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Vortex-induced anomalies in the superconducting quantum interference patterns of topological insulator Josephson junctions npj Quant. Mater. (IF 5.4) Pub Date : 2024-09-17 Arman Rashidi, William Huynh, Binghao Guo, Sina Ahadi, Susanne Stemmer
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An optical atomic clock using 4 D J ... Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-09-16 A Duspayev, C Owens, B Dash and G Raithel
We analyze an optical atomic clock using two-photon transitions in rubidium. Four one- and two-color excitation schemes to probe the and fine-structure states are considered in detail. We compare key characteristics of Rb and two-photon clocks. The clock features a high signal-to-noise ratio due to two-photon decay at favorable wavelengths, low dc electric and magnetic susceptibilities, and minimal
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End-to-end complexity for simulating the Schwinger model on quantum computers Quantum (IF 5.1) Pub Date : 2024-09-17 Kazuki Sakamoto, Hayata Morisaki, Junichi Haruna, Etsuko Itou, Keisuke Fujii, Kosuke Mitarai
The Schwinger model is one of the simplest gauge theories. It is known that a topological term of the model leads to the infamous sign problem in the classical Monte Carlo method. In contrast to this, recently, quantum computing in Hamiltonian formalism has gained attention. In this work, we estimate the resources needed for quantum computers to compute physical quantities that are challenging to compute
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Tensor-network-based variational Monte Carlo approach to the non-equilibrium steady state of open quantum systems Quantum (IF 5.1) Pub Date : 2024-09-17 Dawid A. Hryniuk, Marzena H. Szymańska
We introduce a novel method of efficiently simulating the non-equilibrium steady state of large many-body open quantum systems with highly non-local interactions, based on a variational Monte Carlo optimization of a matrix product operator ansatz. Our approach outperforms and offers several advantages over comparable algorithms, such as an improved scaling of the computational cost with respect to
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Dimension matters: precision and incompatibility in multi-parameter quantum estimation models Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-09-15 Alessandro Candeloro, Zahra Pazhotan and Matteo G A Paris
We study the role of probe dimension in determining the bounds of precision and the level of incompatibility in multi-parameter quantum estimation problems. In particular, we focus on the paradigmatic case of unitary encoding generated by and compare precision and incompatibility in the estimation of the same parameters across representations of different dimensions. For two- and three-parameter unitary
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Unconventional spin textures emerging from a universal symmetry theory of spin-momentum locking npj Quant. Mater. (IF 5.4) Pub Date : 2024-09-14 Yuntian Liu, Jiayu Li, Pengfei Liu, Qihang Liu
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Experimental preparation of multiphoton-added coherent states of light npj Quantum Inform. (IF 6.6) Pub Date : 2024-09-14 Jiří Fadrný, Michal Neset, Martin Bielak, Miroslav Ježek, Jan Bílek, Jaromír Fiurášek
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Demonstration of quantum network protocols over a 14-km urban fiber link npj Quantum Inform. (IF 6.6) Pub Date : 2024-09-14 Stephan Kucera, Christian Haen, Elena Arenskötter, Tobias Bauer, Jonas Meiers, Marlon Schäfer, Ross Boland, Milad Yahyapour, Maurice Lessing, Ronald Holzwarth, Christoph Becher, Jürgen Eschner
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An extremely bad-cavity laser npj Quantum Inform. (IF 6.6) Pub Date : 2024-09-13 Jia Zhang, Tiantian Shi, Jianxiang Miao, Deshui Yu, Jingbiao Chen
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Large-scale simulations of Floquet physics on near-term quantum computers npj Quantum Inform. (IF 6.6) Pub Date : 2024-09-13 Timo Eckstein, Refik Mansuroglu, Piotr Czarnik, Jian-Xin Zhu, Michael J. Hartmann, Lukasz Cincio, Andrew T. Sornborger, Zoë Holmes
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Polarization-entangled photons from a whispering gallery resonator npj Quantum Inform. (IF 6.6) Pub Date : 2024-09-13 Sheng-Hsuan Huang, Thomas Dirmeier, Golnoush Shafiee, Kaisa Laiho, Dmitry V. Strekalov, Gerd Leuchs, Christoph Marquardt
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Quantum autoencoders using mixed reference states npj Quantum Inform. (IF 6.6) Pub Date : 2024-09-13 Hailan Ma, Gary J. Mooney, Ian R. Petersen, Lloyd C. L. Hollenberg, Daoyi Dong
