Evidence of Memory Effects in the Dynamics of Two-Level System Defect Ensembles Using Broadband, Cryogenic Transient Dielectric Spectroscopy

• URL: http://arxiv.org/abs/2505.18263v2
• Date: Wed, 23 Jul 2025 18:31:55 GMT
• Title: Evidence of Memory Effects in the Dynamics of Two-Level System Defect Ensembles Using Broadband, Cryogenic Transient Dielectric Spectroscopy
• Authors: Qianxu Wang, Sara Magdalena Gómez, Juan S. Salcedo-Gallo, Roy Leibovitz, Jake Freeman, Salil Bedkihal, Mattias Fitzpatrick,
• Abstract summary: Two-level system (TLS) defects in dielectrics are a major source of decoherence in superconducting circuits.<n>We introduce a broadband 3D waveguide spectroscopy technique that enables cryogenic probing of ensembles of TLS defects.
• Score: 0.0
• License: http://creativecommons.org/licenses/by/4.0/
• Abstract: Two-level system (TLS) defects in dielectrics are a major source of decoherence in superconducting circuits, yet their atomistic origin, frequency distribution, and dipole moments remain poorly understood. Current probes, which are predominantly based on qubits or resonators, require complex fabrication and only measure defects within a narrow frequency band and limited mode volume, hindering direct insight into TLS defect behaviour in isolated materials and interfaces. Here, we introduce a broadband 3D waveguide spectroscopy technique that enables cryogenic probing of ensembles of TLS defects that we call Broadband Cryogenic Transient Dielectric Spectroscopy (BCTDS). Complementary to the dielectric dipper method, this approach probes a broader spectrum and reveals interference of drive-induced sidebands of the ensembles of TLS defects. The broadband and power-tunable nature of BCTDS makes it especially well-suited to the study of dressed-state physics in driven ensembles of TLS defects, including multi-photon processes and sideband-resolved dynamics. Additionally, BCTDS enables the identification of eigenmode frequencies of the undriven ensembles of TLS defects through characteristic V-shaped features obtained via Fourier analysis of time-domain signals, and shows evidence of memory effects arising from interactions and the broadband nature of our approach. Crucially, our method is modular and can be applied throughout the device fabrication process, informing mitigation strategies and advancing the design of low-loss materials with broad implications for quantum technologies and materials science.

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