Professor Kyriakos Porfyrakis FRSC
Department of Materials
Tel: +44 1865 273724 (Room 195.30.12)
Synthesis, purification, characterization and functionalization of endohedral fullerenes and their derivatives for quantum nano-electronic applications. Fullerenes are a new class of carbon-based materials. Due to their unusual molecular structure, fullerenes have been shown to possess attractive chemical, physical, magnetic, and electronic properties and are finding an increasing number of applications. Perhaps the most interesting feature of the fullerenes is that due to their cage-like structure they can trap atoms inside their empty "shell". The first of the so-called endohedral fullerenes were lanthanum containing fullerene cages, produced by vaporisation of lanthanum-doped graphite rods. To date, group-3 metals (Sc, Y), lanthanides (Ce, Gd, Pr, Ho, etc), group-2 metals (Ca, Sr, Ba), group-15 elements (N, P) and noble gases (He, Ne, Ar, Kr and Xe) have all been encapsulated in fullerenes.
- Alan Glanvill Award, IOM3, 2005
Synthesis and characterization of dimers for quantum entanglement
B.J. Farrington, Dr. K. Porfyrakis, Dr. A.N. Khlobystov*, Dr. A. Ardavan**, Professor G.A.D. Briggs
The fabrication of asymmetric dimers of endohedral fullerenes containing nitrogen atoms will enable spin resonance experiments to be performed that demonstrate entanglement between electron spins. This will constitute a crucial proof of principle of controlled entanglement in carbon nanomaterials. Chemical synthesis routes will be used that preserve the delicate endohedral nitrogen species, including the use of metal atoms to join the fullerenes through metal coordination bonds or via functionalising groups. (*University of Nottingham; **Clarendon Laboratory, Department of Physics)
Dimers for quantum computing
Dr. K. Porfyrakis, Dr. A. Ardavan*, Professor G.A.D. Briggs
Electron spin active dimers could be used to realize a two-qubit system for quantum computing. We have synthesized directly bonded empty fullerene dimers by high speed vibration milling. The same method can be used to synthesize endohedral fullerene dimers to realize a two-qubit system. We are investigating the switchable dimers for a controllable two-qubit system. We are synthesizing azobenzene bridged nitroxyl free radical dimers and fullerene dimers. UV/Vis light can be used to switch the bridge from trans- to cis-, or vice verse, in order to control the qubit interaction, which can be probed by ESR method. (*Clarendon Laboratory, Department of Physics)
Endohedral Fullerenes for Quantum Information Processing
Dr. K. Porfyrakis, Dr. A.M. Khlobystov*, Dr. A. Ardavan**, Professor G.A.D. Briggs
One of the most remarkably robust examples of an unpaired electron spin within a molecule is that of a nitrogen atom trapped inside a spherical fullerene (termed N@C60). We have measured the coherence time of a qubit encoded within this electron spin system and performed single qubit operations using pulsed electron paramagnetic resonance (EPR). We are investigating the synthesis of several types of endohedral fullerene dimers including directly-bonded and oxygen-bridged dimers. These multi-qubit systems will then be characterised by EPR. We shall study the ability to control qubit interactions through the inter-fullerene bridge, and move on to investigate larger qubit arrays. (*University of Nottingham; **Clarendon Laboratory, Department of Physics)
Endohedral fullerene derivatives for Quantum Information Processing
B.J. Farrington, Dr. A. Ardavan**, Professor G.A.D. Briggs, Dr. K. Porfyrakis
Using new high-throughput purification technologies it is now possible to produce high purity N@C60 samples on a sufficiently large scale to allow chemical functionalization of the fullerene cage. We are developing the chemistry of endohedral fullerenes with the aim of synthesizing initially dimeric and subsequently oligomeric chains of spin-active molecules. We shall control the distance between endohedral fullerenes by designing appropriate bridge molecules with varying length. We shall develop the ability to engineer and manipulate spin-spin interactions along these chains. A molecular structure of this kind could constitute a key building block for any technology based on information processing with electron spins. (**Clarendon Laboratory, Department of Physics)
4 public active projects
del Carmen Gimenez-Lopez, M., Gardener, J., Shaw, A.Q., Iwasiewicz-Wabnig, A., Porfyrakis, K., Balmer, C., Dantelle, G., Hatdjipanayi M., Crossley, A., Champness, N.R., Castell, M.R., Briggs, G.A.D. and Khlobystov, N.A., 'Endohedral metallofullerenes in self-assembled monolayers', Physical Chemistry Chemical Physics, 12, (2010), 123 – 131.
Iwasiewicz-Wabnig, A., Porfyrakis, K., Briggs G.A.D., and Sundqvist, B., 'Investigations of N@C60 and N@C70 stability under high pressure and high temperature conditions', Status Solidi B, 246, (11–12), (2009), 2767–2770.
