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Quantum mechanical problems are among the hardest to simulate and, in some cases, remain intractable even for the most powerful computers. Quantum computing has emerged as a new technological platform to address such challenges, with rapid…

Quantum Physics · Physics 2025-09-01 Alexander Miessen

Simulating noisy quantum circuits is vital in designing and verifying quantum algorithms in the current NISQ (Noisy Intermediate-Scale Quantum) era, where quantum noise is unavoidable. However, it is much more inefficient than the classical…

Quantum Physics · Physics 2023-11-27 Mingyu Huang , Ji Guan , Wang Fang , Mingsheng Ying

Reduced density matrices (RDMs) are fundamental in quantum information processing, allowing the computation of local observables, such as energy and correlation functions, without the exponential complexity of fully characterizing quantum…

Quantum Physics · Physics 2025-06-13 Zherui Jerry Wang , David Dechant , Yash J. Patel , Jordi Tura

In the era of noisy intermediate-scale quantum (NISQ), variational quantum circuits (VQCs) have been widely applied in various domains, demonstrating the potential advantages of quantum circuits over classical models. Similar to classic…

Quantum Physics · Physics 2025-08-26 Jun Zhuang , Jack Cunningham , Chaowen Guan

Classically simulating quantum systems is challenging, as even noiseless $n$-qubit quantum states scale as $2^n$. The complexity of noisy quantum systems is even greater, requiring $2^n \times 2^n$-dimensional density matrices. Various…

Quantum Physics · Physics 2025-04-24 Taylor L. Patti , Thien Nguyen , Justin G. Lietz , Alexander J. McCaskey , Brucek Khailany

Characterizing noisy quantum devices requires methods for learning the underlying quantum Hamiltonian which governs their dynamics. Often, such methods compare measurements to simulations of candidate Hamiltonians, a task which requires…

Quantum Physics · Physics 2021-10-13 Assaf Zubida , Elad Yitzhaki , Netanel H. Lindner , Eyal Bairey

Noise and imperfections are among the prevalent challenges in quantum software engineering for current NISQ systems. They will remain important in the post-NISQ area, as logical, error-corrected qubits will be based on software mechanisms.…

Quantum Physics · Physics 2025-09-17 Stefan Raimund Maschek , Jürgen Schwitalla , Maja Franz , Wolfgang Mauerer

Near-term quantum computation holds potential across multiple application domains. However, imperfect preparation and evolution of states due to algorithmic and experimental shortcomings, characteristic in the near-term implementation,…

Variational quantum eigensolver (VQE) is promising to show quantum advantage on near-term noisy-intermediate-scale quantum (NISQ) computers. One central problem of VQE is the effect of noise, especially the physical noise on realistic…

Quantum Physics · Physics 2021-09-30 Jinfeng Zeng , Zipeng Wu , Chenfeng Cao , Chao Zhang , Shiyao Hou , Pengxiang Xu , Bei Zeng

Quantum error mitigation (QEM) is vital for noisy intermediate-scale quantum (NISQ) devices. While most conventional QEM schemes assume discrete gate-based circuits with noise appearing either before or after each gate, the assumptions are…

Quantum Physics · Physics 2021-03-12 Jinzhao Sun , Xiao Yuan , Takahiro Tsunoda , Vlatko Vedral , Simon C. Bejamin , Suguru Endo

With an ever-expanding ecosystem of noisy and intermediate-scale quantum devices, exploring their possible applications is a rapidly growing field of quantum information science. In this work, we demonstrate that variational quantum…

Quantum Physics · Physics 2021-07-16 Johannes Jakob Meyer , Johannes Borregaard , Jens Eisert

Variational Quantum Eigensolvers (VQEs) are a powerful class of hybrid quantum-classical algorithms designed to approximate the ground state of a quantum system described by its Hamiltonian. VQEs hold promise for various applications,…

Quantum Physics · Physics 2025-02-04 Kim A. Nicoli , Luca J. Wagner , Lena Funcke

We consider realistic measurement systems, where measurements are accompanied by decoherence processes. The aim of this work is the construction of methods and algorithms for precise quantum measurements with fidelity close to the…

Quantum Physics · Physics 2017-01-10 Yu. I. Bogdanov , B. I. Bantysh , N. A. Bogdanova , A. B. Kvasnyy , V. F. Lukichev

Quantum error correcting (QEC) stabilizer codes enable protection of quantum information against errors during storage and processing. Simulation of noisy QEC codes is used to identify the noise parameters necessary for advantageous…

Quantum Physics · Physics 2025-03-17 Sascha Heußen , Don Winter , Manuel Rispler , Markus Müller

This paper introduces a Lyapunov-based control approach with homodyne measurement. We study two filtering approaches: (i) the traditional quantum filtering and (ii) a modified version of the extended Kalman filtering. We examine both…

Quantum Physics · Physics 2024-07-09 Nahid Binandeh Dehaghani , A. Pedro Aguiar , Rafal Wisniewski

Contemporary quantum computers have relatively high levels of noise, making it difficult to use them to perform useful calculations, even with a large number of qubits. Quantum error correction is expected to eventually enable…

Virtual distillation has been proposed as an error mitigation protocol for estimating the expectation values of observables in quantum algorithms. It proceeds by creating a cyclic permutation of $M$ noisy copies of a quantum state using a…

Quantum Physics · Physics 2024-08-21 Pontus Vikstål , Giulia Ferrini , Shruti Puri

Quantum simulation is a central application of near-term quantum devices, pursued in both analog and digital architectures. A key challenge for both paradigms is the effect of imperfections and noise on predictive power. In this work, we…

Quantum Physics · Physics 2026-05-05 Jayant Rao , Jens Eisert , Tommaso Guaita

Quantum Krylov subspace diagonalization (QKSD) is an emerging method used in place of quantum phase estimation in the early fault-tolerant era, where limited quantum circuit depth is available. In contrast to the classical Krylov subspace…

Quantum Physics · Physics 2024-09-20 Gwonhak Lee , Dongkeun Lee , Joonsuk Huh

The shot-noise unit in continuous-variable quantum key distribution plays an important and fundamental role in experimental implementation as it is used as a normalization parameter that contribute to perform security analysis and distill…

Quantum Physics · Physics 2020-02-25 Yi-Chen Zhang , Yundi Huang , Ziyang Chen , Zhengyu Li , Song Yu , Hong Guo