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Variational Quantum Linear Solver

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arxiv 1909.05820 v4 pith:FVYIOSJQ submitted 2019-09-12 quant-ph

classification quant-ph
keywords quantumvqlslinearepsilonkapparanglesizecondition
verification ladder T0 review T1 audit T2 compute T3 formal
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abstract

Previously proposed quantum algorithms for solving linear systems of equations cannot be implemented in the near term due to the required circuit depth. Here, we propose a hybrid quantum-classical algorithm, called Variational Quantum Linear Solver (VQLS), for solving linear systems on near-term quantum computers. VQLS seeks to variationally prepare $|x\rangle$ such that $A|x\rangle\propto|b\rangle$. We derive an operationally meaningful termination condition for VQLS that allows one to guarantee that a desired solution precision $\epsilon$ is achieved. Specifically, we prove that $C \geq \epsilon^2 / \kappa^2$, where $C$ is the VQLS cost function and $\kappa$ is the condition number of $A$. We present efficient quantum circuits to estimate $C$, while providing evidence for the classical hardness of its estimation. Using Rigetti's quantum computer, we successfully implement VQLS up to a problem size of $1024\times1024$. Finally, we numerically solve non-trivial problems of size up to $2^{50}\times2^{50}$. For the specific examples that we consider, we heuristically find that the time complexity of VQLS scales efficiently in $\epsilon$, $\kappa$, and the system size $N$.

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Cited by 6 Pith papers

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score.

  1. Neural Quantum Spectral Operator Learning for Solving Partial Differential Equations

    quant-ph 2026-05 unverdicted novelty 7.0 of 10

    NVQLS introduces the first hybrid quantum-classical unsupervised operator learning method for parametric PDEs via Legendre-Galerkin weak form, sign ambiguity resolution, and neural embedding.

  2. Parametrized-circuit-free quantum regression with variance regularization

    quant-ph 2026-07 accept novelty 6.0 of 10

    Symmetry-inspired fixed observables plus classical linear regression with variance regularization predict quantum properties without parameterized circuits and with lower resource cost than VQAs.

  3. Projector Quantum Variational Ansatz

    quant-ph 2026-06 unverdicted novelty 6.0 of 10

    The Projector Variational Ansatz (PVA) is a new VQE ansatz that can match ISQ-QSP or ADAPT-VQE structures and converges with shallower circuits than standard ADAPT-VQE in experiments.

  4. Analog photonic simulator for large-scale transport

    quant-ph 2026-05 unverdicted novelty 5.0 of 10

    Continuous-variable photonic platform with 20,000-mode cluster state simulates advection transport equation, achieving relative errors of 0.8% and 0.92% on first- and second-order moments via homodyne readout.

  5. Measurement-Efficient Variational Quantum Linear Solver for Carleman-Linearized Nonlinear Dynamics

    quant-ph 2026-05 unverdicted novelty 4.0 of 10

    Hybrid VQLS pipeline with Carleman linearization recovers high-fidelity solutions to the weakly nonlinear Duffing equation on IBM and Xanadu hardware using symmetry-grouped measurements and optimized ansatzes.

  6. Variational Quantum Solutions to the Advection-Diffusion Equation for Applications in Fluid Dynamics

    quant-ph 2022-08 unverdicted novelty 4.0 of 10

    Hybrid variational quantum algorithm solves the advection-diffusion equation on small systems using current noisy IBM quantum hardware, with claimed logarithmic scaling in vector space dimension.

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