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Brendon Lovett

Dr Brendon Lovett
Academic Visitor and Royal Society University Research Fellow

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

Tel: +44 1865 273777 (reception)
Fax: +44 1865 273730

Theory of Quantum Nanomaterials website

Summary of Interests

Design and realization of architectures for new forms of information processing, especially quantum computing. Theoretical work relating to the design and characterization of solid state nanostructures for computation, with particular current emphasis on (a) quantum dots systems (b) fullerene systems (nanotubes, endohedral C60, etc.) (c) defects in diamond. In particular, I do calculations of how to control and manipulate interactions between nanostructures such that entangled states might be produced between them.

Energy harvesting; in particular understanding how excitons in networks of coupled chromophores can be made to move to a target site most efficiently. Applications include understanding photosynthesis and solar energy harvesting.

All of these studies involve work on open quantum system theory to understand the nature of environmental interactions in solid state and molecular systems.

Current Research Projects

Quantum energy calculations for artificial and biological nanostructures
Dr. S.C. Benjamin, Dr. B.W. Lovett*, Dr. E.M. Gauger, Mr Higgins, Mr Pollock
In order to best understand how to engineer molecular scale systems that can harvest, transfer and store energy, it is necessary to understand energy transfer at the quantum level. There is evidence to suggest that Nature's molecular technologies, for example the structures involved in photosynthesis, perform energy transfer in a way that involves quantum coherence. This is a surprise since quantum effects are usually thought to be difficult to achieve and more the province of the physics laboratory than a "warm and wet" biological system. We are developing new analytic and numerical techniques to understand energy transfer as a fully quantum mechanical process, and aiming to apply this both to natural systems and to artificial structures created by our experimental collaborators. The task is challenging, but the answers may eventually allow us to design highly efficient molecular scale technologies.(*Heriot-Watt University)

Coherent Control of Spin Systems
Dr. S.C. Benjamin, Dr. B.W. Lovett*, Dr. E.M. Gauger
We are studying the quantum properties of nuclear and electron spins, primarily in molecular systems. Our aim is to provide theory that will allow for the control small numbers of spins, such that the quantum coherence is preserved for as long as possible. We collaborate with the Quantum Spin Dynamics experimental group in London (http://www.ucl.ac.uk/qsd), and together we demonstrated that the quantum state of an electron spin can be transferred coherently to a nuclear spin, thus increasing the coherence time. We are now working on optical methods for further improving coherence, and for coupling several spins together. (*Heriot-Watt University)

Carbon nanostructures
Dr. B.W. Lovett*, Dr. G. Giavaras
We are studying various aspects of carbon-based nanomaterials, specifically fullerenes and nanotubes. Two main themes are currently being pursued. First, a carbon nanotube can be filled with spin-possessing endohedral fullerenes making a so-called peapod material. Certain devices require that the peapod spins interact with one another, and one such interaction could be through the indirect exchange coupling via the conduction electrons of the nanotubes. We are developing various many-body techniques by which this coupling can be calculated. Second, we are interested in the transport properties of carbon nanotubes and peapods. Using master equation techniques, we aim to find methods by which magnetic resonance might be detected in such systems by measuring the electrical current through them. These transport calculations have already revealed that a carbon nanotube can act as a sensitive spin measurement device or as a spin characterization tool. This work is carried out in collaboration with the experimental semiconductor group of Prof Charles Smith at the University of Cambridge http://www.sp.phy.cam.ac.uk/SPWeb/home/cgs4.html. (*Heriot-Watt University)

Architectures and materials for robust and scalable quantum technologies
Dr. S.C. Benjamin, Ms Naomi Nickerson
Today's computers may seem very powerful, but their designs do not take advantange of the enormous potential power of quantum physics. We know that it is possible, in principle, to build an entirely new class of technology that would harness effects like quantum superposition and quantum entanglement in order to profoundly outperform all conventional machines (at least for certain key tasks). However such technologies are very challenging to build in reality. It particular it is difficult to take the small prototype systems in the laboratory and scale them up to the point that they start to exceed the capacities of conventional technologies.  This project is about finding ways to build these technologies that are robust, in the sense that they can operate with realisitic levels of imperfection, and also scalable -- so that once you have a few components working together, it is straightforward to add more and more. For example: One approach would be to build the large machine by networking together many simple processor cells, thus avoiding the need to create a single complex structure. See for example our open Nature Communications paper: http://www.nature.com/ncomms/journal/v4/n4/full/ncomms2773.html

4 public active projects

Research Publications

 

Book:

Introduction to Optical Quantum Information Processing, P. Kok and B. W. Lovett, Cambridge University Press (2010)

 

Papers:

