Microwave spectroscopy of interacting Andreev spins

Abstract

Andreev bound states are fermionic states localized in weak links between superconductors which can be occupied with spinful quasiparticles. Microwave experiments using superconducting circuits with InAs/Al nanowire Josephson junctions have recently enabled probing and coherent manipulation of Andreev states but have remained limited to zero or small fields. Here we use a flux-tunable superconducting circuit in external magnetic fields up to 1T to perform spectroscopy of spin-polarized Andreev states up to ~250 mT, beyond which the spectrum becomes gapless. We identify singlet and triplet states of two quasiparticles occupying different Andreev states through their dispersion in magnetic field. These states are split by exchange interaction and couple via spin-orbit coupling, analogously to two-electron states in quantum dots. We also show that the magnetic field allows to drive a direct spin-flip transition of a single quasiparticle trapped in the junction. Finally, we measure a gate- and field-dependent anomalous phase shift of the Andreev spectrum, of magnitude up to approximately $0.7\pi$. Our observations demonstrate new ways to manipulate Andreev states in a magnetic field and reveal spin-polarized triplet states that carry supercurrent.

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Cited by in corpus (19)

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• Blueprint for all-to-all connected superconducting spin qubits
• Strong nonlocal tuning of the current-phase relation of a quantum dot based Andreev molecule
• Direct microwave spectroscopy of Andreev bound states in planar Ge Josephson junctions
• Green's Function Approach to Josephson Dot Dynamics and Application to Quantum Mpemba Effects
• Ground state phase diagram and "parity flipping'' microwave transitions in a gate-tunable Josephson Junction
• Microwave Signatures of Topological Superconductivity in Planar Josephson Junctions
• Entangling distant systems via universal nonadiabatic passage
• Opportunities for the direct manipulation of a phase-driven Andreev spin qubit
• Quartet Tomography in Multiterminal Josephson Junctions
• Current Flow in Topological Insulator Josephson Junctions due to Imperfections
• Andreev spin relaxation time in a shadow-evaporated InAs weak link
• Many-body quantum dynamics of spin-orbit coupled Andreev states in a Zeeman field
• Microwave Andreev bound state spectroscopy in a semiconductor-based Planar Josephson junction
• Approaching the ultrastrong coupling regime between an Andreev level and a microwave resonator
• Supercurrent from the imaginary part of the Andreev levels in non-Hermitian Josephson junctions
• Error threshold in active steering protocols for few-qubit systems
• Finite Length Effects and Coulomb Interaction in Ge Quantum Well-Based Josephson Junctions Probed with Microwave Spectroscopy
• Effects of electron-electron interaction and spin-orbit coupling on Andreev pair qubits in quantum dot Josephson junctions