Suppression of decoherence and development of quantum error correcting codes in solid state qubits

Nakahara和他的芬兰合作者开发了一种利用多量子位模块有效实现量子算法的方法。该策略首先用于完整量子计算，随后应用于更现实的约瑟夫森结量子比特系统。已经估计了使用三量子位模块分解21需要多少量子位和计算步骤。后来，大阪城市大学的谷村和中原在理想情况下精确地解决了等完整问题，其中相关的纤维束是Stiefel流形上的Grassmann流形。这解决了蒙哥马利在1991年提出的长期等完整问题。中原和近藤在近畿大学建造了一台核磁共振量子计算机。Nakahara和tananimura利用李群的Cartan分解获得了量子算法的时间最优解，Kondo在核磁共振量子计算机上用两个量子位分子执行了这些解。实验证明，由于减少了执行时间和门数，核磁共振谱得到了改善。还指出，通过在U上适当选择一个简单的额外门W，可以加速量子算法U，使算法现在成为WU。在核磁共振量子计算机上再次进行了实验验证，并观察到光谱的改善。这种技术被称为翘曲驱动，而闸门W被称为翘曲闸门。细谷从量子信息的角度研究了黑洞时空中的霍金辐射，分析了测量完成后将测量仪器扔进黑洞时的熵变。他还研究了量子信息几何中的度规。Kuroda分析了一个单分子磁铁Mn12复合物的化学性质，它可能作为一个量子比特，一个具有d态的量子系统。

Nakahara and his Finnish collaborators developed a method for efficient implementation of quantum algorithms utilizing multi-qubit modules. This strategy has been employed for holonomic quantum computation first and subsequently applied to a more realistic Josephson junction qubit system. It has been estimated how many qubits and computational steps are required to factorize 21 using three-qubit modules. Later Tanimura of Osaka City University and Nakahara solved the isoholonomic problem exactly in the idealized siuation, where the relevant fibre bundle is the Stiefel manifold over the Grassmann manifold. This solves the longstanding isoholonomic problem posed by Montgomery in 1991.Nakahara and Kondo built an NMR quantum computer at Kinki University. Nakahara, with Tanimura, obtained time-optimal solutions for quantum algorithms, utilizing the Cartan decomposition of a Lie group, and Kondo executed these solutions on the NMR quantum computer with two-qubit molecules. It was verified experimentally that the NMR spectrum is improved thanks to reductions in execution time and the number of gates. It was also pointed out that a quantum algorithm U may be accelerated by adding a properly chosen simple extra gate W to U so that the algorithm now becomes WU. This is again verified experimentally on the NMR quantum computer and improvement in spectrum has been observed. This technique is called the warp-drive while the gate W is called the warp-gate.Hosoya studied the Hawking radiation in the blackhole spacetime from quantum information point of view and analyzed the entropy change when a measurement instrument is thrown into a blackhole after a measurement is made. He also studied the metric in quantum information geometry.Kuroda analyzed the chemical properties of a single-molecule magnet, Mn12 complex, which might work as a qudit, a quantum system with d states.