a Noncovalently Bound Y@C82 Pair with Double Electron Electron Resonance Spectroscopy has been published in the Journal of American Society [PDF]
  • Our Paper Seeing opportunity in every difficulty Protecting information with weak value techniques has been published in Quantum Studies: Mathematics and Foundations [PDF]
  • Our Paper Spiro-Conjugated Molecular Junctions: Between Jahn-Teller Distortion and Destructive Quantum Interference has been published in The Journal of Physical Chemistry Letters [PDF]
  • Our paper Seeing Opportunity in every difficulty has been published in Quantum Studies: Mathematics and Foundation [PDF]
  • Our paper The spin resonance clock transition of the endohedral fullerene 15N@C60 has been published in Physical Review Letters [PDF]
  • Our paper Field-effect control of graphene−fullerene thermoelectric nanodevices has been published in Nano Letters  [PDF]
  • Our paper Conditioned spin and charge dynamics of a single electron quantum dot has been published in Physical Review A [PDF]
  • Our paper Environment-Assisted Quantum Transport through Single-Molecule Junctions has been published in Physical Chemistry Chemical Physics  [PDF]
  • Our paper CF2-bridged C60 dimers and their optical transitions has been published in ChemPhysChem [PDF]
  • Our paper Environment-Assisted Quantum Transport through Single-Molecule Junctions has been published in Physical Chemistry Chemical Physics  [PDF]
  • Our paper CF2-bridged C60 dimers and their optical transitions has been published in ChemPhysChem [PDF]
  • Strong coupling of microwave photons to antiferromagnetic fluctuations in an organic magnet. Mergenthaler, J. Liu, J.J. Le Roy, N. Ares, A.L. Thompson, L. Bogani, F. Luis, S.J. Blundell, T. Lancaster, A. Ardavan, G.A.D. Briggs, P.J. Leek and E.A. Laird [PDF]
  • Double dot quantum memristor. Li, G.W. Holloway, S.C. Benjamin, G.A.D. Briggs, J. Baugh and J.A. Mol [PDF]
  • One dimensional transport in silicon nanowire junction-less field effect transistors. M.M. Mirza, F.J. Schupp, J.A. Mol, D.A. MacLaren, G.A.D. Briggs, D.J. Paul [PDF]
  • Scaling limits of graphene nanoelectrodes. S.G. Sarwat, P. Gehring, G.R. Hernandez, J.H. Warner, G.A.D. Briggs, J.A. Mol, H. Bhaskaran [PDF]
  • Method for forming nano-gaps in graphene. G.A.D. Briggs, J.A. Mol [PDF]
  • Quantum memristor based on coupled quantum dots. G.W. Holloway, Y. Ling, S.C. Benjamin, G.A.D. Briggs, J. Baugh,  J.A. Mol [PDF]
  • Distinguishing lead and molecule states in graphene-based single-electron transistors. P. Gehring, J.K. Sowa, J. Cremers, Q. Wu, H. Sadeghi, Y. Sheng, J.H. Warner, C.J. Lambert, G.A.D. Briggs, J.A. Mol [PDF]
  • Hyperfine and spin-orbit coupling effects on decay of spin-valley states in a carbon nanotube. Pei, A. Pályi, M. Mergenthaler, N. Ares, A. Mavalankar, J.H. Warner, G.A.D. Briggs, E.A. Laird [PDF]
  • Detecting continuous spontaneous localisation with charged bodies in a Paul trap. Y. Li, A.M. Steane, D. Bedingham , G.A.D. Briggs [PDF]
  • Machine learning and the questions it raises. G.A.D. Briggs, D. Potgieter [PDF]
  • Vibrational effects in charge transport through a molecular double quantum dot. J. K. Sowa, J. A. Mol, G.A.D. Briggs [PDF]
  • Scaling limits of graphene nanoelectrodes. S. G. Sarwat, P.Gehring, G. Rodriguez Hernandez, J. H. Warner, G. A. D. Briggs, J. A. Mol, H. Bhaskaran [PDF]
  • Distinguishing lead and molecule states in graphene-based single-electron transistors. P. Gehring, J. K. Sowa,† J. Cremers, Q. Q. Wu, H. Sadeghi, Y. W. Sheng, J. H. Warner, C. J. Lambert,§ G. A. D. Briggs,  J. A. Mol  (PDF)
