Extended Data Fig. 3: Pulse sequence and typical results of an excitation-exchange measurement.
From: Strong coupling of alkali-metal spins to noble-gas spins with an hour-long coherence time
a. First, we turn off the pumping and bring the two species to strong coupling with a small detuning Δ. We then generate a transverse excitation with a transverse magnetic field pulse. At a later time t, we halt the exchange by increasing the axial magnetic field and setting a large Δ. b. Example of a measured signal with exchange duration t = 11 ms, with Δ = − 1.15J before t, and Δ = 790 Hz ≫ J after t. We measure the alkali electron spin (red) which, once Δ is increased, can be used as a magnetometer that senses the noble-gas spin. The fast oscillations of the signal correspond to the Larmor precession of the alkali spin, and the slow modulation corresponds to the noble-gas precession. The latter is highlighted by the blue line (generated by low-pass filtering of the signal for illustrative purposes). We fit the signal to the model from Eq. (3) (dashed black line) and find the amplitudes of the alkali and noble-gas components at time t, which are used to estimate \(\langle \hat{a}(t)\rangle\) and \(\langle \hat{b}(t)\rangle\), respectively. The same fit also provides pa(t).
