Microwave spectroscopy of hybrid superconductor- semiconductor qubits with Majorana zero modes

Ramón Aguado

Recent experimental 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 my 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]. The corresponding 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]Superconducting gatemon qubit based on a proximitized two-dimensional electron gas, Casparis et al, Nature Nanotechnology, 13, 915, (2018); Semiconductor-Nanowire-Based Superconducting Qubit, T. W. Larsen et al. Phys. Rev. Lett. 115, 127001 (2015); Realization of Microwave Quantum Circuits Using Hybrid Superconducting-Semiconducting Nanowire Josephson Elements, G. de Lange et al. Phys. Rev. Lett. 115, 127002 (2015)
[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, arXiv:2003.02852 (Physical Review B, in press)
[4] Majorana oscillations and parity crossings in semiconductor nanowire-based transmon qubits, J. Avila, E. Prada, P. San-Jose and R. Aguado, arXiv:2003.02858 (Physical Review Research, in press)