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Masao Doi
2009 Volume 78 Issue 5 Pages
052001
Published: May 15, 2009
Released on J-STAGE: December 28, 2011
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Continuum mechanical model is proposed for dynamical processes in gels that involve coupling between the elastic deformation and solvent permeation. Basic equations are derived by two methods, by a physical argument, and by a variational principle. The model is then applied to discuss the swelling of gels, in which solvent permeation causes deformation, and the squeezing of gels, in which mechanical force induce solvent permeation. The model is also applied to the dynamics of the volume transition of gels. It is shown that the elasticity of gels creates various unusual features in the phase transition dynamics.
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Seiji Miyoshi, Masato Okada
2009 Volume 78 Issue 5 Pages
053001
Published: May 15, 2009
Released on J-STAGE: December 28, 2011
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We have analyzed the generalization performance of a student which slowly switches ensemble teachers. By calculating the generalization error analytically using statistical mechanics in the framework of on-line learning, we show that the dynamical behaviors of generalization error have a periodicity that is synchronized with the switching period and that the behaviors differ with the number of ensemble teachers. Furthermore, we show that the smaller the switching period is, the larger the difference in behavior is.
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Dai Aoki, Frédéric Bourdarot, Elena Hassinger, Georg Kne ...
2009 Volume 78 Issue 5 Pages
053701
Published: May 15, 2009
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Combination of neutron scattering and thermal expansion measurements under pressure shows that the so-called hidden order phase of URu
2Si
2 reenters in magnetic field when antiferromagnetism (AF) collapses at
HAF(
T). Macroscopic pressure studies of the HO–AF boundaries were realized at different pressures via thermal expansion measurements under magnetic field using a strain gauge. Microscopic proof at a given pressure is the reappearance of the resonance at
Q0=(1,0,0) under field which is correlated with the collapse of the AF Bragg reflections at
Q0.
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Akira Oosawa, Takao Suzuki, Keishi Kanada, Satoshi Kojima, Takayuki Go ...
2009 Volume 78 Issue 5 Pages
053702
Published: May 15, 2009
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The spin–lattice relaxation rate
T1−1 of
1H-NMR has been measured in (CH
3)
2CHNH
3Cu(Cl
xBr
1−x)
3 with
x=0 and 0.35, in order to investigate their microscopic magnetism. Previous macroscopic magnetization and specific heat measurements suggested that these two exist in a singlet-dimer phase. The temperature dependence of
T1−1 in an
x=0 system decreased exponentially toward zero, providing microscopic evidence of a gapped singlet ground state, which is consistent with results of macroscopic experiments. At the same time, in the
x=0.35 system,
T1−1 showed a sharp peak structure at approximately 7.5 K but no splitting of
1H-NMR spectra, indicative of magnetic ordering. We discuss the observed sharp peak structure in the
x=0.35 system with the soft mode toward the exotic magnetic ground state suggested by recent μSR experiments.
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Mamoru Yogi, Haruo Niki, Mitsuharu Yashima, Hidekazu Mukuda, Yoshio Ki ...
2009 Volume 78 Issue 5 Pages
053703
Published: May 15, 2009
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We report on the evolution of a novel phase transition under magnetic field (
H) in the filled skutterudite compound CeOs
4Sb
12 probed by
121Sb NMR. Measurements of nuclear spin–lattice relaxation rate
121(1⁄
T1) for the oriented powder with
H||[100] have revealed that antiferromagnetic (AFM) spin fluctuations due to the proximity of a quantum critical point at
H=0 are markedly suppressed by the application of
H, which is consistent with the result indicating that the AFM order at
TN=0.9 K with a very small moment of 0.07μ
B collapses, exceeding
H=1 T. As
H increases further, a large reduction in 1⁄
T1T was observed below the temperature
T0, which varies as a dome against
H with a maximum of 1.8 K at
H∼6 T. The values of
T1T=const. well below
T0 decrease with increasing
H, indicating that the residual density of states depends on
H. It is suggested that the field-induced novel transition is associated with the freezing of multipole degree of freedom.
