Planck Spectroscopy and Quantum Noise of Microwave Beam Splitters
M. Mariantoni, E. P. Menzel, Frank Deppe, Miguel Ángel Araque Caballero, A. Baust, Thomas M. Niemczyk, Eric A. Hoffmann, E. Solano, Achim Marx, R. Gross · Physical Review Letters · 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.