Regensburg 2025 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 28: Many-body Quantum Dynamics II (joint session DY/TT)

TT 28.5: Talk

Wednesday, March 19, 2025, 10:30–10:45, H37

Preparing many-body eigenstates via repeated measurements — •Ruoyu Yin^1,2 and Hongzheng Zhao¹ — ¹School of Physics, Peking University, China — ²Physics Department, Bar Ilan University, Israel

This work investigates the challenging problem of preparing an eigenstate of a many-body system, or even a superposition of several eigenstates. We address this problem by periodically projecting a many-body system into the complementary subspace of a predetermined product state. By appropriately manipulating the measurement period, we demonstrate that such a dissipative process can yield a steady state, with no need for fine-tuning criteria. Notably, these non-equilibrium steady states (NESS) are superpositions of energy eigenstates, with coefficients encoding the predetermined product state. More intriguingly, for certain measurement periods, we uncover the possibility of a non-equilibrium phase composed of multiple superposition states, with relative phases determined by their energy differences and the measurement time. This finding reveals the potential of the measurement process to prepare a delicate yet manipulable many-body dynamical phase through dissipation. As a demonstration, we apply this protocol to the paradigmatic spin-1 XY model, which exhibits athermal or scarred eigenstates. We show that, through repeated measurements and post-selection, the system can be driven into a NESS or a dynamical phase with high fidelity. Furthermore, we examine the robustness of the protocol by introducing perturbations that disrupt the nonlocal SU(2) algebra. These results are not restricted to the specific model but are also applicable to systems described by tower algebra.

Keywords: repeated measurements; uncertainty relation; monitored quantum dynamics