Quantum Information Processing without Strong Optical Nonlinearity

人们曾说过，实现量子信息处理需要巨大的光学非线性。然而，自2001年以来，随着包括我们的结果在内的理论研究的贡献，一些量子信息处理变得可能利用线性光学和实际合理的非线性光学的大小。本研究讨论了作为这种量子信息处理的元素的“线性光学量子门”和“光-激子相互作用”的基本性质，并探索了“纠缠操纵”和“量子博弈”作为这种量子信息处理的应用的可能性。我们得到了量子点之间的线性和库仑相互作用下激子动力学的严格解。结果，很明显，利用这种相互作用，可以在点之间产生强烈的纠缠。此外，偶/奇相干态量子比特对退相干的稳健性及其与点大小的依赖关系也已被…为了有组织地处理线性光学量子信息处理的个别方案，我们建立了一个系统的线性光学量子信息处理理论。特别是，在数值上考虑了探测器缺陷的影响。在量子博弈论中，我们从理论上比较了纠缠和经典关联对非合作博弈的影响，得出了纠缠比经典关联更能改变博弈相位的结论。在比较这种效果时，有必要将原始经典游戏作为特例包括在游戏的量子版本中。根据我们的研究，GHz纠缠可以用于这一目的，而W纠缠不能。LOQIP的一个应用例子是B92量子密码，其在实际缺陷下的安全性还没有得到令人满意的证明。从理论上证明了B92协议的安全性，得到了B92协议的安全性条件与缺陷大小的关系。较少

It has been said that gigantic optical nonlinearity is necessary for realization of quantum information processing. Since 2001, however, it became clear, by theoretical research contribution including our results, that some of quantum information processings are possible using linear optics and practically reasonable magnitude of nonlinear optics.This research deals with the fundamental properties of "linear optics quantum gates" and "light-exciton interaction" as the element of such quantum information processing, and also seek the possibility of "entanglement manipulation" and "quantum game" as the application of such quantum information processing.We obtained a rigorous solution for exciton dynamics under linear and Coulomb interactions between quantum dots. As a result, it became clear that a strong entanglement can be generated between the dots using such interactions. Also, the robustness of even/odd-coherent-state qubits against decoherence and its dot-size dependence have been … More investigated.In order to treat individual proposals of linear optics quantum information processing(LOQIP) in an organized way, We built up a systematic theory for LOQIP. Particularly, the influence of detector imperfections has been taken into account numerically. As a result, it became clear that several information processing can be accomplished with high fidelity using exsisting photon counters.In quantum game theory, we theoretically compared the effects of entanglement and classical correlations on non-cooperative games, and obtained a result that in general entanglement is more influential than classical correlations in changing the phase of games. In comparing this kind of effects, it is necessary that a quantum version of a game should include the original classical game as a special case. According to our research, it became clear that GHZ entanglement can be used for this purpose but W entanglement cannot.An application example of LOQIP is B92 quantum cryptography, whose security under practical imperfection has not been proven in a satisfied way. We theoretically proven the security of B92 protocols and obtained the security conditions versus the magnitude of the imperfections. Less