Multiphoton Interference as a Tool to Observe Families of Multiphoton Entangled States

Spontaneous parametric downconversion in combination with linear optics was successfully used to observe a variety of multiphoton entangled states. Yet, experiments performed so far lacked flexibility, as each of the various setups was useful for only a particular multiphoton entangled state. In this paper, we describe how, by using multiphoton interference, one can observe entire families of multiphoton entangled states in the very same linear optical setup. Our method thus goes beyond the commonly used two-photon interference and turns out to be a very useful tool for state observation. We will discuss the interference of four and six photons at different types of beam splitters and show which families of entangled states are observable. The benefits of this approach are demonstrated in a four-photon interference experiment by observing a variety of highly entangled multiphoton states.