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Estimating an $N \times N$ quantum kernel from circuit fidelities requires $\Theta(N^2 S)$ measurement shots, the dominant bottleneck for deployment on near-term hardware. Existing budget-saving methods (Nystr\"om-QKE, ShoFaR, kernel-target…

Machine Learning · Computer Science 2026-05-15 Jian Xu , Chao Li , Delu Zeng , John Paisley , Qibin Zhao

An $n$-qubit quantum circuit is said to be peaked if it has an output probability that is at least inverse-polynomially large as a function of $n$. We describe a classical algorithm with quasipolynomial runtime $n^{O(\log{n})}$ that…

Quantum Physics · Physics 2023-09-18 Sergey Bravyi , David Gosset , Yinchen Liu

Detecting multipartite entanglement in many qubit systems is measurement-intensive, motivating protocols that estimate only selected observables with provable efficiency. In this work we use the classical shadow protocol to study the sample…

Quantum Physics · Physics 2026-01-06 Ziran Zhang

Accurate estimation of observables in quantum systems is a central challenge in quantum information science, yet practical implementations are fundamentally constrained by the limited number of measurement shots. In this work we explore a…

Quantum Physics · Physics 2025-11-05 Keijo Korhonen , Stefano Mangini , Joonas Malmi , Hetta Vappula , Daniel Cavalcanti

Classical shadows provide a versatile framework for estimating many properties of quantum states from repeated, randomly chosen measurements without requiring full quantum state tomography. When prior information is available, such as…

Quantum Physics · Physics 2026-05-27 Jacob Bringewatt , Henry Froland , Andreas Elben , Niklas Mueller

In a recent work a quantum error mitigation protocol was applied to the expectation values obtained from circuits on the IBM Eagle quantum processor with up $127$ - qubits with up to $60 \; - \; \mbox{CNOT}$ layers. To benchmark the…

Quantum Physics · Physics 2023-07-03 Sajant Anand , Kristan Temme , Abhinav Kandala , Michael Zaletel

The classical shadow estimation protocol is a noise-resilient and sample-efficient quantum algorithm for learning the properties of quantum systems. Its performance depends on the choice of a unitary ensemble, which must be chosen by a user…

Quantum Physics · Physics 2024-01-10 Kaifeng Bu , Dax Enshan Koh , Roy J. Garcia , Arthur Jaffe

The 2-Forrelation problem provides an optimal separation between classical and quantum query complexity and is also the problem used for separating $\mathsf{BQP}$ and $\mathsf{PH}$ relative to an oracle. A natural question is therefore to…

Quantum Physics · Physics 2026-04-17 Quentin Buzet , André Chailloux

Despite fundamental interests in learning quantum circuits, the existence of a computationally efficient algorithm for learning shallow quantum circuits remains an open question. Because shallow quantum circuits can generate distributions…

Predicting features of complex, large-scale quantum systems is essential to the characterization and engineering of quantum architectures. We present an efficient approach for constructing an approximate classical description, called the…

Quantum Physics · Physics 2019-11-26 Hsin-Yuan Huang , Richard Kueng

While quantum computing can accomplish tasks that are classically intractable, the presence of noise may destroy this advantage in the absence of fault tolerance. In this work, we present a classical algorithm that runs in…

Quantum Physics · Physics 2025-10-09 Yifan F. Zhang , Su-un Lee , Liang Jiang , Sarang Gopalakrishnan

We introduce a distributed quantum-classical framework that synergizes photonic quantum neural networks (QNNs) with matrix-product-state (MPS) mapping to achieve parameter-efficient training of classical neural networks. By leveraging…

Quantum Physics · Physics 2025-05-14 Kuan-Cheng Chen , Chen-Yu Liu , Yu Shang , Felix Burt , Kin K. Leung

Extracting information from quantum systems is crucial in quantum physics and information processing. Methods based on randomized measurements, like shadow estimation, show advantages in effectively achieving such tasks. However, randomized…

Quantum Physics · Physics 2024-09-10 Zhou You , Qing Liu , You Zhou

We identify a sub-class of BQP that captures certain structural commonalities among many quantum algorithms including Shor's algorithms. This class does not contain all of BQP (e.g. Grover's algorithm does not fall into this class). Our…

Computational Complexity · Computer Science 2015-03-20 Richard J. Lipton , Kenneth W. Regan , Atri Rudra

It is one of the most fundamental objectives in quantum information science to understand the boundary between the computational power of classical and quantum computers. One possible avenue to explore this boundary is to identify classes…

Quantum Physics · Physics 2025-03-28 Christophe Piveteau

We present shadow spectroscopy as a simulator-agnostic quantum algorithm for estimating energy gaps using very few circuit repetitions (shots) and no extra resources (ancilla qubits) beyond performing time evolution and measurements. The…

Quantum Physics · Physics 2025-04-10 Hans Hon Sang Chan , Richard Meister , Matthew L. Goh , Bálint Koczor

Quantum neural networks (QNNs), as currently formulated, are near-term quantum machine learning architectures that leverage parameterized quantum circuits with the aim of improving upon the performance of their classical counterparts. In…

Quantum Physics · Physics 2026-03-11 Marco Maronese , Francesco Ferrari , Matteo Vandelli , Daniele Dragoni

Hierarchical quantum classifiers, such as quantum convolutional neural networks (QCNNs), represent recent progress toward designing effective and feasible architectures for quantum classification. However, their performance on near-term…

Quantum Physics · Physics 2026-02-26 Taehyun Kim , Israel F. Araujo , Daniel K. Park

In this work we explore a correspondence between quantum circuits and low-degree polynomials over the finite field F_2. Any quantum circuit made up of Hadamard, Z, controlled-Z and controlled-controlled-Z gates gives rise to a degree-3…

Quantum Physics · Physics 2017-02-01 Ashley Montanaro

Any technology requires precise benchmarking of its components, and the quantum technologies are no exception. Randomized benchmarking allows for the relatively resource economical estimation of the average gate fidelity of quantum gates…

Quantum Physics · Physics 2019-08-14 E. Onorati , A. H. Werner , J. Eisert