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The Complexity of Being Entangled Quantum (IF 5.1) Pub Date : 2024-09-12 Stefano Baiguera, Shira Chapman, Giuseppe Policastro, Tal Schwartzman
Nielsen's approach to quantum state complexity relates the minimal number of quantum gates required to prepare a state to the length of geodesics computed with a certain norm on the manifold of unitary transformations. For a bipartite system, we investigate binding complexity, which corresponds to norms in which gates acting on a single subsystem are free of cost. We reduce the problem to the study
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Reconstruction of Quantum Particle Statistics: Bosons, Fermions, and Transtatistics Quantum (IF 5.1) Pub Date : 2024-09-12 Nicolás Medina Sánchez, Borivoje Dakić
Identical quantum particles exhibit only two types of statistics: bosonic and fermionic. Theoretically, this restriction is commonly established through the symmetrization postulate or (anti)commutation constraints imposed on the algebra of creation and annihilation operators. The physical motivation for these axioms remains poorly understood, leading to various generalizations by modifying the mathematical
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Incommensurate magnetic order in an axion insulator candidate EuIn2As2 investigated by NMR measurement npj Quant. Mater. (IF 5.4) Pub Date : 2024-09-12 Hikaru Takeda, Jian Yan, Zhongzhu Jiang, Xuan Luo, Yuping Sun, Minoru Yamashita
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Adaptive Online Learning of Quantum States Quantum (IF 5.1) Pub Date : 2024-09-12 Xinyi Chen, Elad Hazan, Tongyang Li, Zhou Lu, Xinzhao Wang, Rui Yang
The problem of efficient quantum state learning, also called shadow tomography, aims to comprehend an unknown $d$-dimensional quantum state through POVMs. Yet, these states are rarely static; they evolve due to factors such as measurements, environmental noise, or inherent Hamiltonian state transitions. This paper leverages techniques from adaptive online learning to keep pace with such state changes
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Heisenberg-limited Hamiltonian learning for interacting bosons npj Quantum Inform. (IF 6.6) Pub Date : 2024-09-11 Haoya Li, Yu Tong, Tuvia Gefen, Hongkang Ni, Lexing Ying
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Bayesian optimization of non-classical optomechanical correlations Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-09-10 Alexander Pitchford, Andrey A Rakhubovsky, Rick Mukherjee, Darren W Moore, Frédéric Sauvage, Daniel Burgarth, Radim Filip and Florian Mintert
Nonclassical correlations provide a resource for many applications in quantum technology as well as providing strong evidence that a system is indeed operating in the quantum regime. Optomechanical systems can be arranged to generate nonclassical correlations (such as quantum entanglement) between the mechanical mode and a mode of travelling light. Here we propose automated optimization of the production
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Universal and holistic privacy protection in quantum computing: a novel approach through quantum circuit equivalence homomorphic encryption Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-09-10 Xuejian Zhang, Yan Chang, Lin Zeng, Weifeng Xue, Lili Yan and Shibin Zhang
Due to the stringent hardware requirements and high cost, quantum computing as a service (QCaaS) is currently the main way to output quantum computing capabilities. However, the current QCaaS has significant shortcomings in privacy protection. The existing researches mainly focus on dataset privacy in some specific quantum machine learning algorithms, and there is no general and comprehensive research
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Efficient Classical Shadow Tomography through Many-body Localization Dynamics Quantum (IF 5.1) Pub Date : 2024-09-11 Tian-Gang Zhou, Pengfei Zhang
Classical shadow tomography serves as a potent tool for extracting numerous properties from quantum many-body systems with minimal measurements. Nevertheless, prevailing methods yielding optimal performance for few-body operators necessitate the application of random two-qubit gates, a task that can prove challenging on specific quantum simulators such as ultracold atomic gases. In this work, we introduce
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Exact results on finite size corrections for surface codes tailored to biased noise Quantum (IF 5.1) Pub Date : 2024-09-11 Yinzi Xiao, Basudha Srivastava, Mats Granath
