Damir Blazina

Preparing High Purity Initial States for Nuclear Magnetic Resonance Quantum Computing

Here we demonstrate how parahydrogen can be used to prepare a two-spin system in an almost pure state which is suitable for implementing nuclear magnetic resonance quantum computation. A 12 ns laser pulse is used to initiate a chemical reaction involving pure parahydrogen (the nuclear spin singlet of H2). The product, formed on the micros time scale, contains a hydrogen-derived two-spin system with an effective spin-state purity of 0.916. To achieve a comparable result by direct cooling would require an unmanageable (in the liquid state) temperature of 6.4 mK or an impractical magnetic field of 0.45 MT at room temperature. The resulting spin state has an entanglement of formation of 0.822 and cannot be described by local hidden variable models.

Applications of the parahydrogen phenomenon in inorganic chemistry

The study of reaction mechanisms by NMR spectroscopy normally suffers from limitations in sensitivity that arise from the physical constraints of the detection method. An overview is presented of how chemical reactions can be studied using parahydrogen assisted NMR spectroscopy where detected signal strengths can exceed those normally seen by factors of over 28,000.

Photochemical pump and NMR probe: chemically created NMR coherence on a microsecond time scale.

We report pump-probe experiments employing laser-synchronized reactions of para-hydrogen (para-H2) with transition metal dihydride complexes in conjunction with nuclear magnetic resonance (NMR) detection. The pump-probe experiment consists of a single nanosecond laser pump pulse followed, after a precisely defined delay, by a single radio frequency (rf) probe pulse. Laser irradiation eliminates H2 from either Ru(PPh3)3(CO)(H)2 1 or cis-Ru(dppe)2(H)2 2 in C6D6 solution. Reaction with para-H2 then regenerates 1 and 2 in a well-defined nuclear spin state. The rf probe pulse produces a high-resolution, single-scan (1)H NMR spectrum that can be recorded after a pump-probe delay of just 10 μs. The evolution of the spectra can be followed as the pump-probe delay is increased by micro- or millisecond increments. Due to the sensitivity of this para-H2 experiment, the resulting NMR spectra can have hydride signal-to-noise ratios exceeding 750:1. The spectra of 1 oscillate in amplitude with frequency 1101 ± 3 Hz, the chemical shift difference between the chemically inequivalent hydrides. The corresponding hydride signals of 2 oscillate with frequency 83 ± 5 Hz, which matches the difference between couplings of the hydrides to the equatorial (31)P nuclei. We use the product operator formalism to show that this oscillatory behavior arises from a magnetic coherence in the plane orthogonal to the magnetic field that is generated by use of the laser pulse without rf initialization. In addition, we demonstrate how chemical shift imaging can differentiate the region of laser irradiation thereby distinguishing between thermal and photochemical reactivity within the NMR tube.

New insights into catalytic hydrogenation by phosphido-substituted triruthenium clusters: confirmation of intact cluster catalysis by parahydrogen NMR

The phosphido-substituted triruthenium cluster Ru(3)(CO)(9)(mu-H)(micro-PPh(2)) is shown to react with H(2) to form the trihydride cluster Ru(3)(CO)(9)(H)(mu-H)(2)(mu-PPh(2)), which undergoes a number of re-arrangement reactions on heating to yield other phosphido-substituted triruthenium clusters. In the presence of alkyne substrates, heating the system leads to catalytic hydrogenation via CO loss and the formation of a Ru(3)(eta(2)-PhC[double bond, length as m-dash]CHPh)(CO)(8)(micro-H)(PHPh(2)) resting state, in a reaction affected by the polarity of the solvent. No mononuclear fragments are observed in the catalytic transformation, confirming directly that the phosphido ligand is able to exert a stabilising influence on the cluster core.

Implementation of NMR quantum computation with parahydrogen-derived high-purity quantum states

We demonstrate the implementation of a quantum algorithm on a liquid-state NMR quantum computer using almost pure states. This was achieved using a two-qubit device where the initial state is an almost pure singlet nuclear spin state of a pair of

Practical implementations of twirl operations

^{1}\mathrm{H}

A combined parahydrogen and theoretical study of H2 activation by 16-electron d8 ruthenium(0) complexes and their subsequent catalytic behaviour

nuclei arising from a chemical reaction involving parahydrogen. We have implemented Deutschs algorithm for distinguishing between constant and balanced functions with a single query.

On the products obtained from reaction of rac-diphenyl[2.2]para-cyclophanylphosphine with (cycloocta-1,5-diene)palladium(II)chloride

Twirl operations, which convert impure singlet states into Werner states, play an important role in many schemes for entanglement purification. In this paper we describe strategies for implementing twirl operations, with an emphasis on methods suitable for ensemble quantum information processors such as nuclear magnetic resonance (NMR) quantum computers. We implement our twirl operation on a general two-spin mixed state using liquid-state NMR techniques, demonstrating that we can obtain the singlet Werner state with high fidelity.

The Study of Inorganic Systems by NMR Spectroscopy in Conjunction with Parahydrogen‐Induced Polarisation

The photochemical reaction of Ru(CO)(3)(L)(2), where L = PPh(3), PMe(3), PCy(3) and P(p-tolyl)(3) with parahydrogen (p-H(2)) has been studied by in-situ NMR spectroscopy and shown to result in two competing processes. The first of these involves loss of CO and results in the formation of the cis-cis-trans-L isomer of Ru(CO)(2)(L)(2)(H)(2), while in the second, a single photon induces loss of both CO and L and leads to the formation of cis-cis-cis Ru(CO)(2)(L)(2)(H)(2) and Ru(CO)(2)(L)(solvent)(H)(2) where solvent = toluene, THF and pyridine (py). In the case of L = PPh(3), cis-cis-trans-L Ru(CO)(2)(L)(2)(H)(2) is shown to be an effective hydrogenation catalyst with rate limiting phosphine dissociation proceeding at a rate of 2.2 s(-1) in pyridine at 355 K. Theoretical calculations and experimental observations show that H(2) addition to the Ru(CO)(2)(L)(2) proceeds to form cis-cis-trans-L Ru(CO)(2)(L)(2)(H)(2) as the major product via addition over the pi-accepting OC-Ru-CO axis.

NMR studies of Ru(3)(CO)(10)(PMe(2)Ph)(2) and Ru(3)(CO)(10)(PPh(3))(2) and their H(2) addition products: detection of new isomers with complex dynamic behavior.

The reaction of Pd(cod)Cl-2 (cod = cycloocta-1,5-diene) with 1 and 2 equiv. of rac-diphenyl[2.2]paracyclophanylphosphine, rac-PPh2(C16H15), affords the dimer [Pd{PPh2(C16H15)}Cl-2](2) (1) and the square-planar complex trans-Pd{PPh2(C16H15)}(2)Cl-2 (2), respectively. In solution the dimer undergoes a fluxional process which has been probed by NMR and involves isomerisation between pseudo-trans- and cis-conformations. The structures of trans -[Pd{Ph-2(C16H15)}Cl-2](2) (1a) and 2 have been established by single crystal X-ray diffraction; the structure of the dimer is severely disordered. In addition, co-crystals containing both these complexes and solvate molecules have been isolated and their structures established by single crystal X-ray diffraction. The structure of the monomer in the homonuclear and co-crystals are not too dissimilar whereas the structure the dimer has a significantly different structure in the homonuclear and co-crystals. In the homonuclear crystal the central Pd2Cl2 unit has a dihedral angle of 26.5degrees between the two planes whereas the Pd2Cl2 unit in the co-crystals is planar