A slight first-order phase shift is observed, arising from the the set 200 ms acquisition delay. As previously discussed, N-ACN is first polarized into the state Ŝ • K. This is followed by adiabatically (b) or suddenly (c) raising the field from zero to 2 µT, which serves as the precession field for ULF detection. In the adiabatic case, this spin order adiabatically transfers to spin order (1/2) Ky -Ŝy Ky (non-observable terms are omitted here and detailed in the Supplementary Information). Upon a 90-degree proton pulse, this spin order results in a single proton resonance peak (termed the ALTADENA spectrum), contrasting with conventional high-field NMR where the J-coupling to the nitrogen splits the proton resonance into a doublet. The suppression of splitting arises from adiabatic process conditioning the nitrogen spin into a fixed projection anti-parallel to the applied magnetic field. The singleshot spectrum is shown by the orange line in the right panel of Fig. ). In the sudden transfer case, the spin order Ŝy Ky , a component of the pumped spin state at ZF, produces an anti-phase doublet after excitation, as shown by the green line in the right panel of Fig. . For reference, spectra with the same pumping followed by a 90-degree N pulse are shown in the left panel of Fig. , with the orange and green lines corresponding to the adiabatic and sudden cases, respectively.