Representation of quantum states as points in a probability simplex associated to a SIC-POVM

The quantum state of a $d$-dimensional system can be represented by the $d^2$ probabilities corresponding to a SIC-POVM, and then this distribution of probability can be represented by a vector of $\R^{d^2-1}$ in a simplex, we will call this set of vectors $\mathcal{Q}$. Other way of represent a $d$-dimensional system is by the corresponding Bloch vector also in $\R^{d^2-1}$, we will call this set of vectors $\mathcal{B}$. In this paper it is proved that with the adequate scaling $\mathcal{B}=\mathcal{Q}$. Also we indicate some features of the shape of $\mathcal{Q}$.Comment: 12 pages. Added journal referenc

NMR evidence for a strong modulation of the Bose-Einstein Condensate in BaCuSi2_2O6_6

We present a $^{63,65}$Cu and $^{29}$Si NMR study of the quasi-2D coupled spin 1/2 dimer compound BaCuSi$_2$O$_6$ in the magnetic field range 13-26 T and at temperatures as low as 50 mK. NMR data in the gapped phase reveal that below 90 K different intra-dimer exchange couplings and different gaps ($\Delta_{\rm{B}}/\Delta_{\rm{A}}$ = 1.16) exist in every second plane along the c-axis, in addition to a planar incommensurate (IC) modulation. $^{29}$Si spectra in the field induced magnetic ordered phase reveal that close to the quantum critical point at $H_{\rm{c1}}$ = 23.35 T the average boson density $\bar{n}$ of the Bose-Einstein condensate is strongly modulated along the c-axis with a density ratio for every second plane $\bar{n}_{\rm{A}}/\bar{n}_{\rm{B}} \simeq 5$. An IC modulation of the local density is also present in each plane. This adds new constraints for the understanding of the 2D value $\phi$ = 1 of the critical exponent describing the phase boundary

Roles of Bond Alternation in Magnetic Phase Diagram of RMnO3

In order to investigate nature of the antiferromagnetic structures in perovskite RMnO3, we study a Heisenberg J1-J2 model with bond alternation using analytical and numerical approaches. The magnetic phase diagram which includes incommensurate spiral states and commensurate collinear states is reproduced. We discuss that the magnetic structure with up-up-down-down spin configuration (E-type structure) and the ferroelectricity emerge cooperatively to stabilize this phase. Magnetoelastic couplings are crucial to understand the magnetic and electric phase diagram of RMnO3.Comment: 5 pages, 6 figure

Phase diagram of Nambu-Jona-Lasinio model with dimensional regularization

We investigate the phase diagram on temperature-chemical potential plane in the Nambu-Jona-Lasinio model with the dimensional regularization. While the structure of the resulting diagram shows resemblance to the one in the frequently used cutoff regularization, some results of our study indicate striking difference between these regularizations. The diagram in the dimensional regularization exhibits strong tendency of the first order phase transition.Comment: 9 pages, 9 figure

Topology Change of Coalescing Black Holes on Eguchi-Hanson Space

We construct multi-black hole solutions in the five-dimensional Einstein-Maxwell theory with a positive cosmological constant on the Eguchi-Hanson space, which is an asymptotically locally Euclidean space. The solutions describe the physical process such that two black holes with the topology of S^3 coalesce into a single black hole with the topology of the lens space L(2;1)=S^3/Z_2. We discuss how the area of the single black hole after the coalescence depends on the topology of the horizon.Comment: 10 pages, Some comments are added. to be published as a letter in Classical and Quantum Gravit

Mechanism of Lattice-Distortion-Induced Electric-Polarization Flop in the Multiferroic Perovskite Manganites

Magnetoelectric phase diagrams of the perovskite manganites, Eu1-xYxMnO3 and Gd1-xTbxMnO3, are theoretically studied. We first construct a microscopic model, and then analyze the model using the Monte-Carlo method. We reproduce the diagrams, which contain two different multiferroic states, i.e., the ab-plane spin cycloid with electric polarization P//a and the bc-plane spin cycloid with P//c. We reveal that their competition originates from a conflict between the single-ion anisotropy and the Dzyaloshinsky-Moriya interaction, which is controlled by the second-neighbor spin exchanges enhanced by the GdFeO3-type distortion. This leads to a P flop from a to c with increasing x in agreement with the experiments.Comment: 5 pages, 5 figures. Recalculated results after correcting errors in the assignment of DM vectors. The conclusion is not affecte

