Planck Spectroscopy and Quantum Noise of Microwave Beam Splitters

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M. Mariantoni, E. P. Menzel, F. Deppe, M. A. Araque-Caballero, A. Baust, T. Niemczyk, E.
Hoffmann, E. Solano, A. Marx, and R. Gross


Phys. Rev. Lett. 105, 133601 (2010)

We use a correlation function analysis of the field quadratures to characterize both the blackbody radiation emitted by a 50  Ω load resistor and the quantum properties of two types of beam splitters in the microwave regime. To this end, we first study vacuum fluctuations as a function of frequency in a Planck spectroscopy experiment and then measure the covariance matrix of weak thermal states. Our results provide direct experimental evidence that vacuum fluctuations represent the fundamental minimum quantum noise added by a beam splitter to any given input signal.