Figure 1
Chirping a two-photon excitation through a single intermediate state (top) and through an equidistant manifold (bottom). The left and right columns show the level system and the resulting excitation probabilities as a function of the chirp parameter
, respectively. In both systems the ground state
is connected by a two-photon transition to the excited state
. In the case of a single intermediate state
with the offset
with respect to the central frequency
discussed in the top row the population
of the excited state displays oscillations for negative chirps, whereas for positive values of the chirp it is decreasing rapidly. The oscillations result from an interference of the direct and the indirect excitation. The direct path is a direct two-photon transition through the virtual state of frequency
. The indirect path consists of first an excitation to the level
and then a transition to
. Here we have used the parameters
,
,
as suggested by the experiment [
14]. In the bottom row we discuss the case of a manifold of
equidistant intermediate states
with
which are shifted by the offset
with respect to the central frequency
. The offset of the central state is
whereas the states in the harmonic manifold are separated by
. The population
of the excited state is due to interference of competing quantum paths via the intermediate states and displays strong modulations as a function of the chirp. Parameters are
,
,
,
,
, and
.
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