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Masahito Mochizuki, Nobuo Furukawa
2009 Volume 78 Issue 5 Pages
053704
Published: May 15, 2009
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We theoretically study a competition between two types of spin cycloids (
ab-plane and
bc-plane ones) in the multiferroic perovskite manganites, which is an origin of intriguing magnetoelectric phenomena in these compounds. Analysis of a microscopic model using the Monte-Carlo method reveals that their competition originates from a conflict between the single-ion anisotropy and the Dzyaloshinsky–Moriya interaction. It is demonstrated that the conflict can be controlled by tuning the second-neighbor spin exchanges through the GdFeO
3-type distortion, which leads to a cycloidal-plane flop from
ab to
bc observed in the solid-solution systems like Eu
1−xY
xMnO
3 and Gd
1−xTb
xMnO
3 with increasing
x.
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Hiroshi Muranaka, Yusuke Doi, Keisuke Katayama, Hitoshi Sugawara, Riki ...
2009 Volume 78 Issue 5 Pages
053705
Published: May 15, 2009
Released on J-STAGE: December 28, 2011
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We succeeded in observing the de Haas–van Alphen (dHvA) effect in LaRuPO, which is a sister compound of iron-based oxypnictide superconductors. All the detected dHvA frequencies, which correspond to the maximum or minimum cross-sectional areas of Fermi surfaces, approximately follow the 1⁄cosθ dependence, where θ is a field-tilted angle from the tetragonal [001] direction to the [100] and [110] directions. The Fermi surfaces are found to consist of two cylindrical hole Fermi surfaces and two cylindrical electron Fermi surfaces on the basis of the similar cylindrical Fermi surfaces in LaFePO and the result of energy band calculations. The cyclotron effective mass in LaRuPO is light, ranging from 0.55 to 0.86
m0, which is compared with a large cyclotron mass in LaFePO. These two-dimensional Fermi surfaces in LaRuPO and LaFePO are also compared with the three-dimensional Fermi surfaces in LaFe
2P
2.
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Hideaki Maebashi, Yasutami Takada
2009 Volume 78 Issue 5 Pages
053706
Published: May 15, 2009
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Based on a model derived from the first-principles Hamiltonian by treating the electron–ion pseudopotential as perturbation, we have studied the local ionic structure of an expanded liquid alkali metal to find that the distance between adjacent ions decreases despite the increase of the mean interionic distance with volume expansion. This anomalous feature of the interionic contraction, which is in quantitatively good accord with experiment for liquid Rb, is attributed to an enhanced attraction working between valence electrons in the low-density electron gas, combined with the existence of the ionic core region from which valence electrons are excluded.
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Jeong Ryeol Choi, Kyu Hwang Yeon, Mustapha Maamache, Salah Menouar
2009 Volume 78 Issue 5 Pages
054001
Published: May 15, 2009
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The quantum states for a time-dependent charged oscillator are investigated by an invariant operator method and a unitary transformation approach. The wave functions are derived precisely in both cases of discrete and continuous quantum spectra. By choosing time functions of the Hamiltonian in different forms, our theory can be applied to diverse types of quantum dynamical systems. In the limit of a simple case, we confirmed that our result associated with a discrete spectrum recovers to that of Storchak.
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Takayuki Tanabe, Kouichi Okunishi
2009 Volume 78 Issue 5 Pages
054002
Published: May 15, 2009
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We revisit the nature of the quasi-one-dimensional Ising model on the basis of Wang–Landau simulation. We introduce the density of states in the two-dimensional energy space corresponding to the intra- and interchain directions. We then analyze the interchain coupling dependence of specific heat of the anistropic two-dimensional Ising model in the context of the density of states, and further discuss the size dependence of peak temperature. We also discuss the feature of the phase transition in the three-dimensional case.
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Masatoshi Nakatani, Ryosuke Shimizu, Kazuki Koshino
2009 Volume 78 Issue 5 Pages
054401
Published: May 15, 2009
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The up-conversion dynamics of two photons in a three-level system is investigated theoretically. The analysis is based on a rigorous formalism that incorporates the multimode nature of the photon field, enabling quantitative handling of the spatial profiles of the photon pulses. We have derived an analytic formula that connects the wavefunction of two input photons to that of an up-converted output photon. The up-conversion efficiency and the output pulse profile are numerically calculated using this formula.
