Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

arXiv:2610.03885

Robustness of Quantum Signal Processing and Resource-aware Polynomial Design

Thiago O. Maciel, Giancarlo Camilo, Allan Tosta, Daniel Stilck-França, Leandro Aolita, Thais de Lima Silva

quant-phSubmitted Oct 2, 2026• Announced Oct 6, 2026• 0 citations
arXivHTMLPDF

Abstract

Quantum signal processing (QSP) realizes operator functions through polynomial transformations of a finite degree. In addition to function approximation errors, realistic implementations incur algorithmic errors also when encoding the input operator and in synthesizing gates into a discrete fault-tolerant gate set. We provide an end-to-end analysis of these errors and show that the input error propagation is governed by the operator-Lipschitz constant $L_\star$ of the implemented function. We then derive an efficient classical algorithm to compute tight lower and upper bounds on $L_\star$, and we show that these bounds induce in turn lower and upper bounds on the total quantum-resource cost (for instance, $T$-gate count) needed for QSP implementations compatible with a target total error. We further devise a procedure to search for a polynomial with minimum cost based solely on its coefficients, yielding a resource-aware polynomial-design procedure for QSP. We illustrate the resulting method for ground state energy estimation via eigenvalue thresholding for the H$_6$ molecular Hamiltonian. In the tested hardware profiles, the resource-aware family improves the total-error budget and reduces the modeled $T$-gate count by $51.9\%$--$56.7\%$ relative to the standard analytical polynomial obtained from an error-function approximation.

Comments
Preliminary version submitted to QIP

Related papers

Realization of quantum signal processing on a noisy quantum computer

Yuta Kikuchi, Conor Mc Keever, Luuk Coopmans +2 more

Abstract Quantum signal processing (QSP) is a powerful toolbox for the design of quantum algorithms and can lead to asymptotically optimal computational costs. Its realization on noisy quantum computers without fault tolerance, however, is challenging because it requires a deep quantum circuit in general. We propose a strategy to run an entire QSP protocol on noisy quantum hardware by carefully reducing overhead costs at each step. To illustrate the approach, we consider the application of Hamiltonian simulation for which QSP implements a polynomial approximation of the time evolution operator. We test the protocol by running the algorithm on the Quantinuum H1-1 trapped-ion quantum computer powered by Honeywell. In particular, we compute the time dependence of bipartite entanglement entropies for Ising spin chains and find good agreements with exact numerical simulations. To make the best use of the device, we determine optimal experimental parameters by using a simplified error model for the hardware and numerically studying the trade-off between Hamiltonian simulation time, polynomial degree, and total accuracy. Our results are the first step in the experimental realization of QSP-based quantum algorithms.

arXiv:2303.05533•npj Quantum Information•Sep 23, 2023•41 citations

Constrained minimax approximation for quantum signal processing

Yulong Dong, James B. Larsen, Lin Lin +1 more

Quantum signal processing (QSP) provides a simple and efficient framework for implementing polynomial transformations using quantum circuits. Its classical design stage leads to a constrained minimax approximation problem: find a polynomial of prescribed parity that approximates a target function uniformly on a fitting set while remaining bounded in magnitude by one on the domain $[0,1]$, which can be viewed as a semi-infinite constraint. Discretization converts the problem into a linear program, but feasibility at a set of finitely many sampled points does not ensure feasibility on the whole domain, especially when an optimal approximant reaches the boundary of the feasible set. We investigate two approaches to address this difficulty. A Remez exchange method combined with active-set constraint enforcement is efficient on many tested instances, but its stability depends on the target and problem geometry. We then introduce nonlinear Fourier retraction, which uses QSP completion and phase synthesis to turn a nearly feasible polynomial into phase factors for a feasible QSP polynomial without increasing the degree. Across representative problems, retraction largely preserves approximation accuracy and remains effective on instances where the Remez heuristic is unstable. The resulting workflow connects classical minimax approximation and semi-infinite optimization with nonlinear Fourier analysis, and is implemented in the qsppack software package.

quant-pharXiv:2608.30937•Sep 1, 2026•0 citations

Quantum Signal Processing for Fault-Tolerant Photonic Computing and Quantum-Enhanced Scientific Intelligence

