Results for "Mikio Fujiwara"

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Multiphoton discrimination at telecom wavelength with charge integration photon detectorMar 04 2005We present a charge integration photon detector (CIPD) that enables the efficient measurement of photon number states at the telecom-fiber wavelengths with a quantum efficiency of 80% and a resolution less than 0.5 electrons at 1 Hz sampling. The CIPD ... More
Photon number resolving detection at telecom wavelength with a charge integration photon detectorDec 09 2005We demonstrate multiphoton discrimination at telecom wavelength with the readout frequency of 40 Hz by charge integration photon detector (CIPD). The CIPD consists of an InGaAs pin photodiode and a GaAs junction field effect transistor as a pre-amplifier ... More
Nonclasscial interference between independent intrinsically pure single photons at telecom wavelengthMar 12 2013Jul 24 2013We demonstrate a Hong-Ou-Mandel interference between two independent, intrinsically pure, heralded single photons from spontaneous parametric down conversion (SPDC) at telecom wavelength. A visibility of $85.5\pm8.3%$ was achieved without using any bandpass ... More
Coexistence of Continuous Variable Quantum Key Distribution and 7 $\times$ 12.5 Gbit/s Classical ChannelsSep 05 2018We study coexistence of CV-QKD and 7 classical 12.5 Gbit/s on-off keying channels in WDM transmission over the C-band. We demonstrate key generation with a distilled secret key rate between 20 to 50 kbit/s in experiments running continuously over 24 hours. ... More
Ultrahigh-sensitivity high-linearity photodetection system using a low-gain avalanche photodiode with an ultralow-noise readout circuitMar 04 2005A highly sensitive photodetection system with a detection limit of 1 photon/s was developed. This system uses a commercially available 200-mm-diameter silicon avalanche photodiode (APD) and an in-house-developed ultralow-noise readout circuit, which are ... More
Superconducting nanowire single photon detectors for quantum information and communicationsMar 01 2010Superconducting nanowire single photon detectors (SNSPD or SSPD) are highly promising devices in the growing field of quantum information and communications technology. We have developed a practical SSPD system with our superconducting thin films and ... More
Ultra fast quantum key distribution over a 97 km installed telecom fiber with wavelength-division multiplexing clock synchronizationMay 15 2008Jun 23 2008We demonstrated ultra fast BB84 quantum key distribution (QKD) transmission at 625 MHz clock rate through a 97 km field-installed fiber using practical clock synchronization based on wavelength-division multiplexing (WDM). We succeeded in over-one-hour ... More
Lax forms of the $q$-Painlevé equationsOct 01 2008All $q$-Painlev\'e equations which are obtained from the $q$-analog of the sixth Painlev\'e equation are expressed in a Lax formalism. They are characterized by the data of the associated linear $q$-difference equations. The degeneration pattern from ... More
Electronic States and Transport Phenomena in Quantum Dot SystemsJan 23 2001Electronic states and transport phenomena in semiconductor quantum dots are studied theoretically. Taking account of the electron-electron Coulomb interaction by the exact diagonalization method, the ground state and low-lying excited states are calculated ... More
Current induced entanglement of nuclear spins in quantum dotsOct 10 2002We propose an entanglement mechanism of nuclear spins in quantum dots driven by the electric current. The current accompanied by the spin flip in quantum dots gradually increases components of larger total spin of nuclei. This entangled state drastically ... More
Finite dimensional approximations in geometryApr 21 2003In low dimensional topology, we have some invariants defined by using solutions of some nonlinear elliptic operators. The invariants could be understood as Euler class or degree in the ordinary cohomology, in infinite dimensional setting. Instead of looking ... More
Continuous-Variable Quantum Teleportation with a Conventional LaserJan 11 2003We give a description of balanced homodyne detection (BHD) using a conventional laser as a local oscillator (LO), where the laser field outside the cavity is a mixed state whose phase is completely unknown. Our description is based on the standard interpretation ... More
Enhancement of Kondo effect in multilevel quantum dotsAug 07 2004We theoretically study enhancement mechanisms of the Kondo effect in multilevel quantum dots. In quantum dots fabricated on semiconductors, the energy difference between discrete levels \Delta is tunable by applying a magnetic field. With two orbitals ... More
New Expressions for Discrete Painlevé EquationsApr 01 2003Jun 09 2003It is known that discrete Painlev\'e equations have symmetries of the affine Weyl groups. In this paper we propose a new representation of discrete Painlev\'e equations in which the symmetries become clearly visible. We know how to obtain discrete Painlev\'e ... More
