arXiv subjects

Y. Yamamoto

Publications and source records attributed to Y. Yamamoto.

At least 91 records · Page 5Linked to original sources

arXiv2007

Recovery of Hidden Interference in Mott Insulators

Particle statistics plays a crucial role in a strongly interacting quantum many-body system. Here, we study the Hubbard model for distinguishable particles at unit filling. Starting from the superfluid-like state in the strong tunneling limit and gradually reducing the tunneling so that the on-site repulsive interaction dominates, the state ends up in a symmetric superposition of Mott insulator states. This result can be experimentally confirmed by the recovery of interference patterns in the density correlation functions. We also show that this state is a maximally entangled state, in contrast to the standard picture.

quant-ph↗

arXiv2006

Four-body structure of $^7_Λ$Li and $ΛN$ spin-dependent interaction

Two spin-doublet states of %$3/2^+$-$1/2^+$ and $7/2^+$-$5/2^+$ in $^7_Λ$Li are studied on the basis of the $α+Λ+n+p$ four-body model. We employ the two-body interactions which reproduce the observed properties of any subsystems composed of $αN$, $αΛ$ and $αNN$, and $αΛN$. Furthermore, the $ΛN$ interaction is adjusted so as to reproduce the $0^+$-$1^+$ splitting of in $^4_Λ$H. The calculated energy splittings of $3/2^+$-$1/2^+$ and $7/2^+$-$5/2^+$ states in $^7_Λ$Li are 0.69 MeV and 0.46 MeV, which are in good agreement with the resent observed data. The spin-dependent components of the $ΛN$ interaction are discussed.

nucl-th↗

arXiv2006

Large magnetoresistance in intermetallic compounds R2Mn3Si5 (R = Tb, Dy and Ho)

Magnetization (M) and magnetoresistance (MR) measurements on polycrystalline R2Mn3Si5 (R = Tb, Dy and Ho) compounds (tetragonal, space group P4/mnc) have been carried out in the temperature range of 2 K-300 K, in various applied fields. Both, the rare earth and the Mn, are found to carry magnetic moments in these compounds. Mn has two sub-lattices (Mn1 and Mn2) that order magnetically at two different temperatures. Rare earth and Mn1 moments order ferromagnetically at TC1 whereas Mn2 is found to magnetically order at TC2 (TC1 = 89 K, 86 K, 78 K and TC2 = 18 K, 34 K, 16 K for R = Tb, Dy and Ho compounds, respectively). Magnetoresistance measurements reveal large negative MR values of about 50 % near TC2 at 9 T in all these compounds. This giant magnetoresistance is attributed to the spin-dependent scattering effects, competing exchange interactions and the layered structure of these compounds

cond-mat.mtrl-sci↗

arXiv2006

Extended-soft-core baryon-baryon model III. $S=-2$ hyperon-hyperon/nucleon interaction

This paper presents the Extended-Soft-Core (ESC) potentials ESC04a-d for baryon-baryon channels with total strangeness $S=-2$. For these channels no experimental scattering data exist, and alsothe information from hypernuclei is very limited.The potential models for $S=-2$ are based on SU(3) extensions of potential models for the $S=0,-1$ sectors, which are fitted to experimental data. Flavor su(3)-symmetry is broken 'kinematically'by the masses of the baryons and the mesons.Moreover, in ESC04a,b aldo the coupling constants are broken, albeit in a well defined way using the $^3P_0$ quark-antiquark pair creation model as a guidance. But the fit to the S=0 and $S=-1$ sectors provides the necessary constraints to fix all free parameters.Therefore, the potentials for the $S=-2$ sectors do not contain additional free parameters, which situation is similar to the soft-core one-boson-exchange NSC97-models. Various properties of the potentials are illustrated by giving results for scattering lengths, bound states, phase-parameters, and total cross sections. The features of $Ξ$-hypernuclei predicted by ESC04d are studied on the basis of the G-matrix approach.

nucl-th↗

arXiv2006

A possible model to high TC ferromagnetism in Gallium Manganese Nitrides based on resonation properties of impurities in semiconductors

The high TC ferromagnetism in (Ga,Mn)N were observed and almost all results are approximately similar to the experimental results in (Ga,Mn)As except the value of TC. Though all standard experiments on magnetism clearly support the results, the value is unexpectedly high. This work present and discuss the possibility of high TC ferromagnetism, after brief review of the experimental results. The key speculation to Bosonization method in three dimensions is resembled with the problems in Anderson localization.

cond-mat.mtrl-sci↗

arXiv2006

Hybrid quantum repeater using bright coherent light

We describe a quantum repeater protocol for long-distance quantum communication. In this scheme, entanglement is created between qubits at intermediate stations of the channel by using a weak dispersive light-matter interaction and distributing the outgoing bright coherent light pulses among the stations. Noisy entangled pairs of electronic spin are then prepared with high success probability via homodyne detection and postselection. The local gates for entanglement purification and swapping are deterministic and measurement-free, based upon the same coherent-light resources and weak interactions as for the initial entanglement distribution. Finally, the entanglement is stored in a nuclear-spin-based quantum memory. With our system, qubit-communication rates approaching 100 Hz over 1280 km with fidelities near 99% are possible for reasonable local gate errors.