  • Interference-based molecular transistors  Y. Li, J.A Mol, S.C. Benjamin and G.A.D. Briggs (PDF)
  • Hyperfine and spin-orbit coupling effects on decay of spin-valley states in a carbon nanotube. T. Pei, A. Pályi, M. Mergenthaler, N. Ares, A. Mavalankar, J. H. Warner, G. A. D. Briggs, E. A. Laird (PDF)
  • Resonant optomechanics with a vibrating carbon nanotube and a radio-frequency cavity. Natalia Ares, Tian Pei, Aquila Mavalankar, Matthias Mergenthaler, Jamie H. Warner, G. A. D. Briggs, Edward A. Laird [PDF]
  • Charge separated states and singlet oxygen generation of mono and bis adducts of C60 and C70.
    P. Dallas, G. Rogers, B. Reid, RA Taylor, H. Shinohara, G.A.D. Briggs and K. Porfyrakis.
    Chemical Physics 465, 28-39(2016) [PDF]
  • Photon-assisted tunneling and charge dephasing in a carbon nanotube double quantum dot.
    A. Mavalankar,  T.Pei,  J. H. Warner,  G.A.D. Briggs,  and E.A. Laird .
    Physical Review B [published online] [PDF]
  • Quantum Interference in Graphene Nanoconstrictions. P. Gehring, H. Sadegh, S. Sangtarash, C.S. Lau, J. Liu, A. Ardavan, J.H. Warner, C.J. Lambert, G.A.D. Briggs and J. A. Mol.
    Nano Letters 16, 4210-4216 (2016) [PDF]
  • Sensitive Radio-Frequency Measurements of a Quantum Dot by Tuning to Perfect Impedance Matching
    N. Ares, F.J. Schupp, A. Mavalankar, G. Rogers, J. Griffiths, G.A.C. Jones, I. Farrer, D. A. Ritchie, C.G. Smith, A. Cotten, G. A. D. Briggs, and E. A. Laird.
    Physical Review Applied 5, 034011 (2016). [PDF]
  • Probing the Dipolar Coupling in a Hetero-spin Endohedral Fullerene-Phthalocyanine Dyad.
    S. Zhou, M. Yamamoto, G. Briggs, H. Imahori, K. Porfyrakis.
    Journal of the American Chemical Society 138, 1313-1319 (2016). [PDF]
  • Redox-dependent Franck-Condon blockade and avalanche transport in a graphene-fullerene nanoelectromechanical oscillator.
    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.
    Nano Letters
     16, 170-176 (2015). [PDF]
  • Three-terminal graphene single-electron transistor fabricated using feedback-controlled electroburning
    P. Puczkarski, P. Gehring, C.S. Lau, J. Liu, A. Ardavan, J.H. Warner, G.A.D. Briggs and J.A. Mol.
    Phys. Lett.
     107, 133105 (2015). [PDF]
  • Graphene-porphyrin single-molecule transistors.
    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.
    Nanoscale 7, 13181-13185 (2015). [PDF]
  • Violation of a Leggett-Garg inequality with ideal non-invasive measurements.
    G.C. Knee, S. Simmons, E.M. Gauger, J.J.L. Morton, H. Riemann, N.V. Abrosimov, P. Becker, H-J. Pohl, K.M. Itoh, M.L. Thewalt, G.A.D. Briggs and S.C. Benjamin.
    Nat. Commun. 3, 606 (2012). [PDF]
  • Storage of multiple coherent microwave excitations in an electron spin ensemble.
    H. Wu, R.E. George, A. Ardavan, J.H. Wesenberg, K. Mølmer, D.I. Schuster, R.J. Schoelkopf, K.M. Itoh, J.J.L. Morton and G.A.D. Briggs.
    Phys. Rev. Lett. 105, 140503 (2011). [PDF]
  • Quantum computing with an electron spin ensemble.
    J.H. Wesenberg, A. Ardavan, G.A.D. Briggs, J.J.L. Morton, R.J. Schoelkopf, D.I. Schuster and K. Mølmer.
    Phys. Rev. Lett. 103, 070502 (2009). [PDF]
  • Structural transformation of graphene studied with high spatial and fast temporal resolution.
    J.H Warner, M.H. Rümmeli, T. Gemming, B. Montanari, N.M. Harrison, B. Büchner, H. Shinohara and G.A.D. Briggs.
    Nature Nanotech. 4, 500-504 (2009). [PDF]
  • Magnetic field sensing beyond the standard quantum limit using 10-spin NOON states.
    J.A. Jones, S.D. Karlen, J. Fitzsimons, A. Ardavan, S.C. Benjamin, G.A.D. Briggs and J.J.L. Morton.
