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Responsable : Çağlar Girit

Page web : https://phi0.org/​.

1Superconducting weak links continue to be a fascinating area of research in condensed matter physics despite being discovered more than half a century ago. This year, our group published two theory papers on the Andreev molecule, a system of two weak links connected to three superconductors. We also published a theory preprint on the Josephson quantum Hall effect device, a five Josephson tunnel junction circuit with a topologically non-trivial energy spectrum. This device also quantizes transconductance and is therefore an all-superconducting system which displays an effective quantum Hall effect. Our goal is to probe the energy spectrum and demonstrate that the circuit is topologically non-trivial.

2As for experiments, we have fabricated and tested two different superconducting devices: an on-chip Josephson junction based spectrometer, and an ultra low noise tunable voltage source for mesoscopic physics. We proposed a novel design for the spectrometer and demonstrated that it works as expected. We then performed linear and non-linear spectroscopy of the energy spectrum of a high-frequency microwave-SQUID in the 40-50 GHz range. We measured the sensitivity of the spectrometer and showed that it outperforms existing ones in a combination of frequency range, coupling, and sensitivity. In the second experiment, we demonstrated that using a Josephson tunnel junction with proper microwave engineering and calibration, one can obtain a stable, continuously tunable, voltage source in the 10 microvolt to 100 microvolt range which has metrological precision and accuracy. Such a source can be used to reduce the emission linewidth of our spectrometer, as well as for experiments on superconducting qubits or semiconductor systems where voltage fluctuations are problematic.

Publications

3Pillet J.-D., Benzoni V., Griesmar J., Smirr J.-L. et Girit Ç., « Scattering description of Andreev molecules », SciPost Physics Core, vol. 2, n^o 2, 2020, art. 009, https://doi.org/​10.21468/​SciPostPhysCore.2.2.009.

Peyruchat L., Griesmar J., Pillet J.-D. et Girit Ç., « Transconductance quantization in a topological Josephson tunnel junction circuit », Physical Review Research, vol. 3, no 1, 2021, art. 013289, https://doi.org/​10.1103/​PhysRevResearch.3.013289.