Fig. 2.

(A) Pulse sequence for demonstrating the storage of longitudinal magnetization as singlet order in low magnetic field. The top trace shows the trajectory of magnetic fields as the sample is transported from the high-field magnet (B_high) into the low-field region B_low. The transport intervals are denoted τ_tr. A 90° radio-frequency pulse (RF) is applied in high field to estimate the final longitudinal magnetization. Transverse audio-frequency (AF) fields are applied at the nuclear Larmor frequency in the low-field region to convert magnetization into singlet order (M2S) and back again (S2M). The low-field storage interval is denoted τ_LF. (B) Detailed view of the M2S pulse sequence. The pulse sequence contains two 90° pulses with phases 270° and 0, and two spin-echo trains, each generated by repeating a unit consisting of the composite 180° pulse [90₉₀240₀90₉₀]_ϕ bracketed by two intervals of duration τ_J/4, where τ_J = J^-1. The numbers of repetitions are n₁ and n₂ in the first and second parts of the pulse sequence, respectively. The overall phases ϕ of the composite pulses run through the four-step cycle {0,0,180°,180°,…}. An additional τ_J/4 interval is inserted immediately after the second 90° pulse, before the second echo train starts. The pulse sequence S2M is the same as M2S, but in reverse chronological order.