Noisy devices Quantum computing has the potential to solve classical intractable problems, but today's quantum devices are limited by noise that can create errors capable of vastly distorting the computation. This notebook introduces simulating and mitigating circuit noise with a focus on the domain of quantum machine learning (QML). We use the PennyLane framework to show how to model common noise channels such as bit flip, depolarizing and amplitude damping and study their effects on quantum circuit outputs. We introduce a number of optimization techniques to fit noise parameters to observed expectation values, giving tools for practical characterization of and compensation for noise in quantum experiments. Recent advances, including noise-aware circuit learning (NACL), use machine learning to automatically design quantum circuits that are resilient to device-specific noise, optimizing the required circuit structure (topology) and depth for the given hardware constraints. These methods are crucial for unlocking the promise of near-term quantum computers, making QML algorithms more resilient and speeding the journey to quantum advantage.
Noisy devices Quantum computing has the potential to solve classical intractable problems, but today's quantum devices are limited by noise that can create errors capable of vastly distorting the computation. This notebook introduces simulating and mitigating circuit noise with a focus on the domain of quantum machine learning (QML). We use the PennyLane framework to show how to model common noise channels such as bit flip, depolarizing and amplitude damping and study their effects on quantum circuit outputs. We introduce a number of optimization techniques to fit noise parameters to observed expectation values, giving tools for practical characterization of and compensation for noise in quantum experiments. Recent advances, including noise-aware circuit learning (NACL), use machine learning to automatically design quantum circuits that are resilient to device-specific noise, optimizing the required circuit structure (topology) and depth for the given hardware constraints. These methods are crucial for unlocking the promise of near-term quantum computers, making QML algorithms more resilient and speeding the journey to quantum advantage.
Quantum computing has emerged as a transformative paradigm capable of addressing computational challenges beyond the reach of classical systems.In the current era of Noisy Intermediate-Scale Quantum (NISQ) devices, practical quantum hardware is characterized by limited qubit counts, short coherence times, gate errors, and the absence of full error correction.Despite these constraints, significant progress has been made in developing quantum machine learning (QML) techniques tailored to operate on near-term quantum processors.This paper presents a comprehensive review of Quantum Machine Learning in the context of NISQ computing.We first outline the fundamental principles of quantum computing, including qubits, superposition, entanglement, and quantum parallelism, followed by a detailed discussion of the NISQ computing model and its hardware limitations.The review then examines hybrid quantum-classical learning frameworks, variational quantum algorithms, quantum data encoding strategies, and noise mitigation techniques that enable practical implementation on existing platforms.Emerging applications across healthcare, finance, cybersecurity, climate modeling, and materials science are also surveyed to highlight the real-world potential of QML.Furthermore, key challenges such as scalability, trainability issues, and algorithmic robustness are analyzed, along with current research efforts aimed at overcoming these barriers.The paper concludes by identifying promising future directions for advancing QML toward quantum advantage.This review aims to provide researchers and practitioners with a structured understanding of the capabilities, limitations, and opportunities of quantum machine learning in the NISQ era .
Machine Learning (ML) has been widely applied across numerous domains due to its ability to automatically identify informative patterns from data for various tasks. The availability of large-scale data and advanced computational power enables the development of sophisticated models and training strategies, leading to state-of-the-art performance, but it also introduces substantial challenges. Quantum Computing (QC), which exploits quantum mechanisms for computation, has attracted growing attention and significant global investment as it may address these challenges. Consequently, Quantum Machine Learning (QML), the integration of these two fields, has received increasing interest, with a notable rise in related studies in recent years. We are motivated to review these existing contributions regarding quantum circuit-based learning models for classical data analysis and highlight the identified potentials and challenges of this technique. Specifically, we focus not only on QML models, both kernel-based and neural network-based, but also on recent explorations of their integration with classical machine learning layers within hybrid frameworks. Moreover, we examine both theoretical analysis and empirical findings to better understand their capabilities, and we also discuss the efforts on noise-resilient and hardware-efficient QML that could enhance its practicality under current hardware limitations. In addition, we cover several emerging paradigms for advanced quantum circuit design and highlight the adaptability of QML across representative application domains. This study aims to provide an overview of the contributions made to bridge quantum computing and machine learning, offering insights and guidance to support its future development and pave the way for broader adoption in the coming years.
Quantum computing promises unparalleled computational power, but its practical implementation is hampered by quantum noise, which affects the reliability of quantum circuits. This paper addresses the critical challenge of noise classification in NISQ ‘Noisy Intermediate-Scale Quantum’ algorithms, focusing on bit flip, phase flip, and depolarising noise. We introduce a novel balanced quantum noise dataset generated through random quantum circuits, ensuring comprehensive coverage of various noise types and intensities. Additionally, we develop a hybrid quantum-classical machine learning model that achieves over 85% accuracy in classifying bit flip and depolarising noise, and perfect accuracy in detecting phase flip noise under our simulation conditions. Our approach builds on a dual quantum architecture, utilising IBM Qiskit for dataset generation and Pennylane for model training. These simulation results indicate potential improvements for noise-aware modelling and error mitigation; however, we emphasise that translating this performance to physical devices requires further validation due to hardware-specific decoherence and calibration effects.
