  We characterize the coherent dynamics of a two-level quantum emitter driven
by a pair of symmetrically-detuned phase-locked pulses. The promise of
dichromatic excitation is to spectrally isolate the excitation laser from the
quantum emission, enabling background-free photon extraction from the emitter.
Paradoxically, we find that excitation is not possible without spectral overlap
between the exciting pulse and the quantum emitter transition for ideal
two-level systems due to cancellation of the accumulated pulse area. However,
any additional interactions that interfere with cancellation of the accumulated
pulse area may lead to a finite stationary population inversion. Our
spectroscopic results of a solid-state two-level system show that while
coupling to lattice vibrations helps to improve the inversion efficiency up to
50\% under symmetric driving, coherent population control and a larger amount
of inversion are possible using asymmetric dichromatic excitation, which we
achieve by adjusting the ratio of the intensities between the red and
blue-detuned pulses. Our measured results, supported by simulations using a
real-time path-integral method, offer a new perspective towards realising
efficient, background-free photon generation and extraction.
