Entanglement has grown from a quantum curiosity into a cornerstone of modern quantum theory, and acts as a resource in new applications currently under development, such as quantum metrology. I will discuss a series of experiments where multiparticle entangled states are created in an ensemble of ~40 atoms using optical fiber microcavities and atom chips. The cavity is used both for entanglement creation and for its analysis. It enables us to perform a direct measurement of the Husimi-Q distribution of the atomic state, with a resolution at the single-particle level. In collaboration with the French time-frequency metrology laboratory SYRTE, we are also testing the application of these tools to atomic clocks at the 10^-13 s^-1/2 fractional stability level.