  Owning to their high controllability, laser pulses have contributed greatly
to our understanding of strongly correlated electron systems. However, typical
multicycle pulses do not control the symmetry of systems that plays an
important role in the emergence of novel quantum phases. Here, we demonstrate
that subcycle pulses whose oscillation is less than one period within a pulse
envelope can control inversion and time-reversal symmetries in the electronic
states of the one-dimensional extended Hubbard model. Using an ultrashort
subcycle pulse, one can generate a steady electric current (SEC) in a
photoexcited state due to an Aharonov-Bohm flux instantaneously introduced
through the phase of an electric field. Consequently, time-reversal symmetry is
broken. In contrast, a broad subcycle pulse does not induce SEC but instead
generates electric polarization, thus breaking inversion symmetry. Both
symmetry breakings in a photoexcited state can be monitored by second harmonic
generation. These findings provide a new methodology for designing the
symmetries of electronic states and open up a new field of subcycle-pulse
engineering.