quant-ph↗

arXiv2006

Evidence for Carrier-Induced High-Tc Ferromagnetism in Mn-doped GaN film

A GaN film doped with 8.2 % Mn was grown by the molecular-beam-epitaxy technique. Magnetization measurements show that this highly Mn-doped GaN film exhibits ferromagnetism above room temperature. It is also revealed that the high-temperature ferromagnetic state is significantly suppressed below 10 K, accompanied by an increase of the electrical resistivity with decreasing temperature. This observation clearly demonstrates a close relation between the ferromagnetism with extremely high-Tc and the carrier transport in the Mn-doped GaN film.

cond-mat.str-el↗

arXiv2006

Extended-soft-core Baryon-Baryon Model II. Hyperon-Nucleon Interaction

The YN results are presented from the Extended-soft-core (ESC) interactions. They consist of local- and non-local-potentials due to (i) One-boson-exchange (OBE), with pseudoscalar-, vector-, scalar-, and axial-vector-nonets, (ii) Diffractive exchanges, (iii) Two-pseudoscalar exchange, and (iv) Meson-pair-exchange (MPE). This model, called ESC04, describes NN and YN in a unified way using broken flavor SU(3)-symmetry. Novel ingredients are the inclusion of (i) the axial-vector-mesons, (ii) a zero in the scalar- and axial-vector meson form factors. We describe simultaneous fits to the NN- and YN-data, using four options in the ESC-model. Very good fits were obtained. G-matrix calculations with these four options are also reported. The obtained well depths (U_Λ, U_Σ, U_Ξ) reveal distinct features of ESC04a-d. The ΛΛ-interactions are demonstrated to be consistent with the observed data of_{ΛΛ}^6He. The possible three-body effects are investigated by considering phenomenologically the changes of the vector-meson masses in a nuclear medium.

nucl-th↗

arXiv2005

Differential phase shift quantum key distribution experiment over 105 km fibre

Since several papers appeared in 2000, the quantum key distribution (QKD) community has been well aware that photon number splitting (PNS) attack by Eve severely limits the secure key distribution distance in BB84 QKD systems with Poissonian photon sources. In attempts to solve this problem, entanglement-based QKD, single-photon based QKD, and entanglement swapping-based QKD, have been studied in recent years. However, there are many technological difficulties that must be overcome before these schemes can become practical systems. Here we report a very simple QKD system, in which secure keys were generated over >100 km fibre for the first time. We used an alternative protocol of differential phase shift keying (DPSK) but with a Poissonian source. We analysed the security of the DPSK protocol and showed that it is robust even against hybrid attacks including collective PNS attack over consecutive pulses, intercept-and-resend (I-R) attack and beamsplitting (BS) attack, because of the non-deterministic collapse of a wavefunction in a quantum measurement. To implement this protocol, we developed a new detector for the 1.5 um band based on frequency up-conversion in a periodically poled lithium niobate (PPLN) waveguide followed by a Si avalanche photodiode (APD). The use of the new detectors increased the sifted key generation rate up to > 1 Mbit/s over 30 km fibre, which is two orders of magnitude larger than the previous record.

quant-ph↗

arXiv2005

Search for Cosmic-Ray Antideuterons

We performed a search for cosmic-ray antideuterons using data collected during four BESS balloon flights from 1997 to 2000. No candidate was found. We derived, for the first time, an upper limit of 1.9E-4 (m^2 s sr GeV/nucleon)^(-1) for the differential flux of cosmic-ray antideuterons, at the 95% confidence level, between 0.17 and 1.15 GeV/nucleon at the top of the atmosphere.

astro-ph↗

arXiv2004

Measurements of Primary and Atmospheric Cosmic-Ray Spectra with the BESS-TeV Spectrometer

Primary and atmospheric cosmic-ray spectra were precisely measured with the BESS-TeV spectrometer. The spectrometer was upgraded from BESS-98 to achieve seven times higher resolution in momentum measurement. We report absolute fluxes of primary protons and helium nuclei in the energy ranges, 1-540 GeV and 1-250 GeV/n, respectively, and absolute flux of atmospheric muons in the momentum range 0.6-400 GeV/c.

astro-ph↗

arXiv2004

Direct evidence for ferromagnetic spin polarization in gold nanoparticles

We report the first direct observation of ferromagnetic spin polarization of Au nanoparticles with a mean diameter of 1.9 nm using X-ray magnetic circular dichroism (XMCD). Owing to the element selectivity of XMCD, only the gold magnetization is explored. Magnetization of gold atoms estimated by XMCD shows a good agreement with the results obtained by conventional magnetometry. This result is evidence of intrinsic spin polarization in nano-sized gold.

