[Paper Review] Clifford-based Circuit Cutting for Quantum Simulation

Kaitlin N. Smith, Michael A. Perlin+6 more|arXiv (Cornell University)|Mar 19, 2023

Quantum Computing Algorithms and Architecture4 citations

TL;DR

This paper introduces SuperSim, a new quantum circuit simulation framework that combines Clifford-based simulation and circuit cutting to enable efficient, high-fidelity simulation of near-Clifford quantum circuits. By isolating Clifford fragments for efficient simulation and using circuit cutting to reconstruct full circuit outputs, SuperSim accelerates simulation of circuits with 100s of qubits using modest classical resources, outperforming state-of-the-art methods by orders of magnitude in key benchmarks.

ABSTRACT

Quantum computing has potential to provide exponential speedups over classical computing for many important applications. However, today's quantum computers are in their early stages, and hardware quality issues hinder the scale of program execution. Benchmarking and simulation of quantum circuits on classical computers is therefore essential to advance the understanding of how quantum computers and programs operate, enabling both algorithm discovery that leads to high-impact quantum computation and engineering improvements that deliver to more powerful quantum systems. Unfortunately, the nature of quantum information causes simulation complexity to scale exponentially with problem size. In this paper, we debut Super.tech's SuperSim framework, a new approach for high fidelity and scalable quantum circuit simulation. SuperSim employs two key techniques for accelerated quantum circuit simulation: Clifford-based simulation and circuit cutting. Through the isolation of Clifford subcircuit fragments within a larger non-Clifford circuit, resource-efficient Clifford simulation can be invoked, leading to significant reductions in runtime. After fragments are independently executed, circuit cutting and recombination procedures allow the final output of the original circuit to be reconstructed from fragment execution results. Through the combination of these two state-of-art techniques, SuperSim is a product for quantum practitioners that allows quantum circuit evaluation to scale beyond the frontiers of current simulators. Our results show that Clifford-based circuit cutting accelerates the simulation of near-Clifford circuits, allowing 100s of qubits to be evaluated with modest runtimes.

Motivation & Objective

• To address the exponential classical simulation cost of large quantum circuits, especially in the noisy intermediate-scale quantum (NISQ) era.
• To overcome the scalability limitations of existing simulators by leveraging structure in near-Clifford circuits.
• To develop a practical, high-performance simulation framework that enables benchmarking and algorithm development for quantum applications.
• To enable simulation of circuits with 100s of qubits using classical hardware by combining efficient Clifford simulation with circuit cutting.
• To support future integration with real quantum hardware and diverse simulators through extensible backend support.

Proposed method

• The framework decomposes a large quantum circuit into subcircuits by identifying and isolating Clifford fragments within a larger non-Clifford circuit.
• Clifford subcircuits are simulated efficiently using quadratic classical complexity via Stim-based simulation backends.
• Non-Clifford fragments are cut from the circuit and executed independently, with results recombined using circuit cutting reconstruction procedures.
• The reconstruction process uses stitching equations that combine probability distributions from fragment simulations to recover the full circuit output.
• Optimizations include skipping downstream stitching calculations when Pauli expectation values are known to be zero in Clifford circuits.
• Future extensions include parallelization of parsing, simulation, and postprocessing steps, as well as GPU acceleration and support for hybrid execution on real quantum hardware and other simulators.

Experimental results

Research questions

• RQ1 Can combining Clifford simulation with circuit cutting enable scalable simulation of large near-Clifford quantum circuits?
• RQ2 How does the performance of SuperSim compare to state-of-the-art simulators in terms of runtime and fidelity for near-Clifford circuits?
• RQ3 To what extent can structural properties of Clifford circuits—such as zero Pauli expectation values—reduce computational overhead in circuit cutting?
• RQ4 What is the upper bound of qubit count that SuperSim can simulate efficiently with current implementation?
• RQ5 How can dynamic backend selection between classical simulators and real quantum hardware improve simulation efficiency?

Key findings

• SuperSim enables simulation of near-Clifford quantum circuits with 100s of qubits using modest classical runtime, exceeding the capabilities of prior simulators.
• The framework achieves orders-of-magnitude speedup over state-of-the-art approaches in two benchmark applications involving near-Clifford circuits.
• The use of Clifford subcircuit isolation reduces simulation cost, as Clifford circuits scale quadratically with qubit count rather than exponentially.
• The framework reduces downstream stitching computations by leveraging the fact that many Pauli expectation values are zero in Clifford states, especially in multi-qubit systems.
• Performance can be further accelerated through parallelization of circuit parsing, fragment simulation, and postprocessing, with GPU and multi-core support planned.
• The open-source release of SuperSim is expected to accelerate research in quantum algorithm design, error correction, and hardware development.