Quantum Machine Learning (QML) offers significant potential for complex tasks like genome sequence classification, but quantum noise on Noisy Intermediate-Scale Quantum (NISQ) devices poses practical challenges. This study systematically evaluates how various quantum noise models including dephasing, amplitude damping, depolarizing, thermal noise, bit-flip, and phase-flip affect key QML algorithms (QSVC, Peg-QSVC, QNN, VQC) and feature mapping techniques (ZFeatureMap, ZZFeatureMap, and PauliFeatureMap). Results indicate that QSVC is notably robust under noise, whereas Peg-QSVC and QNN are more sensitive, particularly to depolarizing and amplitude-damping noise. The PauliFeatureMap is especially vulnerable, highlighting difficulties in maintaining accurate classification under noisy conditions. These findings underscore the critical importance of feature map selection and noise mitigation strategies in optimizing QML for genomic classification, with promising implications for personalized medicine.
Quantum machine learning (QML) holds significant promise for accelerating and enhancing machine learning tasks. However, the inherent fragility of quantum systems to noise poses a substantial challenge to the successful implementation of QML algorithms. This paper investigates and proposes novel noise optimization strategies specifically tailored for QML. The core claim is to design a strategy capable of effectively handling noise within QML algorithms, ultimately boosting model training accuracy and robustness. The proposed mechanism leverages either the quantum decoherence principle to suppress noise or quantum entanglement mechanisms to mitigate its effects. We explore various approaches, focusing on adaptive noise mitigation techniques and incorporating error correction methodologies within the quantum computation framework. The presented framework aims to improve the reliability of QML algorithms and contribute to the development of practical, robust quantum machine learning systems. The research addresses a critical gap in the field by offering a systematic approach to noise management in QML, a crucial step towards realizing the full potential of this technology. The ultimate goal is to demonstrate that, with appropriate noise optimization, QML algorithms can achieve performance comparable to, or exceeding, classical machine learning algorithms.
As quantum devices grow in size while remaining affected by noise, a key challenge is to determine when and how they can surpass classical computation on practical tasks. This requires the development of highly efficient classical simulation algorithms. Pauli backpropagation algorithms are among the most promising, having shown efficiency in simulating certain classes of parameterized quantum circuits, strong candidates for near‑term quantum advantage, under random circuit assumptions and depolarizing noise. However, their efficiency had not been demonstrated for more realistic nonunital noise models, such as amplitude damping, which better capture the behaviour of current hardware. We close this gap by adapting Pauli backpropagation to most single‑qubit noise channels, including nonunital noise, and proving that it remains efficient under these conditions. Our algorithm is parallelizable, memory‑efficient, and requires no assumptions on the locality of the observable, the geometry of the hardware, or the depth of the circuit. While hardware noise can strongly affect computational power in highly structured, fault‑tolerant circuits, our findings indicate little difference for most near‑term variational architectures. This establishes Pauli backpropagation as an efficient method for simulating noisy quantum devices under realistic noise assumptions.While these advances improve our ability to reproduce noisy expectation values of observables, many practical applications, including combinatorial optimization, require direct access to the bitstrings output by quantum circuits, as these encode candidate solutions. Classical replication of such noisy samples has so far been limited beyond the random circuit setting. To bridge this gap, we first focus on problems whose objective functions depend only on two‑body correlations, such as Max‑Cut, and apply Gaussian randomized rounding to the circuit's two‑qubit marginals. This produces classical samples whose expected cost is provably close to that of the noisy quantum device. Large‑scale simulations and experiments on IBMQ hardware confirm that the rounded samples reproduce the full energy distribution, with similar behaviour under various noise models. Coupled with Pauli backpropagation for efficiently estimating noisy marginals, this yields an end‑to‑end classical sampler operating in polynomial time for a broad class of variational circuits. Our results therefore show that sufficiently noisy quantum circuits for combinatorial optimization can be sampled from classically, clarifying where near‑term hardware may or may not outperform classical algorithms.Finally , we go beyond one and two‑body marginals and present an algorithm that samples valid bitstrings directly from a maximum‑entropy distribution matching the given expectation values of the quantum circuit. This method does not rely on the locality or sparsity of the problem's Hamiltonian and performs well across a variety of quantum circuits, including deep circuits on many qubits. When combined with Pauli propagation or error mitigation, it provides a practical pipeline for obtaining samples from quantum circuits in the near term, where full error correction might not yet be available.