Physical Review A
We have simultaneously measured the quantum states of two different spatial modes of the same optical beam by performing quantum-state tomography with an array detector. Both modes are well described by coherent states, but the projection of the signal onto the local oscillator mode contains a mean of 0.09 photons, while a more complicated mode has a mean of 4.3 photons. This demonstrates that for this particular mode the effective detection efficiency when using array detection is over 40 times greater than when using single detectors.
Dawes, A. M., & Beck, M. (2001). Simultaneous quantum-state measurements using array detection. Physical Review Series A 63, 040101(R). DOI: 10.1103/PhysRevA.63.040101