    Science 324, 1166-1168 (2009). [PDF]
    Reported in Electronics Weekly 29 April - 5 May 2009, p. 7; This Week in Science 29 May 2009, p. 1115. 
  • Direct imaging of rotational stacking faults in few layer graphene.
    J.H. Warner, M.H. Rümmeli, T. Gemming, B. Büchner and G.A.D. Briggs.
    Nano Lett. 9, 102-106 (2009). [PDF]
  • Towards a fullerene-based quantum computer.
    S.C. Benjamin, A. Ardavan, G.A.D. Briggs, D.A. Britz, D. Gunlycke, J.H. Jefferson, M.A.G. Jones, D.F. Leigh, B.W. Lovett, A.N. Khlobystov, S. Lyon, J.J.L. Morton, K. Porfyrakis, M.R. Sambrook and A.M. Tyryshkin.
    J. Phys.: Condens. Matter 18, S867-S883 (2006). [PDF]
  • Bang-bang control of fullerene qubits using ultra-fast phase gates.
    J.J.L. Morton, A.M. Tyryshkin, A. Ardavan, S.C. Benjamin, K. Porfyrakis, S.A. Lyon and G.A.D. Briggs.
    Nature Physics 2, 40-43 (2006). [PDF]
  • Molecules in carbon nanotubes.
    A.N. Khlobystov, D.A. Britz and G.A.D. Briggs.
    Accounts of Chemical Research 38, 901-909 (2005). [PDF]
    Selected as a cover article for the December 2005 issue. 
  • High fidelity single qubit operations using pulsed electron paramagnetic resonance.
    J.J.L. Morton, A.M. Tyryshkin, A. Ardavan, K. Porfyrakis, S.A. Lyon and G.A.D. Briggs.
    Phys. Rev. Lett.
     95, 200501 (2005). [PDF]
    Selected for the 21 November 2005 issue of Virtual Journal of Quantum Information, www.vjquantuminfo.org; selected for the 21 November 2005 issue of Virtual Journal of Nanoscale Science & Technologywww.vjnano.org.
  • Chemical reactions inside single-walled carbon nano test-tubes.
    D.A. Britz, A.N. Khlobystov, K. Porfyrakis, A. Ardavan and G.A.D. Briggs.
    Chem. Commun.
     2005, 37-39 (2005). [PDF]
    Chosen by editors as Hot Paper (19 November 2004),   http://www.rsc.org/is/journals/current/chemcomm/cchotpapers.htm; chosen by editors for cover story of Issue 1 of 40th Anniversary Year; reported in Blueprint 5, 3 (18 November 2004); New Scientist (23 November 2004); BBC News, http://news.bbc.co.uk/1/hi/sci/tech/4033641.stmwww.democraticunderground.com; permanent.nouvelobs.comsaltyjesus.squarespace.com (24 November 2004); Iran Daily Newspaper (25 November 2004) p. 4; Financial Times 35621, 13 (26 November 2004); nanotechweb.orgwww.cnpowder.comwww2.e4engineering.com, Chemical & Engineering News 82 (48) 7 (29 November 2004); www.i-uk.comwww.britainusa.comwww.uknow.com.sg (1 December 2004); newstrove.com (13 December 2004); www.geocities.com (14 December 2004); Chemistry World 12 (December 2004), http://www.rsc.org/chemistryworld/Issues/2004/August/novel.asp; Editor’s Choice, Science 306, 1863 (10 December 2004); Smallest reactor ever, Materials Today 8 (1) 9 (January 2005); “The smallest test tube” in The Guinness Book of World Records (2006). ‘The above article was amongst the top twenty most accessed from the online version of ChemComm during 2005.’ www.rsc.org/ChemComm.
  • Observation of ordered phases of fullerene in carbon nanotubes.
    A.N. Khlobystov, D.A. Britz, A. Ardavan and G.A.D. Briggs.
    Phys. Rev. Lett. 
    92, 245507 (2004). [PDF]
    Selected for Virtual Journal of Nanoscale Science & Technology.
  • Optical schemes for quantum computation in quantum dot molecules.
    B.W. Lovett, J.H. Reina, A. Nazir and G.A.D. Briggs.
    Phys. 
    Rev. B 68, 205319, 1-18 (2003). [PDF]
    Selected for Virtual Journal of Nanoscale Science & Technology
  • InGaN quantum dots grown by metalorganic vapor phase epitaxy employing a post-growth nitrogen anneal.
    R.A. Oliver, G.A.D. Briggs, M.J. Kappers, C.J. Humphreys, S. Yasin, J.H. Rice, J.D. Smith and R.A. Taylor.
