固体媒質におけるコヒーレンス及び干渉効果に基づいた量子情報

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During FY2013, we mainly studied quantum manipulation in hybrid quantum circuits, and their application in quantum information science. The main results are :(1) We proposed the methods to realize strong spin-resonator coupling and high-fidelity quantum storage using the hybrid quantum architectures including flux qubits, nitrogen-vacancy center ensemble (NVE) and transmission-line resonator. Firstly, we proposed an experimentally realizable hybrid quantum circuit for achieving a strong coupling between a spin ensemble and a transmission-line resonator via a superconducting flux qubit used as a data bus. Our result show that the spin-resonator coupling strength can be enhanced two orders based on our proposal. Also, we proposed how to realize high-fidelity quantum storage using a hybrid quantum architecture including two coupled flux qubits and a nitrogen-vacancy center ensemble (NVE). This proposed hybrid quantum circuit could enable a long-time quantum memory when storing information in the spin ensemble.(2) We investigated a hybrid electro-optomechanical system that allows us to realize controllable strong Kerr nonlinearities even in the weak-coupling regime. We showed that when the controllable electromechanical subsystem is close to its quantum critical point, strong photon-photon interactions can be generated by adjusting the intensity (or frequency) of the microwave driving field. Nonlinear optical phenomena, such as the appearance of the photon blockade and the generation of nonclassical states (e.g., cat states), are demonstrated in the weak-coupling regime, making the observation of strong Kerr nonlinearities feasible with currently available optomechanical technology.