



00967nas a2200133   4500008004100000245004200041210004200083260001500125490000700140520059600147100002300743700002300766856004400789       2004                        eng d00aSpatial search and the Dirac equation0 aSpatial search and the Dirac equation  c2004/10/190 v703 a  We consider the problem of searching a d-dimensional lattice of N sites for a
single marked location. We present a Hamiltonian that solves this problem in
time of order sqrt(N) for d>2 and of order sqrt(N) log(N) in the critical
dimension d=2. This improves upon the performance of our previous quantum walk
search algorithm (which has a critical dimension of d=4), and matches the
performance of a corresponding discrete-time quantum walk algorithm. The
improvement uses a lattice version of the Dirac Hamiltonian, and thus requires
the introduction of spin (or coin) degrees of freedom.
1 aChilds, Andrew, M.1 aGoldstone, Jeffrey  uhttp://arxiv.org/abs/quant-ph/0405120v1