Spin-lattice relaxation of laser-polarized xenon in human blood

The nuclear spin polarization of 129Xe can be enhanced by several orders of magnitude by using optical pumping techniques. The increased sensitivity of xenon NMR has allowed imaging of lungs as well as other in vivo applications. The most critical parameter for efficient delivery of laser-polarized xenon to blood and tissues is the spin-lattice relaxation time (T1) of xenon in blood. In this work, the relaxation of laser-polarized xenon in human blood is measured in vitro as a function of blood oxygenation. Interactions with dissolved oxygen and with deoxyhemoglobin are found to contribute to the spin-lattice relaxation time of 129Xe in blood, the latter interaction having greater effect. Consequently, relaxation times of 129Xe in deoxygenated blood are shorter than in oxygenated blood. In samples with oxygenation equivalent to arterial and venous blood, the 129Xe T1s at 37°C and a magnetic field of 1.5 T were 6.4 s ± 0.5 s and 4.0 s ± 0.4 s, respectively. The 129Xe spin-lattice relaxation time in blood decreases at lower temperatures, but the ratio of T1 in oxygenated blood to that in deoxygenated blood is the same at 37°C and 25°C. A competing ligand has been used to show that xenon binding to albumin contributes to the 129Xe spin-lattice relaxation in blood plasma. This technique is promising for the study of xenon interactions with macromolecules.

The dynamics of fields of higher spin /

Mode of access: Internet.

G-factor and donor spin-lattice relaxation for electrons in germanium and silicon.

"This group report is based on an article submitted to the Physical review."

Applications of spin resonance techniques to the study of radiation effects,

Includes bibliography.

Global control and fast solid-state donor electron spin quantum computing

We propose a scheme for quantum information processing based on donor electron spins in semiconductors, with an architecture complementary to the original Kane proposal. We show that a naive implementation of electron spin qubits provides only modest improvement over the Kane scheme, however through the introduction of global gate control we are able to take full advantage of the fast electron evolution timescales. We estimate that the latent clock speed is 100-1000 times that of the nuclear spin quantum computer with the ratio T-2/T-ops approaching the 10(6) level.

Utilização de pulsos de radiofrequência fortemente modulados no processamento de informação quântica via ressonância magnética nuclear

Nesta dissertação apresentamos um trabalho de desenvolvimento e utilização de pulsos de radiofreqüência modulados simultaneamente em freqüência, amplitude e fase (pulsos fortemente modulados, SMP, do inglês Strongly Modulated Pulses) para criar estados iniciais e executar operações unitárias que servem como blocos básicos para processamento da informação quântica utilizando Ressonância Magnética Nuclear (RMN). As implementações experimentais foram realizas em um sistema de 3 q-bits constituído por spins nucleares de Césio 133 (spin nuclear 7/2) em uma amostra de cristal líquido em fase nemática. Os pulsos SMP´s foram construídos teoricamente utilizando um programa especialmente desenvolvido para esse fim, sendo o mesmo baseado no processo de otimização numérica Simplex Nelder-Mead. Através deste programa, os pulsos SMP foram otimizados de modo a executarem as operações lógicas desejadas com durações consideravelmente menores que aquelas realizadas usando o procedimento usual de RMN, ou seja, seqüências de pulsos e evoluções livres. Isso tem a vantagem de reduzir os efeitos de descoerência decorrentes da relaxação do sistema. Os conceitos teóricos envolvidos na criação dos SMPs são apresentados e as principais dificuldades (experimentais e teóricas) que podem surgir devido ao uso desses procedimentos são discutidas. Como exemplos de aplicação, foram produzidos os estados pseudo-puros usados como estados iniciais de operações lógicas em RMN, bem como operações lógicas que foram posteriormente aplicadas aos mesmos. Utilizando os SMP\'s também foi possível realizar experimentalmente os algoritmos quânticos de Grover e Deutsch-Jozsa para 3 q-bits. A fidelidade das implementações experimentais foi determinadas utilizando as matrizes densidade experimentais obtidas utilizando um método de tomografia da matriz densidade previamente desenvolvido.

Theoretical investigations of the two-bond proton-carbon-13 coupling constants. Angular variations of the couplings involving carboxyl carbon

A formulation has been developed using perturbation theory to evaluate the π-contribution to the nuclear spin coupling constants involving nuclei at least one of which is an unsaturated center. This fromulation accounts for the π-contribution in terms of the core polarization and one-center exchange at the π-center. The formulation developed together with the Dirac vector model and Penney-Dirac bond-order formalisms was employed to calculate the geminal (two-bond) proton coupling constants of carboxyl carbons in α-disubstituted acetic acids. The calculated coupling constants were found to have an orientational dependence. The results of the calculation are in good agreement with the experimental values.

