Simultaneous quantum state measurements using array detection

Abstract

Here we present the results of the first experiment that uses array detection to measure quantum states of an optical beam [1]. We demonstrate that an array detector can be used to simultaneously measure the quantum states of many different spatial modes of the same beam. Furthermore, we show that array detectors can allow for an improvement in effective detection efficiency over standard detectors when using balanced homodyne detection. This improvement comes from the fact that the local oscillator (LO) and signal fields need not be mode-matched when using array detectors. In our experiment array detection is found to be over forty times more efficient than standard detection for measurements of a particular field mode. The technique we use for determining the state of our field modes is quantum state tomography (QST), and yields the density matrix in the Foch-state basis ρ_mn [2,3].