NSF: Templated Ordered Endohedral Fullerenes as Building Blocks for Quantum Computing

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Composite materials consisting of nanoparticles incorporated within organic matrices offer a diverse range of possible applications, from toughened polymers to cosmetics and sun screens. The inherent ability of some organic materials to self-assemble into larger structures, in particular block copolymers, can be used to achieve well-defined and tuneable morphologies. We intend to exploit this control to achieve hierarchical ordering of endohedral fullerene species within an organic matrix. If the embedded nanostructures have sufficiently well-defined and robust quantum properties, they may be capable of storing and processing quantum information, thus offering the prospect of outperforming classical computation at a fundamental level. The implementation of a basic quantum logic gate in our structures will require control of the interactions between fullerenes, which in turn depend on their alignment within the organic matrix, and thus serves as a demanding test of the success of our project. We propose to achieve controlled alignment of spin-active fullerene species with well defined morphologies, by exploiting self-assembly in organic matrices, within the general context of controlling the hierarchical morphology of polymer nanocomposites. To achieve this, we shall use block copolymers, cyclodextrins and calixarenes. Block copolymers have well-defined nanophase behaviour which has already led to their use in fabricating nanopatterns by lithographic templates. They are also being investigated as systems capable of ordering nanoparticulate inclusions. To achieve controlled alignment of the fullerenes, it is essential that they become fully integrated into the self-assembled structure of the matrix material. We shall follow two approaches: the first is engineering a segregation of the fullerenes into a defined phase, as are often present in block copolymers. The second is to encapsulate fullerene dimers within smaller organic units such as bis-cyclodextrins and bis-calixarenes, which subsequently self-assemble into ordered structures. We shall use a range of techniques to evaluate the development of these techniques, including nuclear magnetic resonance (NMR) and low-voltage (LV) and high resolution (HR) transmission electron microscopy (TEM), and electron spin resonance (ESR) of spin active fullerene dimer molecules acting as alignment probes. Once our alignment strategy has been optimised, we shall demonstrate the exquisite control we have achieved in the resulting nanocomposite by using it to show coherent manipulation of interacting spin systems. The electron spin within certain endohedral fullerenes is an ideal manifestation of quantum information, due to its extremely robust nature and ability to be accurately manipulated. The dipolar interaction between such spins can then be exploited to demonstrate fundamental concepts such as entanglement, and a controlled-NOT operation between spins. Such an interaction is dependent on the orientation of the spin pair with respect to an applied external field. Using an asymmetric fullerene dimer with an individually addressable electron spin trapped in each fullerene unit, we shall have full control over a system of two coupled electron/nuclear spin pairs, capable of embodying up to four or more quantum bits (qubits). We intend to demonstrate quantum entanglement between the electron spins, and consequently a simple quantum computation such as the Deutsch-Josza algorithm. Finally, we shall attempt the same demonstration with the longer lived nuclear spins, in this case using the electron spins to distribute the entanglement. This ambitious experiment places strong demands on our ability to fabricate oriented arrays of functional nanocomposites, and thus forms a compelling demonstration of our new technology.