Input-output description of microwave radiation in the dynamical Coulomb blockade
Abstract
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.
Keywords
Cite
@article{arxiv.1309.3646,
title = {Input-output description of microwave radiation in the dynamical Coulomb blockade},
author = {Juha Leppäkangas and Göran Johansson and Michael Marthaler and Mikael Fogelström},
journal= {arXiv preprint arXiv:1309.3646},
year = {2014}
}
Comments
29 pages, 4 figures