Scaling properties of the dynamics at first-order quantum transitions when boundary conditions favor one of the two phases

We address the out-of-equilibrium dynamics of a many-body system when one of its Hamiltonian parameters is driven across a first-order quantum transition (FOQT). In particular, we consider systems subject to fixed boundary conditions, favoring one of the two phases separated by the FOQT: more precisely, boundary conditions that favor the same magnetized phase (EFBC) or opposite phases (OFBC) at the two ends of the chain. These issues are investigated within the paradigmatic one-dimensional quantum Ising model, in which FOQTs are driven by the longitudinal magnetic field h. We study the dynamic behavior for an instantaneous quench and for a protocol in which h is slowly varied across the FOQT. We develop a dynamic finite-size scaling theory for both EFBC and OFBC, which displays some remarkable differences with respect to the case of neutral boundary conditions. The corresponding relevant time scale shows a qualitative different size dependence in the two cases: it increases exponentially with the size in the case of EFBC, and as a power of the size in the case of OFBC.

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