Experimental Violation Of Bell-like Inequalities By Electronic Shot Noise

Quantum electronic noise, the random current fluctuations generated by electrons crossing a quantum conductor, has been thoroughly studied from the electron point of view. Recent experiments have shown that such noise may have striking properties in terms of the quantum electromagnetic field it generates. Both the existence of vacuum squeezing \cite{PAN_squeezing} and generation of correlated photon pairs \cite{C4quantique} have been observed. Here we demonstrate that this electromagnetic field also violates Bell-like inequalities, thereby proving its true quantum nature. This is achieved by the observation of two-mode quadrature squeezing of vacuum: the electromagnetic field quadratures at two different frequencies can be so correlated that their difference goes below vacuum fluctuations. Thus, electronic noise contains entangled photon pairs, a key ingredient for quantum computing and communication.