Dantelle, G., Tiwari, A., Rahman, R., Plant, S.R., Porfyrakis, K., Mortier, M., Taylor, R.A., and Briggs, G.A.D., 'Optical properties of Er3+ in fullerenes and in β-PbF2 single-crystals', Materials, 32, (2009), 251-256.
Plant, S.R., Cheong Ng, T., Warner, J.H., Dantelle, G., Ardavan, A., Briggs, G.A.D. and Porfyrakis, K., 'A bimetallic endohedral fullerene: PrSc@C80', Communications, (2009), 4082-4084.
Plant, S.R., Dantelle, G., Ito, Y., Cheong Ng, T., Ardavan, A., Shinohara, H., Briggs, G.A.D., and Porfyrakis, K., 'Acuminated fluorescence of Er3+ centres in endohedral fullerenes by inclusion of a carbide cluster', Physics Letters, 476, (1-3), (2009) 41-45.
Norenberg, C., Leigh, D.F., Cattaneo, D., Porfyrakis, D., Li Bassi, A., Casari, C.S., Passoni, M., Owen, J.H.G., and Briggs, G.A.D., 'Self-assembly and electronic effects of Er3N@C80 and Sc3N@C80 on Au(111) and Ag/Si(111) surfaces', Journal of Physics: Conference Series, 100, (2008), 052080.
Tiwari, A., Dantelle, G., Porfyrakis, K., Watt, A.A.R., Ardavan, A., and Briggs, G.A.D., 'Magnetic properties of ErSc2N@C80, Er2ScN@C80 and Er3N@C80 fullerenes', Chemical Physics Letters, 466, (4-6), (2008) 155-158.
Cantone, A.L., Buitelaar, M.R., Smith, C.G., Anderson, D., Jones, G.A.C., Chorley, S.J., Casiraghi, C., Ferrari, A.C., Shinohara, H., Ardavan, A., Warner, J.H., Watt, A.A.R., Porfyrakis, K., and Briggs, G.A.D., 'Electronic transport characterization of Sc@C82 single walled carbon nanotube peapods', Journal of Applied Physics, 104, 8, (2008) 083717.
Tiwari, A., Dantelle, G., Porfyrakis, K., Ardavan, A., and Briggs, G.A.D., 'Temperature-dependent photoluminescence study of ErSc2N@C80 and Er2ScN@C80 fullerenes', Physica Status Solidi B, 245, 10, (2008) 1998-2001.
Silly, F., Shaw, A.Q., Porfyrakis, K., Warner, J.H., Watt, A.A.R., Castell, M.R., Umemoto, H., Akachi, T., Shinohara, H., and Briggs, G.A.D., 'Grating of single Lu@C82 molecules using supramolecular network', Chemical Communications, (2008) 4616-4618.
Morley, G.W., Porfyrakis, K., Ardavan, A., and van Tol, J., 'Dynamic Nuclear Polarization with simultaneous excitation of electronic and nuclear transitions', Applied Magnetic Resonance,34, (2008) 347-353.
Warner, J.H., Ito, Y., Zaka, M., Ge, L., Akachi, T., Okimoto, H., Porfyrakis, K., Watt, A.A.R., Shinohara H., and Briggs, G.A.D., 'Rotating fullerene chains in carbon nano-peapods', Nano Letters, 8, 8, (2008), 2328-2335. Selected as a “research highlight” by Nature Nanotechnology, published online on the 11th of July 2008.
Buitelaar, M.R., Fransson, J., Cantone, A.L., Smith,C.G., Anderson, D., Jones, C.A.G., Ardavan, A., Khlobystov, A.N., Watt, A.A.R., Porfyrakis, K., and Briggs, G.A.D., 'Pa uli spin blockade in carbon nanotube double quantum dots', Physical Review B, 77, (2008) 245439.
Morton, J.J.L., Tiwari, A., Dantelle, G., Porfyrakis, K., Ardavan, A., and Briggs, G.A.D., 'Switchable ErSc2N rotor within a C80 fullerene cage: An EPR and photoluminescence excitation study', Physical Review Letters, 101, (2008) 013002.
Pagona, G., Rotas, G., Khlobystov, A.N., Chamberlain, T.W., Porfyrakis, K., and Tagmatarchis, N., 'Azafullerene encapsulated within single-walled carbon nanotubes', Journal of the American Chemical Society, 130, 19, (2008), 6062-6063.
Warner,J.H., Watt, A.A.R., Ge, L., Porfyrakis, K., Akachi, T., Okimoto, H., Ito, Y., Ardavan, A., Montanari, B., Jefferson, J.H., Harrison, N.M., Shinohara, H., and Briggs, G.A.D., 'Dynamics of paramagnetic metallofullerenes in carbon nanotube peapods', Nano Letters, 8, 4, (2008), 1005-1010.