Murali Krishna Pasupuleti

Abstract: Quantum signal processing (QSP) provides a mathematically economical mechanism for transforming the spectral information of a block-encoded operator through carefully phased single-qubit rotations. Photonic quantum computing, meanwhile, offers high-bandwidth operation, network compatibility and substantial room-temperature functionality, yet remains constrained by optical loss, probabilistic state preparation, finite squeezing, detector imperfections and the resource overhead of logical error correction. This paper develops an integrated analytical framework that connects QSP polynomial synthesis to fault-tolerant photonic execution and to a broader construct termed quantum-enhanced scientific intelligence: the reliable extraction of predictive, explanatory and decision-relevant knowledge from complex scientific operators and data. The study adopts a theory-building and model-based research design. It combines block encoding, QSP and quantum singular-value transformation with open-system dynamics, logical-error modelling, constrained multi-objective optimization and risk-adjusted outcome scoring. The proposed QSP-FTSI framework treats algorithmic approximation error, photonic component quality, decoder performance, logical reliability, resource intensity, uncertainty calibration and scientific utility as coupled rather than independent variables. An illustrative normalized model yields a baseline benefit index of 7.942, a composite risk index of 2.640 and a risk-adjusted score of 6.358 on a ten-point scale; an improved low-loss, high-QEC scenario reaches 7.858, whereas a stressed configuration falls to 3.754. These values are demonstrations, not experimental findings. The principal contribution is a publication-ready mathematical architecture for evaluating when QSP-enabled photonic systems can support scientifically meaningful simulation, inverse modelling, spectral filtering and inference under explicit fault-tolerance and reproducibility constraints. The framework also identifies measurable pathways for experimental validation, hardware–algorithm co-design and responsible scientific deployment. Keywords quantum signal processing; quantum singular-value transformation; fault-tolerant photonic computing; block encoding; Gottesman–Kitaev–Preskill codes; fusion-based quantum computation; logical error suppression; Hamiltonian simulation; scientific machine learning; quantum-enhanced inference; photonic integrated circuits; spectral transformation; quantum error correction; risk-adjusted scientific intelligence; hardware–algorithm co-design

International Journal of Academic and Industrial Research Innovations(IJAIRI)•Jul 22, 2026•0 citations

Hermitian Matrix Function Synthesis without Block-Encoding

Anuradha Mahasinghe, Kaushika De Silva, Xavier Cadet +3 more

Implementing polynomial functions of Hermitian matrices on quantum hardware is a foundational task in quantum computing, critical for accurate Hamiltonian simulation, quantum linear system solving, high-fidelity state preparation, machine learning kernels, and other advanced quantum algorithms. Existing state-of-the-art techniques, including Qubitization, Quantum Singular Value Transformation (QSVT), and Quantum Signal Processing (QSP), rely heavily on block-encoding the Hermitian matrix. These methods are often constrained by the complexity of preparing the block-encoded state, the overhead associated with the required ancillary qubits, or the challenging problem of angle synthesis for the polynomial's phase factors, which limits the achievable circuit depth and overall efficiency. In this work, we propose a novel and resource-efficient approach to implement arbitrary polynomials of a Hermitian matrix by leveraging the Generalized Quantum Signal Processing (GQSP) framework. Our method circumvents the need for block-encoding and avoids the compounding post-selection overheads characteristic of LCU-based constructions, achieving a stable, degree-independent success probability. We derive closed-form expressions for symmetric polynomial expansions and demonstrate how linear combinations of GQSP circuits can realize the desired transformation. This approach reduces resource overhead and opens new pathways for quantum algorithm design for functions of Hermitian matrices, particularly in settings where the Hermitian operator arises naturally from symmetric combinations of unitaries.

quant-pharXiv:2512.18249•Dec 23, 2025•0 citations

Efficient phase-factor evaluation in quantum signal processing

Yulong Dong, Xiang Meng, K. Birgitta Whaley +1 more

Quantum signal processing (QSP) is a powerful quantum algorithm to exactly implement matrix polynomials on quantum computers. Asymptotic analysis of quantum algorithms based on QSP has shown that asymptotically optimal results can in principle be obtained for a range of tasks, such as Hamiltonian simulation and the quantum linear system problem. A further benefit of QSP is that it uses a minimal number of ancilla qubits, which facilitates its implementation on near-to-intermediate term quantum architectures. However, there is so far no classically stable algorithm allowing computation of the phase factors that are needed to build QSP circuits. Existing methods require the use of variable precision arithmetic and can only be applied to polynomials of a relatively low degree. We present here an optimization-based method that can accurately compute the phase factors using standard double precision arithmetic operations. We demonstrate the performance of this approach with applications to Hamiltonian simulation, eigenvalue filtering, and quantum linear system problems. Our numerical results show that the optimization algorithm can find phase factors to accurately approximate polynomials of a degree larger than $10\phantom{\rule{0.16em}{0ex}}000$ with errors below ${10}^{\ensuremath{-}12}$.

