Quantum correlation between the junction-voltage fluctuation and the photon-number fluctuation in a semiconductor laser.

The photon-number fluctuation of the external field from a semiconductor laser - which was reduced to below the standard quantum limit - is shown to be correlated with the measured junction-voltage noise. The spectral density of the sum of the photon-number fluctuation and junction-voltage fluctuation falls below the squeezed photon-number fluctuation. This confirms the theoretical predictions that this correlation, which originates in the dipole interaction between the internal field and electron-hole pairs, extends into the quantum regime.