Norikazu Mizuochi

Robust entanglement at room temperature is a necessary requirement for practical applications in quantum technology. We demonstrate the creation of bipartite- and tripartite-entangled quantum states in a small quantum register consisting of individual 13C nuclei in a diamond lattice. Individual nuclear spins are controlled via their hyperfine coupling to a single electron at a nitrogen-vacancy defect center. Quantum correlations are of high quality and persist on a millisecond time scale even at

The dynamics of single electron and nuclear spins in a diamond lattice with different $^{13}\text{C}$ nuclear spin concentration is investigated. It is shown that coherent control of up to three individual nuclei in a dense nuclear spin cluster is feasible. The free-induction decays of nuclear spin Bell states and single nuclear coherences among $^{13}\text{C}$ nuclear spins are compared and analyzed. Reduction in a free-induction-decay time ${T}_{2}^{\ensuremath{\ast}}$ and a coherence time ${T

The ${T}_{V2a}$ center, which was suggested to be the excited triplet state $(S=1)$ of the neutral silicon vacancy related defect [S\"orman et al., Phys. Rev. B $61,$ 2613 (2000)] in the electron-irradiated n-type $4H\ensuremath{-}\mathrm{SiC}$ has been studied by continuous wave and pulsed electron paramagnetic resonance (EPR). The spin multiplicity of ${T}_{V2a}$ has been determined to be quartet $(S=3/2)$ by the nutation method of pulsed EPR technique. From the temperature dependence of the s

The bisadduct of fullerene (1) having two nitroxide radicals at the trans-3 position was newly synthesized. The ground and photoexcited states of 1 were studied by continuous-wave and pulsed two-dimensional electron paramagnetic resonance spectroscopy. An exchange interaction between the radicals was evaluated to be much smaller than an isotropic hyperfine splitting, showing a doublet (S = 1/2) character in the ground state. It was found from a 2D nutation spectrum that a photoexcited state has

Photoexcited states of 3,4-fulleropyrrolidine-2-spiro-4‘-[2‘,2‘,6‘,6‘-tetramethyl]piperidine-1‘-oxyl (1) were studied by the two-dimensional (2D) EPR nutation method in toluene glass. 2D nutation spectra were observed by varying a pulse length of the first microwave pulse in the spin echo experiment. Three kinds of nutation frequencies were obtained from analyses of the 2D spectra and assigned to those of the excited quartet and doublet states on the basis of the fictitious spin-1/2 theory. The

In this paper, we unambiguously re-determine the spin multiplicity of ${T}_{V2a}$ by pulsed electron nucleus double resonance technique. The ${T}_{V2a}$ center is one of the most commonly observed defects in $4H$-SiC, and its origin was identified as one belonging to a class of negatively charged silicon vacancy by means of continuous-wave electron paramagnetic resonance (EPR) and the two-dimensional nutation method of pulsed EPR technique. However, a model with the spin multiplicity of triplet

The isolated negatively charged silicon vacancy ${(V}_{\mathrm{Si}}^{\ensuremath{-}})$ in the hexagonal lattices of $4H$- and $6H\ensuremath{-}\mathrm{SiC}$ has been studied by electron paramagnetic resonance (EPR). The local structure was suggested to have ${T}_{d}$ symmetry from the isotropic g value within the resolution of the conventional X-band measurements, from the isotropic ${}^{29}\mathrm{Si}$ hyperfine interaction of the next-nearest-neighbor silicon atoms and from the absence of the

An electron paramagnetic resonance (EPR) study of 3,4-fulleropyrrolidine-2-spiro-4′[2′,2′,6′,6′-tetramethyl]piperidine-1′-oxyl (1) was performed on the photoexcited quartet state in toluene glass. The spectrum of the |S,Ms〉=|3/2,±3/2〉⇔|3/2,±1/2〉 transitions was observed selectively by using a two-dimensional (2D) nutation method and analyzed with a spectral simulation in a randomly oriented system. A position of the nitroxide moiety was determined with respect to the zero-field splitting (zfs) a

Recently, ultrashort laser processing has attracted attention for creating nitrogen-vacancy (NV) centers because this method can create single NV centers in spatially-controlled positions, which is an advantage for quantum information devices. On the other hand, creating high-density NV centers in a wide region is also important for quantum sensing because the sensitivity is directly enhanced by increasing the number of NV centers. A recent study demonstrated the creation of high-density NV cent