Renormalization of Electromagnetic Quantities in Small Josephson Junctions
Abstract
This doctorate thesis focuses on the effects of the electromagnetic environment on applied electromagnetic fields in single small junctions as well as arrays. We apply radiofrequency (RF) microwaves in the subgigahertz frequency range on a onedimensional array of small Josephson junctions exhibiting distinct Coulomb blockade characteristics. We observed a gradual lifting of Coulomb blockade with increase in the microwave power which we interpret is due to photonassisted tunneling of Cooper pairs in the classical (multiphoton absorption) regime. We observe that, due to its high sensitivity to microwave power, the array is wellsuited for in situ microwave detection applications in low temperature environments. A detailed analysis of the characteristics in the classical (multiphoton absorption) limit reveals that the microwave amplitude is rescaled (renormalized), which we attribute to the difference in dc and ac voltage response of the array. We proceed to rigorously consider the origin of the aforementioned renormalization effect by considering the effect of the electromagnetic environment of the Josephson junction on applied oscillating voltages. We theoretically demonstrate that its effect is simply to renormalize the amplitude of oscillation in a predictable manner traced to the physics of wave function renormalization (Lehmann weights) consistent with circuitQED. We also introduce Einstein's A and B coefficients for small Josephson junctions, in a bid to relate the renormalization effect to the modification of photon absorption and emission amplitudes. Such renormalization implies that the sensitivity of the single junction and the array to oscillating electromagnetic fields (e.g. microwaves) is modulated and depends on the environmental impedance. The renormalization effect can be exploited to configure `opaque', `translucent' or `transparent' quantum circuits to microwaves.
 Publication:

arXiv eprints
 Pub Date:
 September 2021
 arXiv:
 arXiv:2109.02440
 Bibcode:
 2021arXiv210902440M
 Keywords:

 Condensed Matter  Other Condensed Matter;
 Condensed Matter  Mesoscale and Nanoscale Physics
 EPrint:
 Doctorate thesis (2020): 141 pages, 27 figures, 6 tables