    Appl. Phys. Lett. 83, 755-757 (2003). [PDF]
    Selected for Virtual Journal of Nanoscale Science & Technology. 
  • Gas permeation in silicon-oxide/polymer (SiOx/PET) barrier films: role of the oxide lattice, nano-defects and macro-defects.
    A.P. Roberts, B.M. Henry, A.P. Sutton, C.R.M. Grovenor, G.A.D. Briggs, T. Miyamoto, M. Kano, Y. Tsukahara and M. Yanaka.
    J. Membrane Sci. 208, 75-88 (2002). [PDF]
  • Surface glass transition temperature of amorphous polymers. A new insight with SFM.
    V.N. Bliznyuk, H.E. Assender and G.A.D. Briggs.
    Macromolecules
     35, 6613-6622 (2002). [PDF]
  • STM experiment and atomistic modelling hand in hand: individual molecules on surfaces of semiconductors.
    G.A.D. Briggs and A.J. Fisher.
    Surface Science Reports 33, 1-81 (1999). [PDF]
  • Elastic and shear moduli of single-walled carbon nanotube ropes.
    J.‑P. Salvetat, G.A.D. Briggs, J.‑M. Bonard, R.R. Bacsa, A.J. Kulik, T. Stöckli, N.A. Burnham and L. Forró.
    Phys. Rev. Lett.
     82, 944-947 (1999). [PDF]
  • Imaging the elastic nanostructure of Ge islands by ultrasonic force microscopy.
    O.V. Kolosov, M.R. Castell, C.D. Marsh, G.A.D. Briggs, T.I. Kamins and R. Stanley Williams.
    Phys. Rev. Lett.
     81, 1046-1049 (1998). [PDF]
  • Defect structure of nonstoichiometric CeO2(111) surfaces studied by scanning tunneling microscopy.
    H. Norenberg and G.A.D. Briggs.
    Phys. Rev. Lett.
     79, 4222-4225 (1997). [PDF]
  • Nucleation of “hut” pits and clusters during gas-source molecular-beam epitaxy of Ge/Si(001) in in situ scanning tunneling microscopy.
    I. Goldfarb, P.T. Hayden, J.H.G. Owen and G.A.D. Briggs.
    Phys. Rev. Lett.
     78, 3959-3962 (1997). [PDF]
  • Atomic-resolution STM of a system with strongly correlated electrons: NiO(001) surface structure and defect sites.
    M.R. Castell, P.L. Wincott, N.G. Condon, C. Muggelberg, G. Thornton, S.L. Dudarev, A.P. Sutton and G.A.D. Briggs.
    Phys. Rev. B 55, 7859-7863 (1997). [PDF]
  • How does a Tip Tap?
    N.A. Burnham, O.P. Behrend, F. Oulevey, G. Gremaud, P.J. Gallo, D. Gourdon, E. Dupas A.J. Kulik, H.M. Pollock and G.A.D. Briggs.
    Nanotechnology
     8, 67-75 (1997). [PDF]
    Included in Volume 25 of Nanotechnology (2013) as one of the top ten best papers published to date.
  • Hydrocarbon adsorption on Si(001): When does the Si dimer bond break?
    A.J. Fisher, P.E. Blöchl and G.A.D. Briggs.
    Surf. Sci.
     374, 298-305 (1997). [PDF]
  • Adsorption, abstraction, and pairing of atomic hydrogen on Si(100)-(2 × 1).
    W. Widdra, S.I. Yi, R. Maboudian, G.A.D. Briggs and W.H. Weinberg.
    Phys. Rev. Lett.
     74, 2074-2077 (1995). [PDF]
  • Elastic quantum transport through small structures.
    T.N. Todorov, G.A.D. Briggs and A.P. Sutton.
    J. Phys: Condens. Matter 5, 2389-2406 (1993). [PDF]
  • An STM study of the chemisorption of C2H4 on Si(001)-(2 × 1).
    A.J. Mayne, A.R. Avery, J. Knall, T.S. Jones, G.A.D. Briggs and W.H. Weinberg.
    Surf. Sci. 284, 247-256 (1993). [PDF]
  • A two-dimensional imaging theory of surface discontinuities with the scanning acoustic microscope.
    M.G. Somekh, H.L. Bertoni, G.A.D. Briggs and N.J. Burton.
    Proc. R. Soc. Lond.
     A 401, 29-51 (1985). [PDF]
    Reprinted in Selected Papers on Scanning Acoustic Microscopy (eds B.T. Khuri-Yakub, C.F. Quate), SPIE Milestone Series MS 53, 104-123 (1992).
  • The effect of anisotropy on contrast in the scanning acoustic microscope. M.G. Somekh, G.A.D. Briggs and C. Ilett. Phil. Mag. A 49, 179-204 (1984). [PDF]
  •  

