Generation of non-classical electromagnetic field by a coherent conductor / Génération de champ électromagnétique non classique par un conducteur cohérent

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Progress in the industry of micro-electronics have made possible the fabrication of components of submicron size. Many experiments have been performed to measure the average current in such nanostructures. More subtle, but much more difficult are the measurements of the fluctuations of the current, usually nicknamed “noise”. The behavior of electrons in small conductors at low temperature cannot be explained by usual laws of physics, valid in the macroscopic world at room temperature: instead, one has to invoke quantum mechanics to understand laws of electricity in such conditions. This is true not only for the current but also for the noise. However the noise, fluctuating voltage and current, is nothing but a fluctuating electromagnetic field, i.e. light. Noise is here considered in the microwave domain and in circuits, while light is usually associated with much higher frequencies and propagation in free space, but they are the same. And quantum mechanics applied to light is a branch of physics, called quantum optics. The goal of this research program is precisely to explore and harness what kind of quantum optical signals can be generated by electrons in conductors. In particular, can one apply our knowledge of quantum electronic transport in nanostructures to the generation of microwave radiation with quantum properties useful for the processing of information ? While there is a huge effort to engineer quantum radiation using the usual principles of quantum optics, applied for example to superconductors, can one use the principles of quantum electronics in normal metals or semiconductors to achieve similar goals ? Three main directions will be explored in this research program: 1) the generation of non-Gaussian states of light, known for being resources for quantum information processing. In a macroscopic sample, most random phenomena are described by the Gauss law. Not in quantum conductors. How does that imprint on the emitted radiation ? 2) feedback is an ubiquitous engineering technique that consist of measuring a system and use the result of the measurement to react on the system, in order to steer its behavior. Can one enhance the quantum character of noise by feedback ? 3) quantum aspects fade when the temperature approaches the relevant energy scale of a system, such as the gap in superconductors. In normal conductors, this energy scale is huge, so one should be able to generate quantum signals of very high frequency at relatively high temperature. For this, novel sources and detectors will be designed.