Quantum++

Version 1.0-rc1 - Release Candidate 1, 11 November 2016

Build status: Master Devel

Quantum++ is a modern C++11 general purpose quantum computing library, composed solely of template header files. Quantum++ is written in standard C++11 and has very low external dependencies, using only the Eigen 3 linear algebra header-only template library and, if available, the OpenMP multi-processing library.

Quantum++ is not restricted to qubit systems or specific quantum information processing tasks, being capable of simulating arbitrary quantum processes. The main design factors taken in consideration were the ease of use, high portability, and high performance. The library's simulation capabilities are only restricted by the amount of available physical memory. On a typical machine (Intel i5 8Gb RAM) Quantum++ can successfully simulate the evolution of 25 qubits in a pure state or of 12 qubits in a mixed state reasonably fast.

To report any bugs or ask for additional features/enhancements, please submit an issue with an appropriate label.

If you are interesting in contributing to this project, please contact me. To contribute, you need to have a solid knowledge of C++ (preferably C++11), including templates and the standard library, a basic knowledge of quantum computing and linear algebra, and working experience with Eigen 3.

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 - 2017 Vlad Gheorghiu, vgheorgh AT gmail DOT com.

---

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/.

---

Building instructions for POSIX-compliant platforms

Configuration

• Compiler: g++ version 4.8.2 or later (for good C++11 support)
• Eigen 3 library located in $HOME/eigen
• Quantum++ library located in $HOME/qpp

Optional

• CMake version 3.0.0 or later, highly recommended
• MATLAB compiler include header files: /Applications/MATLAB_R2016a.app/extern/include
• MATLAB compiler shared library files: /Applications/MATLAB_R2016a.app/bin/maci64

Building using CMake (version 3.0.0 or later)

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 commands above build the relase version (default) executable qpp, from the source file ./examples/minimal.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 clean the ./build directory before a fresh build!

Building without an automatic build system

• Example file: $HOME/qpp/examples/minimal.cpp
• Output executable: $HOME/qpp/examples/minimal
• You 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 \
     minimal.cpp -o minimal

Debug version (without MATLAB support)

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

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_R2016a.app/extern/include \
     -L/Applications/MATLAB_R2016a.app/bin/maci64 \
     -lmx -lmat minimal.cpp -o minimal

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_R2016a.app/extern/include \
     -L /Applications/MATLAB_R2016a.app/bin/maci64 \
     -lmx -lmat minimal.cpp -o minimal

Additional building instructions for particular platforms

Windows via Cygwin

• Some earlier versions of Cygwin had a bug related to lack of support for some C++11 math functions, see http://stackoverflow.com/questions/28997206/cygwin-support-for-c11-in-g4-9-2 for more details. Quick fix: patch the standard library header file <cmath> using the provided patch ./cmath_cygwin.patch. Latest Cygwin (as of Nov. 11, 2016) seem to have fixed the issue.

Windows via Visual Studio

• Visual Studio versions preceeding version 2015 do not have full C++11 support. If you decide to use Visual Studio make sure you install version 2015 or later.

• Visual Studio 2015 only supports OpenMP 2.0. Quantum++ uses features from OpenMP 3.0, hence Quantum++ will not compile on Visual Studio 2015 if you enable OpenMP (disabled by default) in

  Project/Properties/Configuration Properties/C_C++/Language/Open MP Support

and #define WITH_OPENMP_ in your source file.

• To create a Visual Studio 2015 or later console solution, start by creating a Win32 Console Application

  File/New/Project.../Installed/Templates/Visual C++/Win32/Win32 Console Application

  Click Next then select Console Application as Application Type. Click Finish to create the solution. Next select

  Project/Properties

  from the main menu. The Property Pages configuration window will open. From the latter select All configurations from the top left Configuration drop box. Next select

  Configuration Properties/C_C++/General

  and add to the field Additional Include Directories the location of Quantum++ ./include folder as well as the location of Eigen 3. It should look similar to

  C:\Users\User\Downloads\eigen;C:\Users\User\Downloads\qpp\include;%(AdditionalIncludeDirectories)

  Finally select

  Configuration Properties/C_C++/Advanced

  and add to the field Disable Specific Warnings the values 4503;4996. Click Ok to save the settings and close the Property Pages window. You are now ready to go.

OS X/macOS

• If you want to compile with clang++ version 3.7 or later, I highly recommend to install it via macports.

• If you run the program 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_mac_MATLAB script. Otherwise, you get a runtime error similar to

  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 script, assumed to be located in the root directory of Quantum++

       #!/bin/sh
       
       MATLAB=/Applications/MATLAB_R2016a.app
       export DYLD_LIBRARY_PATH=$DYLD_LIBRARY_PATH:$MATLAB/bin/maci64
       
       ./build/qpp
    

• If you build a debug version with g++ 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.

Unit testing

Quantum++ was extensively tested under multiple flavours of Linux, OS X/macOS, Windows XP/7/10, Solaris 11.x via a suite of unit tests constructed with Google Test 1.8.0 (included with the project in ./unit_tests/lib/gtest-1.8.0). The source code of the unit tests is provided under ./unit_tests/tests. To build and run the unit tests, I strongly recommend to use CMake version 3.0.0 or later. Assuming you do use CMake, switch to the
./unit_tests directory, create a build directory inside it, then from the newly created ./unit_tests/build type

cmake ..
make

The commands above build ./unit_tests/build/tests/qpp_testing, which you then may run. Note that qpp::Timer tests or tests related to random functions such as qpp::rand() may sometime (very rarely) fail, due to timing imprecision or statistical errors. Such a behaviour is perfectly normal.

Note

The CMake configuration file ./unit_tests/CMakeLists.txt defines the same building options and default choices as the main ./CMakeLists.txt of Quantum++. Therefore you can use the same flags as the ones mentioned at the beginning of this document when customizing the build. You should modify ./unit_tests/CMakeLists.txt accordingly in case your Eigen 3 library or MATLAB include/library files are in a different location than the one assumed in this document.

Additional remarks

• If you use clang++ version 3.7 or later and want to use OpenMP (enabled by default), make sure to modify CLANG_LIBOMP and CLANG_LIBOMP_INCLUDE in CMakeLists.txt so they point to the correct location of the OpenMP library, as otherwise clang++ will not find <omp.h> and the libomp shared library.