Spin counting experiments in the dipolar-ordered state

The dipolar-ordered state ${\mathrm{(\rho \propto H}}_d)$ can be prepared from a state of Zeeman equilibrium at high field by adiabatically removing the Zeeman field. It is also possible to produce dipolar-ordered states in the rotating frame using two well-known methods—adiabatic demagnetization in the rotating frame and the Jeener–Broekaert (JB) pulse pair. Using multiple quantum nuclear magnetic resonance techniques, we illustrate the transient dynamics of the spin system following the JB pulse pair and its evolution to a dipolar-ordered state over a period of approximately 60 $\mu \mathrm{s}$ in a single crystal of ${\mathrm{CaF}}_2$ oriented along the [100] direction, and approximately 100 $\mu \mathrm{s}$ when the crystal is oriented along the [110] direction. By encoding the coherence numbers in an orthogonal basis (the x basis) to the Zeeman basis, we show that the dipolar-ordered state is a two spin correlated state. The observed ratio between double quantum and zero quantum coherences in the x basis confirms the presence of the $I_i^{+}{I}_j^{-}{\mathrm{+I}}_i^{-}{I}_j^{+}$ (flip–flop) terms in the experimentally prepared dipolar-ordered state.