Probing Andreev bound states with circuit quantum electrodynamics
V. Fatemi1,2, P.D. Kurilovich1, Max Hays1, D. Bouman3, T. Connolly1, S. Diamond1, N. E. Frattini1, V. D. Kurilovich1, P. Krogstrup4, J. Nygard4, A. Geresdi3,5, L. I. Glazman1, M. H. Devoret1
1 Yale University, New Haven, Connecticut, USA
2 Cornell University, Ithaca, NY, USA
3 Delft University of Technology, Delft, The Netherlands
4 University of Copenhagen, Copenhagen, Denmark
5 Chalmers University of Technology, Gothenburg, Sweden
Andreev bound states (ABSs), the quantum many-body electronic states that are localized at Josephson weak-links, provide a platform to explore the interplay of superconductivity, spin-orbit interaction, Coulomb interaction, and magnetism, including in topological regimes. ABS carry supercurrent and are thus suited to being probed by the circuit quantum electrodynamics (cQED) toolset, which offers high-resolution, high-bandwidth microwave-domain measurement and manipulation of quantum states. In this talk, I will describe our implementation of cQED to reveal the spectrum, dynamics, and potential applications of quasiparticles trapped in ABSs hosted in a Josephson semiconductor nanowire.
After an introduction to ABS, I will describe our use of superconducting resonators for quantitative measurement of microwave response functions and spectroscopy in the presence of non-equilibrium state populations. With this tool, we developed insights on Coulomb interaction in ABSs1,2, which are conventionally regarded as chargeless states. Second, I will describe the influence of spin-orbit interaction on ABSs3,4 and how we leveraged that interaction to realize the Andreev spin qubit, a supercurrent-carrying spin degree of freedom5,6. I will conclude with an outlook regarding the status of Andreev spin qubits and the immediate challenges ahead.
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[2] Fatemi, V. et al. Microwave Susceptibility Observation of Interacting Many-Body Andreev States. Phys. Rev. Lett. 129, 227701 (2022).
[3] Tosi, L. et al. Spin-Orbit Splitting of Andreev States Revealed by Microwave Spectroscopy. Phys. Rev. X 9, 011010 (2019).
[4] Hays, M. et al. Continuous monitoring of a trapped superconducting spin. Nat. Phys. 16, 1103–1107 (2020).
[5] Chtchelkatchev, N. M. & Nazarov, Yu. V. Andreev Quantum Dots for Spin Manipulation. Phys. Rev. Lett. 90, 226806 (2003).
[6] Hays, M. et al. Coherent manipulation of an Andreev spin qubit. Science 373, 430–433 (2021).