Enhanced qubit performance by integrating altermagnets into superconducting qubit designs

Abstract: Identifying a materials platform for creating qubits that are both tunable and resilient towards environmental noise is one of the main hurdles that need to be overcome to realize quantum computation that is practically useful. One pursued avenue to this end is to use superconducting qubits with intrinsic spin-dependent interactions, such as spin-orbit coupling or magnetism. However, the recently discovered class of materials known as altermagnets remain largely unexplored in this context. We here use microscopic calculations to determine how the properties of superconducting qubits are modified when altermagnetic Josephson junctions are included. The key qubit performance parameters, including splitting, anharmonicity, decoherence, and single/coupled-qubit gate operation times, display rich behavior depending on the characteristic properties of the altermagnetic material, such as the strength of the Néel field and the crystallographic orientation of the altermagnetic relative interfaces in the system. We focus in particular on the transmon design and show that the qubit is very well protected against decoherence and simultaneously shows superior anharmonicity both near 0-$π$ transition points and when it is in a $φ$-state. We propose that by using strain, the altermagnetic qubit can be moved out of its protected regime to enable faster gate-operation times, and then moved back to its protected state. We also discuss how the altermagnetic properties influence flux qubits and fluxonium. Our results suggest that integration of altermagnetic materials into existing superconducting qubit design can substantially improve their performance due to the unique properties of the altermagnetic band-structure.