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Probing nanomagnets and the future of quantum computing - 1.12.2012

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Neutrons confirm their potential to probe nanomagnets and the future of quantum computing - 1.12.2012

Neutron scientists at the ILL have partnered with researchers from the University of Manchester, the University of Parma, the Rutherford Laboratory and the University of Bern to investigate molecular nanomagnets, materials composed of only a few atoms carrying magnetic moments. A publication in Nature Physics.

See also the introduction in News and views


In a world first, researchers have used inelastic neutron scattering on single-crystal samples of these materials to directly probe the motion of magnetic moments within the molecules, a technique which could be used in the future to assess their feasibility and potential application in quantum computers and high-density data storage.

The magnetic properties of materials are caused by a characteristic of their electrons known as spin. When a number of atoms carrying electronic spins come together they can form nanoscale units with a unique magnetic nature. In particular, quantum mechanical effects are enhanced by the finite size of magnetic nanostructures, and profoundly affect the motion of spins. 


In this new experiment, scientists fired a beam of neutrons at a sample containing these nanoscale units, in order to probe their characteristic energies. The novelty of this approach was that the scientists were able to examine in detail the spatial structure of the magnetic excitations. This technique is the most powerful tool available to scientists studying the behaviour of magnetic moments within individual nanoscale magnetic molecules.


The results not only proved the validity of this new technique going forward but also gave a detailed picture of how magnetic moments within the molecule move. The most unusual aspect of the work was that this was done directly, without the use of a mathematical model.
This new technique could aid research into the use of these materials and their magnetic moments for data recording and the next generation of computing technology.  Potential future applications include the encoding of qubits, the unit of quantum information for quantum computing.  Whilst quantum computing will not be hitting the mainstream market for a long time yet, they may in a few years be used for highly specialised government and corporate functions.  The quantum computer is one of the main objectives of modern physics as it is much better than a traditional computer for code breaking and factoring large numbers, and it vastly increases the computational power in simulating quantum systems.


Current technology limits allow for only a few spin qubits to be brought together and controlled in a computing system. It is estimated this will need to increase to between 50 and 100 for even the most simple research-related tasks. This is the next challenge to be overcome:  a large number of molecular nanomagnets will have to be linked together in supramolecular complexes whose geometry enables fundamental logical gates to be implemented.


Scientists are now keen to produce and exploit such exotic systems, and here again inelastic neutron scattering has a role to play.

 



Re.: Nature Physics 8, 906–911 (2012) doi:10.1038/nphys2431

Contact: Dr Hannu Mutka, Dr Jacques Ollivier



Acknowledgements


This new publication is the first demonstration of the spin dynamics of a molecular nanomagnet directly determined using 4D-INS, without need for a spin Hamiltonian model. This opens remarkable perspectives in the understanding of crucial but elusive quantum phenomena in several classes of magnetic molecules. The publication is the latest result highlighting the long-lasting collaboration between chemists and physicists on molecular nanomagnets.


Our warm thanks go to Michael Baker, a former PhD Student at the University of Manchester and at ILL. The present achievements were driven by outstanding theoretical work from physicists at Parma: Stefano Carretta, Giuseppe Amoretti and Paolo Santini, and the ability of a team of chemists from Manchester, Grigore Timco, Eric McInnes and Richard Winpenny, to transform the theoretical physics into large single crystals suitable for this kind of experiment. The remarkable expertise of our colleague from ISIS, Tatiana Guidi, on 4D-INS technique and the long-standing experience of Hans-Uli Güdel from the University of Berne, were important for the success of this work.


As the article states, 'modern neutron TOF spectrometers — such as the IN5 spectrometer at the ILL used by Baker and co-workers - now have the level of detector coverage, energy and momentum resolution, neutron flux and signal-to-noise ratio to provide unprecedentedly detailed information about spin correlations.'

Throughout the years the ILL time-of-flight spectrometer IN5 has been the pivot point for the progress in the study of molecular nanomagnets. The recent upgrade of IN5, with increased efficiency and especially the new generation position sensitive detectors produced at the ILL, together with the advances in data analysis, were indispensable ingredients for the success of these experiments.See more information on IN5 here, and the instrument 3D animation there.

Hannu Mutka and Jacques Ollivier, ILL