Hyperfine structure in the ESR spectra of exchange-coupled pairs—copper diethyidithiocarbamate

A study of the hyperfine interaction in the ESR of coupled Cu---Cu pairs in single crystals of copper diethyldithiocarbamate as a function of temperature has shown distinct differences in the hyperfine structure in the two fine-structure transitions at 20 K; the spectrum does not have the usual binomial hyperfine pattern for the fine-structure transition of the low field in contrast to that of the high field. The details of the structure of both fine-structure transitions in the 20-K spectrum can be explained by recognizing the fact that the mixing of the nuclear spin states caused by the anisotropic hyperfine interaction affects the electron spin states |+1 and |−1 differently. The anomalous hyperfine structure is found to become symmetric at 77 and 300 K. It is proposed that the reason for this lies in the dynamics of spin-lattice interaction, which limits the lifetime of the spin states in each of the electronic levels |−1 , |0 , and |+1 . The estimate of spin-lattice relaxation time in the temperature range where the changes are observed agrees with those indicated by other studies. The model proposed here for the hyperfine interaction of pairs in the electronic triplet state is of general validity.

ESR study of exchange coupled pairs in copper diethyldithiocarbamate—explanation of the low temperature hyperfine anomaly

A study of the hyperfine interaction in the ESR of Cu-Cu pairs in single crystals of copper diethyldithiocarbamate as a function of temperature has shown distinct differences in the hyperfine structure in the two fine structure transitions at 20 K, the spectrum not having the same hyperfine intensity pattern in the low field fine structure transition in contrast to that of the high field transition. The details of the structure of both the fine structure transitions in the 20 K spectrum have now been explained by recognizing the fact that the mixing of the nuclear spin states caused by the anisotropic hyperfine interaction affects the electron spin states | + 1 > and | −> differently. This has incidentally led to a determination of the sign ofD confirming the earlier model. The anomalous hyperfine structure is found to become symmetric at 77 K and 300 K. It is proposed that the reason for this lies in the dynamics of spin-lattice interaction which limits the lifetime of the spin states in each of the electronic levels | − 1 >, | 0 > and | + 1 > The estimate of spin-lattice relaxation time agrees with those indicated from other studies. The model proposed here for the hyperfine interaction of pairs in the electronic triplet state is of general validity.

N-H center dot center dot center dot F hydrogen bonds in fluorinated benzanilides: NMR and DFT study

Using F-19 and H-1-NMR (with N-14 decoupling) spectroscopic techniques together with density functional theoretical (DFT) calculations, we have investigated weak molecular interactions in isomeric fluorinated benzanilides. Simultaneous presence of through space nuclear spin-spin couplings ((1h)J(N-H center dot center dot center dot F)) of diverse strengths and feeble structural fluctuations are detected as a function of site specific substitution of fluorine atoms within the basic identical molecular framework. The transfer of hydrogen bonding interaction energies through space is established by perturbing their strengths and monitoring the effect on NMR parameters. Multiple quantum (MQ) excitation, up to the highest possible MQ orders of coupled protons, is utilized as a tool for accurate H-1 assignments. Results of NMR studies and DFT calculations are compared with the relevant structural parameters taken from single crystal X-ray diffraction studies.

Influence of cross-correlation between dipolar and chemical shift anisotropy relaxation mechanisms upon the transverse relaxation rates of 15N in macromolecules

Heteronuclear multiple-quantum coherence relaxation rate are calculated for the individual transitions of the S spin in an AIS nuclear spin system assuming that the heteronucleus (S spin) has relaxation contributions from both intramolecular dipole-dipole and chemical shift anisotropy relaxation. The individual multiplet components of the heteronuclear zero- and double-quantum coherences are shown to have different transverse relaxation rates. The cross-correlation between the two relaxation mechanisms is shown to be the dominant cause of the calculated differential line broadening. Experimental data are presented using as an example a uniformly 15N labelled sample of human epidermal growth factor.

