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arXiv:2505.24626

Co-designed Quantum Discrete Adiabatic Linear System Solver Via Dynamic Circuits

Boxuan Ai, He, Shuo, Xiang Min Zhao, Lin Yang, Guozhen Liu, Pengfei Gao, Hongbao Liu, Tao Tang, Jiecheng Yang, Wu, Jie

Published May 30, 2025• 0 citations
arXivHTMLPDF

Abstract

Existing quantum discrete adiabatic approaches are hindered by circuit depth that increases linearly with the number of evolution steps, a significant challenge for current quantum hardware with limited coherence times. To address this, we propose a co-designed framework that synergistically integrates dynamic circuit capabilities with real-time classical processing. This framework reformulates the quantum adiabatic evolution into discrete, dynamically adjustable segments. The unitary operator for each segment is optimized on-the-fly using classical computation, and circuit multiplexing techniques are leveraged to reduce the overall circuit depth scaling from $O(\text{steps}\times\text{depth}(U))$ to $O(\text{depth}(U))$. We implement and benchmark a quantum discrete adiabatic linear solver based on this framework for linear systems of $W \in \{2,4,8,16\}$ dimensions with condition numbers $κ\in \{10,20,30,40,50\}$. Our solver successfully overcomes previous depth limitations, maintaining over 80% solution fidelity even under realistic noise models. Key algorithmic optimizations contributing to this performance include a first-order approximation of the discrete evolution operator, a tailored dynamic circuit design exploiting real-imaginary component separation, and noise-resilient post-processing techniques.

