Browsing by Author "Fraas, Martin"

Now showing 1 - 2 of 2
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    Non-Markovian noise that cannot be dynamically decoupled by periodic spin echo pulses
    Burgarth, Daniel; Facchi, Paolo; Fraas, Martin; Hillier, Robin (2021-08)
    Dynamical decoupling is the leading technique to remove unwanted interactions in a vast range of quantum systems through fast rotations. But what determines the timescale of such rotations in order to achieve good decoupling? By providing an explicit counterexample of a qubit coupled to a charged particle and magnetic monopole, we show that such time-scales cannot be decided by the decay profile induced by the noise: even though the system shows a quadratic decay (a Zeno region revealing non-Markovian noise), it cannot be decoupled by periodic spin echo pulses, no matter how fast the rotations.
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    On the Discrete Number of Tree Graphs
    Rhodes, Benjamin Robert (Virginia Tech, 2020-05-22)
    We study a generalization of the problem of finding bounds on the number of discrete chains, which itself is a generalization of the Erdős unit distance problem. Given a set of points in Euclidean space and a tree graph consisting of a much smaller number of vertices, we study the maximum possible number of tree graphs which can be represented by a prescribed tree graph. We derive an algorithm for finding tight bounds for this family of problems up to chain bound discrepancy, and give upper and lower bounds in special cases.