First Detected Arrival of a Quantum Walker on an Infinite Line

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The first detection of a quantum particle on a graph is shown to depend sensitively on the distance xi between the detector and initial location of the particle, and on the sampling time tau. Here, we use the recently introduced quantum renewal equation to investigate the statistics of first detection on an infinite line, using a tight-binding lattice Hamiltonian with nearest-neighbor hops. Universal features of the first detection probability are uncovered and simple limiting cases are analyzed. These include the large xi limit, the small tau limit, and the power law decay with the attempt number of the detection probability over which quantum oscillations are superimposed. For large xi the first detection probability assumes a scaling form and when the sampling time is equal to the inverse of the energy band width nonanalytical behaviors arise, accompanied by a transition in the statistics. The maximum total detection probability is found to occur for tau close to this transition point. When the initial location of the particle is far from the detection node we find that the total detection probability attains a finite value that is distance independent.
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