The code-capacity threshold of a scalable quantum error correcting stabilizer code can be expressed as a thermodynamic phase transition of a corresponding random-bond Ising model. Here we study the XY and XZZX surface codes under phase-biased noise, $p_x=p_y=p_z/(2\eta)$, with $\eta\geq 1/2$, and total error rate $p=p_x+p_y+p_z$. By appropriately formulating the boundary conditions, in the rotated
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The Fractal-Lattice Hubbard Model Quantum (IF 5.1) Pub Date : 2024-09-11 Monica Conte, Vinicius Zampronio, Malte Röntgen, Cristiane Morais Smith
Here, we investigate the fractal-lattice Hubbard model using various numerical methods: exact diagonalization, the self-consistent diagonalization of a (mean-field) Hartree-Fock Hamiltonian and state-of-the-art Auxiliary-Field Quantum Monte Carlo. We focus on the Sierpinski triangle with Hausdorff dimension $1.58$ and consider several generations. In the tight-binding limit, we find compact localised
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The Hadamard gate cannot be replaced by a resource state in universal quantum computation Quantum (IF 5.1) Pub Date : 2024-09-11 Benjamin D. M. Jones, Noah Linden, Paul Skrzypczyk
We consider models of quantum computation that involve operations performed on some fixed resourceful quantum state. Examples that fit this paradigm include magic state injection and measurement-based approaches. We introduce a framework that incorporates both of these cases and focus on the role of coherence (or superposition) in this context, as exemplified through the Hadamard gate. We prove that
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Differential-phase-shift QKD with practical Mach–Zehnder interferometer Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-09-09 Akihiro Mizutani, Masanori Terashita, Junya Matsubayashi, Shogo Mori, Ibuki Matsukura, Suzuna Tagawa and Kiyoshi Tamaki
Differential-phase-shift (DPS) quantum key distribution stands as a promising protocol due to its simple implementation, which can be realized with a train of coherent pulses and a passive measurement unit. To implement the DPS protocol, it is crucial to establish security proofs incorporating practical imperfections in users’ devices, however, existing security proofs make unrealistic assumptions
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Requirements for upgrading trusted nodes to a repeater chain over 900 km of optical fiber Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-09-09 Francisco Ferreira da Silva, Guus Avis, Joshua A Slater and Stephanie Wehner
We perform a numerical study of the distribution of entanglement on a real-world fiber grid connecting the German cities of Bonn and Berlin. The connection is realized using a chain of processing-node quantum repeaters spanning roughly 900 kilometers. Their placement is constrained by the fiber grid we consider, resulting in asymmetric links. We investigate how minimal hardware requirements depend
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Quantum-enhanced learning with a controllable bosonic variational sensor network Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-09-09 Pengcheng Liao, Bingzhi Zhang and Quntao Zhuang
The emergence of quantum sensor networks has presented opportunities for enhancing complex sensing tasks, while simultaneously introducing significant challenges in designing and analyzing quantum sensing protocols due to the intricate nature of entanglement and physical processes. Supervised learning assisted by an entangled sensor network (SLAEN) (Zhuang and Zhang 2019 Phys. Rev. X 9 041023) represents
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Quantum-enhanced mean value estimation via adaptive measurement Quantum (IF 5.1) Pub Date : 2024-09-09 Kaito Wada, Kazuma Fukuchi, Naoki Yamamoto
Quantum-enhanced (i.e., higher performance by quantum effects than any classical methods) mean value estimation of observables is a fundamental task in various quantum technologies; in particular, it is an essential subroutine in quantum computing algorithms. Notably, the quantum estimation theory identifies the ultimate precision of such an estimator, which is referred to as the quantum Cramér-Rao
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A Theory of Inaccessible Information Quantum (IF 5.1) Pub Date : 2024-09-09 Jacopo Surace
What would be the consequences if there were fundamental limits to our ability to experimentally explore the world? In this work we seriously consider this question. We assume the existence of statements whose truth value is not experimentally accessible. That is, there is no way, not even in theory, to directly test if these statements are true or false. We further develop a theory in which experimentally
