2. Qulacs

2.1. Overview

Qulacs is a Python/C++ library for high-speed simulations of quantum circuits. This document will explain how to use Qulacs on Fugaku.

The supported version of Qulacs on Fugaku is v0.5.5.

For more information about Qulacs, refer to the official website.

2.2. How to use Qulacs

Qulacs is available through Spack, a software package management system for high performance computing.

2.2.1. Preparation of Spack environment

The Spack environment on Fugaku can be constructed based on Fugaku Spack User Guide.

This document explains how to use Qulacs assuming the use of public instances of Spack.

2.2.2. Loading Qulacs

If you use Qulacs, load it with the following command.

$ spack load qulacs %fj

2.2.3. Unloading Qulacs

If you do not use Qulacs, unload it with the following command.

$ spack unload qulacs %fj

2.3. Example of Usage

This section shows an example of running Qulacs in a batch job on Fugaku.

Here we will use a sample program (main.cpp) that creates a quantum state called the Bell state, which is a typical quantum entangled state.

$ cat main.cpp
#include <iostream>
#include <cppsim/state.hpp>
#include <cppsim/circuit.hpp>
#include <cppsim/observable.hpp>
#include <cppsim/gate_factory.hpp>
#include <cppsim/gate_merge.hpp>

int main(){
    QuantumState state(2);
    state.set_computational_basis(0b00);

    QuantumCircuit circuit(2);
    circuit.add_H_gate(0);
    circuit.add_CNOT_gate(0,1);
    circuit.update_quantum_state(&state);

    std::cout << state << std::endl;

    Observable observable(2);
    observable.add_operator(1.0, "Z 1 X 0");

    auto value = observable.get_expectation_value(&state);
    std::cout << value << std::endl;

    return 0;
}

2.3.1. Creating batch job script

The following batch job script (run.sh) is an example for running Qulacs on Fugaku.

※ For single account users, the execution group id (check with the id command) must be specified in run.sh.

（Example: #PJM -g hp*****）

$ cat run.sh
#!/bin/sh
#PJM -g hp*****
#PJM -L "node=1"
#PJM -L "rscgrp=small"
#PJM -L "elapse=00:20:00"
#PJM --mpi "max-proc-per-node=12"
#PJM -x PJM_LLIO_GFSCACHE=/vol0004
#PJM -S

export PATH=/opt/FJSVxtclanga/tcsds-1.2.36/bin:$PATH
export LD_LIBRARY_PATH=/opt/FJSVxtclanga/tcsds-1.2.36/lib64:$LD_LIBRARY_PATH
. /vol0004/apps/oss/spack/share/spack/setup-env.sh
spack load qulacs %fj

FCC -Nclang -O2 main.cpp -fopenmp -lcppsim_static -lcsim_static
./a.out

2.3.2. Execution of batch job

Please submit the batch job script (run.sh) by the following command.

$ pjsub run.sh

2.3.3. Confirmation of result

If you obtain the following result in run.sh.job-id.out, Qulacs is working without problems.

 *** Quantum State ***
 * Qubit Count : 2
 * Dimension   : 4
 * State vector :
(0.707107,0)
       (0,0)
       (0,0)
(0.707107,0)

(0,0)