Quantum++

Quantum++ is a C++11 general purpose quantum computing library, composed solely of template header files. It uses the Eigen 3 linear algebra library and, if available, the OpenMP multi-processing library. For additional Eigen 3 documentation see http://eigen.tuxfamily.org/dox/. For a simple Eigen 3 quick ASCII reference see http://eigen.tuxfamily.org/dox/AsciiQuickReference.txt.

Copyright (c) 2013 - 2014 Vlad Gheorghiu, vgheorgh AT gmail DOT com.

If you are interesting in contributing, please let me know. There is still work left to be done, and I can provide you with more details about what I have in mind. To contribute, you need to have a decent knowledge of C++ (preferably C++11), including templates and the standard library, a basic knowledge of quantum computing and linear algebra, and some working experience with Eigen 3.

The ultimate goal of this project is to build a universal quantum simulator, applicable to a vast majority of problems in quantum information/computation. The simulator should be fast but nevertheless user-friendly for anyone with a basic knowledge of C/C++.

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Quantum++ is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

Quantum++ is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with Quantum++. If not, see http://www.gnu.org/licenses/.

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Building instructions

Configuration:

• Compiler: g++ version 4.8 or later (for good C++11 support)
• Eigen 3 library located in $HOME/eigen
• Quantum++ library located in $HOME/qpp
• MATLAB compiler include header files: /Applications/MATLAB_R2014b.app/extern/include
• MATLAB compiler shared library files: /Applications/MATLAB_R2014b.app/bin/maci64

Building without a build system

• Example file: $HOME/qpp/examples/example.cpp
• Output executable: $HOME/qpp/examples/example
• Must run the commands below from inside the directory $HOME/qpp/examples

Release version (without MATLAB support):

g++ -pedantic -std=c++11 -Wall -Wextra -Weffc++ -fopenmp \
     -O3 -DNDEBUG -DEIGEN_NO_DEBUG \
     -isystem $HOME/eigen -I $HOME/qpp/include \
     example.cpp -o example

Debug version (without MATLAB support):

g++ -pedantic -std=c++11 -Wall -Wextra -Weffc++ -fopenmp \
     -g3 -DDEBUG \
     -isystem $HOME/eigen -I $HOME/qpp/include \
      example.cpp -o example

Release version (with MATLAB support):

g++ -pedantic -std=c++11 -Wall -Wextra -Weffc++ -fopenmp \
     -O3 -DNDEBUG -DEIGEN_NO_DEBUG \
     -isystem $HOME/eigen -I $HOME/qpp/include \
     -I/Applications/MATLAB_R2014b.app/extern/include \
     -L/Applications/MATLAB_R2014b.app/bin/maci64 \
     -lmx -lmat example.cpp -o example

Debug version (with MATLAB support):

g++ -pedantic -std=c++11 -Wall -Wextra -Weffc++ -fopenmp \
     -g3 -DDEBUG \
     -isystem $HOME/eigen -I $HOME/qpp/include \
     -I /Applications/MATLAB_R2014b.app/extern/include \
     -L /Applications/MATLAB_R2014b.app/bin/maci64 \
     -lmx -lmat example.cpp -o example

Building using cmake

The current version of the repository has a CMakeLists.txt configuration file for building examples using cmake. To build an example using cmake, I recommend an out-of-source build, i.e., from the root of the project (where ./include is located), type

mkdir ./build
cd ./build
cmake ..
make

The above commands build the relase version (default) executable qpp, from the source file ./examples/example.cpp, without MATLAB support (default), inside the directory ./build. To build a different configuration, e.g. debug version with MATLAB support, type from the root of the project

cd ./build
rm -rf *
cmake -DCMAKE_BUILD_TYPE=Debug -DWITH_MATLAB=ON ..
make

Or, to disable OpenMP support (enabled by default), type

cd ./build
rm -rf *
cmake -DWITH_OPENMP=OFF ..
make

To change the name of the example file, the location of the Eigen 3 library or the location of MATLAB installation, edit the CMakeLists.txt file. See also CMakeLists.txt for additional options. Do not forget to remove everything from the ./build directory before a fresh build!

Additional remarks

• The C++ compiler must be C++11 compliant.

• If your compiler does not support OpenMP (as it is the case e.g with clang++), disable OpenMP in your build, as otherwise the linker may not find the gomp library.

• If you run the program on OS X with MATLAB support, make sure that the environment variable DYLD_LIBRARY_PATH is set to point to the MATLAB compiler library location, see the run_OSX_MATLAB script. Otherwise, you will get a runtime error like dyld: Library not loaded: @rpath/libmat.dylib.

  • I recommend running via a script, as otherwise setting the DYLD_LIBRARY_PATH globally may interfere with macports' cmake installation (in case you use cmake from macports). If you use a script, then the environment variable is local to the script and does not interfere with the rest of the system.

  • Example of running script, run from inside the directory where the executable qpp is located:

      #!/bin/sh # Run Quantum++ under OS X with MATLAB support
      
      export DYLD_LIBRARY_PATH=$DYLD_LIBRARY_PATH:"/Applications/MATLAB_R2014b.app/bin/maci64"
      ./qpp
    

• If you build a debug version with g++ under OS X and use gdb to step inside template functions you may want to add -fno-weak compiler flag. See http://stackoverflow.com/questions/23330641/gnu-gdb-can-not-step-into-template-functions-os-x-mavericks for more details about this problem.