Nonclassical photon pair production in a voltage-biased Josephson junction
Abstract
We investigate electromagnetic radiation emitted by a small voltage-biased Josephson junction connected to a superconducting transmission line. At frequencies below the well known emission peak at the Josephson frequency (2eV/h), extra radiation is triggered by quantum fluctuations in the electromagnetic environment. For weak tunneling couplings and typical ohmic transmission lines, the corresponding photon flux spectrum is symmetric around half the Josephson frequency, indicating that the photons are predominately created in pairs. By establishing an input-output formalism for the microwave field in the transmission line, we give further evidence for this nonclassical photon pair production, demonstrating that it violates the classical Cauchy-Schwarz inequality for two-mode flux cross correlations. In connection to recent experiments, we also consider a stepped transmission line, where resonances increase the signal-to-noise ratio.
Keywords
Cite
@article{arxiv.1210.6276,
title = {Nonclassical photon pair production in a voltage-biased Josephson junction},
author = {Juha Leppäkangas and Göran Johansson and Michael Marthaler and Mikael Fogelström},
journal= {arXiv preprint arXiv:1210.6276},
year = {2013}
}
Comments
5 pages, 2 figures. This version accepted in Physical Review Letters