William P. Power

Benchmarking quantum control methods on a 12-qubit system

In this Letter, we present an experimental benchmark of operational control methods in quantum information processors extended up to 12 qubits. We implement universal control of this large Hilbert space using two complementary approaches and discuss their accuracy and scalability. Despite decoherence, we were able to reach a 12-coherence state (or a 12-qubit pseudopure cat state) and decode it into an 11 qubit plus one qutrit pseudopure state using liquid state nuclear magnetic resonance quantum information processors.

Synthesis and properties of a new (PEO)x[Na(H2O)]0.25MoO3 nanocomposite

Mono- and bi-layers of polyethylene oxide (PEO) have been incorporated into the interlayer gap of AxMoO3, to give ordered (PEO)x[Na(H2O)n]0.25MoO3 nanocomposites (x= 0.40, mono-; or 0.90, bi-) with interlayer distances of 12.9 and 15 A, respectively. The driving force for the insertion reaction arises from the solvation of the cations by the PEO, together with the increase in entropy resulting from displacement of water molecules from the interlamellar region. We propose a model for the structure of the monolayer and bilayer composites based on X-ray diffraction, 13C/23Na solid-state NMR and IR data. We have carried out a preliminary comparative study of the electrochemical insertion of lithium into the two polymer nanocomposites by using the materials as cathodes in rechargeable lithium batteries. Li can be reversibly inserted into both materials. Lithium ion transport is substantially enhanced in the bilayer nanocomposite as a result of PEO incorporation, compared with the monolayer nanocomposite. The monolayer composite also shows a pronounced decrease in cell capacity on cycling by comparison to the bilayer.

High Resolution Magic Angle Spinning – Applications to Solid Phase Synthetic Systems and Other Semi-Solids

Abstract High resolution magic angle spinning, or HRMAS, is the combined application of high resolution NMR experiments with dipolar- and susceptibility-reducing sample rotation to viscous or gel-like samples. This technique has generated a great deal of activity into applications of NMR to questions of structure in systems ranging from solid phase synthesis to materials, whole cells and tissues. This review introduces the principles of this technique, outlines the specialized NMR experiments it has made possible, then describes applications arising from it over the last ten years, with particular emphasis on the last five years.

Deuteron spin-lattice relaxation times in D2–Ar mixtures: A combined experimental and theoretical study

A combined experimental and theoretical study of the NMR spin-lattice relaxation times for the deuteron of D2 in D2–Ar mixtures is presented. A gas-handling system and a sample cell have been designed and successfully employed in the experimental part of this study. Spin-lattice relaxation times for the deuteron of D2 in D2–Ar mixtures have been measured over the temperature range 180–420 K at several densities and mole fractions, and extrapolation to infinite dilution has been carried out. The quality of the results has been tested by analysis of the one-dimensional spectra. Theoretical values of the spin-lattice relaxation times associated with the D2–Ar interaction have been calculated using the XC(fit) potential energy surface obtained by Bissonnette et al. [J. Chem. Phys. 105, 2639 (1996)]. Two reliable methods have been proposed to compare the theoretical and experimental NMR spin-lattice relaxation times obtained for the equilibrium mixture of the two parity isomers of the D2–Ar system under condit...

Ligand exchange processes of OsHCl(CO)(L)(PR3)2 (L=vacant, H2, R′CN, O2; R=Cy, i-Pr)

Abstract The reactivity of complexes formed by the addition of O2, H2 and R′CN to OsHCl(CO)(PR3)2 (1a:R=Cy; 1b:R=i-Pr) has been examined. Under 24 bar H2 and 65°C, the dioxygen ligand of OsHCl(CO)(O2)(PR3)2 (2a,b) is displaced to yield the trans-hydridodihydrogen complexes OsHCl(η2-H2)(CO)(PR3)2 (3a,b). Measurements of the equilibrium constant, KH2=[3a]/[1a][H2], for the direct addition of H2 to 1a yield ΔH°=−49.1±2.4 kJ/mol and ΔS°=−95.7±7.9 J/mol K. 1a,b react reversibly with aryl and alkyl nitriles to produce the isolable complexes, OsHCl(CO)(R′CN)(PR3)2 (4a,b). The phosphine ligands of 1a,b and 3a,b exchange with unbound, bulky alkyl phosphines at a rate that is slow relative to the NMR timescale. In the presence of excess PCy3, complex 3b yields the exchange products OsHCl(η2-H2)(CO)(Pi-Pr3)(PCy3) and 3a. While a tris-phosphine complex cannot be detected, limited kinetic data characterize the exchange as associative process.

