Limit theorems for the interference terms of discrete-time quantum walks on the line

The probability distributions of discrete-time quantum walks have been often investigated, and many interesting properties of them have been discovered. The probability that the walker can be find at a position is defined by diagonal elements of the density matrix. On the other hand, although off-diagonal parts of the density matrices have an important role to quantify quantumness, they have not received attention in quantum walks. We focus on the off-diagonal parts of the density matrices for discrete-time quantum walks on the line and derive limit theorems for them.Comment: Quantum Information and Computation, Vol.13 No.7&8, pp.661-671 (2013

Limit theorems for quantum walks with memory

Recently Mc Gettrick [1] introduced and studied a discrete-time 2-state quantum walk (QW) with a memory in one dimension. He gave an expression for the amplitude of the QW by path counting method. Moreover he showed that the return probability of the walk is more than 1/2 for any even time. In this paper, we compute the stationary distribution by considering the walk as a 4-state QW without memory. Our result is consistent with his claim. In addition, we obtain the weak limit theorem of the rescaled QW. This behavior is striking different from the corresponding classical random walk and the usual 2-state QW without memory as his numerical simulations suggested.Comment: Quantum Information and Computation, Vol.10, No.11&12, pp.1004-1017 (2010