Negative Wigner function at telecommunication wavelength from homodyne detection
Christoph Baune, Jaromı́r Fiurášek, Roman Schnabel · Physical Review A · 2017
Quantum states of light having a Wigner function with negative values represent a key resource in quantum communication and quantum information processing. Here we present the generation of such a state at the telecommunication wavelength of 1550 nm. The state is generated by means of photon subtraction from a weakly squeezed vacuum state and is heralded by the ``click'' of a single photon counter. Balanced homodyne detection is applied to reconstruct the Wigner function, also yielding the state's photon-number distribution. The heralding photons are frequency up-converted to 532 nm to allow for the use of a room-temperature (silicon) avalanche photodiode. The Wigner function reads $W(0,0)=\ensuremath{-}0.063\ifmmode\pm\else\textpm\fi{}0.004$ at the origin of phase space, which certifies negativity with more than 15 standard deviations.