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Rongjun Zhang, Duanzheng Yao, Hongliang Jiang, Hua Xiao
2009 Volume 78 Issue 5 Pages
054402
Published: May 15, 2009
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The energies of 1s states inside and outside the quantum well of a CdSe/ZnS quantum-dot quantum well (QDQW) and the transition dipole moment between these two states have been calculated by effective mass approximation. By using the calculation results, the longitudinal and transversal relaxation times of CdSe/ZnS have been approximated. We obtain a three-pulse photon echo (TPE) signal on the basis of the two states using the optical Bloch equations. We find that there should be four echoes in TPE from our theoretical calculation. In particular, the effects of the variation in core radius and shell thickness have been studied. It has been shown from the numerical calculation that the TPE signal is strongly dependent on the size and structure of the QDQW, and is dominated by relaxation time, which is also dependent on the size and structure.
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Kazuko Inoue, Yasuo Yamaguchi, Yoshinobu Ishii, Hiroki Yamauchi, Toets ...
2009 Volume 78 Issue 5 Pages
054601
Published: May 15, 2009
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The effect of a magnetic field on the martensitic transformation of an off-stoichiometric Heusler type Ni
2.16Mn
0.78Ga
1.06 single crystal has been revealed by neutron diffraction. The alloy undergoes a martensitic transformation at room temperature, which is nearly coincident with its Curie temperature. Splitting of the cubic (020) peak on the reciprocal lattice cubic
c*-plane was traced at 293 K by a triple-axis neutron spectrometer under an increasing magnetic field of up to 10 T. It was found that the magnetic field causes the martensitic transformation from the cubic structure to the orthorhombic structure, which is the same as that caused by decreasing the temperature without a magnetic field. The increase in the magnetic field to 10 T appears to correspond to a decrease in temperature of nearly 12 K, i.e., from 293 to 281 K. The present experiment suggests the possibility of realizing a magnetic-field-induced shape memory alloy.
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Zahra Noorbakhsh, Farhad Shahbazi, Seyed Akbar Jafari, Ganapathy Baska ...
2009 Volume 78 Issue 5 Pages
054701
Published: May 15, 2009
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In this work, a long-range resonating valence bond state is proposed as a variational wave function for the ground-state of the
S=1⁄2 antiferromagnetic Heisenberg model on the honeycomb lattice. Employing the variational Monte Carlo (VMC) method, we show that the ground-state energy obtained from such a resonating valence bond (RVB) wave function, lies well below the energy of the Néel state and compares very well to the energies evaluated on the basis of the spin-wave theory and by the series expansion method. We also obtain the spin–spin correlation function along zig-zag and armchair directions and find that the two correlations are different, which indicates the anisotropic nature of the system. We compare our results with that of the square lattice, and we show that although the quantum fluctuations on the honeycomb lattice are much stronger, they do not destroy the magnetic order completely.
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Takemi Yamada, Youichi Yamakawa, Yoshiaki Ono
2009 Volume 78 Issue 5 Pages
054702
Published: May 15, 2009
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We investigate the electronic states around a single vacancy in silicon crystal by using the Green’s function approach. The triply degenerate vacancy states within the band gap are found to be extended over a large distance ∼20 Å from the vacancy site and contribute to the reciprocal temperature dependence of the quadrupole susceptibility resulting in the elastic softening at low temperture. The Curie constant of the quadrupole susceptibility for the trigonal mode (
Oyz,
Ozx,
Oxy) is largely enhanced as compared to that for the tetragonal mode (
O20,
O22). The obtained results are consistent with the recent ultrasonic experiments in silicon crystal down to 20 mK. We also calculate the dipole and octupole susceptibilities and find that the octupole susceptibilities are extremely enhannced for a specific mode.
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Yoshiaki Hata, Yasushi Kanke, Kenji Ohoyama, Eiji Kita
2009 Volume 78 Issue 5 Pages
054703
Published: May 15, 2009
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Distribution of Fe ions in SrV
6−xFe
xO
11 with 0≤
x≤1.5 has been stuided by means of
57Fe Mössbauer spectroscopy and neutron powder diffraction. Rietveld analysis of the powder diffraction profiles revealed that Fe ions are not located on the octahedral site of V(1). This is consistent with the results taken by the Mössbauer spectroscopy at room temperature and 350 K. It is found that the larger Δ of the Mössbauer subspectrum originates from Fe ions occupied at the V(3) sites, and the V(3) site occupancy of the Fe ions increases up to 60% as reducing
x. It is also found that the valences of Fe ions at the V(2) and V(3) sites are considered to be 3+.
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Ryuta Yagi, Kazuki Tsuboi, Ryohei Morimoto, Toru Matsumura, Hiroaki Ko ...