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SQuADDS: A validated design database and simulation workflow for superconducting qubit design Quantum (IF 5.1) Pub Date : 2024-09-09 Sadman Shanto, Andre Kuo, Clark Miyamoto, Haimeng Zhang, Vivek Maurya, Evangelos Vlachos, Malida Hecht, Chung Wa Shum, Eli Levenson-Falk
We present an open-source database of superconducting quantum device designs that may be used as the starting point for customized devices. Each design can be generated programmatically using the open-source Qiskit Metal package, and simulated using finite-element electromagnetic solvers. We present a robust workflow for achieving high accuracy on design simulations. Many designs in the database are
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Geometrical description and Faddeev-Jackiw quantization of electrical networks Quantum (IF 5.1) Pub Date : 2024-09-09 A. Parra-Rodriguez, I. L. Egusquiza
In lumped-element electrical circuit theory, the problem of solving Maxwell's equations in the presence of media is reduced to two sets of equations, the constitutive equations encapsulating local geometry and dynamics of a confined energy density, and the Kirchhoff equations enforcing conservation of charge and energy in a larger, topological, scale. We develop a new geometric and systematic description
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Equivalence of cost concentration and gradient vanishing for quantum circuits: an elementary proof in the Riemannian formulation Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-09-09 Qiang Miao, Thomas Barthel
The optimization of quantum circuits can be hampered by a decay of average gradient amplitudes with increasing system size. When the decay is exponential, this is called the barren plateau problem. Considering explicit circuit parametrizations (in terms of rotation angles), it has been shown in Arrasmith et al (2022 Quantum Sci. Technol. 7 045015) that barren plateaus are equivalent to an exponential
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Squeezing below the ground state of motion of a continuously monitored levitating nanoparticle Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-09-09 Q Wu, D A Chisholm, R Muffato, T Georgescu, J Homans, H Ulbricht, M Carlesso, M Paternostro
Squeezing is a crucial resource for quantum information processing and quantum sensing. In levitated nanomechanics, squeezed states of motion can be generated via temporal control of the trapping frequency of a massive particle. However, the amount of achievable squeezing typically suffers from detrimental environmental effects. We propose a scheme for the generation of significant levels of mechanical
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Hamiltonian dynamics on digital quantum computers without discretization error npj Quantum Inform. (IF 6.6) Pub Date : 2024-09-07 Etienne Granet, Henrik Dreyer
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Confinement and Kink Entanglement Asymmetry on a Quantum Ising Chain Quantum (IF 5.1) Pub Date : 2024-09-06 Brian J. J. Khor, D. M. Kürkçüoglu, T. J. Hobbs, G. N. Perdue, Israel Klich
In this work, we explore the interplay of confinement, string breaking and entanglement asymmetry on a 1D quantum Ising chain. We consider the evolution of an initial domain wall and show that, surprisingly, while the introduction of confinement through a longitudinal field typically suppresses entanglement, it can also serve to increase it beyond a bound set for free particles. Our model can be tuned
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Encoding optimization for quantum machine learning demonstrated on a superconducting transmon qutrit Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-09-06 Shuxiang Cao, Weixi Zhang, Jules Tilly, Abhishek Agarwal, Mustafa Bakr, Giulio Campanaro, Simone D Fasciati, James Wills, Boris Shteynas, Vivek Chidambaram, Peter Leek, Ivan Rungger
A qutrit represents a three-level quantum system, so that one qutrit can encode more information than a qubit, which corresponds to a two-level quantum system. This work investigates the potential of qutrit circuits in machine learning classification applications. We propose and evaluate different data-encoding schemes for qutrits, and find that the classification accuracy varies significantly depending
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d-wave charge-4e superconductivity from fluctuating pair density waves npj Quant. Mater. (IF 5.4) Pub Date : 2024-09-05 Yi-Ming Wu, Yuxuan Wang
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Kinetic ferromagnetism and topological magnons of the hole-doped Kitaev spin liquid npj Quant. Mater. (IF 5.4) Pub Date : 2024-09-04 Hui-Ke Jin, Wilhelm Kadow, Michael Knap, Johannes Knolle
