応用物理学輪講 I
6月25日
[注意事項]
発表の10日前までに宛てに「氏名」「指導 教員」「発表題目(英語)」「要旨(英語)」「発表言語(英語または日本語)」を送付して下さい。
発表日
2021年6月25日(金)16:50〜

Aグループ

座長
XU Tianyu
指導
教員名
小林 洋平 教授
発表者名 花村 文哉
指導教員名 古澤 明 教授
発表題目(英語) Estimation of Gaussian random displacement using non-Gaussian states
要旨(英語) We consider a quantum estimation problem called "Gaussian random displacement estimation problem", which is a problem to estimate the amount of displacement imposed on a single-mode bosonic state using a Gaussian prior distribution. While if only Gaussian states are used, simultaneous estimation of two parameters of displacement is restricted by Heisenberg's uncertainty, we have shown that one can beat this limit using experimentally feasible non-Gaussian states such as single-photon states [1]. This problem is also closely related to Gaussian quantum error correction, which has been proven to be impossible using only Gaussian
states [2].
 In the presentation, I will talk about the derivation of the Gaussian limit and the estimation using non-Gaussian states. I will also talk about the relation to quantum error correction.
[1] F. Hanamura et al., arXiv:2102.05276 (2021).
[2] Niset, J., Fiurášek,J., & Cerf, N. J. (2009). PRL, 102, 120501.
発表言語 英語
発表者名 早野 陽紀
指導教員名 古川 亮 准教授
発表題目(英語) Rheology of active suspensions
要旨(英語) Active matter is a class of materials that consume chemical energy and turn it into mechanical work. Examples of active matter include all forms of living matter ranging from self organization of cells and bacteria to schools of fish and flocks of birds. In our study, we especially focus on swimming microorganisms (microswimmers) that live in a fluid environment, such as E. coli and Chlamydomonas: they are self-propelled particles on the order of micrometers, moving through a fluid medium by non-reciprocal cyclic flagellar motion. Suspensions of microswimmers are observed novel collective behaviors and transport properties that are quite different from those observed in "passive" matter systems. One of the most fascinating examples is that the viscosity of a dilute E. coli suspension is significantly smaller than that of a pure solvent, which indicates a violation of the well-known Einstein viscosity describing the viscosity of dilute passive particle suspensions. While it has been generally thought that this anomalous rheological behavior is attributable to the anisotropic changes in the mean swimming directions under an external flow field, its detailed mechanism, especially the role of the hydrodynamic effect, is still debated today. We are aiming to elucidate this problem through a systematic numerical study of minimal microorganism models using a hybrid simulation method.
In this talk, after a brief review of recent studies of the rheology of active suspensions, I will show our preliminary hydrodynamic simulation results for a model microorganism suspension.
発表言語 日本語
発表者名 福田 大地
指導教員名 鹿野田 一司 教授
発表題目(英語) NMR Study of Uniaxial-Strain-Induced Metal-Insulator Transition in the Charge-Frustrated System θ-(ET)2I3
要旨(英語) The θ-(ET)2X family of layered organic conductors, composed of conducting ET layers with triangular lattices and insulating layers of anion molecules X, is the representative charge-frustrated system. The strength of charge frustration is varied by X and determines ground states; for weak frustration, the system exhibits a charge ordering (CO) transition upon cooling, whereas the long-range CO is prevented in a strongly frustrated system, yielding a charge glass (CG) state.
 θ-(ET)2I3, which is the most charge-frustrated system with a nearly isotropic triangular lattice, however, does not show the CG or CO transition and remains in the metallic state down to very low temperature, invoking a quantum melting of charges caused by charge frustration. Remarkably, under a uniaxial strain of 2 kbar applied in a direction to reduce the frustration, the electrical resistivity abruptly increases around 140 K, possibly suggesting that the insulating state is induced by the uniaxial strain. However, the microscopic electronic state of this phase has not been uncovered.
 Thus, in the present study, we examine the microscopic electronic state of θ-(ET)2I3 under uniaxial strains using the 13C NMR spectroscopy. Under the uniaxial pressure of 2 kbar, the four sharp lines emerge in addition to the spectra that are almost unchanged from those at ambient pressure. The spin-lattice relaxation rates of the additional lines at 50 K, where the resistivity shows an insulating-like behavior, is about one order of magnitude smaller than that in the metallic state at ambient pressure. These results suggest that the metallic and insulating states coexist under uniaxial strain and the latter is a CO state, not CG with the broad spectra. The volume fraction of CO to metal is increased with pressure.
発表言語 日本語