 

Projects Available

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

Also see homepages: Andrew Briggs Jan Mol

Bench-top experimental tests of gravitation in quantum systems
Dr N. Ares / 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 a mechanical oscillator inside a 3D microwave cavity, whose interaction will allow for measurement of the mechanical oscillator’s temperature. The microwave cavity is fabricated from an aluminium block and the mechanical resonators are 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. 

Also see homepages: Natalia Ares Andrew Briggs

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.

Also see homepages: Andrew Briggs

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. You will join an active and lively laboratory with an international atmosphere, and 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.

Also see homepages: Lapo Bogani Andrew Briggs

Efficient quantum device tuning using machine learning
Dr N. Ares / Professor G. A. D. Briggs

Fault-tolerant quantum computers 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. 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.

The objective is to achieve automated tuning of semiconductor qubits encoded in gate-defined quantum dots. These qubits are an ideal testbed because the physics is known and the device parameters are conveniently optimized by gate voltages. Nonetheless, tuning a simple device by hand takes days to weeks, which is clearly not scalable.  We expect this machine learning approach to enable the tuning of large quantum circuits.

 

Also see homepages: Natalia Ares Andrew Briggs

Thermodynamics at the nanoscale
Dr N. Ares / Professor G. A. D. Briggs

Experimental techniques for manipulating small fluctuating systems, such as qubits, are now mature and a great effort for developing quantum technologies is in place.  These quantum devices are systems that evolve, fluctuate and couple to each other and to the environment. As larger quantum circuits are pushed forward, studying the thermodynamics of small systems becomes crucial.  With an experimentally grounded understanding of thermodynamics at the nanoscale, it will be possible to refine future quantum devices through their fully informed design. There is also the possibility of unique behaviours that would open the way for new technologies, such as new refrigeration and sensing techniques, as well as innovative means of storing energy and powering engines. 

To constitute the simplest and most paradigmatic thermodynamic system, we require a system coupled to a heat bath and a battery. In the proposed platform, the system is a two-level quantum system coupled to a nanomechanical resonator, a vibrating carbon nanotube. The resonator stores and provides mechanical work, playing the role of a battery. A cavity will give access to time-resolved measurements of the “battery” and, therefore, will enable direct measurements of the work exchanges in a nanoscale device.

 

Also see homepages: Natalia Ares Andrew Briggs

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 homepages: Andrew Briggs Kyriakos Porfyrakis

Also see a full listing of New projects available within the Department of Materials.