Lattice-Renormalized Tunneling Models for Superconducting Qubit Materials

Journal Article · Sat Dec 20 00:00:00 UTC 2025 · No journal information

OSTI ID:3023414

Pritchard, P. G. ^[1]; Rondinelli, James M. ^[1]

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1. Northwestern U.

We present a lattice-renormalized formalism for configurational tunneling two-level systems (TLS) that overcomes limitations of minimum-energy-path and light-particle models. Derived from the nuclear Hamiltonian, our formulation introduces composite phonon coordinates to capture lattice distortions between degenerate potential wells. This approach resolves deficiencies in prior models and enables accurate computation of tunnel splittings and excitation spectra for hydrogen-based TLS in bcc Nb. Our results bound experimental tunnel splittings and reveal strong anharmonic couplings between tunneling atoms and lattice phonons, establishing a direct link between TLS dynamics and phonon-mediated strain interactions. The formalism further generalizes to multi-level systems (MLS), providing insight into defect-induced decoherence in superconducting qubits and guiding strategies for materials design to suppress TLS-related loss.

• Research Organization: Northwestern U.
• Sponsoring Organization: US Department of Energy
• DOE Contract Number: 89243024CSC000002
• OSTI ID: 3023414
• Report Number(s): FERMILAB-PUB-25-1004-SQMS-V; oai:inspirehep.net:3094935; arXiv:2512.18156
• Journal Information: No journal information, Journal Name: No journal information
• Country of Publication: United States
• Language: English