Speaker
Description
In quantum field theory, quantum fluctuations can trigger the decay of a field from a metastable state (false vacuum) to the ground state (true vacuum) through the macroscopic tunneling across a many-body energy barrier [1]. False vacuum decay, which is thought to manifest via the spontaneous nucleation of spatially localized bubbles, is a fascinating phenomenon for a rich variety of systems, ranging from condensed matter [2] to cosmology [3]. Nevertheless, its experimental verification has been elusive so far, due to the extreme energy scales involved and the lack of tunable parameters. Here, I will present the first experimental evidences [4,5] of false vacuum decay in a metastable ferromagnetic superfluid. In this novel platform, realized with ultracold sodium atoms in two coherently-coupled internal states [6] in an ultrastable magnetic field environment [7], the superfluid acts as the quantum field, and macroscopic tunneling events are observed through the nucleation of spin bubbles via thermal fluctuations. Our results find good agreement with numerical simulations and instanton theory, opening the way for the simulation of out-of-equilibrium phenomena in a highly controllable and tunable atomic system.
References
[1] The Fate of the False Vacuum. 1. Semiclassical Theory, S. R. Coleman, Phys. Rev. D 16, 1248 (1977).
[2] False vacuum decay in quantum spin chains, G. Lagnese et al., Phys. Rev. B 104, L201106 (2021).
[3] Phase transitions in the early universe, M. Hindmarsh et al. SciPost Phys. Lect. Notes 24 (2021).
[4] False vacuum decay via bubble formation in ferromagnetic superfluids, A. Zenesini et al, Nat. Phys. 20, 558 (2024).
[5] Observation of Temperature Effects in False Vacuum Decay, R. Cominotti, C. Baroni et al, arXiv 2504.03528.
[6] Ferromagnetism in an Extended Coherently Coupled Atomic Superfluid, R. Cominotti, A. Berti et al. Phys. Rev. X 13, 021037 (2023).
[7] Design and characterization of a compact magnetic shield for ultracold atomic gas experiments, A. Farolfi et al., Rev. Sci. Instrum. 90, 115114 (2019).
