Observation of microwave absorption and emission from incoherent electron tunneling through a normal-metal-insulator-superconductor junction

Research output: Contribution to journalArticleScientificpeer-review


Research units

  • University of Oulu
  • University of Freiburg


We experimentally study nanoscale normal-metal-insulator-superconductor junctions coupled to a superconducting microwave resonator. We observe that bias-voltage-controllable single-electron tunneling through the junctions gives rise to a direct conversion between the electrostatic energy and that of microwave photons. The measured power spectral density of the microwave radiation emitted by the resonator exceeds at high bias voltages that of an equivalent single-mode radiation source at 2.5 K although the phonon and electron reservoirs are at subkelvin temperatures. Measurements of the generated power quantitatively agree with a theoretical model in a wide range of bias voltages. Thus, we have developed a microwave source which is compatible with low-temperature electronics and offers convenient in-situ electrical control of the incoherent photon emission rate with a predetermined frequency, without relying on intrinsic voltage fluctuations of heated normal-metal components or suffering from unwanted losses in room temperature cables. Importantly, our observation of negative generated power at relatively low bias voltages provides a novel type of verification of the working principles of the recently discovered quantum-circuit refrigerator.


Original languageEnglish
Article number3966
Pages (from-to)1-8
JournalScientific Reports
Issue number1
Publication statusPublished - 1 Dec 2018
MoE publication typeA1 Journal article-refereed

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