Compactly packaged superconducting nanowire single-photon detector with an optical cavity for multichannel systemFeb 28 2010We developed superconducting nanowire single-photon detectors with an optical cavity (OC-SNSPDs) for multichannel systems. For efficient coupling, the devices were installed in compact fiber-coupled packages after their substrate thickness was reduced ... More
Characteristics of superconducting single photon detector in DPS-QKD system under bright illumination blinding attackAug 10 2013We derive the time-dependent photo-detection probability equation of a superconducting single photon detector (SSPD) to study the responsive property for a pulse train at high repetition rate. Using this equation, we analyze the characteristics of SSPDs ... More
Development of SNSPD System with Gifford-McMahon CryocoolerMar 02 2010A superconducting nanowire single photon detector (SNSPD) system for telecommunication wavelength using a GM cryocooler was developed and its performance was verified. The cryocooler based SNSPD system can operate continuously with a 100 V AC power supply ... More
Photon level crosstalk between parallel fibers installed in urban areaAug 05 2010We estimate the channel characteristics of field-installed dark fibers at single photon levels for quantum key distribution (QKD). Measured fibers are telecom single-mode dark fibers over 45 km connecting a center and suburbs of Tokyo. Their total losses ... More
Multi-channel SNSPD system with high detection efficiency at telecommunication wavelengthApr 01 2010We developed a four-channel superconducting nanowire single-photon detector system based on a Gifford-McMahon cryocooler. All channels showed a system detection efficiency (at a 100 Hz dark-count rate) higher than 16% at 1550 nm wavelength, and the best ... More
Exceeding classical capacity limit in quantum optical channelApr 04 2003The amount of information transmissible through a communications channel is determined by the noise characteristics of the channel and by the quantities of available transmission resources. In classical information theory, the amount of transmissible ... More
Wavelength division multiplexed and double-port pumped time-bin entangled photon pair generation using Si ring resonatorFeb 09 2017We report a wavelength division multiplexed time-bin entangled photon pair source in telecom wavelength using a 10 {\mu}m radius Si ring resonator. This compact resonator has two add ports and two drop ports. By pumping one add port by a continuous laser, ... More
Spatial pattern of discrete and ultradiscrete Gray-Scott modelMay 23 2013Ultradiscretization is a limiting procedure transforming a given difference equation into a cellular automaton. In addition the cellular automaton constructed by this procedure preserves the essential properties of the original equation, such as the structure ... More
Kondo effect in coupled quantum dots under magnetic fieldsApr 05 2001The Kondo effect in coupled quantum dots is investigated theoretically under magnetic fields. We show that the magnetoconductance (MC) illustrates peak structures of the Kondo resonant spectra. When the dot-dot tunneling coupling $V_C$ is smaller than ... More
Quantum Dot Spin Filter in Resonant Tunneling and Kondo RegimesOct 28 2010Nov 20 2010A quantum dot with spin-orbit interaction can work as an efficient spin filter if it is connected to N (> 2) external leads via tunnel barriers. When an unpolarized current is injected to a quantum dot from a lead, polarized currents are ejected to other ... More
The hamburger theoremMar 23 2015Aug 02 2016We generalize the ham sandwich theorem to $d+1$ measures in $\mathbb{R}^d$ as follows. Let $\mu_1,\mu_2, \dots, \mu_{d+1}$ be absolutely continuous finite Borel measures on $\mathbb{R}^d$. Let $\omega_i=\mu_i(\mathbb{R}^d)$ for $i\in [d+1]$, $\omega=\min\{\omega_i; ... More
Molecular stochastic process on gold surface observed in broadband-infrared, background-suppressed, sum frequency generation spectroscopy: picosecond heat transfer to self-assembled monolayersMay 26 2014The picosecond thermal response of a normal octadecanethiol self-assembled monolayer on a gold surface was studied using pump-probe, broadband-infrared, background-suppressed and vibrational sum frequency generation spectroscopy. The orientation fluctuations ... More
An Accurate Quadrature Rule on the Sphere for Fast Computation of the Radiative Transport EquationAug 30 2014We present an accurate quadrature formula on the sphere with less localized quadrature points for efficient numerical computation of the radiative transport equation (RTE) in the three dimensions. High accuracy of the present method dramatically reduces ... More
A note for the global non-existence of semirelativistic equations with non-gauge invariant power type nonlinearityJan 15 2018The non-existence of global solutions for semirelativistic equations with non-gauge invariant power type nonlinearity is revisited by a relatively direct way with a pointwise estimate of fractional derivative of some test functions.
