Extended Data Fig. 3: Quantum logic-assisted internal state preparation of Ar¹³⁺.

The m_1/2 = −1/2 state of the ²P_1/2 level is deterministically populated by a series of five clock laser sideband π-pulses (1–5), which excite the two-ion crystal from the motional ground state \({|0\rangle }_{m}\) (solid lines) into the excited state \({|1\rangle }_{m}\) (dashed lines). By means of Raman sideband cooling pulses acting on the ⁹Be⁺ ion, the crystal is returned to the motional ground state after each transfer pulse. This ensures unidirectional optical pumping⁹. To increase the state-preparation efficiency, this sequence is repeated four times. The other Zeeman ground state (²P_1/2, m_1/2 = +1/2) is prepared in an analogous manner.