Experimental Research Of EPR-quantum Information Processing Based On Doped Spins

Quantum information science is a scientific field about the new processing method for information, which is based on quantum dynamics and information science. It includes quantum cryptography, quantum communication and quantum computation. Quantum computer, as a main branch of quantum information science, is a new kind of computer based on quantum dynamics and which can perform simultaneously mathematic arithmetic and logical arithmetic with high efficiency. Quantum computer not only can process complexity calculations that could not solved by classical computer which based on classical physics, but also can process and store quantum information. In principal quantum computation is the research subject upon how to build up such a new kind of computer. Quantum computer is prior to classical computer in the aspect that for classical computer, the demand of smaller integral chips conflicts with the fact that if smaller, it obeys quantum principles rather than classical principles; another one is the problem of heat dissipation for the latter. These two problems restrict the efficiency of classical computer but nor accur in quantum computer. Moreover, several problems that are insurmoutable for classical computer, such as the factorization of a number, which can however be solved using quantum computer. Therefore, quantum computer pave a new way for the development of computer science. Experimentally, the achievement and realization of quantum computer firstly needs to initialize the quantum system, coherent control and then operate on this initialized system, and measure or readout finally. Up to date, several different systems are available for the experimental realization of quantum computer: nuclear spins, electron spins, photons, trapped ions, superconductor Josephson junctions. Among them, the electron spins have the advantages of that the operating time is three orders of magnitude smaller than that in nuclear spins and of the potential scalability.The physical systems for electron spins are the materials containing one or more unpaired electrons. In this thesis, we studied two chemically synthesized molecular magnets, the endohedral fullerene and the V15cluster. At first, the paramagnetic properties of endohedral fullerene are investigated, which makes it a suitable material as quantum bit (qubit) for quantum computer based on the theoretical and experimental studies. The series experiments are including the sample preparations, separation and purification, continuous-wave EPR measurements, spectra analysis, and further pulsed EPR measurements, such as readout of coherent state, measurement of relaxation times (T1and T2), as well as experiments of quantum operations and fast control of nuclear spins. Experimentally, N@C6o was prepared in an aligned way, the ordered N@C6o sample-N@C6o@C6oH28single crystals. The electronic structure was unveiled by the EPR technique which reveals larger zero-field splitting (ZFS). The larger ZFS enriches the energy level to distinguish the transitions originated from different ms and to make the N@C60a four-bit system rather than a two-bit system. Furthermore, the comparative studies were investigated in series of metallo endohedral fullerenes. Unlike N@C6o, the embedded metal ions locate not right in the central position of carbon cage, and the unpaired electron(s) are delocalized along the cage, meanwhile in N@C60the unpaired electrons are localized. Y@C82was studied selectively by EPR measurements. It is worth pointing that endohedral fullerenes can be observed with AFM or STM in where the detection and operation on single molecules (or single spins) becomes true in future.In another study, a unique metalorganic exchanged-coupling compounds which contains several transitional metal ions, the so-called single molecule magnet (SMM). SMM is a kind of fascinating new material since the single molecule exhibits magnetic hysteresis which is only possible for macroscopic magnets, and the single molecule is small enough to show quantum properties. The Ke[VⅣ15AsⅢ6H2O)](V15), a SMM, which exhibits the paramagnetic properties which is thermal accessible by using X-band EPR spectroscopy. The Ⅴ15single crystals were experimentally synthetized and the trichloromethane solution of Ⅴ15together with the surfactant [DODA]Br was also prepared for the pulsed EPR measurements. The coherent evolution and quantum oscillation of ground states of Ⅴ15SMM are the first experimental observation in the present study up to date in the literatures.Base on the above EPR studies of endohedral fullerene and Ⅴ15, the theoretical and experimental basises are prerequisite for the appropriated materials as qubits for quantum computation. The further readout and operation of single molecules or single spins can be achieved by putting endohedral fullerene molecules on the substrate of AFM or STM. Also, there is possibility that scalable quantum computer based on NV center coupled magnetically with the electron spin(s) in endohedral fullerenes.