  1.  Phonon induced Rabi frequency renormalization of optically driven single InGaAs/GaAs quantum dots, A. J. Ramsay, T. M. Godden, S. J. Boyle, E. M. Gauger, A. Nazir, B. W. Lovett, A. M. Fox, M. S. Skolnick, Phys. Rev. Lett., 105 177402 (2010)

  2. Entangling remote nuclear spins linked by a chromophore, M. Schaffry, V. Filidou, S. D. Karlen, E. M. Gauger, S. C. Benjamin, H. L. Anderson, A. Ardavan, G. A. D. Briggs, K. Maeda, K. B. Henbest, F. Giustino, J. J. L. Morton and B. W. Lovett, Phys. Rev. Lett. 104 200501 (2010)

  3. Excitation-induced-dephasing of quantum dot excitonic Rabi rotations, A. J. Ramsay, Achanta Venu Gopal, E. M. Gauger, A. Nazir, B. W. Lovett, A. M. Fox and M. S. Skolnick, Phys. Rev. Lett. 104 017402 (2010)

  4. Spin detection at elevated temperatures using a driven double quantum dot, G. Giavaras, J. Wabnig, B. W. Lovett, J. H. Jefferson, and G. A. D. Briggs, Phys. Rev. B 82 085410 (2010)

  5. Quantum metrology with molecular ensembles, M. Schaffry, E. M. Gauger, J. J. L. Morton, J. Fitzsimons, S. C. Benjamin, and B. W. Lovett,  Phys. Rev. A 82, 042114 (2010)

  6. Spin lifetimes in quantum dots from noise measurements, J. Wabnig, B. W. Lovett, J. H. Jefferson and G. A. D. Briggs, Phys. Rev. Lett. 102 016802 (2009)

  7. Comment on Multipartite Entanglement Among Single Spins in Diamond, B. W. Lovett and S. C. Benjamin, Science 323 DOI 10.1126/science.1168458 (2009)

  8. Prospects for measurement-based quantum computing with solid state spins, S. C. Benjamin, B. W. Lovett and J. M. Smith, Laser and Photonics Reviews, 3 556 (2009)

  9. Aspects of quantum coherence in nanosystems, B. W. Lovett and A. Nazir, European Journal of Physics 30 S89 (2009)

  10. Large spin entangled current from a passive device, A. Kolli, S. C. Benjamin, J. Garcia Coello, S. Bose, and B. W. Lovett, New J. Phys. 11 013018 (2009)

  11. Measurement-based approach to entanglement generation in coupled quantum dots, A. Kolli, S. C. Benjamin, B. W. Lovett and T. M. Stace, Phys. Rev. B 79 035315 (2009)

  12. Solid state quantum memory using the 31P nuclear spin, J. J. L. Morton, A. M. Tyryshkin, R. M. Brown, S. Shankar, B. W. Lovett, A. Ardavan, T. Schenkel, E. E. Haller, J. W. Ager and S. A. Lyon, Nature 455 1085 (2008)

  13. High fidelity all-optical control of quantum dot spins: Detailed study of the adiabatic approach, E. M.Gauger, S. C. Benjamin, A. Nazir and B. W. Lovett, Phys. Rev. B 77 115322 (2008)

  14. Freezing distributed entanglement in spin chains, I. D’Amico, B. W. Lovett and T. P. Spiller Phys. Rev. A 76 030302 (2007)

  15. All-optical measurement-based quantum-information processing in quantum dots, A. Kolli, B. W. Lovett, S. C. Benjamin and T. M. Stace, Phys. Rev. Lett. 97 250504 (2006)

  16. Materials science - Qubits in the pink, P. Kok and B. W. Lovett, Nature 444, 49 (2006)

  17. Quantum computing with spin qubits interacting through delocalized excitons: Overcoming hole mixing, B. W. Lovett, A. Nazir, E. Pazy and G. A. D. Briggs, Phys. Rev. B 72 115324 (2005)

  18. Anticrossings in Foerster coupled quantum dots, A. Nazir, B. W. Lovett, S. D. Barrett, J. H. Reina, and G. A. D. Briggs, Phys. Rev. B 71 045334 (2005)

  19. Selective spin coupling through a single exciton, A. Nazir, B. W. Lovett, S. D. Barrett, T. P. Spiller and G. A. D. Briggs, Phys. Rev. Lett. 93, 150502 (2004)

  20. Controlling excitonic entanglement in quantum dots through the optical Stark effect, A. Nazir, B.W.Lovett and G. A. D. Briggs, Phys. Rev. A 70, 052301 (2004)

  21. All-optical control of perpetually coupled qubits, S.C.Benjamin, B.W.Lovett and J.H.Reina, Phys.Rev. A 70 060305 (2004)

  22. Optical schemes for quantum computing in quantum dot molecules, B. W. Lovett, J. H. Reina, A. Nazir and G. A. D. Briggs, Phys. Rev. B 68 205319 (2003)