# Negative Wigner function at telecommunication wavelength from homodyne detection

## TL;DR

This paper demonstrates the generation and detection of a quantum state with a negative Wigner function at 1550nm, using photon subtraction, frequency up-conversion, and homodyne detection, advancing quantum communication capabilities.

## Contribution

It reports the first generation of a negative Wigner function state at telecommunication wavelength with room-temperature detection methods.

## Key findings

- Wigner function negativity certified with high statistical significance
- Successful photon subtraction at 1550nm using frequency up-conversion
- High-fidelity state reconstruction via homodyne detection

## Abstract

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 1550nm. 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 532nm to allow for the use of a room-temperature (silicon) avalanche photo diode. 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.