Properties of a beam-splitter entangler with Gaussian input states
Xiang‐Bin Wang · Physical Review A · 2002
An explicit formula is given for the quantity of entanglement in the output state of a beam splitter, given the squeezed vacuum states input in each mode. For the general Gaussian states input, the necessary and sufficient condition for the inseparability of the output state from a beam splitter is given. The beam splitter is one of the few quantum devices that may act as the entangler. The entangler properties of a beam splitter have been studied in the past [1–7]. In laboratory, coherent states and squeezed states are two popularly existing robust states. It is well known that no entanglement is produced if the input states are coherent states. Therefore it is important to know the entanglement property when squeezed states are used as the input. The output entanglement quantity is studied in ref [4] given the squeezed state input. In particular, an explicit formula expressing the output state in the form of two mode squeezed states are given. However, the result there is limited to a type of rather specific case. For example, the beam splitter there is limited to the 50:50 beam splitter, the input squeezed states can only have the real squeezing parameters and so on. In this paper, we shall investigate this problem in a rather general background. We will give an explicit formuly for the entanglement quantity of the output state. In general, the input state could be a mixed state. So far there is no good meassure for the