Quantum Up-Conversion of Squeezed Vacuum States from 1550 to 532 nm
Christina E. Vollmer, Christoph Baune, Aiko Samblowski, T. Eberle, Vitus Händchen, Jaromı́r Fiurášek, Roman Schnabel · Physical Review Letters · 2014
Squeezed vacuum states constitute a particularly useful resource in quantum information as well as in quantum metrology. The frequency conversion of these states is important to provide the bridge between different wavelengths within a sequence of downstream applications and also to provide a way for squeezed-state generation at so-far inaccessible wavelengths. Here we demonstrate the external quantum up-conversion of carrier-light-free squeezed vacuum states for the first time. Our result proves that nondegenerate sum-frequency generation preserves the coherences that are present between photon pairs and higher-order photon pairs of the squeezed input state.