Instantaneous Quantum Channel Estimation during Quantum Information ProcessingMay 24 2014We present a nonintrusive method for reliably estimating the noise level during quantum computation and quantum communication protected by quantum error-correcting codes. As preprocessing of quantum error correction, our scheme estimates the current noise ... More
Block synchronization for quantum informationJun 01 2012Feb 12 2013Locating the boundaries of consecutive blocks of quantum information is a fundamental building block for advanced quantum computation and quantum communication systems. We develop a coding theoretic method for properly locating boundaries of quantum information ... More
The second bounded cohomology of a group with infinitely many endsMay 16 1995We study the second bounded cohomology of an amalgamated free product of groups, and an HNN extension of a group. As an application, we have a group with infinitely many ends has infinite dimensional second bounded cohomology.
Finite type invariants of words and Arnold's invariantsAug 27 2008We define a new finite type invariant for stably homeomorphic class of curves on compact oriented surfaces without boundaries and extend to a regular homotopy invariant for spherical curves.
Scaling analysis of Kondo screening cloud in a mesoscopic ring with an embedded quantum dotDec 01 2010The Kondo effect is theoretically studied in a quantum dot embedded in a mesoscopic ring. The ring is connected to two external leads, which enables the transport measurement. Using the "poor man's" scaling method, we obtain analytical expressions of ... More
Kondo resonant spectra in coupled quantum dotsMar 05 2001The Kondo effect in coupled quantum dots is investigated from the viewpoint of transmission spectroscopy using the slave-boson formalism of the Anderson model. The antiferromagnetic spin-spin coupling $J$ between the dots is taken into account. Conductance ... More
Electronic States in Silicon Quantum Dots: Multivalley Artificial AtomsApr 10 2003Electronic states in silicon quantum dots are examined theoretically, taking into account a multivalley structure of the conduction band. We find that (i) exchange interaction hardly works between electrons in different valleys. In consequence electrons ... More
Ability of stabilizer quantum error correction to protect itself from its own imperfectionSep 09 2014Dec 02 2014The theory of stabilizer quantum error correction allows us to actively stabilize quantum states and simulate ideal quantum operations in a noisy environment. It is critical is to correctly diagnose noise from its syndrome and nullify it accordingly. ... More
Quantum error correction via less noisy qubitsFeb 20 2013Apr 23 2013Known quantum error correction schemes are typically able to take advantage of only a limited class of classical error-correcting codes. Entanglement-assisted quantum error correction is a partial solution which made it possible to exploit any classical ... More
Self-synchronizing pulse position modulation with error toleranceJan 15 2013May 05 2013Pulse position modulation (PPM) is a popular signal modulation technique which creates M-ary data by means of the position of a pulse within a time interval. While PPM and its variations have great advantages in many contexts, this type of modulation ... More
A Numerical Study of Spectral Flows of Hermitian Wilson-Dirac Operator and the Index Theorem in Abelian Gauge Theories on Finite LatticesDec 06 2000Jan 17 2001We investigate the index of the Neuberger's Dirac operator in abelian gauge theories on finite lattices by numerically analyzing the spectrum of the hermitian Wilson-Dirac operator for a continuous family of gauge fields connecting different topological ... More
Level optimization in the totally real caseFeb 27 2006In this paper, congruences between holomorphic Hilbert modular forms are studied. We show the best possible level optimization result outside l for l > 2 by solving the remaining case of Mazur principle when the degree of the totally real field is even. ... More
