title: Coherence and multimode correlations from vacuum fluctuations in a microwave superconducting cavity.
abstract: The existence of vacuum fluctuations is one of the most important predictions of modern quantum field theory. In the vacuum state, fluctuations occurring at different frequencies are uncorrelated. However, if a parameter in the Lagrangian of the field is modulated by an external pump, vacuum fluctuations stimulate spontaneous downconversion processes, creating squeezing between modes symmetric with respect to half of the frequency of the pump. Here we show that by double parametric pumping of a superconducting microwave cavity, it is possible to generate another type of correlation, namely coherence between photons in separate frequency modes. The coherence correlations are tunable by the phases of the pumps and are established by a quantum fluctuation that stimulates the simultaneous creation of two photon pairs. Our analysis indicates that the origin of this vacuum-induced coherence is the absence of which-way information in the frequency space.
authors: Department of Applied Physics, Low Temperature Laboratory, Aalto University School of Science, PO Box 15100, FI-00076 Aalto, Finland.
authors: Pasi
authors: P
authors: Lähteenmäki
authors: Department of Applied Physics, Low Temperature Laboratory, Aalto University School of Science, PO Box 15100, FI-00076 Aalto, Finland.
authors: Gheorghe Sorin
authors: GS
authors: Paraoanu
authors: VTT Technical Research Centre of Finland, FI-02044 Espoo, Finland.
authors: Juha
authors: J
authors: Hassel
authors: Department of Applied Physics, Low Temperature Laboratory, Aalto University School of Science, PO Box 15100, FI-00076 Aalto, Finland.
authors: Pertti J
authors: PJ
authors: Hakonen