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We establish an intriguing connection between quantum phase transitions and bifurcations in the reduced fidelity between two different reduced density matrices for quantum lattice many-body systems with symmetry-breaking orders. Our finding…

Strongly Correlated Electrons · Physics 2009-05-20 Jin-Hua Liu , Qian-Qian Shi , Jian-Hui Zhao , Huan-Qiang Zhou

In the present noisy intermediate scale quantum computing era, there is a critical need to devise methods for the efficient implementation of gate-based variational quantum circuits. This ensures that a range of proposed applications can be…

Quantum Physics · Physics 2024-08-27 Ankit Kulshrestha , Xiaoyuan Liu , Hayato Ushijima-Mwesigwa , Bao Bach , Ilya Safro

The variational quantum algorithm (VQA) with a parametrized quantum circuit is widely applicable to near-term quantum computing, but its fundamental issues that limit optimization performance have been reported in the literature. For…

Variational quantum algorithms are promising algorithms for achieving quantum advantage on near-term devices. The quantum hardware is used to implement a variational wave function and measure observables, whereas the classical computer is…

Quantum Physics · Physics 2022-07-01 Stefan H. Sack , Raimel A. Medina , Alexios A. Michailidis , Richard Kueng , Maksym Serbyn

We present a general variational approach to determine the steady state of open quantum lattice systems via a neural network approach. The steady-state density matrix of the lattice system is constructed via a purified neural network ansatz…

Quantum Physics · Physics 2019-07-03 Filippo Vicentini , Alberto Biella , Nicolas Regnault , Cristiano Ciuti

Quantum annealing aims at solving optimization problems efficiently by preparing the ground state of an Ising spin-Hamiltonian quantum mechanically. A prerequisite of building a quantum annealer is the implementation of programmable…

Quantum Gases · Physics 2020-11-10 Xingze Qiu , Peter Zoller , Xiaopeng Li

The emergence of the Barren Plateau phenomenon poses a significant challenge to quantum machine learning. While most Barren Plateau analyses focus on single-qubit rotation gates, the gradient behavior of Parameterized Quantum Circuits built…

Quantum Physics · Physics 2026-02-06 Yuhan Yao , Yoshihiko Hasegawa

Quantum heuristics have shown promise in solving various optimization problems, including lattice protein folding. Equally relevant is the inverse problem, protein design, where one seeks sequences that fold to a given target structure. The…

We investigate the barren plateau (BP) phenomenon in variational quantum algorithms using a statistical approach. Using Gaussian function models, we identify three distinct types of BPs. The first type, which we called localized-dip BPs,…

Quantum Physics · Physics 2025-08-13 Le Bin Ho , Jesus Urbaneja , Sahel Ashhab

One promising application of near-term quantum devices is to prepare trial wavefunctions using short circuits for solving different problems via variational algorithms. For this purpose, we introduce a new circuit design that combines…

Quantum Physics · Physics 2025-01-24 Abhinav Anand , Kenneth R. Brown

Finding the ground state of a Hamiltonian system is of great significance in many-body quantum physics and quantum chemistry. We propose an improved iterative quantum algorithm to prepare the ground state of a Hamiltonian. The crucial point…

Quantum Physics · Physics 2022-10-25 Jin-Min Liang , Qiao-Qiao Lv , Shu-Qian Shen , Ming Li , Zhi-Xi Wang , Shao-Ming Fei

Quantum data loading plays a central role in quantum algorithms and quantum information processing. Many quantum algorithms hinge on the ability to prepare arbitrary superposition states as a subroutine, with claims of exponential speedups…

Quantum Physics · Physics 2025-09-25 Chun-Tse Li , Hao-Chung Cheng

Parameterized quantum circuits serve as ans\"{a}tze for solving variational problems and provide a flexible paradigm for programming near-term quantum computers. Ideally, such ans\"{a}tze should be highly expressive so that a close…

Quantum Physics · Physics 2022-03-31 Zoë Holmes , Kunal Sharma , M. Cerezo , Patrick J. Coles

We present a systematic study of how quantum circuit design, specifically the depth of the variational ansatz and the choice of quantum feature mapping, affects the performance of hybrid quantum-classical neural networks on a causal…

Quantum Physics · Physics 2026-02-10 Silvie Illésová , Tomasz Rybotycki , Piotr Gawron , Martin Beseda

The variational quantum eigensolver is a promising way to solve the Schr\"odinger equation on a noisy intermediate-scale quantum (NISQ) computer, while its success relies on a well-designed wavefunction ansatz. Compared to physically…

Quantum Physics · Physics 2023-01-20 Xiongzhi Zeng , Yi Fan , Jie Liu , Zhenyu Li , Jinlong Yang

Barren Plateaus are a formidable challenge for hybrid quantum-classical algorithms that lead to flat plateaus in the loss function landscape making it difficult to take advantage of the expressive power of parameterized quantum circuits…

Quantum Physics · Physics 2024-06-21 Michelle Gelman

Quantum annealing (QA) is a hardware-based heuristic optimization and sampling method applicable to discrete undirected graphical models. While similar to simulated annealing, QA relies on quantum, rather than thermal, effects to explore…

Variational quantum algorithms rely on gradient based optimization to iteratively minimize a cost function evaluated by measuring output(s) of a quantum processor. A barren plateau is the phenomenon of exponentially vanishing gradients in…

Quantum Physics · Physics 2021-10-26 Alexey Uvarov , Jacob Biamonte

Variational quantum algorithms (VQAs) are expected to be a path to quantum advantages on noisy intermediate-scale quantum devices. However, both empirical and theoretical results exhibit that the deployed ansatz heavily affects the…

Quantum Physics · Physics 2022-05-31 Yuxuan Du , Tao Huang , Shan You , Min-Hsiu Hsieh , Dacheng Tao

We propose an algorithm for variational quantum algorithms (VQAs) to optimize the structure of parameterized quantum circuits (PQCs) efficiently. The algorithm optimizes the PQC structure on-the-fly in VQA by sequentially replacing a…

Quantum Physics · Physics 2024-05-17 Kaito Wada , Rudy Raymond , Yuki Sato , Hiroshi C. Watanabe