arXiv:2002.11649•Physical Review A•Apr 22, 2021•140 citations

Ensemble-Based Quantum Signal Processing for Error Mitigation

Suying Liu, Yulong Dong, Dong An +1 more

Despite rapid advances in quantum hardware, noise remains a central obstacle to deploying quantum algorithms on near-term devices. In particular, random coherent errors that accumulate during circuit execution constitute a dominant and fundamentally challenging noise source. We introduce a noise-resilient framework for Quantum Signal Processing (QSP) that mitigates such coherent errors without increasing circuit depth or ancillary qubit requirements. Our approach uses ensembles of noisy QSP circuits combined with measurement-level averaging to suppress random phase errors in Z rotations. Building on this framework, we develop robust QSP algorithms for implementing polynomial functions of Hermitian matrices and for estimating observables, with applications to Hamiltonian simulation, quantum linear systems, and ground-state preparation. We analyze the trade-off between approximation error and hardware noise, which is essential for practical implementation under the stringent depth and coherence constraints of current quantum hardware. Our results establish a practical pathway for integrating error mitigation seamlessly into algorithmic design, advancing the development of robust quantum computing, and enabling the discovery of scientific applications with near- and mid-term quantum devices.

quant-pharXiv:2601.20073•Jan 29, 2026•0 citations
Quantum signal processing (QSP) realizes operator functions through polynomial transformations of a finite degree. In addition to function approximation errors, realistic implementations incur algorithmic errors also when encoding the input operator and in synthesizing gates into a discrete fault-tolerant gate set. We provide an end-to-end analysis of these errors and show that the input error propagation is governed by the operator-Lipschitz constant L⋆L_\starL⋆​ of the implemented function. We then derive an efficient classical algorithm to compute tight lower and upper bounds on L⋆L_\starL⋆​, and we show that these bounds induce in turn lower and upper bounds on the total quantum-resource cost (for instance, TTT-gate count) needed for QSP implementations compatible with a target total error. We further devise a procedure to search for a polynomial with minimum cost based solely on its coefficients, yielding a resource-aware polynomial-design procedure for QSP. We illustrate the resulting method for ground state energy estimation via eigenvalue thresholding for the H6_66​ molecular Hamiltonian. In the tested hardware profiles, the resource-aware family improves the total-error budget and reduces the modeled TTT-gate count by 51.9%51.9\%51.9%--56.7%56.7\%56.7% relative to the standard analytical polynomial obtained from an error-function approximation.
Abstract Quantum signal processing (QSP) is a powerful toolbox for the design of quantum algorithms and can lead to asymptotically optimal computational costs. Its realization on noisy quantum computers without fault tolerance, however, is challenging because it requires a deep quantum circuit in general. We propose a strategy to run an entire QSP protocol on noisy quantum hardware by carefully reducing overhead costs at each step. To illustrate the approach, we consider the application of Hamiltonian simulation for which QSP implements a polynomial approximation of the time evolution operator. We test the protocol by running the algorithm on the Quantinuum H1-1 trapped-ion quantum computer powered by Honeywell. In particular, we compute the time dependence of bipartite entanglement entropies for Ising spin chains and find good agreements with exact numerical simulations. To make the best use of the device, we determine optimal experimental parameters by using a simplified error model for the hardware and numerically studying the trade-off between Hamiltonian simulation time, polynomial degree, and total accuracy. Our results are the first step in the experimental realization of QSP-based quantum algorithms.
Quantum signal processing (QSP) provides a simple and efficient framework for implementing polynomial transformations using quantum circuits. Its classical design stage leads to a constrained minimax approximation problem: find a polynomial of prescribed parity that approximates a target function uniformly on a fitting set while remaining bounded in magnitude by one on the domain [0,1][0,1][0,1], which can be viewed as a semi-infinite constraint. Discretization converts the problem into a linear program, but feasibility at a set of finitely many sampled points does not ensure feasibility on the whole domain, especially when an optimal approximant reaches the boundary of the feasible set. We investigate two approaches to address this difficulty. A Remez exchange method combined with active-set constraint enforcement is efficient on many tested instances, but its stability depends on the target and problem geometry. We then introduce nonlinear Fourier retraction, which uses QSP completion and phase synthesis to turn a nearly feasible polynomial into phase factors for a feasible QSP polynomial without increasing the degree. Across representative problems, retraction largely preserves approximation accuracy and remains effective on instances where the Remez heuristic is unstable. The resulting workflow connects classical minimax approximation and semi-infinite optimization with nonlinear Fourier analysis, and is implemented in the qsppack software package.
