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Adaptive Phase Estimation with Squeezed Vacuum Approaching the Quantum Limit Quantum (IF 5.1) Pub Date : 2024-09-25 M. A. Rodríguez-García, F. E. Becerra
Phase estimation plays a central role in communications, sensing, and information processing. Quantum correlated states, such as squeezed states, enable phase estimation beyond the shot-noise limit, and in principle approach the ultimate quantum limit in precision, when paired with optimal quantum measurements. However, physical realizations of optimal quantum measurements for optical phase estimation
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Wigner’s friend’s memory and the no-signaling principle Quantum (IF 5.1) Pub Date : 2024-09-25 Veronika Baumann, Časlav Brukner
The Wigner's friend experiment is a thought experiment in which a so-called superobserver (Wigner) observes another observer (the friend) who has performed a quantum measurement on a physical system. In this setup Wigner treats the friend, the system and potentially other degrees of freedom involved in the friend's measurement as one joint quantum system. In general, Wigner's measurement changes the
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Mitigating controller noise in quantum gates using optimal control theory Quantum (IF 5.1) Pub Date : 2024-09-25 Aviv Aroch, Ronnie Kosloff, Shimshon Kallush
All quantum systems are subject to noise from the environment or external controls. This noise is a major obstacle to the realization of quantum technology. For example, noise limits the fidelity of quantum gates. Employing optimal control theory, we study the generation of quantum single and two-qubit gates. Specifically, we explore a Markovian model of phase and amplitude noise, leading to the degradation
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Optimal light cone for macroscopic particle transport in long-range systems: A quantum speed limit approach Quantum (IF 5.1) Pub Date : 2024-09-25 Tan Van Vu, Tomotaka Kuwahara, Keiji Saito
Understanding the ultimate rate at which information propagates is a pivotal issue in nonequilibrium physics. Nevertheless, the task of elucidating the propagation speed inherent in quantum bosonic systems presents challenges due to the unbounded nature of their interactions. In this study, we tackle the problem of macroscopic particle transport in a long-range generalization of the lattice Bose-Hubbard
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Tight and Efficient Gradient Bounds for Parameterized Quantum Circuits Quantum (IF 5.1) Pub Date : 2024-09-25 Alistair Letcher, Stefan Woerner, Christa Zoufal
The training of a parameterized model largely depends on the landscape of the underlying loss function. In particular, vanishing gradients are a central bottleneck in the scalability of variational quantum algorithms (VQAs), and are known to arise in various ways. However, a caveat of most existing gradient bound results is the requirement of t-design circuit assumptions that are typically not satisfied
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Efficient entanglement purification based on noise guessing decoding Quantum (IF 5.1) Pub Date : 2024-09-19 André Roque, Diogo Cruz, Francisco A. Monteiro, Bruno C. Coutinho
In this paper, we propose a novel bipartite entanglement purification protocol built upon hashing and upon the guessing random additive noise decoding (GRAND) approach recently devised for classical error correction codes. Our protocol offers substantial advantages over existing hashing protocols, requiring fewer qubits for purification, achieving higher fidelities, and delivering better yields with
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Sampling Error Analysis in Quantum Krylov Subspace Diagonalization Quantum (IF 5.1) Pub Date : 2024-09-19 Gwonhak Lee, Dongkeun Lee, Joonsuk Huh
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 diagonalization (KSD) or the Lanczos method, QKSD exploits the quantum computer to efficiently estimate the eigenvalues of large-size Hamiltonians through a faster
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Safeguarding Oscillators and Qudits with Distributed Two-Mode Squeezing Quantum (IF 5.1) Pub Date : 2024-09-19 Anthony J. Brady, Jing Wu, Quntao Zhuang
Recent advancements in multi-mode Gottesman-Kitaev-Preskill (GKP) codes have shown great promise in enhancing the protection of both discrete and analog quantum information. This broadened range of protection brings opportunities beyond quantum computing to benefit quantum sensing by safeguarding squeezing — the essential resource in many quantum metrology protocols. However, the potential for quantum
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Efficient validation of Boson Sampling from binned photon-number distributions Quantum (IF 5.1) Pub Date : 2024-09-19 Benoit Seron, Leonardo Novo, Alex Arkhipov, Nicolas J. Cerf
In order to substantiate claims of quantum computational advantage, it is crucial to develop efficient methods for validating the experimental data. We propose a test of the correct functioning of a boson sampler with single-photon inputs that is based on how photons distribute among partitions of the output modes. Our method is versatile and encompasses previous validation tests based on bunching
