Distribution of polarization squeezed light through a 20 km fiber channel

We prepared and distributed the polarization squeezed light through a 20 km fiber channel. After this distribution, a polarization squeezed light with −0.57 dB squeezing is still observed. We demonstrate that the quantum variance of Ŝ₃ and Ŝ₂ decreases with the increase in the fiber length, while the variance of Ŝ₁ increases, because of the increase in the loss and excess noise. By introducing the technique of suppressing decoherence into the distribution experiment, the transmission distance of the polarization squeezed light can be extended further. Our work thus takes a crucial step toward enabling future practical applications based on polarization squeezed light.