Abstract: Quantum signal processing (QSP) provides a mathematically economical mechanism for transforming the spectral information of a block-encoded operator through carefully phased single-qubit rotations. Photonic quantum computing, meanwhile, offers high-bandwidth operation, network compatibility and substantial room-temperature functionality, yet remains constrained by optical loss, probabilistic state preparation, finite squeezing, detector imperfections and the resource overhead of logical error correction. This paper develops an integrated analytical framework that connects QSP polynomial synthesis to fault-tolerant photonic execution and to a broader construct termed quantum-enhanced scientific intelligence: the reliable extraction of predictive, explanatory and decision-relevant knowledge from complex scientific operators and data. The study adopts a theory-building and model-based research design. It combines block encoding, QSP and quantum singular-value transformation with open-system dynamics, logical-error modelling, constrained multi-objective optimization and risk-adjusted outcome scoring. The proposed QSP-FTSI framework treats algorithmic approximation error, photonic component quality, decoder performance, logical reliability, resource intensity, uncertainty calibration and scientific utility as coupled rather than independent variables. An illustrative normalized model yields a baseline benefit index of 7.942, a composite risk index of 2.640 and a risk-adjusted score of 6.358 on a ten-point scale; an improved low-loss, high-QEC scenario reaches 7.858, whereas a stressed configuration falls to 3.754. These values are demonstrations, not experimental findings. The principal contribution is a publication-ready mathematical architecture for evaluating when QSP-enabled photonic systems can support scientifically meaningful simulation, inverse modelling, spectral filtering and inference under explicit fault-tolerance and reproducibility constraints. The framework also identifies measurable pathways for experimental validation, hardware–algorithm co-design and responsible scientific deployment. Keywords quantum signal processing; quantum singular-value transformation; fault-tolerant photonic computing; block encoding; Gottesman–Kitaev–Preskill codes; fusion-based quantum computation; logical error suppression; Hamiltonian simulation; scientific machine learning; quantum-enhanced inference; photonic integrated circuits; spectral transformation; quantum error correction; risk-adjusted scientific intelligence; hardware–algorithm co-design
Implementing polynomial functions of Hermitian matrices on quantum hardware is a foundational task in quantum computing, critical for accurate Hamiltonian simulation, quantum linear system solving, high-fidelity state preparation, machine learning kernels, and other advanced quantum algorithms. Existing state-of-the-art techniques, including Qubitization, Quantum Singular Value Transformation (QSVT), and Quantum Signal Processing (QSP), rely heavily on block-encoding the Hermitian matrix. These methods are often constrained by the complexity of preparing the block-encoded state, the overhead associated with the required ancillary qubits, or the challenging problem of angle synthesis for the polynomial's phase factors, which limits the achievable circuit depth and overall efficiency. In this work, we propose a novel and resource-efficient approach to implement arbitrary polynomials of a Hermitian matrix by leveraging the Generalized Quantum Signal Processing (GQSP) framework. Our method circumvents the need for block-encoding and avoids the compounding post-selection overheads characteristic of LCU-based constructions, achieving a stable, degree-independent success probability. We derive closed-form expressions for symmetric polynomial expansions and demonstrate how linear combinations of GQSP circuits can realize the desired transformation. This approach reduces resource overhead and opens new pathways for quantum algorithm design for functions of Hermitian matrices, particularly in settings where the Hermitian operator arises naturally from symmetric combinations of unitaries.
Quantum signal processing (QSP) is a powerful quantum algorithm to exactly implement matrix polynomials on quantum computers. Asymptotic analysis of quantum algorithms based on QSP has shown that asymptotically optimal results can in principle be obtained for a range of tasks, such as Hamiltonian simulation and the quantum linear system problem. A further benefit of QSP is that it uses a minimal number of ancilla qubits, which facilitates its implementation on near-to-intermediate term quantum architectures. However, there is so far no classically stable algorithm allowing computation of the phase factors that are needed to build QSP circuits. Existing methods require the use of variable precision arithmetic and can only be applied to polynomials of a relatively low degree. We present here an optimization-based method that can accurately compute the phase factors using standard double precision arithmetic operations. We demonstrate the performance of this approach with applications to Hamiltonian simulation, eigenvalue filtering, and quantum linear system problems. Our numerical results show that the optimization algorithm can find phase factors to accurately approximate polynomials of a degree larger than 1000010\phantom{\rule{0.16em}{0ex}}00010000 with errors below ${10}^{\ensuremath{-}12}$.
Despite rapid advances in quantum hardware, noise remains a central obstacle to deploying quantum algorithms on near-term devices. In particular, random coherent errors that accumulate during circuit execution constitute a dominant and fundamentally challenging noise source. We introduce a noise-resilient framework for Quantum Signal Processing (QSP) that mitigates such coherent errors without increasing circuit depth or ancillary qubit requirements. Our approach uses ensembles of noisy QSP circuits combined with measurement-level averaging to suppress random phase errors in Z rotations. Building on this framework, we develop robust QSP algorithms for implementing polynomial functions of Hermitian matrices and for estimating observables, with applications to Hamiltonian simulation, quantum linear systems, and ground-state preparation. We analyze the trade-off between approximation error and hardware noise, which is essential for practical implementation under the stringent depth and coherence constraints of current quantum hardware. Our results establish a practical pathway for integrating error mitigation seamlessly into algorithmic design, advancing the development of robust quantum computing, and enabling the discovery of scientific applications with near- and mid-term quantum devices.