Proton and deuteron spin-lattice relaxation times in HD–Ar mixtures: A combined experimental and theoretical study

A combined experimental and theoretical study of the nuclear magnetic resonance (NMR) spin-lattice relaxation times for the proton and deuteron of HD in HD–Ar mixtures is presented. Spin-lattice relaxation times for the proton and deuteron of HD in HD–Ar mixtures have been measured over the temperature range 180–420 K at several densities and mole fractions, and extrapolation to infinite dilution has been carried out. Theoretical values of the spin-lattice relaxation times associated with the HD–Ar interaction have been calculated using the XC(fit) potential energy surface obtained by Bissonnette et al. [J. Chem. Phys. 105, 2639 (1996)], transformed to allow displacement of the center-of-mass of the HD molecule from its center-of-force. Both experimental and theoretical results show that the density-dependence of the deuteron relaxation times lies in the linear regime, while that of the proton lies in the non-linear regime. The experimental and theoretical results for the relaxation times of the proton ar...

Solid-state 27Al nuclear magnetic resonance investigation of three aluminum-centered dyes

We report the first solid-state 27Al NMR study of three aluminum phthalocyanine dyes: aluminum phthalocyanine chloride, AlPcCl (1); aluminum-1,8,15,22-tetrakis(phenylthio)-29H,31H-phthalocyanine ch...

Experimental and theoretical study of proton spin-lattice relaxation in H2–Ar gas mixtures: Critical examination of the XC(fit) potential energy surface

Proton nuclear magnetic resonance spin-lattice relaxation time measurements have been carried out at 500 MHz proton Larmor frequency on two hydrogen-argon gas mixtures with 1.90% and 3.93% hydrogen at four different temperatures in the range 225 K < T < 337 K and at two different number densities. The results for different hydrogen mole percentages have been extrapolated to infinite dilution to obtain the contributions to the overall relaxation times arising from the hydrogen-argon interaction. The extrapolated relaxation times fall in the reciprocal regime in which relaxation times are inversely proportional to the density. Relaxation times have also been calculated using quantum mechanical close-coupled computations based on the H2-Ar XC(fit) potential energy surface obtained by Bissonnette et al. [J. Chem. Phys. 105, 2639 (1996)]. Significant differences found between the experimental and theoretical results indicate that the short-range anisotropy of the XC(fit) potential surface is too weak. The reciprocal regime is shown to have a much higher sensitivity to changes in the anisotropic component of the intermolecular potential energy surface.

Lewis-base adducts of the diborane(4) compounds B2(1,2-E2C6H4)2(E=O or S)

The reactivity of the diborane(4) compounds B 2 (1,2-E 2 C 6 H 4 ) 2 (E = O or S) have been studied with respect to their ability to co-ordinate Lewis bases, specifically 4-methylpyridine (mpy) and the phosphines PMe 2 Ph and PEt 3 . Four monoadducts have been characterised by X-ray crystallography, namely B 2 (1,2-O 2 C 6 H 4 ) 2 (mpy), B 2 (1,2-S 2 C 6 H 4 ) 2 (mpy), B 2 (1,2-S 2 C 6 H 4 ) 2 (PMe 2 Ph) and B 2 (1,2-S 2 C 6 H 4 ) 2 (PEt 3 ), together with three bis adducts B 2 (1,2-O 2 C 6 H 4 ) 2 (mpy) 2 , B 2 (1,2-S 2 C 6 H 4 ) 2 (mpy) 2 and B 2 (1,2-S 2 C 6 H 4 ) 2 (PMe 2 Ph) 2 . In the former set of compounds the one base is co-ordinated to one boron centre which adopts a tetrahedral geometry, the remaining boron being trigonal planar as in the structure of the parent compound. For the bis adducts each of the two borons is co-ordinated to a mpy or phosphine with both borons tetrahedral. Bond-length changes associated with ligand co-ordination are discussed. Multinuclear solution-state NMR studies have also been performed for solutions containing B 2 (1,2-O 2 C 6 H 4 ) 2 and mpy, B 2 (1,2-S 2 C 6 H 4 ) 2 and mpy and B 2 (1,2-S 2 C 6 H 4 ) 2 and PEt 3 . All of these studies indicate that intermolecular exchange of base between the parent compound, the mono- and the bis-adducts occurs in solution together with intramolecular exchange between the two boron centres in the monoadducts. The various rates of these processes, inasmuch as they have been determined accurately, are discussed and rationalised. The monoadducts B 2 (1,2-O/S 2 C 6 H 4 ) 2 (mpy) are nominally isoelectronic with the phenonium cation.