  Semiconductor quantum dots are excellent candidates for ultrafast coherent
manipulation of qubits by laser pulses on picosecond timescales or even faster.
In inhomogeneous ensembles a macroscopic optical polarization decays rapidly
due to dephasing, which, however, is reversible in photon echoes carrying
complete information about the coherent ensemble dynamics. Control of the echo
emission time is mandatory for applications. Here, we propose a novel concept
to reach this goal. In a two-pulse photon echo sequence, we apply an additional
resonant control pulse with multiple of 2pi area. Depending on its arrival
time, the control slows down dephasing or rephasing of the exciton ensemble
during its action. We demonstrate for self-assembled (In,Ga)As quantum dots
that the photon echo emission time can be retarded or advanced by 5 ps relative
to its nominal appearance time without control. This versatile protocol may be
used to obtain significantly longer temporal shifts for suitably tailored
control pulses.
