Spin-gap spectroscopy in a bosonic flux ladder

Ultracold bosonic atoms trapped in a two-leg ladder pierced by a magnetic field provide a minimal and quasi-one-dimensional instance to study the interplay between orbital magnetism and interactions. Using time-dependent matrix-product-state simulations, we investigate the properties of the so-called 'Meissner' and 'vortex' phases which appear in such a system, focusing on the experimentally accessible observables. We discuss how to experimentally monitor the phase transition, and show that the response to the modulation of the density imbalance between the two legs of the ladder is qualitatively different in the two phases. We argue that this technique can be used as a tool for many-body spectroscopy, allowing us to quantitatively measure the spin gap in the Meissner phase. We finally discuss its experimental implementation.