2009 Volume 78 Issue 5 Pages
054704
Published: May 15, 2009
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We observed recombination time dependent on the quasi particle density by performing injection experiments using multi-terminal device consisting of a narrow aluminum wire and DC-SQUID junctions. At low temperatures where injected quasi-particle density are considerably larger than that of thermally excited quasi-particles, we found that the relaxation length of the quasi-particle density reduced about 30% when the injection current was increased from 200 to 600 nA. The result could be interpreted as the intrinsic quasi-particle recombination time proportional to the square of quasi-particle density.
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Kenji Yonemitsu
2009 Volume 78 Issue 5 Pages
054705
Published: May 15, 2009
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The suppression of rectification at metal–Mott-insulator interfaces, which was previously shown by numerical solutions to the time-dependent Schrödinger equation and experiments on real devices, is reinvestigated theoretically using nonequilibrium Green’s functions. The one-dimensional Hubbard model is used for a Mott insulator. The effects of attached metallic electrodes are incorporated into the self-energy. A scalar potential originating from work-function differences and satisfying the Poisson equation is added to the model. For electron density, we decompose it into three parts. One is obtained by integrating the local density of states over energy to the midpoint of the electrodes’ chemical potentials. The others, obtained by integrating lesser Green’s functions, are due to couplings with the electrodes and correspond to an inflow and an outflow of electrons. In Mott insulators, incoming electrons and holes are extended over the whole system, avoiding further accumulation of charges relative to that in the case without bias. This induces collective charge transport and results in the suppression of rectification.
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Makoto Iwata, Zdravko Kutnjak, Yoshihiro Ishibashi, Robert Blinc
2009 Volume 78 Issue 5 Pages
054706
Published: May 15, 2009
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The hydrostatic pressure–temperature (
P–
T) and Ca-concentration–temperature (
x–
T) phase diagrams of Ba
1−xCa
xTiO
3 (BCT) are discussed separately within the simple Landau–Devonshire theory. It is pointed out that it is not appropriate to discuss these phase diagrams under the assumption that physical factors governing the phase diagrams are the same. It is clarified that, in the
P–
T phase diagram, a decisive role is played by the effect in the second order in polarization, while in the
x–
T phase diagram, by that in the fourth order in polarization.
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Harukazu Kato, Takuya Tsuruta, Masahiro Matsumura, Takashi Nishioka, H ...
2009 Volume 78 Issue 5 Pages
054707
Published: May 15, 2009
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NQR/NMR measurements, including spin–lattice relaxation rate (1⁄
T1) and Knight shift (
K) evaluations, have been carried out for Cu and Ru nuclear spins in the
A-site ordered perovskite system CaCu
3Ru
4O
12, which exhibits a mass-enhancement-like behavior although it possesses no
f electrons. The temperature evolution of
T1 for Cu, which was measured up to 700 K, exhibits 1⁄
T1T = constant behavior at high enough temperatures. This clearly denies the existence of a Cu localized moment, which was previously suggested as the origin of the mass enhancement in a dense Kondo scenario. Furthermore,
K and (1⁄
T1T) for Cu exhibit significant temperature dependences with two characteristic temperatures
TF=20 K and
TX=180 K, suggesting a temperature-induced transition of microscopic electronic character at
TF and
TX. We propose a two–band model, where the effective density of states for one of the bands shows a significant temperature dependence in
TF<
T<
TX. Possible origins are discussed.
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Takao Morinari
2009 Volume 78 Issue 5 Pages
054708
Published: May 15, 2009
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Motivated by recent quantum oscillation observations in the underdoped high-temperature superconductors, the effect of the short-range antiferromagnetic correlations on the electronic properties of the short-ranged d-density wave state is investigated. At intermediate d-density wave correlations, the cross section of the energy dispersion at the Fermi energy consists of hole pockets and an electron pocket. It is argued that the electron pocket feature is smeared out by the effect of the short-range antiferromagnetic correlation, which could be the reason why any electron pockets have never been observed in the angle resolved photoemission experiments. The Hall resistance is calculated for the system with the electron band and the hole band using a finite temperature formula assuming Dirac fermion spectrum for the latter. It is argued that the scattering effect in the hole band should be anomalously large or much suppressed by superconductivity correlations and/or vortex contributions to explain the recent quantum oscillation observations.
