  The fluorescence spectrum of a strongly pumped two level system is
characterised by the Mollow triplet that has been observed in a variety of
systems, ranging from atoms to quantum dots and superconducting qubits. We
theoretically studied the fluorescence of a strongly pumped intersubband
transition in a quantum well. Our results show that the many-electron nature of
such a system leads to a modification of the usual Mollow theory. In
particular, the intensity of the central peak in the fluorescence spectrum
becomes a function of the electron coherence, allowing access to the coherence
time of a two dimensional electron gas through a fluorescence intensity
measurement.
