SliQSim - A BDD-based Quantum Circuit Simulator

Introduction

SliQSim is a BDD-based quantum circuit simulator implemented in C/C++ on top of CUDD package. In SliQSim, a bit-slicing technique based on BDDs is used to represent quantum state vectors. For more details of the simulator, please refer to the paper.

Build

To build the simulator, one needs to first configure CUDD:

cd cudd
./configure --enable-dddmp --enable-obj --enable-shared --enable-static 
cd ..

Next, build the binary file SliQSim:

make

Execution

The circuit format being simulated is OpenQASM used by IBM's Qiskit, and the gate set supported in this simulator now contains Pauli-X (x), Pauli-Y (y), Pauli-Z (z), Hadamard (h), Phase and its inverse (s and sdg), π/8 and its inverse (t and tdg), Rotation-X with phase π/2 (rx(pi/2)), Rotation-Y with phase π/2 (ry(pi/2)), Controlled-NOT (cx), Controlled-Z (cz), Toffoli (ccx and mcx), SWAP (swap), and Fredkin (cswap). One can find some example benchmarks in examples folder.

For simulation types, we provide both "sampling" and "all_amplitude" simulation options. The help message states the details:

$ ./SliQSim --help
Options:
--help                produce help message
--sim_qasm arg        simulate qasm file string
--seed [=arg(=1)]     seed for random number generator
--print_info          print simulation statistics such as runtime, memory, etc.
--type arg (=0)       the simulation type being executed.
                      0: sampling mode (default option), where the sampled outcomes will be provided. 
                      1: all_amplitude mode, where the final state vector will be shown. 
--shots arg (=1)      the number of outcomes being sampled in "sampling mode" .
--r arg (=32)         integer bit size.
--reorder arg (=1)    allow variable reordering or not.
                      0: disable reordering.
                      1: enable reordering (default option).
--alloc arg (=1)      allocate new BDDs when overflow is detected.
                      0: do not allocate new BDDs. This may lead to numerical errors.
                      1: allocate new BDDs (default option).

To use the sampling mode (default), it is required to have measurement operations included in the qasm file. Conversely, in all_amplitude mode, measurement operations are generally omitted, but if they are present in the qasm file, the final state vector will collapse based on the measurement result. It is important to note that all_amplitude mode is not recommended for simulations involving a large number of qubits, as it could result in a significantly long runtime.

For example, simulating example/bell_state_measure.qasm, which is a 2-qubit bell state circuit with measurement gates at the end, with the sampling mode simulation option can be executed by

./SliQSim --sim_qasm examples/bell_state_measure.qasm --type 0 --shots 1024

Then the sampled results will be shown:

{ "counts": { "11": 542, "00": 482 } }

If option --print_info is used, simulation statistics such as runtime and memory usage will also be provided:

  Runtime: 0.014433 seconds
  Peak memory usage: 12611584 bytes
  #Applied gates: 2
  Max #nodes: 13
  Precision of integers: 32
  Accuracy loss: 2.22045e-16

To demostrate the all_amplitude mode simulation, we use example/bell_state.qasm, which is the same circuit as in the sampling mode simulation example except that the measurement gates are removed:

./SliQSim --sim_qasm examples/bell_state.qasm --type 1

This will show the resulting state vector:

{"statevector": ["0.707107", "0", "0", "0.707107"] }

One may also execute our simulator as a backend option of Qiskit through SliQSim Qiskit Interface.

Citation

Please cite the following paper if you use our simulator for your research:

Y.-H. Tsai, J.-H. R. Jiang, and C.-S. Jhang, “Bit-slicing the hilbert space: Scaling up accurate quantum circuit simulation,” in Design Automation Conference (DAC), 2021, pp. 439–444.

@INPROCEEDINGS{9586191,
  author={Tsai, Yuan-Hung and Jiang, Jie-Hong R. and Jhang, Chiao-Shan},
  booktitle={Design Automation Conference (DAC)}, 
  title={Bit-Slicing the Hilbert Space: Scaling Up Accurate Quantum Circuit Simulation}, 
  year={2021},
  pages={439-444},
  doi={10.1109/DAC18074.2021.9586191}
}

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