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応用物理学輪講 Ⅰ

        
2018年1月5日(金)16:50~ 
62号講義室(2F) 
 座長:藤代 有絵子
64号講義室(2F)  
座長: 福原 竜馬、古川 頼誉
氏名: 若松  浩大
指導教員名: 鹿野田 一司 教授
発表題目(英語): Measurements of thermoelectric effect and magnetization in the spin-liquid candidate material κ -(ET)_4 Hg_2.89 Br_8 under pressure.
要旨(英語): κ -(ET)_4 Hg_2.89 Br_8 is a quasi-2D hole-doped organic conductor and is expected to be a candidate material for the doped spin liquid.
  In the previous study, this material was found to exhibit non-Fermi liquid (NFL)-like behavior in resistivity and strong temperature dependence of Hall coefficient at low pressures. At high pressures, those behaviors transition to Fermi liquid (FL)-like one. The coherence length of superconductivity that emerges at low temperatures also changes with increasing pressure, suggesting a crossover from local to extended paring. These results imply a NFL-to-FL crossover in the normal state and a BEC-to-BCS crossover in the superconducting state, driven by the change of electron correlation. 
 In the present work, I measured thermoelectric effects, which are useful to reveal the electric states, for κ -(ET)_4 Hg_2.89 Br_8 under pressure.
  In the superconducting phase, the magnetic penetration depth is known to characterize the superfluid density, which is one of the primary indices of superconductivity. To estimate the penetration depth, I have attempted to measure superconducting magnetization in κ -(ET)_4 Hg_2.89 Br_8under pressure but am now confronted with technical problems in performing the experiments under pressure.
 In this presentation, I’d like to talk about the results and the difficulties of the measurements under pressure.

発 表言語: 日本語
氏名: ダ ワースレン アマルサナー
指導教員名: 中村 泰信 教授
発表題目(英語):  Quantum Error Correction with Machine Learning
要旨(英語):  Quantum Error Correction (QEC) is crucial for constructing a scalable quantum computer.  In QEC, information about errors is encoded onto a syndrome space which we can later decode with classical computers. Traditional statistical decoders such as Minimum Weight Perfect Matching (MWPM) method decode the syndrome by searching for the most probable error pattern with brute-force which is often slow. However, a fast and near-optimal decoder is demanded for experimentally realizing quantum computers as real time decoding becomes necessary. In my presentation, I show that our machine learning based decoder can perform satisfactory both in computation time and decoding accuracy with a small training data set size.
発表言語: 英語 
氏名: 金  東錫
指導教員名: 志村 努 教授
発表題目(英語): GPU acceleration for numerical calculation and new phase detection method on time series phase modulated collinear holographic memory
要旨(英語):  The holographic memory is expected as a next-generation of data storage technology. Compared to conventional optical data storage technologies, it has larger data capacities because of its three-dimensional recording property. While conventional data storage records and recovers data one bit at a time, the holographic memory can stream multiple data at the same time. This enables us to transfer data with higher speed.
 In the typical holographic memory, the information is coded in a two-dimensional digital data page format, and each data page is recorded and recovered independently. Compared to this, we can code information in multi-channel continuous signals using time series data coding method. This method has already been applied to optical data storage such as CD, DVD, and Blu-Ray, and we expect we can even improve the density of data capacities.
 As a candidate for a practical holographic memory, we are studying time series phase modulated collinear holographic memory(TPCH). In this system, we interpret the time series signal as 0(1) when the phase of readout signal light is 0(π).
 However, there are challenging problems in the study of TPCH. First, if we assume TPCH system, too much time is needed to perform numerical calculations. Secondly, there is no suitable phase detecting method for TPCH. To solve these problems, we introduced GPU acceleration to the numerical calculation on TPCH and devised a new phase detection method for TPCH system. In this presentation, I will show the results of acceleration of the numerical calculation on TPCH by implementing GPU acceleration, and a method of time-sequential detection of the phase of readout signal light on TPCH system.
発表言語: 日本語 
氏名: 王 昊 宇
指導教員名: 香 取 秀俊 教授
発表題目(英語):  Light shift reduction of Strontium optical lattice clock using Volume Bragg Grating
要旨(英語):  Since the idea of an optical lattice clock has proposed in 2001, lots of research has been performed worldwide and the uncertainty of the Sr optical lattice clock is now reaching 10^(-18). As optical lattice clocks develop, various applications using it have been coming in sight. In order to run optical lattice clocks outside of the laboratory and put into practical use in the future, it is absolutely essential to miniaturize the clock, as well as making it transportable.
 For the laser source of the Sr optical lattice (813nm), a Ti:Sapphire laser has been used since it can generate a high power CW beam of few W at single-mode. However, from the perspective of miniaturizing the clock, it might be a nice idea to replace it with a semiconductor laser(LD), which has a size far smaller than that of a Ti:Sapphire laser. Although LD is very compact, its output power is too small to run the clock, hence a tapered amplifier(TA) is also used to increase the power. When the beam is amplified through the TA, amplified spontaneous emission(ASE) would be caused which makes the spectrum of the light broader. It can lead to a larger lattice light shift, which is a critical issue in the way of achieving high accuracy.
 In this presentation, I will first refer to the optical lattice clock, and then talk about the idea and some calculation results of reducing the light shift with a Volume Bragg Grating(VBG).
発表言語: 日本語 
氏名: 梁  東賢
指導教員名: 田中 肇 教授
発表題目(英語): One step toward verifying how driving force of kinesin’s movement is produced using DNA origami
要旨(英語): Investigating the  dynamics of kinesin, several methods, including attachment of immobile kinesin and usage of optical tweezer, have been implemented to put kinesin under load. Those methods, although powerful in many senses, could not be applied to in-depth study including observation of mutated kinesins with weak microtubule affinity. This study, with implementation of DNA origami technology, mutant kinesins’ movement under load was observed. In this presentation, I will talk about how force-dependency of each mutant kinesins could be obtained, and how the result suggests which step of kinesin is involved in production of driving force.
発表言語:  英語
氏名: 周 静芳
指導教員名: 小芦 雅斗 教授
発表題目(英語):  computational power of quantum phase
要旨(英語):  Measurement-based quantum computer (MBQC) is an interesting quantum computational model. It allows you to build a most powerful quantum computer (universal quantum computer) with only single-body measurements on a sufficiently entangled many-body system. But the problem is, how to prepare such a useful entangled resource which allows universal quantum computation?
 In 2017, Stephen et al. proposed a way to evaluate the computational power of one dimensional (1D) symmetry protected topological (SPT) phase as a resource of MBQC. However, the 2D resource is required for universal quantum computation. Whether their discussion can be extended to higher dimensions and other types of quantum phases is an intriguing open question.
 My talk is divided into three parts. First, I will introduce basic concepts in MBQC and SPT. Then I will show the outline of the result in 1D SPT phase. And lastly, I will briefly explain the difficulty in extending to 2D SPT and the possible approach.
発表言語: 日本語

 
 

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