Zhang, J., Porfyrakis, K., Morton, J.J.L., Sambrook, M.R., Xiao, L., Ardavan, A. and Briggs, G.A.D. (2008) 'Photo-isomerization of a fullerene dimer' Journal of Physical Chemistry C 112(8) 2802-2804.
Ardavan, A., Morton, J.J.L., Benjamin, S.C., Porfyrakis, K., Briggs, G.A.D., Tyryshkin, A.M. and Lyon, S.A. (2007) 'Manipulation of quantum information in N@C60 using electron and nuclear magnetic resonance' Physica Status Solidi B 244(11) 3874-3878.
Deak, D.S., Porfyrakis, K. and Castell, M.R. (2007) 'C70 ordering on nanostructured SrTiO3(001)' Chemical Communications 2941-2943.
Deak, D.S., Silly, F., Porfyrakis, K. and Castell, M.R. (2007) 'Controlled surface ordering of endohedral fullerenes with a SrTiO3 template' Nanotechnology 18(7) 075301.
Leigh, D.F., Nörenberg, C., Cattaneo, D., Owen, J.H.G., Porfyrakis, K., Li Bassi, A., Ardavan A. and Briggs, G.A.D. (2007) 'Self-assembly of Trimetallic Nitride Template Fullerenes on Surfaces Studied by STM' Surface Science 601 2750-2755.
Morley, G.W., van Tol, J., Ardavan, A., Porfyrakis, K., Zhang J. and Briggs, G.A.D. (2007) 'Efficient Dynamic Nuclear Polarization at High Magnetic Fields' Physical Review Letters 95 220501.
Morton, J.J.L., Tyryshkin, A.M., Ardavan, A., Porfyrakis, K., Lyon, S.A. and Briggs, G.A.D. (2007) 'Environmental effects on electron spin relaxation in N@C60' Physical Review B 76 085418 (quant-ph/0611108).
Porfyrakis, K., Sambrook, M.R., Hingston, T.J., Zhang, J., Ardavan, A. and Briggs, G.A.D. (2007) 'Synthesis of fullerene dimers with controllable length' Physica Status Solidi B 244(11) 3849-3852.
Silly, F., Shaw, A.Q., Porfyrakis, K., Briggs, G.A.D. and Castell, M.R. (2007) 'Pairs and heptamers of C70 molecules ordered via PTCDI-melamine supramolecular networks' Applied Physics Letters 91 253109.
Tiwari, A., Dantelle, G., Porfyrakis, K., Taylor, R.A., Watt, A.A.R., Ardavan A. and Briggs, G.A.D.(2007)'Configuration-selective spectroscopic studies of Er3+ centers in ErSc2N@C80 and Er2ScN@C80 fullerenes' Journal of Chemical Physics 127 194504.
2-Qubit systems based on endohedral fullerene dimer molecules
Professor K. Porfyrakis
Quantum information has the potential to change a whole range of currently used computational technologies. Carbon nanomaterials offer the potential for bottom-up control of the quantum information processing building blocks. Endohedral nitrogen fullerenes exhibit some of the longest lifetimes for electron spins due to the excellent protection offered to the incarcerated spins by the carbon cage. The project involves the synthesis of two-qubit systems via covalently linking two endohedral nitrogen fullerene molecules. The spin coupling between adjacent electron spins shall be controlled by varying the length of the bridge molecule and by careful alignment of the dimer molecules within a liquid crystal matrix. The research is interdisciplinary. It will involve the development of chemical functionalization methodologies and electron spin resonance manipulation for quantum physics experiments.
Also see homepages: Kyriakos Porfyrakis
Enhancing the photoluminescence of Er-containing endohedral fullerenes via linking them to gold nanoparticles
Professor K. Porfyrakis, Dr P Dallas
Erbium ions or erbium containing organometallic complexes have been used as amplifiers in optical fibers, either silica or poly methyl methacrylate (pmma). Erbium doped fiber amplifiers can amplify light in the 1520 nm, a fingerprint emission from the erbium ion, a wavelength where telecommunication fibers are demonstrating their loss minimum. The project involves the synthesis of dyad molecules made from Er-endohedral fullerenes and gold nanoparticles with the aim to enhance the photoluminescence from the fullerene moiety. The distance between the fullerenes and the plasmonics nanoparticles influences the degree of enhancement of the quantum yield and the photoluminescence intensity. The research is interdisciplinary. It will involve the development of chemical functionalization methodologies and photoluminescence experiments in collaboration with Prof. R. A. Taylor’s group in the department of Physics.
Also see homepages: Kyriakos Porfyrakis
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.
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.
Also see a full listing of New projects available within the Department of Materials.