Understanding Intermolecular Multiple-Quantum Coherences and Their Applications.

Bernard M. Siow, Sun, L, Andrew Matthew Blamire

Arman Kussainov

Christian Kerskens, David López Pérez

Abstract We have recently suggested a proposal to explore non-classicality in the brain, for which we developed an entanglement witness protocol using MRI. The witness protocol intended to find spin interactions which could not be explained by classical interactions, based on intermolecular multiple quantum coherence (iMQC). As for Warren’s comments, we show in more detail that this was indeed the case; our observations were certainly not generated by interactions based on the iMQC model. Further, we discuss some additional details not present in the original paper.

Arun K. Setty

Rainer Kimmich, Ioan Ardelean

In recent years evidence was presented that two radio frequency pulses in combination with suitably matched field gradient pulses produce cross peaks in two-dimensional NMR spectroscopy that reveal all the features of multiple-quantum/single-quantum coherence transfer signals. This experiment was termed CRAZED by Warren et al. Quite amazingly, identical signals were predicted on a purely classical basis. Thus the intriguing question arises whether this means that a classical analog to multiple-quantum coherences exists. In this study we show that this is clearly not the case. Coherence pathways of a purely single-quantum basis are excited anyway and lead independently to superimposed identical signals in parallel. Moreover, the observation of CRAZED signals per se neither disproves the adequacy of the high-temperature approximation, which was questioned in this context, nor proves a strong influence of intermolecular multiple-quantum coherences. However, the indispensable prerequisite for the description of the manifold CRAZED phenomena is that long-range dipolar interactions are taken into account either explicitly or in the continuous-limit form.

Ding Shang

A large body of conspicuous publications in recent years asserts that the high temperature approximation (HTA), a mostly tested and most widely used assumption in NMR spectroscopy and MRI technology, is invalid for concentrated samples in high magnetic fields such as for a proton COSY spectrum of water. A by product of the alleged collapse of HTA, which is equally surprising, is the existence of intermolecular multi quantum coherences (MQC) in low viscosity liquids such as water. In this work, both HTA and intermolecular MQCs in liquids will be critically examined in light of our theoretical analysis and experimental results. Our conclusions are: (1) There are no macroscopic quantum systems in conventional NMR samples such as water at room temperature. (2) At room temperature, high temperature approximation is still one of the most trustworthy approximations applicable to NMR and (3) The MQCs observed in proton COSY spectrum in, e.g., water, have nothing to do with quantum mechanical intermolecular spin interactions.