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Engineered dissipation to mitigate barren plateaus npj Quantum Inform. (IF 6.6) Pub Date : 2024-09-04 Antonio Sannia, Francesco Tacchino, Ivano Tavernelli, Gian Luca Giorgi, Roberta Zambrini
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Handbook for Efficiently Quantifying Robustness of Magic Quantum (IF 5.1) Pub Date : 2024-09-05 Hiroki Hamaguchi, Kou Hamada, Nobuyuki Yoshioka
The nonstabilizerness, or magic, is an essential quantum resource to perform universal quantum computation. Robustness of magic (RoM) in particular characterizes the degree of usefulness of a given quantum state for non-Clifford operation. While the mathematical formalism of RoM can be given in a concise manner, it is extremely challenging to determine the RoM in practice, since it involves superexponentially
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Digital quantum simulation of lattice fermion theories with local encoding Quantum (IF 5.1) Pub Date : 2024-09-04 Marco Ballarin, Giovanni Cataldi, Giuseppe Magnifico, Daniel Jaschke, Marco Di Liberto, Ilaria Siloi, Simone Montangero, Pietro Silvi
We numerically analyze the feasibility of a platform-neutral, general strategy to perform quantum simulations of fermionic lattice field theories under open boundary conditions. The digital quantum simulator requires solely one- and two-qubit gates and is scalable since integrating each Hamiltonian term requires a finite (non-scaling) cost. The exact local fermion encoding we adopt relies on auxiliary
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Generalized quantum Arimoto–Blahut algorithm and its application to quantum information bottleneck Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-09-04 Masahito Hayashi, Geng Liu
Quantum information bottleneck was proposed by Grimsmo and Still (2016 Phys. Rev. A 94 012338) as a promising method for quantum supervised machine learning. To study this method, we generalize the quantum Arimoto–Blahut algorithm by Ramakrishnan et al (2021 IEEE Trans. Inf. Theory 67 946) to a function defined over a set of density matrices with linear constraints so that our algorithm can be applied
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Daemonic quantum battery charged by thermalization Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-09-04 Matias Araya Satriani, Felipe Barra
The reduced state of a small system strongly coupled to a charger in thermal equilibrium may be athermal and used as a small battery once disconnected. By harnessing the battery-charger correlations, the battery’s extractable energy can increase above the ergotropy. We introduce a protocol that uses a quantum system as a memory that measures the charger and leaves the battery intact in its charged
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Entanglement buffering with two quantum memories Quantum (IF 5.1) Pub Date : 2024-09-03 Bethany Davies, Álvaro G. Iñesta, Stephanie Wehner
Quantum networks crucially rely on the availability of high-quality entangled pairs of qubits, known as entangled links, distributed across distant nodes. Maintaining the quality of these links is a challenging task due to the presence of time-dependent noise, also known as decoherence. Entanglement purification protocols offer a solution by converting multiple low-quality entangled states into a smaller
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Perfect quantum protractors Quantum (IF 5.1) Pub Date : 2024-09-03 Michał Piotrak, Marek Kopciuch, Arash Dezhang Fard, Magdalena Smolis, Szymon Pustelny, Kamil Korzekwa
In this paper we introduce and investigate the concept of a $\textit{perfect quantum protractor}$, a pure quantum state $|\psi\rangle\in\mathcal{H}$ that generates three different orthogonal bases of $\mathcal{H}$ under rotations around each of the three perpendicular axes. Such states can be understood as pure states of maximal uncertainty with regards to the three components of the angular momentum
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MadQCI: a heterogeneous and scalable SDN-QKD network deployed in production facilities npj Quantum Inform. (IF 6.6) Pub Date : 2024-09-02 V. Martin, J. P. Brito, L. Ortíz, R. B. Méndez, J. S. Buruaga, R. J. Vicente, A. Sebastián-Lombraña, D. Rincón, F. Pérez, C. Sánchez, M. Peev, H. H. Brunner, F. Fung, A. Poppe, F. Fröwis, A. J. Shields, R. I. Woodward, H. Griesser, S. Roehrich, F. de la Iglesia, C. Abellán, M. Hentschel, J. M. Rivas-Moscoso, A. Pastor-Perales, J. Folgueira, D. López
