Double-periodic Josephson junctions in a quantum dissipative environment

Abstract

Embedded in an ohmic environment, the Josephson current peak can transfer part of its weight to finite voltage and the junction becomes resistive. The dissipative environment can even suppress the superconducting effect of the junction via a quantum phase transition occuring when the ohmic resistance Rs exceeds the quantum resistance Rq = h/(2e) 2 . For a topological junction hosting Majorana bound states with a 4π periodicity of the superconducting phase, the phase transition is shifted to 4Rq. We consider a Josephson junction mixing the 2π and 4π periodicities shunted by a resistor, with a resistance between Rq and 4Rq. Starting with a quantum circuit model, we derive the non-monotonic temperature dependence of its differential resistance resulting from the competition between the two periodicities; the 4π periodicity dominating at the lowest temperatures. The nonmonotonic behaviour is first revealed by straightforward perturbation theory and then substantiated by a fermionization to exactly solvable models when Rs = 2Rq: the model is mapped onto a helical wire coupled to a topological superconductor when the Josephson energy is small and to the Emery-Kivelson line of the two-channel Kondo model in the opposite case.

Spectral response of Josephson junctions with low-energy quasiparticles

“…In the case of Andreev qubits, detailed models which are amenable to an analytical approach are available in simple limits, such as that of a short Josephson junction with a single conducting channel [36,[45][46][47]. On the other hand, most of the theory literature treating the presence of MZMs in superconducting circuits [48][49][50][51][52][53][54][55][56][57][58][59][60][61][62][63][64][65] relies on simple toy-models with phenomenological terms representing Majorana couplings, bypassing a microscopic description of the topological phase.…”