Atom-Photon interaction is everywhere in quantum information, and it is never good enough. Optical cavities with small mode cross-section and lowest loss therefore play a key role, enhancing the interaction in quantum interfaces, but also providing effective coupling that creates entanglement between particles. Fiber Fabry-Perot cavities (FFPs) with laser- machined, ultralow roughness micromirrors are one cavity type that is being used quite successfully with an increasing range of emitters, ranging from ultracold atoms to diamond NV centers and carbon nanotubes. I will give an overview of this cavity technology and its latest developments, and describe two experiments where FFP cavities are used to generate many-particle entanglement. In the first, the cavity measurement effectively blocks part of the qubits' Hilbert space, and entanglement emerges when the coherently driven qubits approach this blocked bart. The second experiment is a trapped-atom clock on an atom chip, where the FFP cavity has allowed us to generate long-lived spin squeezed states in a metrological environment.
Jakob Reichel is a professor at Sorbonne Université and member of Laboratoire Kastler Brossel at ENS Paris, where his group explores cavity-based quantum technologies with ultracold atoms. He also has an interest in compact atomic clocks, which he pursues in collaboration with the French metrology laboratory, SYRTE, and in miniaturized devices for AMO applications.