Nonclassical Photon Pair Production in a Voltage-Biased Josephson Junction
Journal article, 2013

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 transmission line. 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.


Juha Leppäkangas

Chalmers, Microtechnology and Nanoscience (MC2), Applied Quantum Physics

Göran Johansson

Chalmers, Microtechnology and Nanoscience (MC2), Applied Quantum Physics

M. Marthaler

Mikael Fogelström

Chalmers, Microtechnology and Nanoscience (MC2), Applied Quantum Physics

Physical Review Letters

0031-9007 (ISSN) 1079-7114 (eISSN)

Vol. 110 26 267004- 267004

Areas of Advance

Nanoscience and Nanotechnology (SO 2010-2017, EI 2018-)

Subject Categories

Physical Sciences

Condensed Matter Physics


Basic sciences



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Latest update

4/5/2022 6