  We demonstrate control over the localization of high-lying Rydberg wave
packets in argon atoms with phase-locked orthogonally polarized two-color (OTC)
laser fields. With a reaction microscope, we measured ionization signals of
high-lying Rydberg states induced by a weak dc field and black-body radiation
as a function of the relative phase between the two-color fields. We find that
the dc-field ionization yields of high-lying Rydberg argon atoms oscillate with
the relative two-color phase with a period of $2\pi$ while the photoionization
signal by black-body radiation shows a period of $\pi$. These observations are
a clear signature of the asymmetric localization of electrons recaptured into
high-lying Rydberg states after conclusion of the laser pulse and are supported
by a semiclassical simulation of argon-OTC laser interaction. Our findings thus
open an effective pathway to control the localization of high-lying Rydberg
wave packets.
