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Abstract
Previous studies of photonassisted tunneling through normalmetal–insulator–superconductor junctions have exhibited potential for providing a convenient tool to control the dissipation of quantumelectric circuits in situ. However, the current literature on such a quantumcircuit refrigerator (QCR) does not present a detailed description for the charge dynamics of the tunneling processes or the phase coherence of the open quantum system. Here, we derive a master equation describing both quantumelectric and charge degrees of freedom, and discover that typical experimental parameters of low temperature and yet lower charging energy yield a separation of time scales for the charge and quantum dynamics. Consequently, the minor effect of the different charge states can be taken into account by averaging over the charge distribution. We also consider applying an ac voltage to the tunnel junction, which enables control of the decay rate of a superconducting qubit over four orders of magnitude by changing the drive amplitude; we find an orderofmagnitude drop in the qubit excitation in 40 ns and a residual reset infidelity below 10−4. Furthermore, for the normal island, we consider the case of charging energy and singleparticle level spacing large compared to the superconducting gap, i.e., a quantum dot. Although the decay rates arising from such a dot QCR appear low for use in qubit reset, the device can provide effective negative damping (gain) to the coupled microwave resonator. The Fano factor of such a millikelvin microwave source may be smaller than unity, with the latter value being reached close to the maximum attainable power.
Original language  English 

Article number  042001 
Number of pages  18 
Journal  AVS Quantum Science 
Volume  3 
Issue number  4 
DOIs  
Publication status  Published  1 Dec 2021 
MoE publication type  A1 Journal articlerefereed 
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Dive into the research topics of 'Charge dynamics in quantumcircuit refrigeration: Thermalization and microwave gain'. Together they form a unique fingerprint.Projects
 5 Finished

SCAR: Scalable fabrication process for quantumcircuit refrigerators
Möttönen, M., Keränen, A., Sah, A., Ma, J. & Mörstedt, T.
22/12/2020 → 30/06/2022
Project: EU: ERC grants

SPINBUS: Quantum Bus for a Quantum Computer Based on Spins in Silicon
Tan, K., Gunyho, A., Tuohino, S., Suominen, H., Duda, R. & Kivijärvi, H.
01/09/2020 → 31/08/2022
Project: Academy of Finland: Other research funding

Quantum Enhanced Microwave Backscatter Communications
Möttönen, M., Mörstedt, T., Rasola, M., Gunyho, A., Heinsoo, J., Santos Teixeira, W., Yu, F., Keränen, A., Lahtinen, V. & Catto, G.
01/01/2019 → 31/12/2021
Project: Academy of Finland: Other research funding