Daisuke Shiomi

Molecular electron-spin quantum computers and quantum information processing: pulse-based electron magnetic resonance spin technology applied to matter spin-qubits

Pulse-based Electron–Nuclear and ELectron–electron DOuble Resonance (ENDOR/ELDOR) techniques have been applied to molecular spins in order to implement ensemble electron spin-qubit based quantum computers/computing (QC) and quantum information processing (QIP) in the solid state. Pulsed ENDOR-based QC/QIP experiments for super dense coding (SDC) have for the first time been carried out by the use of molecular electron- and nuclear-spin entities such as the stable malonyl radical as matter spin-qubits. The spin-qubit manipulation technology for quantum gate operations in this work is based on the time-proportional-phase-increment (TPPI) technique, enabling us to distinguish between the phases of spin-qubit based entangled states. The TPPI technique, as firstly applied by Mehring et al. (M. Mehring, J. Mende and W. Scherer, Phys. Rev. Lett., 2003, 90, 153001), has illustrated the establishment of quantum entanglement between electron- and nuclear-spin states and mutual interconversion between the electron–nuclear Bell states. The electron-spin 4π-periodicity in phase shows up in the QC/QIP experiments, explicitly and experimentally illustrating the electron-spin spinor nature for the first time. Tripartite QC experiments have been made, showing the occurrence of separable states. Also, the development of novel electron-spin technology to manipulate multi-electron spin-qubits is described. In this work, the pulsed coherent-dual ELDOR for QC/QIP has for the first time been implemented by invoking a novel microwave dual phase-rotation technique. Thus, applications of the coherent-dual ELDOR to molecular electron spin-qubit systems are also discussed, emphasising designing the molecular two electron-qubit systems appropriate for QC/QIP. g- and/or hyperfine A-tensor engineering approaches give us the two- and multi-electron-qubit systems, which have been a materials challenge to implement matter spin-qubit based QC/QIP. The targeted matter spin-qubits can be used to facilitate selective resonant microwave excitations achieved by the pulsed ELDOR technique. In addition to DiVincenzos five criteria, general requisites for scalable electron spin-qubit systems as 1D periodic robust spin structures are described. According to the requisites, double- or triple-stranded helicates embedding open-shell metal cations are proposed instead of organic molecular spin-qubits.

A New Ferrimagnet Based on a Radical-Substituted Radical Cation Salt

Radical-substituted radical cations are attractive spin building blocks of molecule-based magnets. The introduction of an additional spin as a counteranion provides a unique three-spin system wherein the magnetic interactions between the spins of the radical substituent and the radical cation (J(intra)) and those between the spins of the radical cation and the anion (J(inter)) play decisive roles in determining the magnetic properties of the system. We report the first demonstration of a ferrimagnet by utilizing a large-J(intra) system, nitronyl nitroxide-substituted dihydrophenazine radical cation (NNDPP(*+)) in combination with tetrabromoferrate (FeBr(4)(-)) as the counteranion. On the basis of measurements of dc and ac magnetic susceptibilities and heat capacity, the magnetic properties of NNDPP(*+) x FeBr(4)(-) are elucidated to be those of a three-dimensional long-range-ordered ferrimagnet with T(c) = 6.7 K.

Macrocyclic High‐Spin (S=2) Molecule: Spin Identification of a Sterically Rigid Metacyclophane‐Based Nitroxide Tetraradical by Two‐Dimensional Electron Spin Transient Nutation Spectroscopy

36. Molecular electron-spin quantum computers and quantum information processing: Pulse-based electron magnetic resonance spin technology applied to matter spin-qubits Sato, K.; Nakazawa, S.; Rahimi, R.; Ise, T.; Nishida, S.; Yoshino, T.; Mori, N.; Toyota, K.; Shiomi, D.; Yakiyama, Y.; Morita, Y.; Kitagawa, M.; Nakasuji, K.; Nakahara, M.; Hara, H.; Carl, P.; Höfer, P.; Takui, T. J. Mater. Chem., in press.

Preparation, structure, and magnetic interaction of a Mn(hfac)2-bridged [2-(3-pyridyl)(nitronyl nitroxide)–Mn(hfac)2]2 chain complex

A new one-dimensional chain complex, Mn(hfac)(2)-bridged [2-(3-pyridyl)(nitronyl nitroxide)Mn(hfac)(2)](2), was prepared and its structure and magnetic properties were elucidated; the complex exhibited a large antiferromagnetic interaction of J(1)=-185 K between the three Mn(ii) atoms and the two nitronyl nitroxides to give S=13/2 spin units and a small ferromagnetic interaction of J(3)=+0.02 K between these spin units at low temperatures (50-1.9 K), compatible with the theoretical analysis for model compounds.

Pyrene-Dihydrophenazine Bis(Radical Cation) in a Singlet Ground State

A new pyrene-dihydrophenazine dyad was prepared. Oxidation of the neutral species produced a bis(radical cation) species, which was characterized by the absorptions of their component radical cations in the visible region. A thermally accessible triplet state was observed in the ESR measurement in frozen n-PrCN. The energy gap between the singlet and triplet states was determined to be 2J/k(B) = -36 +/- 3 K.

A guanine-substituted nitronyl nitroxide radical forming a one-dimensional ferromagnetic chain

A stable guanine-substituted nitronyl nitroxide radical 1 has been synthesized and characterized. The single-crystal structure analyses and magnetic susceptibility measurements exhibit a one-dimensional architecture of guanine base resulting from carbonyl-amino hydrogen bonds in the solid state, giving a 1D ferromagnetic chain of the radical moieties.

Cytosine–guanine base pairing in a hydrogen-bonded complex of stable open-shell molecules with S = 1 spins

A bio-inspired motif of hydrogen-bonded nucleobases is introduced to stable organic biradical crystals. We have synthesized a hydrogen-bonded complex based on both a cytosine-substituted nitronyl nitroxide biradical (1) and a closed-shell alkyl-substituted guanine (2). From single-crystal X-ray structure analyses, the cytosine and guanine moieties are found to form a Watson–Crick pair with threefold hydrogen bonds. Magnetic susceptibility measurements reveal that the cytosine-substituted biradical 1 has a triplet (S = 1) ground state with a singlet–triplet energy gap of 2J/kB = 27.0 K. This complex is the first example of Watson–Crick type base pair possessing stable high-spin organic radical moieties, which is fully characterized by single-crystal X-ray structure analysis. A face-to-face overlapping is found between the planar nucleobases, while side-by-side hydrogen bonds are found between the Watson–Crick pairs. Thus, the introduction of the radical substituent into the nucleobase results in little disturbance to the molecular arrangement usually found in nucleobase molecules: the ground-state spin multiplicity of biradical 1 is maintained.