Fig. 1: Energy level diagram and experimental sequence.
From: Elimination of noise in optically rephased photon echoes
a Energy-level structure of 151Eu3+ in a Y2SiO5 crystal at zero magnetic fields. The laser is resonant with 5D0 and 7F0 electronic states at 580 nm. Signal pulse (yellow) is resonant with \({\left|\pm 1/2\right\rangle }_{{\rm{g}}}\leftrightarrow {\left|\pm 5/2\right\rangle }_{{\rm{e}}}\), and control pulses are resonant with \({\left|\pm 3/2\right\rangle }_{{\rm{g}}}\leftrightarrow {\left|\pm 5/2\right\rangle }_{{\rm{e}}}\) (red) and \({\left|\pm 1/2\right\rangle }_{{\rm{g}}}\leftrightarrow {\left|\pm 3/2\right\rangle }_{{\rm{e}}}\) (orange), respectively. The back pump light (blue) which is resonant with \({\left|\pm 5/2\right\rangle }_{{\rm{g}}}\leftrightarrow {\left|\pm 3/2\right\rangle }_{{\rm{e}}}\) is employed in the preparation step for isolating a single class of ions in the inhomogeneously broadened ensemble. b Experimental pulse sequence. Including the signal sequence and the pump sequence for the memory crystal (MC) and filter pump sequence for filter crystal (FC). We use fij to denote the center frequency of light, which is resonant with the atomic transition. The preparation process includes three steps: class cleaning, spin polarization, and back pump (see the text for details). After the preparation process, the signal pulse incidents at t0, and control pulses π35, π13, π13, π35 incident at t1, t2, t3, and t4, respectively. Finally, the NLPE emits at t5 = t4 + t3 − t2 − t1 + t0.
