Berlin 2015 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 57: Transport: Fluctuations and Noise (jointly with CPP, DY)
TT 57.4: Vortrag
Mittwoch, 18. März 2015, 12:15–12:30, H 3005
Input-output description of microwave radiation in the dynamical Coulomb blockade — Juha Leppäkangas1, Göran Johansson1, •Michael Marthaler2, and Mikael Fogelström1 — 1Microtechnology and Nanoscience, MC2, Chalmers Universit y of Technology, SE-412 96 Göteborg, Sweden — 2Institut für Theoretische Festkörperphysik, Karlsruhe Institute of Technology, D-76128 Karlsruhe, Germany
We study microwave radiation emitted by a small voltage-biased Josephson junction connected to a superconducting transmission line. An input-output formalism for the radiation field is established, using a perturbation expansion in the junction's critical current. Using output field operators solved up to the second order, we estimate the spectral density and the second-order coherence of the emitted field. For typical transmission line impedances and at frequencies below the main emission peak at the Josephson frequency, radiation occurs predominantly due to two-photon emission. This emission is characterized by a high degree of photon bunching if detected symmetrically around half of the Josephson frequency. Strong phase fluctuations in the transmission line make related nonclassical phase-dependent amplitude correlations short lived, and there is no steady-state two-mode squeezing. However, the radiation is shown to violate the classical Cauchy-Schwarz inequality of intensity cross-correlations, demonstrating the nonclassicality of the photon pair production in this region.