Enhanced spin Hall effect in semiconductor heterostructures with artificial potentialMay 28 2009We theoretically investigate an extrinsic spin Hall effect (SHE) in semiconductor heterostructures due to the scattering by an artificial potential created by antidot, STM tip, etc. The potential is electrically tunable. First, we formulate the SHE in ... More
Resonant tunneling and Fano resonance in quantum dots with electron-phonon interactionJan 16 2006Jan 21 2006We theoretically study the resonant tunneling and Fano resonance in quantum dots with electron-phonon (e-ph) interaction. We examine the bias-voltage ($V$) dependence of the decoherence, using Keldysh Green function method and perturbation with respect ... More
Unitary Quantum Error Correction without Error DetectionJan 02 2011Jan 07 2011We propose a quantum error correction without error detection. A quantum state $\rho_0$ combined with an ancilla state $\sigma$ is encoded unitarily and an error operator is applied on the encoded state. The recovery operation then produces a tensor product ... More
The hamburger theoremMar 23 2015Dec 16 2018We generalize the ham sandwich theorem to $d+1$ measures in $\mathbb{R}^d$ as follows. Let $\mu_1,\mu_2, \dots, \mu_{d+1}$ be absolutely continuous finite Borel measures on $\mathbb{R}^d$. Let $\omega_i=\mu_i(\mathbb{R}^d)$ for $i\in [d+1]$, $\omega=\min\{\omega_i; ... More
Using arbitrary parity-check matrices for quantum error correction assisted by less noisy qubitsJul 30 2014Recently a framework for assisted quantum error correction was proposed in which a specific type of error is allowed to occur on auxiliary qubits, which is in contrast to standard entanglement assistance that requires noiseless auxiliary qubits. However, ... More
Parsing a sequence of qubitsJul 04 2012Jul 02 2013We develop a theoretical framework for frame synchronization, also known as block synchronization, in the quantum domain which makes it possible to attach classical and quantum metadata to quantum information over a noisy channel even when the information ... More
Visualizing a large-scale structure of production network by N-body simulationJan 16 2009Our recent study of a nation-wide production network uncovered a community structure, namely how firms are connected by supplier-customer links into tightly-knit groups with high density in intra-groups and with lower connectivity in inter-groups. Here ... More
Even-freeness of cyclic 2-designsOct 28 2012A Steiner 2-design of block size k is an ordered pair (V, B) of finite sets such that B is a family of k-subsets of V in which each pair of elements of V appears exactly once. A Steiner 2-design is said to be r-even-free if for every positive integer ... More
Zipf Law in Firms BankruptcyOct 03 2003Using an exhaustive list of Japanese bankruptcy in 1997, we discover a Zipf law for the distribution of total liabilities of bankrupted firms in high debt range. The life-time of these bankrupted firms has exponential distribution in correlation with ... More
Deformation rings and Hecke algebras in the totally real caseFeb 27 2006Jul 25 2006One of the basic questions in number theory is to determine semi-simple l-adic representations of the absolute Galois group of a number field. In this paper, we discuss the question for two dimensional representations over a totally real number field. ... More
A stable cohomotopy refinement of Seiberg-Witten invariants: IApr 29 2002The monopole map defines an element in an equivariant stable cohomotopy group refining the Seiberg-Witten invariant. This first of two articles presents the details of the definition of the stable cohomotopy invariant and discusses its relation to the ... More
The perturbation of the Seiberg-Witten equations revisitedMay 06 2014Jun 21 2016We introduce a new class of perturbations of the Seiberg-Witten equations. Our perturbations offer flexibility in the way the Seiberg-Witten invariants are constructed and also shed a new light to LeBrun's curvature inequalities.
