Non-classical electromagnetic radiation created by superconducting quantum circuits.A tool for highly sensitive spectroscopy.

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In this project we plan to pursue ideas (i) to use superconducting quantum circuits as a source of non-classical electromagnetic radiation, and (ii) to use this radiation to enhance the signal to noise ratio for Raman spectroscopy. We suggest to exploit a laser-like process to generate a strongly sub-Poissonian photon distribution in a cavity coupled to an ensemble of superconducting qubits. Due to the Josephson effect the coupling is highly nonlinear. It has been shown that by using sub-Poissonian photon distributions for spectroscopy one can drastically enhance the signal-to-noise ratio. Frequently microwave spectroscopy should be performed at elevated temperatures, e.g., for the study of biological molecules the temperature should be not lower than 4K. On the other hand, the superconducting circuits should be operated at around 20mK. The consequences of this large temperature difference need to be addressed and constitute another major part (iii) of our research project.