  We study a pair of quantum dot exciton qubits interacting with a number of
fluctuating charges that can induce a Stark shift of both exciton transition
energies. We do this by solving the optical master equation using a numerical
transfer matrix method. We find that the collective influence of the charge
environment on the dots can be detected by measuring the correlation between
the photons emitted when each dot is driven independently. Qubits in a common
charge environment display photon bunching, if both dots are driven on
resonance or if the driving laser detunings have the same sense for both
qubits, and antibunching if the laser detunings have in opposite signs. We also
show that it is possible to detect several charges fluctuating at different
rates using this technique. Our findings expand the possibility of measuring
qubit dynamics in order to investigate the fundamental physics of the
environmental noise that causes decoherence.