DOI
10.48550/arxiv.2505.24626

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Linear system solvers are widely used in scientific computing, with the primary goal of solving linear system problems. Classical iterative algorithms typically rely on the conjugate gradient method. The rise of quantum computing has spurred interest in quantum linear system problems (QLSP), particularly following the introduction of the HHL algorithm by Harrow et al. in 2009, which demonstrated the potential for exponential speedup compared to classical algorithms. However, the performance of the HHL algorithm is constrained by its dependence on the square of the condition number. To address this limitation, alternative approaches based on adiabatic quantum computing (AQC) have been proposed, which exhibit complexity scaling linearly with the condition number. AQC solves QLSP by smoothly varying the parameters of the Hamiltonian. However, this method suffers from high Hamiltonian simulation complexity. In response, this work designs new Hamiltonians and proposes a quantum discrete adiabatic linear solver based on block encoding and eigenvalue separation techniques (BEES-QDALS). This approach bypasses Hamiltonian simulation through a first-order approximation and leverages block encoding to achieve equivalent non-unitary operations on qubits. By comparing the fidelity of the original algorithm and BEES-QDALS when solving QLSP with a fixed number of steps, and the number of steps required to reach a target fidelity, it is found that BEES-QDALS significantly outperforms the original algorithm. Specifically, BEES-QDALS achieves higher fidelity with the same number of steps and requires fewer steps to reach the same target fidelity.
This paper proposes a novel approach to quantum algorithm optimization through dynamically reconfigurable quantum circuits. The core concept involves adapting the structure of a quantum circuit during its execution, responding to real-time feedback derived from quantum state analysis. Traditional quantum circuit design often relies on static, pre-defined architectures, limiting their adaptability and potential for optimization. This work introduces a control system capable of monitoring qubit states and dynamically altering circuit topology – specifically, adjusting gate sequences and potentially even adding or removing qubits – to minimize gate count and maximize coherence, thereby improving overall algorithm efficiency. The theoretical framework presented here outlines the key components and operational principles of such a system, highlighting its potential to overcome the limitations of static circuits and usher in a new era of adaptive quantum computation. We demonstrate, through a mathematical model, how this dynamic reconfiguration can be strategically implemented to address specific algorithmic challenges, focusing on reducing circuit complexity and enhancing the fidelity of quantum computations. The key to this approach lies in continuous feedback loops and a sophisticated control algorithm that leverages quantum state information to guide circuit modifications. This allows for a more tailored and efficient execution of quantum algorithms compared to static designs.
Variational quantum algorithms (VQAs) hold significant promise for solving complex problems across diverse fields. However, their practical implementation on near-term quantum devices is severely hampered by the pervasive effects of quantum noise. Traditional quantum circuit compilation techniques are largely static, failing to account for the unique noise profiles inherent in individual quantum hardware. This paper introduces a novel adaptive quantum circuit compilation framework designed to mitigate these limitations. The core concept centers around dynamically adjusting the circuit layout and gate decomposition in real-time, leveraging measurements of the quantum hardware's noise characteristics to optimize both the accuracy and circuit depth of the compiled quantum circuit. This approach represents a critical step towards unlocking the full potential of VQAs by enabling them to effectively operate within the constraints of noisy quantum computers. The framework incorporates feedback loops for continuous refinement, adapting to evolving noise conditions. The methodology is described, focusing on the key components: noise profiling, adaptive gate decomposition, and circuit re-optimization. Simulation results demonstrate the effectiveness of the adaptive approach in reducing circuit depth and improving the fidelity of VQA computations compared to static compilation methods. This work lays the foundation for robust and efficient VQA execution on future quantum hardware.
In this paper, we propose a revisited variational quantum solver for linear systems, designed to circumvent the barren plateau phenomenon by combining two key techniques: adiabatic evolution and warm starts. To this end, we define an initial Hamiltonian with a known ground state which is easily implemented on the quantum circuit, and then “adiabatically” evolve the Hamiltonian by tuning a control variable in such a way that the final ground state matches the solution to the given linear system. This evolution is carried out in incremental steps, and the ground state at each step is found by minimizing the energy using the parameter values corresponding to the previous minimum as a warm start to guide the search. As a first test case, the method is applied to several linear systems obtained by discretizing a one-dimensional heat flow equation with different physical assumptions and grid choices. Our method successfully and reliably improves upon the solution to the same problem as obtained by a conventional quantum solver, reaching very close to the global minimum also in the case of very shallow circuit implementations.
Recently, several approaches to solving linear systems on a quantum computer have been formulated in terms of the quantum adiabatic theorem for a continuously varying Hamiltonian.Such approaches have enabled near-linear scaling in the condition number κ of the linear system, without requiring a complicated variable-time amplitude amplification procedure.However, the most efficient of those procedures is still asymptotically suboptimal by a factor of log(κ).Here, we prove a rigorous form of the adiabatic theorem that bounds the error in terms of the spectral gap for intrinsically discrete-time evolutions.In combination with the qubitized quantum walk, our discrete adiabatic theorem gives a speed-up for all adiabatic algorithms.Here, we use this combination to develop a quantum algorithm for solving linear systems that is asymptotically optimal, in the sense that the complexity is strictly linear in κ, matching a known lower bound on the complexity.Our O[κ log(1/ )] complexity is also optimal in terms of the combined scaling in κ and the precision .Compared to existing suboptimal methods, our algorithm is simpler and easier to implement.Moreover, we determine the constant factors in the algorithm, which would be suitable for determining the complexity in terms of gate counts for specific applications.
ABSTRACT Quantum discrete adiabatic linear‐system algorithms may require increasingly long coherent circuit sequences as the number of evolution steps grows. A batchwise quantum discrete adiabatic linear‐system solver is presented, in which the evolution is partitioned into sequentially dependent circuit batches. Each batch is followed by computational‐basis measurement, classical state reconstruction, and state re‐preparation for the next batch, thereby reducing the longest uninterrupted coherent circuit depth while preserving the intended discrete evolution structure. The reconstruction exploits the real–imaginary structure of the evolving state together with a sign‐prediction procedure. Selected DeepQuantum simulations evaluate the conditional solution fidelity under different evolution settings, sampling budgets, noise levels, sign‐prediction thresholds, condition numbers, and matrix dimensions. The results indicate that high conditional solution fidelity can be retained under suitable discretization and reconstruction settings and clarify the trade‐off among coherent depth, measurement overhead, and classical processing. The proposed framework provides a simulation‐based foundation and practical design guidance for future quantum‐hardware studies of adiabatic linear‐system solvers.