Abstract: We investigate the delocalization of quantum information in the nonequilibrium dynamics of the XY spin chain with asymptotically decaying interactions similar to 1/r(alpha). As a figure of merit, we employ the tripartite mutual information (TMI), the sign of which indicates if quantum information is predominantly shared globally. Interestingly, the sign of the TMI distinguishes regimes of the exponent a that are known for different behaviors of information propagation. While an effective causal region bounds the propagation of information, if interactions decay sufficiently fast, this information is mainly delocalized, which leads to the necessity of global measurements. Furthermore, the results indicate that mutual information is monogamous for all possible partitionings in this case, implying that quantum entanglement is the dominant correlation. If interactions decay sufficiently slow, though information can propagate (quasi-)instantaneously, it is mainly accessible by local measurements at early times. Furthermore, it takes some finite time until correlations start to become monogamous, which suggests that entanglement is not the dominant correlation at early times. Our findings give new insights into the dynamics and structure of quantum information in many-body systems with long-range interactions, and might get verified on state-of-the-art experimental platforms.
Abstract: We propose a setup, based on a periodically driven spin chain, that can realize a high-quality quantum router. We present two protocols, which utilize this setup, that can either generate highly entangled two-qubit states over an arbitrary distance or transfer single-qubit states with high fidelity to any desired location on the chain. In addition, we can execute several protocols at the same time and also store quantum states on the spin chain. Our protocols exploit the effect of coherent destruction of tunneling to control, which spins on the chain couple to each other. This control is acquired by suitably shaping the external driving field. The success of our protocols does not depend on the values of the couplings between the spins as long as they are finite and much smaller than the driving frequency. Our setup is scalable, robust against errors, and may be of practical use for future quantum information technologies.