Bath-Induced Dissipative Phase Transitions

Anchor paper: B. Min, K. Agarwal, D. Segal, "Role of bath-induced many-body interactions in the dissipative phases of the Su-Schrieffer-Heeger model," Phys. Rev. B 110, 125415 (2024). [arXiv:2406.13878]

Background

The Su-Schrieffer-Heeger (SSH) chain is a paradigmatic 1D symmetry-protected topological insulator, in the same topological-model family as the Kitaev chain that hosts Majorana zero modes. Coupling such a chain to a dissipative thermal bath is known to reshape its phase diagram, but prior treatments largely relied on weak-coupling/Markovian approximations that only renormalize single-particle (hopping) terms. Open question: how is the SSH chain's topological/trivial phase structure reorganized when system-bath coupling is treated non-perturbatively, strong enough that the bath generates genuine many-body (interaction) terms rather than just single-particle corrections?

New results

Using a reaction-coordinate polaron transform to derive an effective Hamiltonian valid at strong coupling, the authors show local thermal baths — coupled either intracell or intercell — generate dimerized many-body fermion-fermion interactions alongside the expected hopping renormalization. Via exact diagonalization and the ensemble geometric phase, intracell coupling suppresses the topology-favoring hopping and produces interactions penalizing doubly-occupied unit cells, shrinking the topological window; intercell coupling suppresses the topology-breaking hopping while its many-body term favors the topological phase, expanding it. In both cases the bath-induced many-body interaction — not single-particle renormalization — dominates the reshaping of phase boundaries; the same mechanism extends to the related Rice-Mele model.

Fig. 2 — ensemble-geometric-phase phase diagrams of the dissipative SSH chain for intracell (top) vs. intercell (bottom) bath coupling, showing bath-induced many-body interactions shrinking or expanding the topological region.

Related work in this direction

Co-author B. Min is also a collaborator on Agarwal's Majorana-qubit robustness papers (e.g. "Dynamical approach to improving Majorana qubits and distinguishing them from trivial bound states," PRB 105, 155412, 2022). This study uses the SSH chain — a simpler cousin of the Kitaev chain — as a testbed for exactly the kind of strong-coupling, non-Markovian bath effects that matter for assessing the dissipative robustness of Majorana zero modes in wire-based qubits.