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Alexander Grimm

Josephson photonics: Statistics of photons emitted by inelastic Cooper pair tunneling

Published on 2 October 2015

Thesis presented October 02, 2015

This thesis contributes to the emerging field of Josephson photonics through the study of correlations between microwave photons emitted by inelastic Cooper pair tunneling across a voltage-biased Josephson junction. We show that the photon statistics can be strongly modified by embedding the junction into a carefully engineered electromagnetic environment. Doing so, we have elaborated and measured a bright on-demand radiation source, capable of emitting bunched and anti-bunched microwave photons depending only on a single in-situ tunable parameter. In order to conduct this experiment, we have implemented a Hanbury-Brown & Twiss setup for photon correlation measurements using linear amplifiers in a dilution refrigerator. Furthermore, we have designed microwave circuits presenting specific frequency-dependent impedances to the junction. To build these devices we have developed a nano-fabrication process for vertical Josephson junctions made from niobium nitride and using magnesium oxide as a tunnel barrier. Finally, we have contributed to the theoretical advances associated with the understanding of these devices, which extend the so-called P(E) theory of inelastic Cooper pair tunneling to include correlations between tunneling events. These results pave the way for further developments, notably with the possibility to extend the frequency range of these radiation sources to the THz domain but also in view of other devices based on the same physics, such as detectors and amplifiers close to the quantum limit.

Quantum nanoelectronics, Josephson photonics, Microwave quantum optics, Superconducting circuits

On-line thesis.