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Abstract: In a tunnel junction, electrons cross randomly the insulating barrier in very short times. This generates a broadband electromagnetic field. Quantum mechanics adds an ingredient to this: the voltage bias V imposed on the electrons translates into a correlation time h/eV in the current fluctuations and the generated field. With a time-resolved experiment we show how these correlations occur within a single cycle of an ac excitation at 4 GHz. This allows to generate squeezing and entanglement between far apart frequencies in the 10GHz range. In a broadband signal however, frequency is not a very relevant concept. We have developed an experiment to analyze the statistics of bicolor or broadband photons. From this we show that a tunnel junction excited at 12 GHz generates squeezed vacuum over the 3-9 GHz bandwidth. Our setup could be used to analyze any signal in the 1-10GHz range.