Observation of Topological and Parity-dependent Phase of $m=0$ Spin StatesMay 22 2007Oct 09 2007A Ramsey interrogation scheme was used to measure the phase shift of laser-cooled $^{87}$Rb clock-transition pseudospins arising as a result of a reversal of a bias magnetic field, i.e., $\textbf{B} \to -\textbf{B}$, during the interrogation. While no ... More
Satellite-to-ground quantum communication using a 50-kg-class micro-satelliteJul 12 2017Recent rapid growth in the number of satellite-constellation programs for remote sensing and communications, thanks to the availability of small-size and low-cost satellites, provides impetus for high capacity laser communication (lasercom) in space. ... More
Displacement receiver for phase-shift-keyed coherent statesAug 09 2012Quantum receiver is an important tool for overcoming the standard quantum limit (SQL) of discrimination errors in optical communication. We theoretically study the quantum receivers for discriminating ternary and quaternary phase shift keyed coherent ... More
Optical phase estimation via coherent state and displaced photon countingApr 15 2016Jun 21 2016We consider the phase sensing via weak optical coherent state at quantum limit precision. A new detection scheme for the phase estimation is proposed which is inspired by the suboptimal quantum measurement in coherent optical communication. We theoretically ... More
Optimum detection for extracting maximum information from symmetric qubit setsJun 29 2001Sep 06 2001We demonstrate a class of optimum detection strategies for extracting the maximum information from sets of equiprobable real symmetric qubit states of a single photon. These optimum strategies have been predicted by Sasaki et al. [Phys. Rev. A{\bf 59}, ... More
Projective measurement onto arbitrary superposition of coherent state basesFeb 21 2017Feb 15 2018One of the peculiar features in quantum mechanics is that a superposition of macroscopically distinct states can exits. In optical system, this is highlighted by a superposition of coherent states (SCS), i.e. a superposition of classical states. Recently ... More
Optimal conditions for Bell test using spontaneous parametric down-conversion sourcesAug 25 2018We theoretically and experimentally investigate the optimal conditions for the Bell experiment using spontaneous parametric down conversion (SPDC) sources. In theory, we show that relatively large average photon number (typically $\sim$0.5) is desirable ... More
Maintenance-free Operation of WDM Quantum Key Distribution System through a Field Fiber over 30 DaysAug 05 2013Maintenance-free wavelength-division-multiplexing quantum key distribution for 30 days was achieved through a 22-km field fiber. Using polarization-independent interferometers and stabilization techniques, we attained a quantum bit error rate as low as ... More
Temperature Dependent Performances of Superconducting Nanowire Single-Photon Detectors in an Ultralow-Temperature RegionSep 21 2010We present the performances of a superconducting nanowire single-photon detector (SNSPD) in an ultralow-temperature region from 16 mK to 4 K. The system detection efficiency of the SNSPD showed saturation in the bias-current and temperature dependences, ... More
Quantum receiver beyond the standard quantum limit of coherent optical communicationMar 29 2011The most efficient modern optical communication is known as coherent communication and its standard quantum limit (SQL) is almost reachable with current technology. Though it has been predicted for a long time that this SQL could be overcome via quantum ... More
Sub-shot-noise-limit discrimination of on-off keyed coherent signals via a quantum receiver with a superconducting transition edge sensorFeb 15 2010We demonstrate a sub-shot-noise-limit discrimination of on-off keyed coherent signals by an optimal displacement quantum receiver in which a superconducting transition edge sensor is installed. Use of a transition edge sensor and a fiber beam splitter ... More
QKD from a microsatellite: the SOTA experienceOct 26 2018The transmission and reception of polarized quantum-limited signals from space is of capital interest for a variety of fundamental-physics experiments and quantum-communication protocols. Specifically, Quantum Key Distribution (QKD) deals with the problem ... More
