Multiple quantum transfer echo

Chapter 6 introduces the product operator formalism for analysing NMR experiments. This approach is quantum mechanical, in contrast to the semi-classical approach taken by the vector model. We will see that the formalism is well adapted to describing pulsed NMR experiments, and that despite its quantum mechanical rigour it retains a relatively intuitive approach. Using product operators we can describe important phenomena such as the evolution of couplings during spin echoes, coherence transfer and the generation of multiple quantum coherences. 

The sequence shown opposite can be used to generate multiple quantum coherence from equilibrium magnetization during the spin echo anti-phase magnetization develops and the final pulse transfers this into multiple quantum coherence. Let us suppose that we wish to generate double quantum, with p = 2, as show by the CTP opposite. 

When dealing with homonuclear multiple-spin systems, polarization transfer in the zero-quantum subspace of the effective dipolar Hamiltonian is advantageous as the spin dynamics of the process may be described by a kinetic matrix. The USEME (unified spin echo and magic echo) and RIL (rotating/laboratory frame) sequences follow this zero-quantum-subspace philosophy and aim at broadband properties of the pulse sequence. 

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