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Enhancing quantum annealing accuracy through replication-based error mitigation** Preliminary version of this paper appeared in the proceedings of the 21st ACM International Conference on Computing Frontiers, Ischia, Italy, 2024. The current version includes expanded analysis of previous work on error mitigation in quantum computing, new sections related to solving chained problems and, in particular Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-09-02 Hristo N Djidjev
Quantum annealers like those manufactured by D-Wave Systems are designed to find high quality solutions to optimization problems that are typically hard for classical computers. They utilize quantum effects like tunneling to evolve toward low-energy states representing solutions to optimization problems. However, their analog nature and limited control functionalities present challenges to correcting
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Quantum battery supercharging via counter-diabatic dynamics Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-08-30 L F C de Moraes, Alan C Duriez, A Saguia, Alan C Santos, M S Sarandy
We introduce a counter-diabatic (CD) approach for deriving Hamiltonians modeling superchargable quantum batteries (QBs). A necessary requirement for the supercharging process is the existence of multipartite interactions among the cells of the battery. Remarkably, this condition may be insufficient no matter the number of multipartite terms in the Hamiltonian. We analytically illustrate this kind of
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Tutorial: projector approach to master equations for open quantum systems Quantum (IF 5.1) Pub Date : 2024-08-29 C. Gonzalez-Ballestero
Most quantum theorists are familiar with different ways of describing the effective quantum dynamics of a system coupled to external degrees of freedom, such as the Born-Markov master equation or the adiabatic elimination. Understanding the deep connection between these -- sometimes apparently unrelated -- methods can be a powerful tool, allowing us to derive effective dynamics in unconventional systems
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On the connection between least squares, regularization, and classical shadows Quantum (IF 5.1) Pub Date : 2024-08-29 Zhihui Zhu, Joseph M. Lukens, Brian T. Kirby
Classical shadows (CS) offer a resource-efficient means to estimate quantum observables, circumventing the need for exhaustive state tomography. Here, we clarify and explore the connection between CS techniques and least squares (LS) and regularized least squares (RLS) methods commonly used in machine learning and data analysis. By formal identification of LS and RLS "shadows" completely analogous
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Unraveling the emergence of quantum state designs in systems with symmetry Quantum (IF 5.1) Pub Date : 2024-08-29 Naga Dileep Varikuti, Soumik Bandyopadhyay
Quantum state designs, by enabling an efficient sampling of random quantum states, play a quintessential role in devising and benchmarking various quantum protocols with broad applications ranging from circuit designs to black hole physics. Symmetries, on the other hand, are expected to reduce the randomness of a state. Despite being ubiquitous, the effects of symmetry on quantum state designs remain
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Analysis of quantum Krylov algorithms with errors Quantum (IF 5.1) Pub Date : 2024-08-29 William Kirby
This work provides a nonasymptotic error analysis of quantum Krylov algorithms based on real-time evolutions, subject to generic errors in the outputs of the quantum circuits. We prove upper and lower bounds on the resulting ground state energy estimates, and the error associated to the upper bound is linear in the input error rates. This resolves a misalignment between known numerics, which exhibit
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Synchronization-induced violation of thermodynamic uncertainty relations Quantum Sci. Technol. (IF 5.6) Pub Date : 2024-08-29 Luca Razzoli, Matteo Carrega, Fabio Cavaliere, Giuliano Benenti, Maura Sassetti
Fluctuations affect the functionality of nanodevices. Thermodynamic uncertainty relations (TURs), derived within the framework of stochastic thermodynamics, show that a minimal amount of dissipation is required to obtain a given relative energy current dispersion, that is, current precision has a thermodynamic cost. It is therefore of great interest to explore the possibility that TURs are violated
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Device-independent lower bounds on the conditional von Neumann entropy Quantum (IF 5.1) Pub Date : 2024-08-27 Peter Brown, Hamza Fawzi, Omar Fawzi