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Tetsu Tanaka, Yu Kawasaki, Shigeki Endou, Satoshi Kimura, Yukiichi Ide ...
2009 Volume 78 Issue 5 Pages
054709
Published: May 15, 2009
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To clarify the electronic state in a two-dimensional triangular lattice LiVS
2, we have performed
51V- and
7Li-NMR measurements. Below the phase transition temperature
Tc of about 310 K from the paramagnetic state to a nonmagnetic state, the Knight shift of both
51V and
7Li does not depend on temperature. The
51V and
7Li spin–lattice relaxation rates 1⁄
T1 show the exponential temperature dependence below
Tc, which indicates a gap structure of the electronic state. These results are in agreement with a trimer singlet of V
3+ spins below
Tc. The increase in
7Li 1⁄
T1 above
Tc indicates the existence of the pseudo gap and agrees with the increase in paramagnetic susceptibility with increasing temperature and with the small entropy change at
Tc compared with that in LiVO
2.
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Igor Solovyev
2009 Volume 78 Issue 5 Pages
054710
Published: May 15, 2009
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With the increase of the lattice distortion, the orthorhombic manganites
RMnO
3 (
R=La, Pr, Nd, Tb, and Ho) are known to undergo the phase transition from the layered A-type antiferromagnetic (AFM) state to the zigzag E-type AFM state. We consider the microscopic origin of this transition. Our approach consists of the two parts. First, we construct an effective low-energy model for the manganese 3
d-bands and derive parameters of this model from the first-principles electronic structure calculations. Then, we solve this model in the Hartree–Fock approximation (HFA) and analyze the behavior of the interatomic magnetic interactions. We argue that the nearest-neighbor interactions decrease with the increase of the distortion and at certain stage start to compete with the longer range (particularly, second- and third-neighbor) AFM interactions in the orthorhombic
ab-plane, which trigger the formation of the E-phase. The origin of these interactions is closely related to the orbital ordering, which takes place in the distorted orthorhombic structure. The model is able to capture the main experimental trends and explain why LaMnO
3 develops the A-type AFM order and why it tends to transform to the E-type AFM order in the more distorted compounds. Nevertheless, the quantitative agreement with the experimental data crucially depends on other factors, such as the magnetic polarization of the oxygen sites as well as the correlation interactions beyond HFA.
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Kiyoichiro Motoya, Yuji Muro, Tokuya Igarashi
2009 Volume 78 Issue 5 Pages
054711
Published: May 15, 2009
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A neutron scattering study on a concentrated spin-glass alloy Fe
65(Ni
0.78Mn
0.22)
35 has been performed under magnetic field. The amplitude of the magnetic diffuse scattering pattern arising from short-range ferromagnetic correlations is markedly reduced by increasing magnetic field. On the other hand, the effect of external field on the diffuse scattering pattern arising from antiferromagnetic short-range correlations is small. These results show that the regions of ferromagnetic and antiferromagnetic short-range correlations (ferromagnetic and antiferromagnetic clusters) coexist separately in this random magnetic material.
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James M. Chappell, Azhar Iqbal, M. A. Lohe, Lorenz von Smekal
2009 Volume 78 Issue 5 Pages
054801
Published: May 15, 2009
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We analyze the quantum penny flip game using geometric algebra and so determine all possible unitary transformations which enable the player
Q to implement a winning strategy. Geometric algebra provides a clear visual picture of the quantum game and its strategies, as well as providing a simple and direct derivation of the winning transformation, which we demonstrate can be parametrized by two angles θ,φ. For comparison we derive the same general winning strategy by conventional means using density matrices.
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Wei-Guo Jin, Yoshikazu Nemoto, Tatsuya Minowa
2009 Volume 78 Issue 5 Pages
055001
Published: May 15, 2009
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Yuta Asano, Kazuhiro Fuchizaki
2009 Volume 78 Issue 5 Pages
055002
Published: May 15, 2009
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Yoshihito Ogasawara, Akihiko Kitada
2009 Volume 78 Issue 5 Pages
057001
Published: May 15, 2009
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Shoji Ishibashi, Kiyoyuki Terakura
2009 Volume 78 Issue 5 Pages
058001
Published: May 15, 2009
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Soshi Takeshita, Ryosuke Kadono, Masatoshi Hiraishi, Masanori Miyazaki ...
2009 Volume 78 Issue 5 Pages
058002
Published: May 15, 2009
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