Physics – Quantum Physics
Scientific paper
2005-04-06
New J. Phys. 7 (2005) 156
Physics
Quantum Physics
23 pages, many eps embedded figures; v2 published version: better quality figures on journal website (open access) at http:/
Scientific paper
10.1088/1367-2630/7/1/156
Quantum walks, both discrete (coined) and continuous time, form the basis of several recent quantum algorithms. Here we use numerical simulations to study the properties of discrete, coined quantum walks. We investigate the variation in the entanglement between the coin and the position of the particle by calculating the entropy of the reduced density matrix of the coin. We consider both dynamical evolution and asymptotic limits for coins of dimensions from two to eight on regular graphs. For low coin dimensions, quantum walks which spread faster (as measured by the mean square deviation of their distribution from uniform) also exhibit faster convergence towards the asymptotic value of the entanglement between the coin and particle's position. For high-dimensional coins, the DFT coin operator is more efficient at spreading than the Grover coin. We study the entanglement of the coin on regular finite graphs such as cycles, and also show that on complete bipartite graphs, a quantum walk with a Grover coin is always periodic with period four. We generalize the 'glued trees' graph used by Childs et al (2003 Proc. STOC, pp 5968) to higher branching rate (fan out) and verify that the scaling with branching rate and with tree depth is polynomial.
Carneiro Ivens
Girerd Mathieu
Kendon Viv
Knight Peter L.
Loo Meng
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