Unbreakable distributed storage with quantum key distribution network and password-authenticated secret sharingJul 02 2016Distributed storage plays an essential role in realizing robust and secure data storage in a network over long periods of time. A distributed storage system consists of a data owner machine, multiple storage servers and channels to link them. In such ... More
Time-bin entangled photon pair generation from Si micro-ring resonatorJan 23 2015We demonstrate time-bin entanglement generation in telecom wavelength using a 7 {\mu}m radius Si micro-ring resonator pumped by a continuous wave laser. The resonator structure can enhance spontaneous four wave mixing, leading to a photon pair generation ... More
Effective-Range Expansion of the Neutron-Deuteron Scattering Studied by a Quark-Model Nonlocal Gaussian PotentialOct 11 2010Jan 15 2011The S-wave effective range parameters of the neutron-deuteron (nd) scattering are derived in the Faddeev formalism, using a nonlocal Gaussian potential based on the quark-model baryon-baryon interaction fss2. The spin-doublet low-energy eigenphase shift ... More
Coarse-graining and Self-similarity of Price FluctuationsJan 12 2001We propose a new approach for analyzing price fluctuations in their strongly correlated regime ranging from minutes to months. This is done by employing a self-similarity assumption for the magnitude of coarse-grained price fluctuation or volatility. ... More
Data processing for qubit state tomography: An information geometric approachAug 29 2016A statistically feasible data post-processing method for the conventional qubit state tomography is studied from an information geometrical point of view. It is shown that the space $(-1,1)^3$ of the Stokes parameters $(\xi_1, \xi_2,\xi_3)$ that specify ... More
Uncorrectable Errors of Weight Half the Minimum Distance for Binary Linear CodesApr 25 2008Apr 30 2008A lower bound on the number of uncorrectable errors of weight half the minimum distance is derived for binary linear codes satisfying some condition. The condition is satisfied by some primitive BCH codes, extended primitive BCH codes, Reed-Muller codes, ... More
Relations between the Local Weight Distributions of a Linear Block Code, Its Extended Code, and Its Even Weight SubcodeAug 02 2005Relations between the local weight distributions of a binary linear code, its extended code, and its even weight subcode are presented. In particular, for a code of which the extended code is transitive invariant and contains only codewords with weight ... More
New algorithm of the high-temperature expansion for the Ising model in three dimensionsSep 03 2002New algorithm of the finite lattice method is presented to generate the high-temperature expansion series of the Ising model. It enables us to obtain much longer series in three dimensions when compared not only to the previous algorithm of the finite ... More
Electronic structure of the MO oxides (M=Mg, Ca, Ti, V) in the GW approximationOct 20 2001Dec 19 2002The quasiparticle band structures of nonmagnetic monoxides, MO (M=Mg, Ca, Ti, and V), are calculated by the GW approximation. The band gap and the width of occupied oxygen 2p states in insulating MgO and CaO agree with experimental observation. In metallic ... More
Symmetry consideration and eg bands in NdNiO3 and YNiO3Oct 20 2001Group theoretical analyses are applied to the magnetic and electronic structures of NdNiO3 and YNiO3, whose electronic structures have been studied very recently by the LSDA+U method. The Jahn-Teller distortion cannot satisfy the experimentally observed ... More
Charge and orbital order in RNiO3 (R=Nd,Y) by LSDA+U methodMay 01 2001Oct 20 2001Electronic structure of NdNiO3 and YNiO3 are calculated by using LSDA+U method with rotational invariance. No orbital order on Ni sites is observed in both systems but different charge orderings. In a small distorting system NdNiO3, all Ni ions are trivalent ... More
Convexity in the Figure Eight Solution to the Three-Body ProblemAug 27 2003Sep 02 2003The figure eight is a remarkable solution to the Newtonian three-body problem in which the three equal masses chase each around a planar curve having the qualitative shape and symmetries of a figure eight. Here we prove that each lobe of this eight is ... More