cond-mat.mtrl-sci↗

arXiv2004

Diameter dependence of ferromagnetic spin moment in Au nanocrystals

Au nanoparticles exhibit ferromagnetic spin polarization and show diameter dependence in magnetization. The magnetic moment per Au atom in the particle attains its maximum value at a diameter of about 3 nanometer (nm) in the Magnetization-Diameter curve. Because Au metal is a typical diamagnetic material, its ferromagnetic polarization mechanism is thought to be quite different from the ferromagnetism observed in transition metals. The size effect strongly suggests the existence of some spin correlation effect at the nanoscale. The so-called ``Fermi hole effect'' is the most probable one given in the free electron gas system. Ferromagnetism in Au nanoparticles is discussed using this model.

cond-mat.mtrl-sci↗

arXiv2003

Polarization phenomena in hyperon-nucleon scattering

We investigate polarization observables in hyperon-nucleon scattering by decomposing scattering amplitudes into spin-space tensors, where each component describes scattering by corresponding spin-dependent interactions, so that contributions of the interactions in the observables are individually identified. In this way, for elastic scattering we find some linear combinations of the observables sensitive to particular spin-dependent interactions such as symmetric spin-orbit (LS) interactions and antisymmetric LS ones. These will be useful to criticize theoretical predictions of the interactions when the relevant observables are measured. We treat vector analyzing powers, depolarizations, and coefficients of polarization transfers and spin correlations, a part of which is numerically examined in $Σ^{+} p$ scattering as an example. Total cross sections are studied for polarized beams and targets as well as for unpolarized ones to investigate spin dependence of imaginary parts of forward scattering amplitudes.

nucl-th↗

arXiv2003

Measurements of atmospheric muon spectra at mountain altitude

We report new measurements of the atmospheric muons at mountain altitude. The measurement was carried out with the BESS detector at the top of Mt. Norikura, Japan. The altitude is 2,770 m above sea level. Comparing our results and predictions given by some interaction models, a further appropriate model has been investigated. These studies would improve accuracy of atmospheric neutrino calculations.

astro-ph↗

arXiv2003

Hyperonic mixing in five-baryon double-strangeness hypernuclei in a two-channel treatment

Properties of hypernuclei $_{ΛΛ}^5$H and $_{ΛΛ}^5$He are studied in a two-channel approach with explicit treatment of coupling of channels ^3\text{Z}+Λ+Λand α+Ξ. Diagonal ΛΛand coupling ΛΛ-ΞN interactions are derived within G-matrix procedure from Nijmegen meson-exchange models. Bond energy ΔB_{ΛΛ} in $_{ΛΛ}^5$He exceeds significantly that in $_{ΛΛ}^5$H due to the channel coupling. Diagonal Ξαattraction amplifies the effect, which is sensitive also to Λ-core interaction. The difference of the ΔB_{ΛΛ} values can be an unambiguous signature of the ΛΛ-ΞN coupling in ΛΛhypernuclei. However, improved knowledge of the hyperon-nucleus potentials is needed for quantitative extraction of the coupling strength from future data on the ΛΛhypernuclear binding energies.

nucl-th↗

arXiv2003

Quantum Shot Noise Suppression in Single-Walled Carbon Nanotubes

We study the low frequency current correlations of an individual single-walled carbon nanotube at liquid He temperature. We have distinguished two physical regimes -- zero dimensional quantum dot and one dimensional quantum wire -- in terms of an energy spacing from the finite tube length in both differential conductance and shot noise measurements. In a one dimensional wire regime, we observed a highly suppressed shot noise from all measured tube devices, suggesting that electron-electron interactions play an important role.

cond-mat.mes-hall↗

arXiv2003

Shot Noise Suppression at Non-integer Conductance Plateaus in a Quantum Point Contact

We study non-equilibrium differential conductance and current fluctuations in a single quantum point contact. The two-terminal electrical transport properties -- differential conductance and shot noise -- are measured at 1.5 K as a function of the drain-source voltage and the Schottky split-gate voltage. In differential conductance measurements, conductance plateaus appear at integer multiples of $2e^2/h$ when the drain-source voltage is small, and the plateaus evolve to a fractional of $2e^2/h$ as the drain-source voltage increases. Our shot noise measurements correspondingly show that the shot noise signal is highly suppressed at both the integer and the non-integer conductance plateaus. This main feature can be understood by the induced electrostatic potential model within a single electron picture. In addition, we observe the 0.7 structure in the differential conductance and the suppressed shot noise around 0.7 ($2e^2/h$); however, the previous single-electron model cannot explain the 0.7 structure and the noise suppression, suggesting that this characteristic relates to the electron-electron interactions.

cond-mat.mes-hall↗