The demonstrate intraband coherences induced by quantum correlations betwee
n the field and carrier density in a semiconductor quantum-well microcavity
. A pair of phase-controlled optical pulses manipulate quantum states of lo
wer mode polaritons, which lead to the quantum correlations revealed as osc
illations in the time-resolved reflectivity of the upper mode. The intraban
d coherences live much longer than the interband dephasing time.