Bグループ

座長
天野 元揮
指導
教員名
求 幸年 教授
座長
石塚 悠也
指導
教員名
小林 洋平 教授
発表者名 馬場 正太郎
指導教員名 中村 泰信 教授
発表題目(英語) Design of broadband Josephson parametric amplifiers based on a coupled-resonator model
要旨(英語) Superconducting qubits are an outstanding candidate for quantum computing. However, to develop a fault-tolerant quantum computer with many superconducting qubits, one big problem is how to control many qubits in the dilution refrigerator and decrease the number of room temperature control instruments. Frequency-multiplexed qubit readout is one solution to tackle this problem and broadband JPAs are necessary for frequency-multiplexed qubit readout.
 A standard way to measure qubit states is a reflection measurement of a resonator coupled to a qubit. This protocol is widely used because of small measurement back action and protection of qubit decoherence by readout resonators. However, due to the low signal-to-noise ratio(SNR), we need low noise, high gain amplifiers for qubit measurement by one microwave pulse and Josephson parametric amplifiers(JPA) are necessary for this purpose. We have to amplify some microwave frequencies simultaneously by one amplifier for frequency-multiplexed qubit readout, so we need broadband JPAs.
 There are two approaches to construct broadband JPAs. One is to achieve impedance matching between JPA and the outside world coupled to JPA[1,2]. The other is to use a nonlinear transmission line with many Josephson junctions[3].
 In this presentation, I will explain the operation and the impedance matching of broadband JPAs and talk about methods to design broadband JPAs based on a coupled-resonator model by focusing on the similarity between JPAs with impedance matching and bandpass filters. I also show JPAs designed by a coupled-resonator model can achieve wide bandwidth and high gain compared to JPAs with impedance matching.
[1]T.Roy et al., Appl. Phys. Lett. 107, 262601 (2015).
[2]J.Y.Mutus et al., Appl. Phys. Lett. 104, 263513 (2014).
[3]C.Macklin et al., Science 350, 307 (2015).
発表言語 日本語
発表者名 西澤 葉
指導教員名 賀川 史敬 准教授
発表題目(英語) MFM measurement of multi-ferroics (FexZn1-x)2Mo3O8 (The topic could be changed)
要旨(英語) The multi-ferroic material Fe2Mo3O8 shows anomalous hysteresis broadening with doping of Zn in Fe sites. I'm trying to discover what process leads this broadening. I use the MFM (Magnetic Force Microscopy) method to measure real space images. It is implied that anomalously broadening areas showed different phase change dynamics with not anomalously broadening areas.
発表言語 日本語
発表者名 半田 光
指導教員名 高橋 陽太郎 准教授
発表題目(英語) Terahertz spectroscopy of soft phonon in (Pb,Sn)Te thin film
要旨(英語) In terahertz region, dynamics of elementary excitation and electron, for example Drude response, phonon and antiferromagnetic resonance of spin, can be observed, so terahertz region recently attracts a great deal of attention.
 It has been reported that in SrTiO3, by using intense terahertz pulses, soft mode resonance frequency hardens at high field, so nonlinearity is observed [1]. And it has also been reported that by using intense terahertz pulses, ferroelectric soft mode in SrTiO3 drives strongly and, displacement of ferroelectric soft mode is comparable to ferroelectric phase induced by pressure [2]. These studies suggest that transient ferroelectric phase is induced by intense terahertz pulses.
 (Pb, Sn)Te is good candidate for large nonlinearity by intense terahertz pulses.
 (Pb, Sn)Te is narrow gap semiconductor, and PbTe is paraelectric and SnTe is ferroelectric.
 In this presentation, I will talk about composition ratio dependence of soft mode in (Pb, Sn)Te and nonlinearity induced by intense terahertz pulses. I will explain the nonlinearity by using anharmonic potential model.
[1] I. Katayama *et al*., PRL(2012)
[2] X. Li *et al*., Science (2019).
発表言語 日本語
発表者名 福田 光
指導教員名 十倉 好紀 卓越教授
発表題目(英語) Topological transport properties of non-coplanar magnets
要旨(英語) In recent years, there has been a lot of research that has brought a topological perspective to physics, including the quantum Hall effect.
 Topological materials are considered to be candidates for the next generation of electronic devices because of their non-dissipative nature and robustness to fluctuations. According to the Berry phase theory, it is the Berry curvature that characterizes these topological materials, which acts as a giant effective magnetic field. This shows that controlling Berry curvature is equivalent to controlling giant effective magnetic field and non-dispersive currents. Wavenumber space, like topological insulators, is the most typical example where Berry curvature appears, but the Berry curvature of the electronic band is difficult to control by the external field because its energy scale is much larger than that of the external field. On the other hand, since Berry curvature occurs in arbitrary parameter space, the policy of using Berry curvature in spin space has also been proposed. For example, in a non-coplanar magnetic structure, the itinerant electrons are subjected to a huge effective magnetic field.
 Therefore, in non-coplanar magnetic materials, the Berry curvature can be easily controlled by a magnetic field through the manipulation of spins. In this presentation, I will talk about the non-coplanar magnets *R*2Mo2O7 (*R* : rare-earth elements) and their exotic transport properties.
発表言語 日本語