You are cordially invited to the IPB COLLOQUIUM which will be held on Monday, 31 March 2025 at 13:00 in the “Zvonko Marić” lecture hall of the Institute of Physics Belgrade. The talk entitled

Hybrid superconductor-semiconductor devices as building blocks for quantum computers

will be given by Dr. Rok Žitko (Jozef Štefan Institute, Ljubljana, Slovenia). The abstract of the talk:

Superconducting electronics is one of the most advanced technologies for building quantum computing hardware. A relatively recent addition to the cookbook of circuit elements are hybrid superconductor-semiconductor nanowires, often in the form of Josephson junctions connecting two superconducting contacts, which can serve to build novel types of qubits, such as Andreev qubits. Their properties can be tuned by setting voltages to gate electrodes. In particular, this can be used to trap a small number of electrons in the junction to form a quantum dot. Such Josephson junction quantum dots have been recently used to build devices implementing Andreev spin qubits that carry two quantum degrees of freedom: the spin carried by the trapped electron in the quantum dot and the two-level system formed by the superconducting condensate. Both degrees of freedom can be probed and coherently manipulated [1,2,3]. These devices can be modelled using the Anderson impurity model with superconducting leads. Depending on the size of the charging energy, the leads can be described either with the mean-field BCS Hamiltonian or with the charge-conserving Richardson model [4]. In this talk we will present recent results on the properties of the discrete states in the superconducting gap which govern the basic physics. We have developed methods that are applicable in all parameter regimes, including for strong coupling (hybridization) and in parameter ranges where all effects (quantum dot spin physics, Josephson coupling, charging effects, spin-orbit coupling) need to be treated at the same level [5,6,7,8].

[1] A. Bargerbos, M. Pita-Vidal, R. Žitko et al., PRX Quantum 3, 030311 (2022).
[2] A. Bargerbos, M. Pita-Vidal, R. Žitko et al., Phys. Rev. Lett. 131, 097101 (2023).
[3] M. Pita-Vidal, A. Bargerbos, R. Žitko et al., Nat. Phys. 19, 1110 (2023).
[4] L. Pavešić, D. Bauernfeind, and R. Žitko, Phys. Rev. B 104, L241409 (2021).
[5] L. Pavešić, M. Pita-Vidal, A. Bargerbos, and R. Žitko, SciPost Phys. 15, 070 (2023).
[6] J. C. E. Saldaña,  L. Pavešić, A. Vekris et al., Phys. Rev. B 108, 224507 (2023).
[7] L. Pavešić, R. Aguado, and R. Žitko, Phys. Rev. B 109, 125131 (2024).
[8] L. Pavešić and R. Žitko, Phys. Rev. B 109, 155164 (2024).