Domain-wall dynamics near a quantum critical point

Abstract

We study the real-time domain-wall dynamics near a quantum critical point of the one-dimensional anisotropic ferromagnetic spin 1 / 2 chain. By numerical simulation, we find that the domain wall is dynamically stable in the Heisenberg-Ising model. Near the quantum critical point, the width of the domain wall diverges as ͑⌬ −1͒ −1/2 .

Dynamics of two qubits in a spin bath with anisotropicXYcoupling

“…In this paper, we study an open two-spin-qubit system in a spin bath of star-like configuration, which is similar to the cases studied in Ref. [9,17]. But the two qubits' distance is far enough so that the direct coupling between them could be neglected.…”

“…However, the spin qubits are open systems which is impossible to avoid interactions with their environments [6,7,8,9]. Finally, the states of the qubits will relax into a set of "pointer states" in the Hilbert space [10]; and the entanglement between the spin qubits will also vanish.…”

“…Yuan and co-workers [9] used a novel operator technique to obtain the dynamics of the two coupled spins in quantum Heisenberg XY high symmetry spin model. The results of all the above works are very exciting.…”

“…And in Ref. [9], their analytical results are dependent on some particular initial states and essentially the interaction between the spins in their model is isotropic. Here we introduce a "half analytical and half numerical" method to solve such an open quantum system problem in an anisotropic Heisenberg XY model.…”

Universal front propagation in the quantum Ising chain with domain-wall initial states

“…Under time evolution the initial inhomogeneity spreads ballistically, creating a front region which grows linearly in time. While the overall shape of the front is simple to obtain from a hydrodynamic (semiclassical) picture in terms of the fermionic excitations [9], the fine structure is more involved and shows universal features around the edge of the front [10,11] The melting of domain walls has been considered in various different lattice models, such as the transverse Ising [12,13], the XY [14] and XXZ chains [15][16][17][18], hard-core bosons [19][20][21], as well as in the continuum for a Luttinger model [22], the Lieb-Liniger gas [23] or within conformal field theory [24,25]. Instead of a sharp domain wall, the melting of inhomogeneous interfaces can also be studied by applying a magnetic field gradient, which is then suddenly quenched to zero [26][27][28].…”