Spin system trajectory analysis under optimal control pulses

TL;DR

This paper introduces methods for analyzing and visualizing high-dimensional spin system trajectories, revealing that seemingly noisy optimal control pulses in NMR and EPR are actually smooth and well-controlled.

Contribution

It proposes new analysis techniques focusing on subspace populations to better interpret complex spin dynamics in quantum simulations.

Findings

Spin dynamics are smoother than they appear in control pulses.

Subspace populations simplify interpretation of high-dimensional data.

Optimal control pulses are more orderly than their raw signals suggest.

Abstract

Several methods are proposed for the analysis, visualization and interpretation of high-dimensional spin system trajectories produced by quantum mechanical simulations. It is noted that expectation values of specific observables in large spin systems often feature fast, complicated and hard-to-interpret time dynamics and suggested that populations of carefully selected subspaces of states are much easier to analyze and interpret. As an illustration of the utility of the proposed methods, it is demonstrated that the apparent "noisy" appearance of many optimal control pulses in NMR and EPR spectroscopy is an illusion - the underlying spin dynamics is shown to be smooth, orderly and very tightly controlled.