初期時間領域におけるコヒーレントフォノン生成量子ダイナミックスの理論研究

この博士論文は全文公表に適さないやむを得ない事由があり要約のみを公表していましたが、解消したため、令和元(2019)年11月11日に全文を公表しました。筑波大学 (University of Tsukuba)201

IoT-REX: A Secure Remote-Control System for IoT Devices from Centralized Multi-Designated Verifier Signatures

IoT technology has been developing rapidly, while at the same time, notorious IoT malware such as Mirai is a severe and inherent threat. We believe it is essential to consider systems that enable us to remotely control infected devices in order to prevent or limit malicious behaviors of infected devices. In this paper, we design a promising candidate for such remote-control systems, called IoT-REX (REmote-Control System for IoT devices). IoT-REX allows a systems manager to designate an arbitrary subset of all IoT devices in the system and every device can confirm whether or not the device itself was designated; if so, the device executes a command given from the systems manager. Towards realizing IoT-REX, we introduce a novel cryptographic primitive called centralized multi-designated verifier signatures (CMDVS). Although CMDVS works under a restricted condition compared to conventional MDVS, it is sufficient for realizing IoT-REX. We provide an efficient CMDVS construction from any approximate membership query structures and digital signatures, yielding compact communication sizes and efficient verification procedures for IoT-REX. We then discuss the feasibility of IoT-REX through cryptographic implementation of the CMDVS construction on a Raspberry Pi. Our promising results demonstrate that the CMDVS construction can compress communication size to about 30% and thus its resulting IoT-REX becomes three times faster than a trivial construction over typical low-power wide area networks with an IoT device. It is expected that IoT-REX can control 12,000 devices within a second.Comment: Updated as a whole. 26 page

Ground state degeneracy on torus in a family of ZN\mathbb{Z}_N toric code

Topologically ordered phases in $2+1$ dimensions are generally characterized by three mutually-related features: fractionalized (anyonic) excitations, topological entanglement entropy, and robust ground state degeneracy that does not require symmetry protection or spontaneous symmetry breaking. Such degeneracy is known as topological degeneracy and usually can be seen under the periodic boundary condition regardless of the choice of the system size $L_1$ and $L_2$ in each direction. In this work we introduce a family of extensions of the Kitaev toric code to $N$ level spins ($N\geq2$). The model realizes topologically ordered phases or symmetry-protected topological phases depending on parameters in the model. The most remarkable feature of the topologically ordered phases is that the ground state may be unique, depending on $L_1$ and $L_2$, despite that the translation symmetry of the model remains unbroken. Nonetheless, the topological entanglement entropy takes the nontrivial value. We argue that this behavior originates from the nontrivial action of translations permuting anyon species.Comment: 17 pages, 6 figures; v2: references added; typos corrected. Proof of Eq. (A4) is newly added in Appendix