Early Stage Researcher 4, AALTO, FINLAND


Project title and work package:

Quantum thermodynamics by nanocalorimetry, work package Quantum thermodynamics



You will study the measurement of single microwave photons emitted by superconducting quantum circuits. The task is to develop a nanocalorimeter, which is capable of measuring sub-kelvin energy quanta with microsecond time resolution. The noise-equivalent temperature that can be reached is in few µK/Hz1/2 range, limited by fundamental energy fluctuations. The measurement requires RF-detection with a temperature sensitive element coupled to a very low heat capacity absorber thus providing a wide-band detector. An immediate choice is a hybrid NIS tunnel junction as a thermometer and a nanofabricated metallic or semiconducting absorber. A well-mastered variant of this approach is proximity supercurrent detection in a tunnel junction for thermometry, which will be carried out in collaboration with Early Stage Researcher 11 (CTH, Sweden).

You will analyse such a calorimeter theoretically (in collaboration with Early Stage Researcher 7, UKON Germany), optimise its parameters and materials and implement it in a low temperature set-up (dilution refrigerator). The calorimeter will be tested (i) by applying external Joule-heating and measuring thermal relaxation time and heat capacity of the absorber, (ii) by injecting hot-electron excitations of energy D from superconducting aluminium, and by measuring these “quanta” calorimetrically, and finally (iii) by combining the calorimeter with a superconducting quantum bit acting as a single-photon source.


Expected Results:

- Measurement of thermal relaxation times and heat capacity of a metallic nanoabsorber.

- Measurement of fluctuation relations and distribution of dissipation in an open quantum circuit.

- Measurement of single microwave photons calorimetrically down to 10 GHz frequencies.

- Theoretical analysis of single photon exchange mediating quantum heat transport, responsible for “quantum jumps”.


Planned secondments:

at UKON, Germany (1 month, Year 1) to get trained on non-equilibrium Green’s functions, at RAITH, Germany (2 months, Year 2) to learn EBL-based nanofabrication, at CNRS, France (1 month, Year 3) to get trained on the quantum jump technique.