Microwave-Free Dynamic Nuclear Polarization via Sudden Thermal Jumps
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Abstract:
Dynamic nuclear polarization (DNP) presently stands as the preferred strategy to enhance the sensitivity of nuclear magnetic resonance measurements, but its application relies on the use of high-frequency microwave to manipulate electron spins, an increasingly demanding task as the applied magnetic field grows. Here we investigate the dynamics of a system hosting a polarizing agent formed by two distinct paramagnetic centers near a level anticrossing. We theoretically show that nuclear spins polarize efficiently under a cyclic protocol that combines alternating thermal jumps and radio-frequency pulses connecting hybrid states with opposite nuclear and electronic spin alignment. Central to this process is the difference between the spin-lattice relaxation times of either electron spin species, transiently driving the electronic spin bath out of equilibrium after each thermal jump. Without the need for microwave excitation, this route to enhanced nuclear polarization may prove convenient, particularly if the polarizing agent is designed to feature electronic level anticrossings at high magnetic fields.Keywords:
Thermal equilibrium
The spin polarization of conduction electrons in a paramagnetic layer due to an adjacent magnetic layer has been derived based on the mixing interaction between the local and conduction electrons. Specifically, based on the band structure of paramagnetic chromium, we have calculated the spin polarization in a Cr layer on Fe(100) substrates. The results are in reasonably good agreement with recent experimental data.
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Thermal equilibrium
Lattice (music)
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Diamagnetism
Crystal (programming language)
Atmospheric temperature range
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The considered system of parallel spins of different magnitudes with random distribution of spins requires statistical approach to the problem. So, we can find the most probable distribution. Using this distribution we substitute the system of random spins with simple system having the spins of equal magnitude, whose properties can be determined by usual methods.
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Feature (linguistics)
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Quantum number
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A perturbation method deals with dipolar coupling spins in solids is presented. As examples of the application the method, the multile-quantum coherence dynamics in clusters of a linear chain of four nuclear spins and a ring of six spins coupled by dipole-dipole interaction are considered. The calculated 0Q- and 2Q intensities in a linear chain of four nuclear spins and 6Q intensity in a ring of six spins vs the duration of the preparation period agree well with the exact solutions (for linear chain of four nuclear spins) and simulation data (for linear chain of four nuclear spins and a ring of six spin).
Magnetic dipole–dipole interaction
Residual dipolar coupling
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We give a complete analysis of covariant measurements on two spins. We consider the cases of two parallel and two antiparallel spins, and we consider both collective measurements on the two spins and measurements that require only local quantum operations and classical communication (LOCC). In all cases we obtain the optimal measurements for arbitrary fidelities. In particular, we show that if the aim is to determine as accurately as possible the direction in which the spins are pointing, it is best to carry out measurements on antiparallel spins (as already shown by Gisin and Popescu), second best to carry out measurements on parallel spins, and worst to be restricted to LOCC measurements. If the aim is to determine as accurately as possible a direction orthogonal to that in which the spins are pointing, it is best to carry out measurements on parallel spins, whereas measurements on antiparallel spins and LOCC measurements are both less suitable but equivalent.
Antiparallel (mathematics)
Carry (investment)
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