Microscopic nature and interactions of two-level systems in amorphous solids

Identify the microscopic nature of two-level systems in amorphous solids and determine how interactions between two-level systems influence low-temperature properties of these materials.

Background

The paper notes that some low-temperature anomalies of amorphous solids can be captured by phenomenological models of noninteracting two-level systems, but the microscopic origin of these entities and the role of their interactions remain unresolved. Understanding these aspects is crucial for a complete microscopic theory of amorphous solids at low temperatures.

The authors argue that programmable Rydberg-atom platforms, capable of emulating interacting spin models without intrinsic lattice order, may enable systematic exploration of such questions, especially in regimes challenging for classical simulations.

References

In this regard, note that some low-temperature properties of amorphous solids have been already explained by models based on noninteracting two-level systems, but there are still many open questions concerning the nature of the two-level systems, and the effect of interactions.

— Amorphous quantum magnets in a two-dimensional Rydberg atom array  (2402.02852 - Julià-Farré et al., 2024) in Section 'Conclusion and Outlook'

The microscopic Hamiltonian identifies the coupling subspaces, while this common signed rotation is an additional mesoscopic assumption whose realization by a native TLS ensemble remains to be justified.

— Directional transfer from coherence to longitudinal polarization and algebraic storage in a transmon with Markovian dephasing and a glassy environment: A non-Markovian fractional renewal model  (2609.37270 - Erdoğan et al., 29 Sep 2026) in Section 3.2, subsection “Renewal map and renewal equation”

The problem of disentangling their microscopic origin between structural or chemical defects in dielectrics, trapped quasiparticles, surface spins, etc., which could all coexist, remains open.

— Superconducting circuits host two-level systems with lifetimes exceeding one second  (2610.21853 - Féchant et al., 15 Oct 2026) in Section 1, opening paragraph