Squeezing in Photo-assisted Electron Quantum Shot Noise

The current/voltage fluctuations generated by a conductor are another point of view of a randomly fluctuating electromagnetic field, i.e. ``white'' light. We demonstrate experimentally that this light is naturally squeezed, i.e. that the noise on one quadrature can go below the vacuum fluctuations, for a tunnel junction at very low temperature irradiated by a microwave. A classical current in a conductor generates a coherent state of light. We show that a quantum current can emit non-classical light.