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About Qulacs

Qulacs is a fast quantum circuit simulator for simulating large, noisy, or parametric quantum circuits.

Qulacs is licensed under the MIT license.


  • Fast quantum circuit simulation with parallelized C/C++ backend
  • Noisy quantum gate for simulation of NISQ devices
  • Parametric quantum gates for variational methods
  • Circuit compression for fast simulation
  • GPU support for fast simulation
  • Many utility functions for research


  • Compared following libraries on January, 2020
Package Version
Qulacs GPU 0.1.9
Cirq 0.6.0
Qiskit Aer 0.3.4
ProjectQ 0.4.2
qHiPSTER latest master branch
Python interface of QuEST (PyQuest-cffi) 3.0.0

Test environment:

  • Azure NC6s_v3 (6vcpu / Mem112GiB)
  • Intel(R) Xeon(R) CPU E5-2690 v4 @ 2.60GHz
  • Tesla V100 PCIE (driver 440.33.01)

What is Benchmarked

for each qubit number N:

  • Apply simultaneous random single-qubit Pauli-X rotation

and then repeat:

  • Apply CNOT(i,(i+1)%N) for all i in [0..N-1]
  • Apply simultaneous random single-qubit Pauli-X rotation

for N times.

Note that measured time include time for create quantum circuit.

Single thread benchmark

single thread benchmark

Multi thread / GPU benchmark

multi thread benchmark

This benchmark was done with major quantum circuit simulator with python interface.
Yao is quantum circuit simulator using Julia that is as fast as Qulacs.
Benchmark include Yao can be found here.


  • C++ compiler (gcc or VisualStudio)
    • gcc/g++ >= 7.0.0 (checked in Linux, MacOS, cygwin, MinGW, and WSL)
    • Microsoft VisualStudio C++ 2015 or 2017
  • python 2.7 or 3.x
  • cmake >= 3.0
  • git
  • (option) CUDA >= 8.0
  • (option) AVX2 support

If your system supports AVX2 instructions, SIMD optimization is automatically enabled. If you want to enable GPU simulator, install qulacs through qulacs-gpu package or build from source.

Qulacs is tested on the following systems.

  • Ubuntu 16.04 / 18.04
  • MacOS X Sierra
  • Windows 10