The rates of several device-independent (DI) protocols, including quantum key-distribution (QKD) and randomness expansion (RE), can be computed via an optimization of the conditional von Neumann entropy over a particular class of quantum states. In this work we introduce a numerical method to compute lower bounds on such rates. We derive a sequence of optimization problems that converge to the conditional
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Quantum Chaos and Coherence: Random Parametric Quantum Channels Quantum (IF 5.1) Pub Date : 2024-08-27 Apollonas S. Matsoukas-Roubeas, Tomaž Prosen, Adolfo del Campo
The survival probability of an initial Coherent Gibbs State (CGS) is a natural extension of the Spectral Form Factor (SFF) to open quantum systems. To quantify the interplay between quantum chaos and decoherence away from the semi-classical limit, we investigate the relation of this generalized SFF with the corresponding $l_1$-norm of coherence. As a working example, we introduce Parametric Quantum
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Double or nothing: a Kolmogorov extension theorem for multitime (bi)probabilities in quantum mechanics Quantum (IF 5.1) Pub Date : 2024-08-27 Davide Lonigro, Fattah Sakuldee, Łukasz Cywiński, Dariusz Chruściński, Piotr Szańkowski
The multitime probability distributions obtained by repeatedly probing a quantum system via the measurement of an observable generally violate Kolmogorov's consistency property. Therefore, one cannot interpret such distributions as the result of the sampling of a single trajectory. We show that, nonetheless, they do result from the sampling of one $pair$ of trajectories. In this sense, rather than
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Quantum computation from dynamic automorphism codes Quantum (IF 5.1) Pub Date : 2024-08-27 Margarita Davydova, Nathanan Tantivasadakarn, Shankar Balasubramanian, David Aasen
We propose a new model of quantum computation comprised of low-weight measurement sequences that simultaneously encode logical information, enable error correction, and apply logical gates. These measurement sequences constitute a new class of quantum error-correcting codes generalizing Floquet codes, which we call dynamic automorphism (DA) codes. We construct an explicit example, the DA color code
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Hamiltonian simulation for low-energy states with optimal time dependence Quantum (IF 5.1) Pub Date : 2024-08-27 Alexander Zlokapa, Rolando D. Somma
We consider the task of simulating time evolution under a Hamiltonian $H$ within its low-energy subspace. Assuming access to a block-encoding of $H':=(H-E)/\lambda$, for some $\lambda \gt 0$ and $E \in \mathbb R$, the goal is to implement an $\epsilon$-approximation to the evolution operator $e^{-itH}$ when the initial state is confined to the subspace corresponding to eigenvalues $[-1, -1+\Delta/\lambda]$
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Fast erasure decoder for hypergraph product codes Quantum (IF 5.1) Pub Date : 2024-08-27 Nicholas Connolly, Vivien Londe, Anthony Leverrier, Nicolas Delfosse
We propose a decoder for the correction of erasures with hypergraph product codes, which form one of the most popular families of quantum LDPC codes. Our numerical simulations show that this decoder provides a close approximation of the maximum likelihood decoder that can be implemented in $O(N^2)$ bit operations where $N$ is the length of the quantum code. A probabilistic version of this decoder can
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Expanding the reach of quantum optimization with fermionic embeddings Quantum (IF 5.1) Pub Date : 2024-08-28 Andrew Zhao, Nicholas C. Rubin
Quadratic programming over orthogonal matrices encompasses a broad class of hard optimization problems that do not have an efficient quantum representation. Such problems are instances of the little noncommutative Grothendieck problem (LNCG), a generalization of binary quadratic programs to continuous, noncommutative variables. In this work, we establish a natural embedding for this class of LNCG problems
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Quantum multi-anomaly detection Quantum (IF 5.1) Pub Date : 2024-08-28 Santiago Llorens, Gael Sentís, Ramon Muñoz-Tapia
A source assumed to prepare a specified reference state sometimes prepares an anomalous one. We address the task of identifying these anomalous states in a series of $n$ preparations with $k$ anomalies. We analyze the minimum-error protocol and the zero-error (unambiguous) protocol and obtain closed expressions for the success probability when both reference and anomalous states are known to the observer