Evolution of quantum discord and its stability in two-qubit NMR systems

We investigate evolution of quantum correlations in ensembles of two-qubit nuclear spin systems via nuclear magnetic resonance techniques. We use discord as a measure of quantum correlations and the Werner state as an explicit example. We, first, introduce different ways of measuring discord and geometric discord in two-qubit systems and then describe the following experimental studies: (a) We quantitatively measure discord for Werner-like states prepared using an entangling pulse sequence. An initial thermal state with zero discord is gradually and periodically transformed into a mixed state with maximum discord. The experimental and simulated behavior of rise and fall of discord agree fairly well. (b) We examine the efficiency of dynamical decoupling sequences in preserving quantum correlations. In our experimental setup, the dynamical decoupling sequences preserved the traceless parts of the density matrices at high fidelity. But they could not maintain the purity of the quantum states and so were unable to keep the discord from decaying. (c) We observe the evolution of discord for a singlet-triplet mixed state during a radio-frequency spin-lock. A simple relaxation model describes the evolution of discord, and the accompanying evolution of fidelity of the long-lived singlet state, reasonably well.

Magnetometry using Ramsey interferometry in a Yb atomic beam

We use the Ramsey separated oscillatory fields technique in a 400 degrees C thermal beam of ytterbium (Yb) atoms to measure the Larmor precession frequency (and hence the magnetic field) with high precision. For the experiment, we use the strongly allowed S-1(0) P-1(1) transition at 399 nm, and choose the odd isotope Yb-171 with nuclear spin I = 1/2, so that the ground state has only two magnetic sublevels m(F) = +/- 1/2. With a magnetic field of 22.2 G and a separation of about 400 mm between the oscillatory fields, the central Ramsey fringe is at 16.64 kHz and has a width of 350 Hz. The technique can be readily adapted to a cold atomic beam, which is expected to give more than an order-of-magnitude improvement in precision. The signal-to-noise ratio is comparable to other techniques of magnetometry; therefore it should be useful for all kinds of precision measurements such as searching for a permanent electric dipole moment in atoms.

In Situ NMR Insights into the Electrochemical Reaction of Cu3P Electrodes in Lithium Batteries

This study reports a multinuclei in situ (real-time) NMR spectroscopic characterization of the electrochemical reactions of a negative Cu3P electrode toward lithium. Taking advantage of the different nuclear spin characteristics, we have obtained real-time P-31 and Li-7 NMR data for a comprehensive understanding of the electrochemical mechanism during the discharge and charge processes of a lithium battery. The large NMR chemical shift span of P-31 facilitates the observation of the chemical evolutions of different lithiated and delithiated LixCu3-xP phases, whereas the quadrupolar line features in Li-7 enable identification of asymmetric Li sites. These combined NMR data offer an unambiguous identification of four distinct LixCu3-xP phases, Cu3P, Li0.2Cu2.8P, Li2CuP, and. Li3P, and the characterization of their involvement in the electrochemical reactions. The NMR data led us to propose a delithiation process involving the intercalation of metallic Cu-0 atomic aggregates into the Li2CuP structure to form a Cu-0-Li2-xCu1-xP phase. This process might be responsible for the poor capacity retention in Cu3P lithium batteries when cycled to a low voltage.

Dilution refrigeration and a calorimetric measurement of the quadruple coupling constant in rhenium metal

A dilution refrigerator has been constructed capable of producing steady state temperatures less than .075°K. The first part of this work is concerned with the design and construction of this machine. Enough theory is presented to allow one to understand the operation and critical design factors of a dilution refrigerator. The performance of our refrigerator is compared with the operating characteristics of three other dilution refrigerators appearing in the present literature.

The dilution refrigerator constructed was used to measure the nuclear contribution to the low temperature specific heat of a pure, single-crystalline sample of rhenium metal. Measurements were made in magnetic fields from 0 to 12.5 kOe for the temperature range .13°K - .52°K. The second part of this work discusses the results of these experiments. The expected nuclear contribution is not found when the sample is in the superconducting state. This is believed to be due to the long spin-lattice relaxation times in superconductors. In the normal state, for the temperature range studied, the nuclear contribution is given by A/T² where A = .061 ± .002 millijoules-K/mole. The value of A is found to increase to A = .077 ± .004 millijoules-K/mole when the sample is located in a magnetic field of 12.5 kOe.

From the measured value of A the splitting of the energy levels of the nuclear spin system due to the interaction of the internal crystalline electric field gradients with the nuclear quadrupole moments is calculated. A comparison is made between the predicted and measured magnetic dependence of the specific heat. Finally, predictions are made of future nuclear magnetic resonance experiments which may be performed to check the results obtained by calorimetery here and further, to investigate existing theories concerning the sources of electric field gradients in metals.