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A critical question for the field of quantum computing in the near future is whether quantum devices without error correction can perform a well-defined computational task beyond the capabilities of state-of-the-art classical computers,…

Standard randomized benchmarking protocols entail sampling from a unitary 2 design, which is not always practical. In this article we examine randomized benchmarking protocols based on subgroups of the Clifford group that are not unitary 2…

Quantum Physics · Physics 2018-06-20 Winton G. Brown , Bryan Eastin

Estimating the fidelity between a desired target quantum state and an actual prepared state is essential for assessing the success of experiments. For pure target states, we use functional representations that can be measured directly and…

Quantum Physics · Physics 2024-09-09 Omar Fawzi , Aadil Oufkir , Robert Salzmann

The fidelity susceptibility serves as a universal probe for quantum phase transitions, offering an order-parameter-free metric that captures ground-state sensitivity to Hamiltonian perturbations and exhibits critical scaling. Classical…

Quantum Physics · Physics 2025-09-03 Yukun Zhang , Xiao Yuan

Randomized algorithms are crucial subroutines in quantum computing, but the requirement to execute many types of circuits on a real quantum device has been challenging to their extensive implementation. In this study, we propose an…

Quantum Physics · Physics 2026-04-23 Shu Kanno , Ikko Hamamura , Rudy Raymond , Qi Gao , Naoki Yamamoto

Modeling and simulation is essential for predicting and verifying the behavior of fabricated quantum circuits, but existing simulation methods are either impractically costly or require an unrealistic simplification of error processes. We…

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

Classical shadow estimation (CSE) is a powerful tool for learning the properties of quantum states and quantum processes. Here we consider the CSE task for quantum unitary channels. By querying an unknown unitary channel $\mathcal{U}$…

Quantum Physics · Physics 2025-12-30 Zihao Li , Changhao Yi , You Zhou , Huangjun Zhu

Shadow estimation provides an efficient framework for estimating observable expectation values using randomized measurements. While originally developed for discrete-variable systems, its recent extensions to continuous-variable (CV)…

Quantum Physics · Physics 2025-12-16 Ruyu Yang , Xiaoming Sun , Hongyi Zhou

Randomized benchmarking is a useful scheme for evaluation the average fidelity of a noisy quantum circuit. However, it is insensitive to the unitary error. Here, we propose a method of randomized benchmarking in which a unitary t-design is…

Quantum Physics · Physics 2017-12-13 Linxi Zhang , Chuanghua Zhu , Changxing Pei

In present work, we shall develope a protocol to estimate the average fidelity for the bipartite system. We show that the average fidelity should be known if the three measurable quantities, the average survive probability of the product…

Quantum Physics · Physics 2015-09-30 Long Huang , Xiaohua Wu

With the advent of quantum processors exceeding $100$ qubits and the high engineering complexities involved, there is a need for holistically benchmarking the processor to have quality assurance. Linear cross-entropy benchmarking (XEB) has…

Quantum Physics · Physics 2024-11-11 Jianxin Chen , Dawei Ding , Cupjin Huang , Linghang Kong

The performance of quantum algorithms for ground-state energy estimation is directly impacted by the quality of the initial state, where quality is traditionally defined in terms of the overlap of the input state with the target state. An…

We introduce Quantum Functional Information (QFI), a new metric to quantify the rarity and utility of quantum states and circuits. Unlike standard measures such as fidelity or entropy, QFI captures the balance between functionality and…

Quantum Physics · Physics 2025-09-16 Rodrigo Pasti , Jonas Krause

Clifford circuits -- i.e. circuits composed of only CNOT, Hadamard, and $\pi/4$ phase gates -- play a central role in the study of quantum computation. However, their computational power is limited: a well-known result of Gottesman and…

Quantum Physics · Physics 2018-06-21 Adam Bouland , Joseph F. Fitzsimons , Dax Enshan Koh

To address the challenge posed by noise in real quantum devices, quantum error mitigation techniques play a crucial role. These techniques are resource-efficient, making them suitable for implementation in noisy intermediate-scale quantum…

Quantum Physics · Physics 2024-11-26 Jordi Pérez-Guijarro , Alba Pagès-Zamora , Javier R. Fonollosa

Encoding quantum information to protect it from errors is essential for performing large-scale quantum computations. Performing a universal set of quantum gates on encoded states demands a potentially large resource overhead and minimizing…

High-fidelity, efficient quantum nondemolition readout of quantum bits is integral to the goal of quantum computation. As superconducting circuits approach the requirements of scalable, universal fault tolerance, qubit readout must also…

Efficient verification of the functioning of quantum devices is a key to the development of quantum technologies, but is a daunting task as the system size increases. Here we propose a simple and general framework for verifying unitary…

Quantum Physics · Physics 2020-04-17 Huangjun Zhu , Haoyu Zhang

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