Active pump-seed-pulse synchronization for OPCPA with sub-2-fs residual timing jitter

In the original manuscript, a residual RMS timing jitter below 2 fs between pump and seed pulses in the stabilized case was claimed. Following a reevaluation of the data, this was underestimated. Due to a rounding error in the calibration routine, a miscalculated calibration factor was extracted. By using a higher precision, the updated residual timing jitter amounts to 2.76 fs, or sub-3 fs. In this erratum, the calibration routine is briefly reviewed and Fig. 4, which presents the timing jitter in the stabilized and unstabilized case, is updated. All other results remain unaffected.