Tunneling states limit quantum lifetimes in microresonators

Researchers have developed a quantum master equation to calculate phonon decoherence caused by two-level tunneling states in quartz microresonators. The work addresses a surprising limitation; even as fabrication techniques improve and resonators achieve the quantum ground state, phonon lifetimes are restricted by these tunneling states found in native oxides or damaged surface layers. This suggests a previously underestimated source of decoherence, as mechanical losses decrease and TLS emerge as the dominant mechanism. The team finds that phonon coherence time is maximized at low temperatures despite increased mechanical dissipation, and phonon-TLS coupling can be reduced for modes with strain nodes at surfaces. These TLSs, inherent to amorphous materials, introduce a dissipation mechanism that unexpectedly intensifies at lower temperatures, a phenomenon observed in silicon, lithium niobate, quartz, and other crystalline media. The research detailed in a paper published on September 22, 2026, focuses on understanding and quantifying this decoherence source as fabrication techniques improve and push the boundaries of quantum coherence. Prior to this work, a quantitative description of the interplay between phonon modes and large ensembles of TLSs remained elusive, hindering progress in optimizing these…