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Nonclassical Photon Pair Production in a Voltage-Biased Josephson Junction

Juha Leppäkangas (Institutionen för mikroteknologi och nanovetenskap, Tillämpad kvantfysik) ; Göran Johansson (Institutionen för mikroteknologi och nanovetenskap, Tillämpad kvantfysik) ; Michael Marthaler ; Mikael Fogelström (Institutionen för mikroteknologi och nanovetenskap, Tillämpad kvantfysik)
Physical Review Letters (0031-9007). Vol. 110 (2013), 26, p. 267004.
[Artikel, refereegranskad vetenskaplig]

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.



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Denna post skapades 2013-07-01. Senast ändrad 2014-10-23.
CPL Pubid: 179612

 

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