Negative Wigner function at telecommunication wavelength from homodyne detection

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) = -0.063 +/- 0.004 at the origin of phase space, which certifies negativity with more than 15 standard deviations.