座長：上村 洋平、大坪 舜
| 氏名： 横田
指導教員名： 酒井 啓司 教授
発表題目（英語）： Frequency shift of oscillating microdroplets with large amplitude
要旨（英語）： With inkjet technique, we are developing a system to make microstructures such as microcapsules by colliding droplets in the air. In order to create such structure with an arbitrary shape, it is necessary to understand the dynamics of molecules after the collision.
We have developed a method to observe flying microdroplets and to measure the physical properties such as surface tension and viscosity with high temporal resolution from the droplet oscillation. (DOF)
With our method, we succeeded in observing liquid dynamics in a macroscopic time scale. However, the oscillation just after the collision of two droplets has large amplitude, and that makes frequency shift. In the DOF method, it is assumed that the oscillation of a droplet has a minute amplitude, so it is difficult to measure the surface dynamics of collided droplet with large amplitude accurately.
In this study, we modified the analyzing way of DOF for a large amplitude and succeeded to measure the surface dynamics of collided droplet accurately.
| 氏名： 吉沢
指導教員名： 沙川 貴大 准教授
発表題目（英語）： Large deviation analysis of Eigenstate thermalization hypothesis
要旨（英語）： In recent years, thermalization of isolated quantum systems has received much attention. Various numerical calculations have shown that non-integrable systems relax to thermal equilibrium, even though dynamics of isolated systems are unitary and time-reversible. A possible mechanism of thermalization is the eigenstate thermalization hypothesis (ETH), which states that all (or at least almost all) energy eigenstates have thermal properties. In more precise, there are two types of ETH: one is the strong ETH corresponding to "all" above, and the other is the weak ETH corresponding to "almost all".
In the present work, we performed systematic numerical calculations by focusing on the large deviation properties of ETH. Especially, we numerically calculated the ratio of athermal (i.e., atypical) energy eigenstates in the energy shell, which is analogous to the large deviation of classical probability distributions. Such a ratio is expected to be exactly zero if the strong ETH is true, while exponentially small but nonzero if only the weak ETH is true. However, these expectations have neither been proved mathematically nor investigated numerically. Our results for the first time provide numerical results on the large deviation theory of quantum many-body systems, and shed new light on mechanism of thermalization, especially in terms of the weak and the strong ETHs in integrable and non-integrable systems.
| 氏名： アサ
指導教員名： 古澤 明 教授
発表題目（英語）： Toward generation of time-domain multiplexing two-dimensional cluster state for scalable universal quantum computation
要旨（英語）： Optical quantum computation possesses many advantages over other physical systems such as ability to perform computation at room temperature and affinity with telecommunication. However, the lack of scalability has plagued optical quantum computation and is an obstacle preventing realization of usable quantum computation. By utilizing one-way quantum computation with cluster state instead of well-known quantum circuit model, scalable universal quantum computation can be achieved. Our laboratory has already succeeded in the generation of one-dimensional cluster state with time-domain multiplexing. For universal quantum computation, however, two-dimensional cluster state is a necessary resource. In this talk, I will explain about one-way computation using cluster state, and how to generate two-dimensional cluster state. In particular, I will talk about characteristics of two-dimensional cluster state that will be generated using an experimental setup we proposed and experimental progress thus far.
発表言語： 英語 古川亮
| 氏名： 厳
指導教員名： 嶽山 正二郎 教授
発表題目（英語）： 1/2 magnetization plateau of Breathing Pyrochlore Antiferromagnet LiMCr4O8 (M=Ga, In) in Magnetic Fields up to 130 T
要旨（英語）： Geometrically frustrated spin systems have attracted considerable attention for decades because they present a rich playground for exotic ground states such as spin liquid and spin ice. Cr spinel oxides ACr2O4 (A=Hg, Cd, Zn, Mg) where Cr3+ ions form a pyrochlore lattice have been extensively studied as good model materials. One of the most distinctive features of ACr2O4 is its field-induced magnetic phase transitions, represented by a 1/2 plateau phase.
We focus on breathing pyrochlore antiferromagnets, LiMCr4O8 (M=Ga, In), in which Cr4 tetrahedra with small and large size are alternately arranged, causing two different exchange interactions, J and J'. The value of J'/J is estimated to be about 0.5 for LiGaCr4O8 and 0.1 for LiInCr4O8. Breathing pyrochlore spin systems with various values of J'/J provide the opportunity to understand the frustration and the possibility of discovering novel quantum phases. We conducted magnetization measurements by the single-turn coil techniques in high magnetic fields up to 130 T at very low temperature. The observed magnetization curve of LiInCr4O8 exhibits a sharp jump to a 1/2 plateau at around 90 T, which continues at least up to 130 T, suggesting the presence of strong spin-lattice coupling. As future work, I will try magneto-optical measurements by electro-magnetic flux compression method in ultra-high magnetic fields above 300 T in order to observe all magnetic phases up to a fully polarized phase for both compounds.
後藤 大 輝
指導教員名： 古川 亮 准教授
発表題目（英語）： Nonlinear rheology of model micro-organisms
要旨（英語）： Active suspensions are the fluids that contain self-propelling particles such as swimming micro-organisms. The first seminal study of the rheology of active suspensions predicted the reduction of effective viscosity for pusher (such as E. coli) suspensions and oppositely the increase for puller (such as algae) suspensions, assuming high enough concentrations to describe the micro-organisms as a coarse-grained continuum model. Numerous experiments, however, revealed that even dilute suspensions exhibited the significant rheological properties such as frictionless flows. Although in several microscopic studies the degrees of freedom of suspended particles are considered, they are only in the dilute limit, where hydrodynamic/steric interactions are negligible. In order to consider these interactions and their effects on the rheological properties, we construct a model of a pusher and perform hybrid hydrodynamic simulations. In this talk, after reviewing previous studies on the rheology of active suspensions, I will explain our scheme and show preliminary simulation results.