Counting subgraphs in hyperbolic graphs with symmetryNov 18 2013This note addresses some questions that arise in the series of works by Kyoji Saito on the growth functions of graphs. We study "hyperbolike" graphs, which include Cayley graphs of hyperbolic groups. We generalize some well-known results on hyperbolic ... More
A Z$_2$ index of Dirac operator with time reversal symmetryMay 22 2009With time reversal symmetry a Dirac operator has vanishing index and Chern number. We show that we can nevertheless define a nontrivial Z$_2$ index as well as a corresponding topological invariant given by gauge field, which implies that such a Dirac ... More
Quantization of non-Abelian Berry phase for time reversal invariant systemsMar 18 2009We present a quantized non-Abelian Berry phase for time reversal invariant systems such as quantum spin Hall effect. Ordinary Berry phase is defined by an integral of Berry's gauge potential along a loop (an integral of the Chern-Simons one-form), whereas ... More
Electronic Structure of Transition Metals Fe, Ni and Cu in the GW ApproximationNov 12 2002Mar 18 2003The quasiparticle band structures of 3d transition metals, ferromagnetic Fe, Ni and paramagnetic Cu, are calculated by the GW approximation. The width of occupied 3d valence band, which is overestimated in the LSDA, is in good agreement with experimental ... More
Generalized index theorem for topological superconductors with Yang-Mills-Higgs couplingsApr 04 2012We investigate an index theorem for a Bogoliubov-de Gennes Hamiltonian (BdGH) describing a topological superconductor with Yang-Mills-Higgs couplings in arbitrary dimensions. We find that the index of the BdGH is determined solely by the asymptotic behavior ... More
New Algorithm of the Finite Lattice Method for the High-temperature Expansion of the Ising Model in Three DimensionsAug 31 2002We propose a new algorithm of the finite lattice method to generate the high-temperature series for the Ising model in three dimensions. It enables us to extend the series for the free energy of the simple cubic lattice from the previous series of 26th ... More
Electronic structure and effects of dynamical electron correlation in ferromagnetic bcc-Fe, fcc-Ni and antiferromagnetic NiOSep 25 2008Sep 26 2008LDA+DMFT method in the framework of the iterative perturbation theory (IPT) with full LDA Hamiltonian without mapping onto the effective Wannier orbitals. We then apply this LDA+DMFT method to ferromagnetic bcc-Fe and fcc-Ni as a test of transition metal, ... More
k-dependent spectrum and optical conductivity near metal-insulator transition in multi-orbital Hubbard bandsDec 16 2004We apply the dynamical mean field theory (DMFT) in the iterative perturbation theory(IPT) to doubly degenerate eg bands and triply degenerate tg bands on a simple cubic lattice and calculate the spectrum and optical conductivity in arbitrary electron ... More
Quasi-homomorphisms on mapping class groupsFeb 09 2007We refine the construction of quasi-homomorphisms on mapping class groups. It is useful to know that there are unbounded quasi-homomorphisms which are bounded when restricted to particular subgroups since then one deduces that the mapping class group ... More
Graph manifolds as ends of negatively curved Riemannian manifoldsMar 18 2019We prove that for a flip manifold $M$, which is a certain (3-dimensional) graph manifold, there exists a complete Riemannian metric on $\Bbb R \times M$ which is an ``eventually warped cusp metric'' with the sectional curvature $K$ satisfying $-1 \le ... More
Bounded cohomology of subgroups of mapping class groupsDec 14 2000Mar 06 2002We show that every subgroup of the mapping class group MCG(S) of a compact surface S is either virtually abelian or it has infinite dimensional second bounded cohomology. As an application, we give another proof of the Farb-Kaimanovich-Masur rigidity ... More
Combable functions, quasimorphisms, and the central limit theoremMay 13 2008Jun 17 2009A function on a discrete group is weakly combable if its discrete derivative with respect to a combing can be calculated by a finite state automaton. A weakly combable function is bicombable if it is Lipschitz in both the left and right invariant word ... More
