This code calculates the photon loss (kappa) due to the capacitive coupling between CPWs and input/output transmission lines in a quantum circuit.

Two cases are treated: In the first case, three arguments are passed to the function kappa_in and the resonant frequency of the CPW is input as a float. In the second case, six arguments are passed to kappa_in and the frequency of the CPW is calculated assuming an ideal CPW.

Key References:

D. Schuster, Ph.D. Thesis, Yale University (2007) https://rsl.yale.edu/sites/default/files/files/RSL_Theses/SchusterThesis.pdf

T. McConkey, Ph.D. Thesis, University of Waterloo (2018) https://uwspace.uwaterloo.ca/bitstream/handle/10012/13464/McConkey_Thomas.pdf?sequence=3&isAllowed=y

Mohebbi and Majedi, Superconducting Science and Technology 22, 125028 (2009) https://iopscience.iop.org/article/10.1088/0953-2048/22/12/125028/meta

P. Krantz, et al. Physical Review Applied 6, 021318 (2019) https://aip.scitation.org/doi/10.1063/1.5089550



A simple calculator for the kappa value of a readout resonator.


A simple calculator for the kappa value of a readout resonator.

  • freq (float) – The frequency of interest, in Hz

  • C_in (float) – Effective capacitance between CPW and environment (from Q3D), in Farads

  • freq_res (float) – Lowest resonant frequency of a CPW (from HFSS), in Hz

  • length (float) – Length of the CPW readout resonator, in meters

  • res_width (float) – Width of the resonator trace (center) line, in meters

  • res_gap (float) – Width of resonator gap (dielectric space), in meters

  • eta (float) – 2.0 for half-wavelength resonator; 4.0 for quarter-wavelength resonator


Kappa value

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