Fermion parity switches in Majorana-Transmon qubits

Recent efforts have focused on replacing the weak link in the Josephson Junction (JJ) of a superconducting qubit by electrostatically-gateable technologies compatible with high magnetic fields [1]. Such alternatives are crucial in order to reach a regime relevant for readout of topological qubits based on Majorana zero modes (MZMs) [2]. In this talk, I will focus on JJs based on semiconducting nanowires that can be driven to a topological superconductor phase with MZMs. A fully microscopic theoretical description of such hybrid semiconductor-superconducting qubit allows to unveil new physics originated from the coherent interaction between the MZMs and the superconducting qubit degrees of freedom [3]. In the transmon regime, the microwave spectroscopy presents nontrivial features, including a full mapping of zero energy crossings and fermionic parity switches in the nanowire owing to Majorana oscillations [4].

[1] A perspective on semiconductor-based superconducting qubits, Applied Physics Letters, 117, 240501 (2020).

[2] Majorana qubits for topological quantum computing, R. Aguado and Leo Kouwenhoven, Physics Today 73, 6, 44 (2020)

[3]Superconducting islands with semiconductor-nanowire-based topological Josephson junctions, J. Avila, E. Prada, P. San-Jose and R. Aguado, Physical Review B, 102, 094518 (2020)

[4] Majorana oscillations and parity crossings in semiconductor nanowire-based transmon qubits, J. Avila, E. Prada, P. San-Jose and R. Aguado, Physical Review Research, 2, 033493 (2020).