Photon sources for multi-photon entanglement experiments are commonly based on the process of spontaneous
parametric down conversion. Due to the probabilistic photon production, such experiments suffer from low multiphoton
count rates. To increase this count rate, we present a novel SPDC pump source based on a femtosecond
UV enhancement cavity that increases the available pump power while maintaining a high repetition rate of
80MHz. We apply the cavity as photon source for realizing symmetric, multi-partite entangled Dicke states,
which are observed with a high rate and high fidelity. We characterize the observed Dicke states of up to six
photons using efficient tools exploiting the state's symmetries.
Entanglement between quantum objects can be used to enhance the sensitivity of measurements. We demonstrate this
effect by using entangled multi-photon states to go beyond the shot noise limit when observing polarization rotations.
We present strategies to obtain different classes of three and four photon entangled symmetric states from a
single experimental setup. The basic idea originates from the property of the symmetric Dicke state with two
excitations to connect the two inequivalent types of genuine tripartite entanglement. We experimentally confirm
the distinct types of entanglement of the observed states. We further propose an extension of the applied scheme
that allows one to obtain different classes of four-photon entanglement by adding a fifth photon. The requirement
of a single fifth photon is currently a technical challenge, and thus we consider the approach of using a strongly
attenuated weak coherent beam instead.