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Manuscript Title: The QWalk Simulator of Quantum Walks
Authors: F.L. Marquezino, R. Portugal
Program title: QWalk
Catalogue identifier: AEAX_v1_0
Distribution format: tar.gz
Journal reference: Comput. Phys. Commun. 179(2008)359
Programming language: C.
Computer: Any computer with a C compiler that accepts ISO C99 complex arithmetic (recent versions of GCC, for instance). Pre-compiled Windows versions are also provided.
Operating system: The software should run in any operating system with a recent C compiler. Successful tests were performed in Linux and Windows.
RAM: Less than 10 MB were required for a two-dimensional lattice of size 201 x 201. About 400 MB, for a two-dimensional lattice of size 1601 x 1601.
Keywords: Quantum walk, quantum computing, Quantum Mechanics, simulation, double-slit, broken links, C.
PACS: 03.67.Lx, 05.40.Fb, 03.65.Yz.
Classification: 16.5.

Nature of problem:
Classical simulation of discrete quantum walks in one- and two-dimensional lattices.

Solution method:
Iterative approach without explicit representation of evolution operator.

Restrictions:
The available amount of RAM memory imposes a limit on the size of the simulations.

Unusual features:
The software provides an easy way of simulating decoherence through detectors or random broken links. In the two-dimensional simulations it also allows the definition of permanent broken links, besides calculation of total variation distance (from the uniform and from an approximate stationary distribution) and the choice between two different physical lattices. It also provides an easy way of performing measurements on specific sites of the 2D lattice and the analysis of observation screens. In one-dimensional simulations it allows the choice between three different lattices. Both one- and two-dimensional simulations facilitates the generation of graphics by automatically generating gnuplot scrips.

Additional comments:
  • An earlier version of QWalk was first presented in [1].
  • The simulator generates gnuplot scripts that can be used to make graphics of the output data.
  • Several examples of input files are provided.

Running time:
The simulation of 100 steps for a two-dimensional lattice of size 201 x 201 took less than 2 seconds on a Pentium IV 2.6GHz with 512MB of RAM memory, 512KB of cache memory and under Linux. It also took about 15 minutes for a lattice of size 1601 x 1601 on the same computer. Optimization option -O2 was used during compilation for these tests.

References:
[1] Marquezino, F.L. and Portugal, R., QWalk: Simulador de Caminhadas Quânticas, in Proceedings of 2nd WECIQ, pages 123-132, Campina Grande, Brazil, 2007, IQuanta.