Anomalous Coexistence of Ferroelectric Phases (P∥aP\parallel a and P∥cP\parallel c) in Orthorhombic Eu1−y_{1-y}Yy_yMnO3_3 (y>0.5y>0.5) Crystals

We have investigated the magnetic and dielectric properties of orthorhombic Eu$_{1-y}$Y$_y$MnO$_3$ ($0\leq y\leq 0.6$) single crystals without the presence of the 4$f$ magnetic moments of the rare-earth ions. In $y\geq 0.2$, the magnetic-structure driven ferroelectricity is observed. The ferroelectric transition temperature is steeply reducing with increasing $y$. In $y\geq 0.52$, two ferroelectric phases ($P\parallel a$ and $P\parallel c$) are coexistent at low temperatures. In these phases, ferroelectricity has different origin, which is evidenced by the distinctive poling-electric-field dependence of electric polarization. Namely, the electric polarization along the c axis ($P_c$) is easily saturated by a poling electric field, therefore $P_c$ is caused by the $bc$ spiral antiferromagnetic order. On the other hand, the electric polarization along the a axis ($P_a$) is probably attributed to the collinear $E$-type antiferromagnetic order, because $P_a$ is unsaturated even in a poling field of $10^6$ V/m.Comment: 10 pages, 4figures, to be published in Journal of the Physical Society of Japa

AERODYNAMIC STUDY FOR THE GROUND EFFECT OF SKI JUMPING

We investigated the aerodynamic forces just before taking telemark of the landing phase. The full size model was employed to measure the lift area, the drag area and the moment volume, which was mounted in a 3-meter low speed wind tunnel. The ground plate was set in the test section of the wind tunnel. The height between the ground plate and the toe of the model was from 0.4 m to 1.0 m. In the case of the V style flight, the lift area with the ground plate is always larger than that without the ground plate, though the drag area with the ground plate is comparable to that without the ground plate. The ground effect of V style flight contributes to making the larger lift in the latter half of the flight. In the case of the parallel style, the lift and the drag areas with the ground plate are comparable to that without the plate

Film Edge Nonlocal Spin Valves

Spintronics is a new paradigm for integrated digital electronics. Recently established as a niche for nonvolatile magnetic random access memory (MRAM), it offers new functionality while demonstrating low power and high speed performance. However, to reach high density spintronic technology must make a transition to the nanometer scale. Prototype devices are presently made using a planar geometry and have an area determined by the lithographic feature size, currently about 100 nm. Here we present a new nonplanar geometry in which one lateral dimension is given by a film thickness, the order of 10 nm. With this new approach, cell sizes can shrink by an order of magnitude. The geometry is demonstrated with a nonlocal spin valve, where we study devices with an injector/detector separation much less than the spin diffusion length.Comment: 10 pages, 3 figure

Scattering Theory of Current-Induced Spin Polarization

We construct a novel scattering theory to investigate magnetoelectrically induced spin polarizations. Local spin polarizations generated by electric currents passing through a spin-orbit coupled mesoscopic system are measured by an external probe. The electrochemical and spin-dependent chemical potentials on the probe are controllable and tuned to values ensuring that neither charge nor spin current flow between the system and the probe, on time-average. For the relevant case of a single-channel probe, we find that the resulting potentials are exactly independent of the transparency of the contact between the probe and the system. Assuming that spin relaxation processes are absent in the probe, we therefore identify the local spin-dependent potentials in the sample at the probe position, and hence the local current-induced spin polarization, with the spin-dependent potentials in the probe itself. The statistics of these local chemical potentials is calculated within random matrix theory. While they vanish on spatial and mesoscopic average, they exhibit large fluctuations, and we show that single systems typically have spin polarizations exceeding all known current-induced spin polarizations by a parametrically large factor. Our theory allows to calculate quantum correlations between spin polarizations inside the sample and spin currents flowing out of it. We show that these large polarizations correlate only weakly with spin currents in external leads, and that only a fraction of them can be converted into a spin current in the linear regime of transport, which is consistent with the mesoscopic universality of spin conductance fluctuations. We numerically confirm the theory.Comment: Final version; a tunnel barrier between the probe and the dot is considered. To appear in 'Nanotechnology' in the special issue on "Quantum Science and Technology at the Nanoscale