QUROPE Quantum Information Processing and Communication in Europe

We analyse the sensitivity, quantied by the helicity modulus and the stiness, of the long-time stationary state of a many-body quantum system to an innitesimal twist at the boundary conditions. The standard thermalisation framework cannot be straightforwardly employed in this context, since such quantities are non-local. We apply our theory to two paradigmatic examples of hard-core bosons in a one-dimensional ring, quenched to/from super uid/insulating phases. We show that the out-of-equilibrium stiness is qualitatively dierent from the equilibrium case.