Search Results

This chapter discusses the use of multiple quantum coherence as a vehicle for imprinting phase information arising from translational dynamics, along with limitations imposed by transfer efficiency and relaxation. It presents examples from the use of dipolar, quadrupolar, and homo- and hetero-scalar coupling interactions, along with suitable pulse sequences and discusses the use of specially prepared singlet states to provide extended timescale for diffusion measurement. The chapter also traverses the role of quantum coherence arising from intra-molecular dipolar interactions in determining the signal observed in liquids, with an examination of the validity of the High Temperature Approximation for the equilibrium density matrix. Multiple echo and CRAZED experiments are explained and the role of symmetry discussed, along with reference to the use of intra-molecular dipolar interaction effects in structural studies.

Nuclear magnetic resonance (NMR) exploits the interaction of nuclei with magnetic fields. A strong static field is applied to polarise the nuclear magnetic moments, time-dependent magnetic radio frequency fields are used to stimulate the spectroscopic response, and magnetic-field gradients are needed to obtain spatial resolution. Following the description of the different magnetic fields used in NMR spectroscopy and imaging, the behaviour of magnetic nuclei exposed to these fields is treated first in terms of the classic vector model, and then the density-matrix concept is introduced. The latter is required to describe the couplings among nuclei, for example, the dipole-dipole interaction which dominates the ¹H NMR spectrum of most solid materials. In addition, knowledge of the density matrix is helpful to understand multi-quantum coherences as well as the imaging methods developed for investigations of solid materials.

This chapter describes a method to control and measure quantum cavities, achieved using a superconducting phase qubit, a type of electronic atom. The phase qubit has been under intensive development for use as a quantum processing element in a quantum computer. It has recently been used to demonstrate the quantum control and measurement of excitations in resonant cavities, including controlling photons in superconducting microwave resonators, as well as phonons in microwave-frequency mechanical resonators. The discussion here focuses on the quantum control of electromagnetic resonators.