Quantum synchronizable codes from finite geometriesNov 14 2013Sep 06 2014Quantum synchronizable error-correcting codes are special quantum error-correcting codes that are designed to correct both the effect of quantum noise on qubits and misalignment in block synchronization. It is known that in principle such a code can be ... More
Quark-model Baryon-Baryon Interaction Applied to the Neutron-Deuteron Scattering. I Noyes-Kowalski Approach to the AGS EquationsAug 23 2010Feb 15 2011We solve the neutron-deuteron (nd) scattering in the Faddeev formalism, employing the NN sector of the quark-model baryon-baryon interaction fss2. The energy-dependence of the NN interaction, inherent to the resonating-group formulation of the quark-model ... More
Probabilistic bounds on the trapping redundancy of linear codesApr 04 2016The trapping redundancy of a linear code is the number of rows of a smallest parity-check matrix such that no submatrix forms an $(a,b)$-trapping set. This concept was first introduced in the context of low-density parity-check (LDPC) codes in an attempt ... More
Streda formula for the Hofstadter-Wilson-Dirac model in two and four dimensionsSep 09 2016Nov 29 2016We rederive the spectral asymmetry of the Wilson-Dirac model in external fields, paying attention to the Chern number due to the Berry connection. We interpret the smooth part of the spectral asymmetry as the Streda formula that is originally derived ... More
Large-scale electronic structure theory for simulating nanostructure processOct 20 2006Fundamental theories and practical methods for large-scale electronic structure calculations are given, in which the computational cost is proportional to the system size. Accuracy controlling methods for microscopic freedoms are focused on two practical ... More
Dynamical brittle fractures of nanocrystalline silicon using large-scale electronic structure calculationsOct 17 2002Jul 10 2003A hybrid scheme between large-scale electronic structure calculations is developed and applied to nanocrystalline silicon with more than 10$^5$ atoms. Dynamical fracture processes are simulated under external loads in the [001] direction. We shows that ... More
On the joint spectral radius for isometries of non-positively curved spaces and uniform growthApr 02 2018We recast the notion of joint spectral radius in the setting of groups acting by isometries on non-positively curved spaces and give geometric versions of results of Berger-Wang and Bochi valid for $\delta$-hyperbolic spaces and for symmetric spaces of ... More
Random groups have fixed points on CAT(0) cube complexesDec 19 2010We prove that a random group has fixed points when it isometrically acts on a CAT(0) cube complex. We do not assume that the action is simplicial.
Graph manifolds as ends of negatively curved Riemannian manifoldsMar 18 2019Apr 03 2019Let $M$ be a graph manifold such that each piece of its JSJ decomposition has the $\Bbb H^2 \times \Bbb R$ geometry. Assume that the pieces are glued by isometries. Then, there exists a complete Riemannian metric on $\Bbb R \times M$ which is an "eventually ... More
Duality between front and rear mutations in cluster algebrasAug 06 2018We study the duality between the mutations and the rear mutations in cluster algebras, where the rear mutations are the transformations of rational expressions of cluster variables in terms of the initial cluster under the change of the initial cluster. ... More
Efficient detection of a highly bright photon source using superconducting nanowire single photon detectorsSep 05 2013May 06 2014We investigate the detection of an ultra-bright single-photon source using highly efficient superconducting nanowire single-photon detectors (SNSPDs) at telecom wavelengths. Both the single-photon source and the detectors are characterized in detail. ... More
Countermeasure against tailored bright illumination attack for DPS-QKDAug 10 2013We propose a countermeasure against the so-call tailored bright illumination attacl dor Differential-Phase-Shift QKD (DPS-QKD). By Monitoring a rate of coincidence detection at a pair of superconducting nanowire single photon detectors (SSPDs) which is ... More