We probe the local detection efficiency in a nanowire superconducting single-photon detector along the cross-section of the wire with a spatial resolution of 10 nm. We experimentally find a strong variation in the local detection efficiency of the de
vice. We demonstrate that this effect explains previously observed variations in NbN detector efficiency as function of device geometry.
We use a quantum non-demolition measurement to generate a spin squeezed state and to create entanglement in a cloud of 10^5 cold cesium atoms, and for the first time operate an atomic clock improved by spin squeezing beyond the projection noise limit
in a proof-of-principle experiment. For a clock-interrogation time of 10 mus the experiments show an improvement of 1.1 dB in the signal-to-noise ratio, compared to the atomic projection noise limit.
