[en] The spin state of FeCl₃ was measured by Nuclear Magnetic Resonance (NMR) as a function of temperature and magnetic field. The sublattice magnetization obtained from the ⁵⁷Fe NMR spectrum fits well with the theoretical prediction for an antiferromagnet with a magnetic anisotropy field of less than 70 mT in the ab-plane. The field dependence of the ⁵⁷Fe NMR spectrum shows that a spin rotation plane of helical order starts to align perpendicularly to the external field direction as the field increases from 0 and ends around 4 T with no phase transition. From the spin tilting angle analysis, we obtained the quantitative relation among the exchange coupling constants. - Highlights: • It was controversial whether FeCl₃ undergoes quantum phase transitions or not. • The NMR spectra obtained for various magnetic fields show that is not true. • NMR data gives M(T) curve, which is unobtainable by magnetization measurement. • Exchange coupling constants were obtained from the analysis of the spin canting angle

[en] The zero-field ⁵⁵Mn nuclear magnetic resonance (NMR) spectra for antiferromagnetic α-Mn₂O₃ were obtained at low temperatures. The Gaussian-shaped spectrum was positioned around 314 MHz in the zero-temperature limit, and the linewidth was about 5 MHz. The magnetic moment estimated from the resonance frequency was 2.6μ_B per Mn³⁺ ion, which corresponds to 65% of 4μ_B, which is expected when only the contribution of spin to the magnetic moment is considered. The temperature dependence of the sublattice magnetization does not fit Bloch's T² law well but instead fits the exponential form applicable when there is an initial energy gap in the dispersion relation of the spin wave. From the fitting, we obtained an energy gap of 1.82 meV and an anisotropy energy of 0.22 meV. The spin-spin relaxation time measured as a function of frequency shows that the Suhl-Nakamura interaction is suppressed by this energy gap. The line broadening is mostly influenced by the dipolar hyperfine interaction.

[en] With a three-bit nuclear magnetic resonance quantum computer, we have experimentally realized a quantum search algorithm that can take a desired function value (or target) t as its input and give the corresponding function argument x₀ such that f(x₀)=t as a result. The function value is not retrieved from an existing table, but evaluated by the search algorithm in the manner of a typical algorithmic search. A single-query version of the quantum search algorithm is used to search for one of two function arguments

[en] We investigate quantum teleportation through noisy quantum channels by solving analytically and numerically a master equation in the Lindblad form. We calculate the fidelity as a function of decoherence rates and angles of a state to be teleported. It is found that the average fidelity and the range of states to be accurately teleported depend on types of noises acting on quantum channels. If the quantum channels are subject to isotropic noise, the average fidelity decays to 1/2, which is smaller than the best possible value of 2/3 obtained only by the classical communication. On the other hand, if the noisy quantum channel is modeled by a single Lindblad operator, the average fidelity is always greater than 2/3

[en] We present a scheme to store unitary operators with self-inverse generators in quantum states and a general circuit to retrieve them with definite success probability. The continuous variable of the operator is stored in a single-qubit state and the information about the kind of the operator is stored in classical states with finite dimension. The probability of successful retrieval is always 1/2 irrespective of the kind of the operator, which is proved to be maximum. In case of failure, the result can be corrected with additional quantum states. The retrieving circuit is almost as simple as that which handles only the single-qubit rotations and CNOT as the basic operations. An interactive way to transfer quantum dynamics, that is, to distribute naturally copy-protected programs for quantum computers is also presented using this scheme

[en] We describe a magnetic resonance force microscopy experiment carried out using both a fast-relaxing spin system and a frequency-modulation mode detection method, presenting a validation of the measured signal and sensitivity. The detection method applied along with a self-excited cantilever oscillation worked stably without any serious interference due to spurious cantilever excitation despite application of first-harmonic microwave modulation, and thereby successfully created almost the maximum available signal. The signal could be measured without distortion while the magnetic field was swept at a rate of 1.9 G s^-1. The measured sensitivity approached the thermal noise limit of the cantilever with a high quality factor. The experimental results for both signal and noise were in good agreement with theoretical predictions

[en] The quantum Fourier transform is a key factor in achieving exponential speedup relative to classical algorithms. We implemented the phase estimation algorithm, which is the very basic application example of the quantum Fourier transform, on a three-bit nuclear magnetic resonance quantum-information processor. The algorithm was applied to one-bit Grover operators to estimate eigenvalues. We also demonstrated the counting algorithm with the same operators to obtain the number of the marked states. The results of projective measurements required by the algorithms were obtained from the split peak positions in the spectra

[en] We demonstrate experimentally the hyperfine-interaction control by an electric field, which is the operating principle of the addressable qubit operation in a silicon-based solid-state quantum computer in a new quantum computer system, a magnetic crystal. The transferred hyperfine field at a F^- nucleus caused by neighboring Mn²⁺ electron spins in an antiferromagnetic MnF₂ single crystal was measured by ¹⁹F nuclear magnetic resonance (NMR) with an external electric field applied along the [110] crystal direction. The electric field splits the ¹⁹F NMR peak into two resolved lines that come from the F nuclei located at geometrically equivalent sites. A line splitting of 56 kHz was achieved at an electric field of 3.4 V/μm. One of the F^- nuclear spins could be flipped selectively by a composite radio-frequency pulse while leaving the other unchanged, thereby demonstrating qubit addressing via electric field control of the hyperfine interaction.

[en] The microscopic magnetic and electronic properties of La_1-xSr_xMnO₃ (0.5≤x≤0.6) were investigated using ⁵⁵Mn nuclear magnetic resonance (NMR). The NMR spectral intensity showed a large decrement as x increases above the boundary (x∝0.52) of ferromagnetic (FM) and A-type antiferromagnetic (AFM) phases. The spectrum of the samples shows a coexistence of two different phases, i.e., a metallic major phase and an insulating minor phase. The spin-spin relaxation time strongly depends on the resonance frequency, indicating that the Shul-Nakamura process by spin-wave excitation is the dominant relaxation mechanism. This type of frequency dependence of the spin-spin relaxation time was not observed in the CE-type AFM manganite Nd_0.5Sr_0.5MnO₃. The A-type AFM spin structure and the Shul-Nakamura relaxation process appears to be a unique characteristics of La_1-xSr_xMnO₃ (0.54≤x≤0.6) that is related to the 2D-like spin coupling in a nearly tetragonal crystal structure. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

[en] The present study investigates the magnetic properties of a natural haematite (α-Fe₂O₃) crystal at the temperature of liquid helium using magnetometry and ⁵⁷Fe nuclear magnetic resonance (NMR) methods. The magnetization curve shows that the net magnetization in the (111) plane vanishes at the Morin temperature (260 K) but weakly reappears as the temperature decreases below 40 K. A comparison of the magnetization and NMR results indicates that the spin state, direction and canting angle, at a low temperature, is identical to that in a weak-ferromagnetic state above the Morin temperature. Its volume, however, occupies only 3% of the entire sample. The relaxation of magnetization with time, the difference of the zero-field-cooled and field-cooled magnetization, and the rise of the NMR echo intensity with increasing magnetic field exhibit the superparamagnetic behaviour of the reentrant weak ferromagnetic phase. The cluster size of the weak ferromagnetic phase is smaller than 10² nm and the blocking temperature is higher than 40 K. The fact that the results from the natural crystal and pure powder are similar implies that the reentrant weak-ferromagnetic phase at a low temperature is due to the intrinsic magnetic instability of haematite.