座長：高橋 忠宏、中澤 佑介
座長： 田中 未羽子
| 氏名： 松浦
指導教員名： 小芦 雅斗 教授
発表題目（英語）： Quantum computation and quasiprobabilities
要旨（英語）： Quantum computer is believed to be more powerful than classical computer. However, if available operations and states in quantum mechanical system are restricted, it can often be simulated efficiently by classical computation. The important nontrivial classically simulable circuits in quantum computation and their symmetry properties are mentioned. Furthermore, quasiprobabilities are introduced as representations that reflect those symmetry properties. The main topic of the presentation is our recent study about quasiprobability representation of Fermionic Linear Optics.
| 氏名： 水嶋
指導教員名： 香取 秀俊 教授
発表題目（英語）： Reduction of residual amplitude modulation for achieving high-stability cavity-stabilized laser
要旨（英語）： A highly stable laser which is realized by stabilizing its frequency to a reference optical cavity is one of the key tools which enables precise optical measurement, such as spectroscopy and interferometry.
For operating optical lattice clocks, an optical cavity is used as the reference to stabilize the frequency of the clock laser which interrogates the atoms. Since the instability of the cavity-stabilized laser can limit the stability of the clock, highly stable optical cavity is essential to the optical lattice clocks. Stability of an optical cavity is ultimately limited by the thermal noise of the mirror-coating and the reduction of this thermal noise limitation is demonstrated with using crystalline-coated mirrors in the optical cavity.
To generate an error signal for stabilizing the laser frequency to the optical cavity, the Pound-Drever-Hall (PDH) technique is widely utilized. Since the PDH technique requires phase modulation of the laser, the stability of the laser frequency is often degraded by residual amplitude modulation (RAM) making a frequency offset to the error signal and thus the RAM-induced laser frequency instability must be reduced.
In this presentation, after briefly referring to the optical lattice clock and PDH technique, I show the way of reducing RAM and the result of the experiment.
| 氏名： 丸橋
指導教員名： 川﨑 雅司 教授
発表題目（英語）： Fabrication and magnetotransport properties of high mobility EuTiO3 quantum wells
要旨（英語）： EuTiO3 is a magnetic semiconductor which has local 4f spins of 7 Bohr magnetons on Eu2+ site. 4f spins order antiferromagnetically under 5.5 K. Electron carriers can be doped into Ti t2g conduction band by substituting Eu2+ by La3+. EuTiO3 has simple band structure. Therefore, this is ideal system to investigate anomalous Hall effect (AHE) controlling Fermi level by electron doping. In past research of compressive strained EuTiO3 thin films on LSAT substrate, it is known that the sign of AHE changes by carrier density reflecting the band crossing points of Ti t2g band.
In this research, we fabricated quantum well of EuTiO3 on SrTiO3 substrate. The mobility of electrons is two orders of magnitude higher than that of compressive strained films and the maximum value reaches 3000 cm2/Vs. As a result, we observed new phenomena such as Shubnikov-de Haas oscillation and peculiar anomaly of AHE.
| 氏名： メ
指導教員名： 石 渡 晋太郎 准教授
発表題目（英語）： High-pressure synthesis and magneto-transport measurements of magnetic semimetal α-EuP3
要旨（英語）： Black phosphorus(BP) is a narrow-gap semiconductor in ambient pressure, consisting of phosphorene layers stacked via van der Waals bonding. It is known that BP goes under a topological transition by applying high pressure, resulting in a semimetallic band structure.
Moreover, recent theoretical calculations predict that α-SrP3, whose crystal structure is closely related to BP, has a semimetallic band structure assumably originated from the character of BP. In this research, we replace Sr2+ ions with magnetic Eu2+ ions and investigate the correlation between the electronic and magnetic properties.
| 氏名： 長谷
指導教員名： 千葉 大地 准教授
発表題目（英語）： Effect of oxidation on spin-orbit torques in heavy metal/ferromagnetic heterostructures
要旨（英語）： In-plane current induced magnetization switching in heavy metal/ferromagnetic heterostructures has attracted much interest as a new method for writing information in magnetic memory devices with extremely high speed. This magnetization switching is caused by spin-orbit torques (SOTs), which consist of damping like (DL) and field like (FL) terms, on the magnetization in ferromagnetic layer. Although two possible sources of the DL and FL torques are suggested; the bulk spin-Hall effect in the heavy metal and the interfacial Rashba effect, the origin of SOTs is still unclear. In order to realize the faster switching and lower energy consumption, it is important to reveal the origin of SOTs.
We examine the effect of interfacial oxidation on SOTs. Our group previously reported the enhanced FL torque in a Pt/Co system with naturally oxidized Co layer, namely Pt/Co/CoOx system. On the other hand, it was found that the oxidization effect on the DL torque, which mainly attributes to the magnetization switching, is small in this system. In my study, I investigate a Co/CoOx/Pt system, in which the interface between Co and Pt has been oxidized. The modulation of the DL torque is expected in this system because the amount of spin current injecting in Co layer from the Pt layer is considered to change. In this presentation, I will talk about SOTs and other magnetic properties in a Co/CoOx/Pt system in detail.