Hybrid superconducting devices constitute a long-standing cornerstone of QNES activity. In collaboration with F. Lefloch at INAC-SPSMS, we have studied Josephson junction where the normal metal weak link can show multiple Andreev reflections effect, like quartets, and cross-correlations effects. SQUID devices properties, in particular the presence of hysteresis, are studied in collaboration with A. K. Gupta at IIT Kanpur.
Electronic cooling can be obtained in tunnel junctions between a superconductor and a normal metal biased at a voltage just below the superconductor’s gap. As the coupling of cooled electrons to the lattice phonons is believed to be the main link to the thermal bath, the question of phonon cooling is essential. We have demonstrated the existence of an independent phonon bath in such a quantum device, exhibiting phonon cooling. This experimental work is complemented by a theoretical effort in collaboration with F. Hekking at LPMMC, for exemple on the question of photonic heat transport. We have also worked towards larger cooling powers and lower operating temperatures. In collaboration with J. P. Pekola at Aalto University, we demonstrated a nanoWatt cooling power and a 30 mK electronic temperature, starting from a 150 mK bath temperature.
We also study quantum electron transport in superconducting junctions incorporating a single quantum dot. In collaboration with the Nanospin team at NEEL, nanometer sized gaps are created by electromigration in narrow superconducting constrictions, into which a single sub-10 nm gold nanoparticle is inserted. In such a device, an a.c. drive with frequency f on the gate electrode can generate a quantized current I = ef accross the device - the so-called electron turnstile principle. This experiment holds promises for metrological applications and allows for studying the quantum coherent transport properties of the setup. We now routinely prepare such devices and achieve relative turnstile current accuracies 1e-3 at output currents of 10 - 100 pA. An in-depth study of the quantum dot spectral density in the presence of coupling to the superconducting leads is in progress.
Single electron turnstile using a gold nanoparticle
Electronic and thermal properties of SIN tunnel junctions
Multi-terminal electron transport and thermal effects in SNS junctions