Seminars: Ramon Aguado and Felix von Oppen

Back to back seminars, with a coffee break:

Felix von Oppen

Dahlem Center for Complex Quantum Systems, FU Berlin


Ramon Aguado

Instituto de Ciencia de Materiales de Madrid

Felix von Oppen: Yu-Shiba-Rusinov chains: classical vs quantum

Abstract: According to experiment, magnetic adatoms on superconducting substrates should be considered as quantum spins. Nevertheless, most theoretical works on chains of magnetic adatoms, a popular platform for topological superconductivity, treats them as classical. I will show that dilute chains of quantum spins actually exhibit qualitatively different physics, which is interesting in its own right and has ramifications in the context of topological superconductivity.

Ramon Aguado: Fermion parity switches in a Majorana-Transmon qubit

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 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]. If time permits, I will briefly discuss other effects, originated from quantum dot parity crossings in the junction  [5]. 

[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).

[5] Singlet-doublet transitions of a quantum dot Josephson junction revealed in a transmon circuit, Arno Bargerbos, Marta Pita Vidal, Rok Zitko, Jesús Ávila Camuñas, Lukas Grünhaupt, Lukas Splitthoff, Jaap Wesdorp, Yu Liu, Peter Krogstrup, Christian Andersen, Leo Kouwenhoven, Ramón Aguado, Angela Kou, Bernard van Heck, manuscript in preparation (2021)