Kenjiro Hashi

Achievement of 1020 MHz NMR

We have successfully developed a 1020MHz (24.0T) NMR magnet, establishing the worlds highest magnetic field in high resolution NMR superconducting magnets. The magnet is a series connection of LTS (low-Tc superconductors NbTi and Nb3Sn) outer coils and an HTS (high-Tc superconductor, Bi-2223) innermost coil, being operated at superfluid liquid helium temperature such as around 1.8K and in a driven-mode by an external DC power supply. The drift of the magnetic field was initially ±0.8ppm/10h without the (2)H lock operation; it was then stabilized to be less than 1ppb/10h by using an NMR internal lock operation. The full-width at half maximum of a (1)H spectrum taken for 1% CHCl3 in acetone-d6 was as low as 0.7Hz (0.7ppb), which was sufficient for solution NMR. On the contrary, the temporal field stability under the external lock operation for solid-state NMR was 170ppb/10h, sufficient for NMR measurements for quadrupolar nuclei such as (17)O; a (17)O NMR measurement for labeled tri-peptide clearly demonstrated the effect of high magnetic field on solid-state NMR spectra.

1020 MHz single-channel proton fast magic angle spinning solid-state NMR spectroscopy

This study reports a first successful demonstration of a single channel proton 3D and 2D high-throughput ultrafast magic angle spinning (MAS) solid-state NMR techniques in an ultra-high magnetic field (1020MHz) NMR spectrometer comprised of HTS/LTS magnet. High spectral resolution is well demonstrated.

Optical pumping NMR in the compensated semiconductor InP:Fe

The optical pumping nuclear-magnetic-resonance effect in the compensated semiconductor InP:Fe has been investigated in terms of the dependences of photon energy E p , helicity σ ′ , and exposure time τ L of infrared lights.The 3 1 P and 1 5 In signal enhancements show large σ ′ asymmetries and anomalous oscillations as a function of E p . We find that (i) the oscillation period as a function of E p is similar for 3 1 P and 1 1 5 In and almost field independent in spite of significant reduction of the enhancement in higher fields. (ii) A characteristic time for buildup of the 3 1 P polarization under the light exposure shows strong E p dependence, but is almost independent of σ ′ . (iii) The buildup times for 3 1 P and 1 1 5 In are of the same order (10 3 s), although the spin-lattice relaxation times T 1 are different by more than three orders of magnitude between them. The results are discussed in terms of (1) discrete energy spectra due to donor-acceptor pairs in compensated semiconductors and (2) interplay between 3 1 P and dipolar ordered indium nuclei, which are optically induced.

High-Field NMR up to 30 T with a Hybrid Magnet

NMR measurements up to 30 T were performed with the hybrid magnet installed in the National Institute for Materials Science (NIMS). The field profile and stability of superconducting, resistive and their hybrid magnets were measured using 63Cu NMR of a Cu metal. The field homogeneity of the hybrid magnet at 30 T is 186±4 ppm in the region ±5 mm from the field center along the z-axis. The magnetic field fluctuates with a total amplitude of about 30 G at 30 T (100 ppm). The present status of the hybrid magnet for high-resolution solid-state NMR measurements is discussed.

Decoupling-free NMR quantum computer on a quantum spin chain

A method of switching a controlled-NOT gate in a solid-stae NMR quantum computer is presented. Qubits of I = 1/2 nuclear spins are placed periodically along a quantum spin chain (1-D antiferromagnet) having a singlet ground state with a finite spin gap to the lowest excited state caused by some quantum effect. Irradiation of a microwave tuned to the spin gap energy excites a packet of triplet magnons at a specific part of the chain where control and target qubits are involved. The packet switches on the Suhl-Nakamura interaction between the qubits, which serves as a controlled NOT gate. The qubit initialization is achieved by a qubit initializer consisting of semiconducting sheets attached to the spin chain, where spin polarizations created by the optical pumping method in the semiconductors are transferred to the spin chain. The scheme allows us to separate the initialization process from the computation, so that one can optimize the computation part without being restricted by the initialization scheme, which provides us with a wide selection of materials for a quantum computer.

