QuaSARQ

QuaSARQ stands for Quantum Simulation and Automated Reasoning. It is a parallel simulator of quantum stabilizer circuits capable of harnessing NVIDIA CUDA-enabled GPUs to accelerate the simulation of stabilizer gates.

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Requirements

• CUDA-capable GPU with a pre-installed NVIDIA driver
• CUDA Toolkit v12 or later
• cuArena GPU memory allocator library
• CMake 3.18 or later (to build cuArena)
• GCC/G++ with C++20 support

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Build

1. Install CUDA

For Ubuntu 24.04:

wget https://developer.download.nvidia.com/compute/cuda/repos/ubuntu2404/x86_64/cuda-keyring_1.1-1_all.deb
sudo dpkg -i cuda-keyring_1.1-1_all.deb
sudo apt-get update
sudo apt-get -y install cuda-toolkit-12-8

The source code is also platform-compatible with Windows and WSL2. To install CUDA on those platforms, follow the installation guide in https://docs.nvidia.com/cuda/.

2. Install QuaSARQ

• Clone the cuArena library before building QuaSARQ:

git clone https://github.com/muhos/cuArena.git /path/to/cuArena

• Build the simulator by pointing it at the cuArena directory:

make CUARENA_DIR=/path/to/cuArena

Make will build cuArena first then the quasarq binary and the library libquasarq.a will be created by default in the build directory.

Debug and Testing

Add assert=1 argument with the make command to enable assertions or debug=1 to collect debugging information.

make CUARENA_DIR=/path/to/cuArena assert=1

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Usage

quasarq [<circuit.stim|circuit.qasm>] [<circuit2.stim|circuit2.qasm>] [<option> ...]

QuaSARQ operates in four modes depending on the arguments given.

Single-shot simulation: simulate a circuit from a file and report the final stabilizer state:

quasarq circuit.stim
quasarq circuit.qasm --verbose=2

Many-shot sampling: sample measurement outcomes over many shots using GPU-based Pauli frames:

quasarq circuit.stim --shots=1024
quasarq circuit.stim --shots=10000 --seed=42

Equivalence checking: verify that two circuits produce identical stabilizer evolution:

quasarq circuit1.stim circuit2.stim

Prints EQUIVALENT or NOT EQUIVALENT (with the failing initial state). Accepts .stim and .qasm files in any combination.

Random circuit generation: generate and simulate a random stabilizer circuit without an input file:

quasarq --qubits=1000 --depth=500
quasarq --qubits=5000 --depth=1000 --shots=256

Key options

Option	Description	Default
--shots=<n>	Number of measurement shots (enables sampling mode)	0
--qubits=<n>	Number of qubits for random generation	1
--depth=<n>	Circuit depth for random generation	1
--initial=<0|1|2>	Initial state: 0 = |0⟩, 1 = |+⟩, 2 = |i⟩	0
--timeout=<s>	Abort after this many seconds	0 (off)
--verbose=<0..3>	Verbosity level	1
--seed=<n>	Random seed for sampling	0
--write-circuit=<1|2>	Write generated circuit to file (1: stim, 2: chp)	0
-report / -no-report	Print statistics after simulation	on
-progress / -no-progress	Show per-step progress	on
-q	Quiet mode (suppress all output)	off

For the full option list run:

quasarq -h
quasarq --helpmore

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Simulation Benchmarking

QuaSARQ implements two GPU-accelerated simulation modes:

• Single-shot simulation: applies parallel Gaussian elimination via a three-pass prefix-XOR formulation to handle projective measurements, eliminating sequential dependencies present in CPU-based approaches like Stim.
• Many-shot sampling: uses GPU-based Pauli frames to amortize tableau collapse costs across thousands of shots in parallel without repeated Gaussian elimination.

Benchmarks were run on an RTX 4090 (24 GB) against Stim, Qiskit-Aer (CPU/GPU), Qibo, Cirq, and PennyLane, across two suites:

• Light suite: 100–10,000 qubits, depths ∈ {100, 500, 1000}
• Heavy suite: 1,000–180,000 qubits, depths ∈ {100, 500, 1000} (~130M gates at peak)

QuaSARQ completes 177 circuits within 72 hours on the heavy suite, vs. Stim's 125 circuits in 132 hours, with up to 105× speedup on tableau evolution and over 80% energy reduction on demanding instances. For 1,024-shot sampling, QuaSARQ's Pauli-frame sampler shows flat runtime across circuit sizes while Stim's cost scales steeply.

Check our paper on arXiv for full algorithmic details.

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Equivalence Checking

QuaSARQ supports equivalence checking of two stabilizer circuits. For example, quasarq C1.stim C2.stim checks if C1 == C2. The outcome will be EQUIVALENT or otherwise NOT EQUIVALENT, indicating the failing initial state. Check our paper in TACAS'25 for more insights. The following plots compares the performance of QuaSARQ against CCEC (a Stim-based checker) and Quokka-Sharp (universal circuit simulator based on model counting). Circuits have qubits in range of 1,000 to 500,000 qubits.