The chirality flips with periods in the femtosecond (a) and attosecond (b) time domains are induced by two circularly polarized laser pulses (schematic) with the same (a, ++) and with opposite (b, -+) polarizations, respectively, cf. Fig. 1 . The laser pulses for the cases (a) and (b) have the same parameters, see supplementary Table 1 . The snapshots show the positive (red) and negative (blue) time-dependent parts of the electronic densities. They are almost always chiral, except at the periodic instants labeled Tn++ or Tn-+ ( n=0,1,2ldots ) when they have mirror planes at phin++ or phin-+ for chirality flips from S a to R a or back from R a to S a , cf. Table 1.
