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The Journal of Open Source Software

QXTools: A Julia framework for distributed quantum circuit simulation

John Brennan, L. ORiordan, Kenneth Hanley, Myles Doyle, Momme Allalen, David Brayford, Luigi Iapichino, Niall Moran

Published Feb 15, 2022• 7 citations
Publisher

Abstract

QXTools is a framework for simulating quantum circuits using tensor network methods.Weak simulation is the primary use case where given a quantum circuit and input state QXTools will efficiently calculate the probability amplitude of a given output configuration or set of configurations.Given this ability one can sample from the output distribution using random sampling approaches.QXTools is intended to be used by researchers interested in simulating circuits larger than those possible with full wave-function simulators or those interested in research and development of tensor network circuit simulation methods.See Brennan et al. (2021) for more complete background and scaling results and Brayford et al. ( 2021) for details about deploying in containerised environments.

DOI
10.21105/joss.03711

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QXTools is a framework for simulating quantum circuits using tensor network methods.Weak simulation is the primary use case where given a quantum circuit and input state QXTools will efficiently calculate the probability amplitude of a given output configuration or set of configurations.Given this ability one can sample from the output distribution using random sampling approaches.QXTools is intended to be used by researchers interested in simulating circuits larger than those possible with full wave-function simulators or those interested in research and development of tensor network circuit simulation methods.See Brennan et al. (2021) for more complete background and scaling results and Brayford et al. ( 2021) for details about deploying in containerised environments.
The accurate simulation of quantum circuits remains a significant challenge due to the exponential scaling of computational resources with circuit size. This work explores the application of tensor network methods, specifically Matrix Product States (MPS), to provide a scalable approach for simulating quantum circuits. We demonstrate how tensor networks can efficiently represent and manipulate the states of quantum circuits, reducing the computational burden associated with traditional methods. The core claim of this research is that tensor networks offer a viable path to accurately simulating larger and more complex quantum systems. This research introduces a novel framework for symbolic simulation, leveraging the power of tensor network representations to overcome the limitations of conventional simulation techniques. The effectiveness of this approach is illustrated through theoretical analysis and conceptual examples.
We present a tensor-network-based method for simulating a weakly-measured quantum circuit. In particular, we use a Markov chain to efficiently sample measurements and contract the tensor network, propagating their effect forward along the spatial direction. Applications of our algorithm include validating quantum computers (capable of mid-circuit measurements) in regimes of easy classical simulability, and studying generative-machine-learning applications, where sampling from complex stochastic processes is the main task. As a demonstration of our algorithm, we consider a (1+1)-dimensional brickwall circuit of Haar-random unitaries, interspersed with generalized single-qubit measurements of variable strength. We simulate the dynamics for tens to hundreds of qubits if the circuit exhibits area-law entanglement (under strong measurements), and tens of qubits if it exhibits volume-law entanglement (under weak measurements). We observe signatures of a measurement-induced phase transition between the two regimes as a function of measurement strength.
The study of quantum circuit simulation using classical computers is a key research topic that helps define the boundary of verifiable quantum advantage, solve quantum many-body problems, and inform development of quantum hardware and software. Tensor networks have become forefront mathematical tools for these tasks. Here we introduce a method to approximately simulate quantum circuits using sparsely-populated tensors. We describe a sparse tensor data structure that can represent quantum states with no underlying symmetry, and outline algorithms to efficiently contract and truncate these tensors. We show that the data structure and contraction algorithm are efficient, leading to expected runtime scalings versus qubit number and circuit depth. Our results motivate future research in optimization of sparse tensor networks for quantum simulation.
This paper explores the potential of tensor networks for enabling distributed quantum simulation, a crucial step towards scaling up quantum computations. Traditional quantum simulation faces limitations due to the exponential growth of state vector sizes required for complex systems. Distributed quantum simulation aims to overcome this by partitioning the simulation across multiple quantum processors. However, efficient representation and manipulation of the resulting distributed quantum state remain a significant challenge. This work proposes utilizing tensor networks as a framework for representing and processing these distributed quantum states. Tensor networks offer an inherent structure that facilitates efficient parallel computation and minimizes communication overhead between quantum processors. We outline a theoretical framework, detailing the application of tensor network contractions and disentanglement techniques specifically tailored for distributed quantum simulation scenarios. The core claim of this work is that scaling up quantum simulations requires efficient methods for representing and manipulating quantum states, and tensor networks provide a promising avenue for achieving this goal. We present a method to reduce the computational complexity associated with simulating large quantum systems by leveraging the properties of tensor networks. The approach allows for a more scalable simulation strategy, moving beyond the limitations of traditional state vector representations. Further research will explore specific tensor network architectures and optimization strategies for different simulation problems.
The numerical simulation of quantum circuits is an indispensable tool for development, verification, and validation of hybrid quantum-classical algorithms intended for near-term quantum co-processors. The emergence of exascale high-performance computing (HPC) platforms presents new opportunities for pushing the boundaries of quantum circuit simulation. We present a modernized version of the Tensor Network Quantum Virtual Machine (TNQVM) that serves as the quantum circuit simulation backend in the eXtreme-scale ACCelerator (XACC) framework. The new version is based on the scalable tensor network processing library ExaTN (Exascale Tensor Networks). It provides multiple configurable quantum circuit simulators that perform either an exact quantum circuit simulation via the full tensor network contraction or an approximate simulation via a suitably chosen tensor factorization scheme. Upon necessity, stochastic noise modeling from real quantum processors is incorporated into the simulations by modeling quantum channels with Kraus tensors. By combining the portable XACC quantum programming frontend and the scalable ExaTN numerical processing backend, we introduce an end-to-end virtual quantum development environment that can scale from laptops to future exascale platforms. We report initial benchmarks of our framework, which include a demonstration of the distributed execution, incorporation of quantum decoherence models, and simulation of the random quantum circuits used for the certification of quantum supremacy on Google’s Sycamore superconducting architecture.