Successful Upgrading of 920-MHz NMR Superconducting Magnet to 1020 MHz Using Bi-2223 Innermost Coil

We succeeded in upgrading the 920-MHz nuclear magnetic resonance (NMR) superconducting magnet (21.6 T) to 1020 MHz (24.0 T) by replacing the innermost Nb3Sn coil with a (Bi,Pb)2Sr2Ca2Cu3O10 (Bi-2223) coil. The 920-MHz NMR spectrometer had been installed in the National Institute for Materials Science, Tsukuba, Japan, in 2001. It has been operated in the persistent mode for six years. The upgrading project started in 2006. A Bi-2223 coil was developed as the innermost coil instead of the Nb3Sn one. The newly installed Bi-2223 innermost coil is connected to Nb3Sn and NbTi coils in series. The upgraded NMR magnet was seriously damaged by the Great East Japan Earthquake in March 2011. After more than two years of restoration and additional improvements of current leads and the power supply system, the magnet was cooled down to below 1.8 K in August 2014. The magnet successfully generated 24.0 T, corresponding to 1020 MHz, in October 2014. To achieve the required homogeneity and stability of the magnetic field, not only superconducting and room-temperature shim coils but also ferromagnetic shims were used. The 1020-MHz superconducting NMR magnet has been operated in a power-supply-driven mode for six months.

Optical Pumping System for a Qubit Initializer in a Solid-state NMR Quantum Computer

We present an optical pumping NMR system working at low temperatures developed for the qubit initialization in a solid-state NMR quantum computer. Demonstrations of the initialization experiments of 31P nuclear spins in InP:Fe at 4.2 K are also presented, where the signal enhancements of 31P by two orders of magnitude compared to that at thermal equilibrium are achieved.

Optical-pumping double-resonance NMR system for semiconductors

We describe an optical-pumping double-resonance NMR system equipped with a single-coil double-tuning (XY) probe with an optical fiber attachment working in a helium-gas flow cryostat. The system enables simultaneous control of an infrared light and two radio-frequency fields irradiated to a sample, so that solid-state NMR techniques such as spin locking, decoupling, and cross polarization can be invoked under the optical-pumping condition. A nuclear hyperpolarization transfer experiment in optically pumped InP:Fe is presented.

NMR study of thermally activated paramagnetism in metallic low-silica X zeolite filled with sodium atoms

We report a \^{23}Na and \^{27}Al nuclear magnetic resonance (NMR) investigation of low-silica X (LSX) zeolite with chemical formula Na_{12}Al_{12}Si_{12}O_{48} (Na_{12}-LSX) loaded with n additional guest sodium atoms. Na_{n}/Na_{12}-LSX exhibits an insulator-to-metal transition around n=11.6, which is accompanied by a significant enhancement of bulk magnetic susceptibility. Paramagnetic moments are thermally activated in the metallic Na_{12}/Na_{12}-LSX with an activation energy of around 0.1 eV. At the same time, a new shifted component (SC) appears in the \^{23}Na NMR, whose large and positive NMR shift scales with bulk magnetic susceptibility. Its spin-lattice relaxation rate 1/T_{1} is governed by the fluctuations determined by the same activation energy as obtained from the bulk magnetic susceptibility data. The timescale of these fluctuations is typical for atomic motions, which suggest strong electron-phonon coupling, a hallmark of polaron states. The insulator-to-metal transition in Na_{n}/Na_{12}-LSX is thus discussed within a polaron model.

Multinuclear solid-state NMR spectroscopy of a paramagnetic layered double hydroxide

NMR spectroscopy is rarely utilized when analytes include paramagnetic ions. We show that multinuclear solid-state NMR is actually potentially useful for investigating nanostructures of a layered double hydroxide (LDH) containing paramagnetic Ni2+ cations. In particular, 13C NMR spectra of interlayer carbonate anions are well resolved by using conventional MAS/DD.