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Early Stage Researcher 1, CNRS, FRANCE


Project title and work package:

Energy transport and relaxation dynamics in a single quantum dot device, work packages Quantum thermodynamics and Electron transport in reduced dimensionality.



You will study quantum dot-based single electron transistors formed by electromigration in an all-metal circuitry. The device will consist of a finite size normal metallic region N connected on one side to a superconducting lead (S) and on the other to a quantum dot junction. When properly tuned, the quantum dot selectively can let hot charge carriers leave N, which are replaced by entropy-free Andreev pairs from S. Additional superconducting tunnel junctions to N can provide an independent temperature measurement. You will test and characterise electronic cooling in such devices. Here, the quantum dot will display extremely well defined spectral features, the metallic region to be cooled has a large and continuous density of states, and finally charging effects are vanishing in N. These facts will allow strong improvements over the state-of-the-art of quantum dot-based refrigerators. The theoretical analysis of the experimental results will be led in collaboration with the Early Stage Researcher 3 at CNRS (France).

If the leads to the quantum dot are all superconducting, sequential quasiparticle transport is completely suppressed at small biases < 2∆/e. A tuned microwave excitation at frequency f can drive transitions of the quantum dot electrons to higher orbital levels, leading to a DC current onset at 2∆/e - hf. The amplitude of the generated current carries information about the relative dynamics of pumping, tunnelling and relaxation in the quantum dot. In collaboration with the Early Stage Researcher 7 UKON (Germany) for the theory, you will thereby investigate the energy relaxation mechanisms in a system with a finite level spacing.


Expected Results:           

- Electronic cooling demonstrated in nanoparticle quantum dot-based device

- Energy relaxation mechanisms studied by photon-assisted tunnelling with rf excitation



Planned secondments:

at Air Liquide, France (2 months, Year 1) to get trained on cryogenics, at AALTO, Finland (1 month, Year 2) to get trained on metrology-grade current measurement, at UKON, Germany (1 month, Year 3) for training in the break-junction technique.



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