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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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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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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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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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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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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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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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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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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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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
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GraphiQ: Quantum circuit design for photonic graph states Quantum (IF 5.1) Pub Date : 2024-08-28 Jie Lin, Benjamin MacLellan, Sobhan Ghanbari, Julie Belleville, Khuong Tran, Luc Robichaud, Roger G. Melko, Hoi-Kwong Lo, Piotr Roztocki
$\tt{GraphiQ}$ is a versatile open-source framework for designing photonic graph state generation schemes, with a particular emphasis on photon-emitter hybrid circuits. Built in Python, GraphiQ consists of a suite of design tools, including multiple simulation backends and optimization methods. The library supports scheme optimization in the presence of circuit imperfections, as well as user-defined
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Classical-to-quantum non-signalling boxes Quantum (IF 5.1) Pub Date : 2024-08-22 Carolina Moreira Ferrera, Robin Simmons, James Purcell, Daniel Collins, Sandu Popescu
Here we introduce the concept of classical input – quantum output (C-Q) non-signalling boxes, a generalisation of the classical input – classical output (C-C) non-signalling boxes. We argue that studying such objects leads to a better understanding of the relation between quantum nonlocality and non-locality beyond quantum mechanics. The main issue discussed in the paper is whether there exist 'genuine'
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Taming Quantum Time Complexity Quantum (IF 5.1) Pub Date : 2024-08-23 Aleksandrs Belovs, Stacey Jeffery, Duyal Yolcu
Quantum query complexity has several nice properties with respect to composition. First, bounded-error quantum query algorithms can be composed without incurring log factors through error reduction $exactness$. Second, through careful accounting $thriftiness$, the total query complexity is smaller if subroutines are mostly run on cheaper inputs -- a property that is much less obvious in quantum algorithms
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Certification of quantum state functions under partial information Quantum (IF 5.1) Pub Date : 2024-08-16 Leonardo Zambrano, Donato Farina, Egle Pagliaro, Marcio M. Taddei, Antonio Acin
Convex functions of quantum states play a key role in quantum physics, with examples ranging from Bell inequalities to von Neumann entropy. However, in experimental scenarios, direct measurements of these functions are often impractical. We address this issue by introducing two methods for determining rigorous confidence bounds for convex functions based on informationally incomplete measurements.
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Approximate Quantum Codes From Long Wormholes Quantum (IF 5.1) Pub Date : 2024-08-14 Gregory Bentsen, Phuc Nguyen, Brian Swingle
We discuss families of approximate quantum error correcting codes which arise as the nearly-degenerate ground states of certain quantum many-body Hamiltonians composed of non-commuting terms. For exact codes, the conditions for error correction can be formulated in terms of the vanishing of a two-sided mutual information in a low-temperature thermofield double state. We consider a notion of distance
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Quantum Reference Frames for Lorentz Symmetry Quantum (IF 5.1) Pub Date : 2024-08-14 Luca Apadula, Esteban Castro-Ruiz, Časlav Brukner
Since their first introduction, Quantum Reference Frame (QRF) transformations have been extensively discussed, generalising the covariance of physical laws to the quantum domain. Despite important progress, a formulation of QRF transformations for Lorentz symmetry is still lacking. The present work aims to fill this gap. We first introduce a reformulation of relativistic quantum mechanics independent
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Study of noise in virtual distillation circuits for quantum error mitigation Quantum (IF 5.1) Pub Date : 2024-08-14 Pontus Vikstål, Giulia Ferrini, Shruti Puri
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 sequence of controlled-swap gates. If the noise does not shift the dominant eigenvector of the density operator away from the ideal state, then the error in expectation-value
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Non-Markovianity in High-Dimensional Open Quantum Systems using Next-generation Multicore Optical Fibers Quantum (IF 5.1) Pub Date : 2024-08-12 Santiago Rojas-Rojas, Daniel Martínez, Kei Sawada, Luciano Pereira, Stephen P. Walborn, Esteban S. Gómez, Nadja K. Bernardes, Gustavo Lima
With the advent of quantum technology, the interest in communication tasks assisted by quantum systems has increased both in academia and industry. Nonetheless, the transmission of a quantum state in real-world scenarios is bounded by environmental noise, so that the quantum channel is an open quantum system. In this work, we study a high-dimensional open quantum system in a multicore optical fiber
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Maximum expectation of observables with restricted purity states Quantum (IF 5.1) Pub Date : 2024-08-13 Vikesh Siddhu, John Aaron Smolin
Assessment of practical quantum information processing (QIP) remains partial without understanding limits imposed by noise. Unfortunately, mere description of noise grows exponentially with system size, becoming cumbersome even for modest sized systems of imminent practical interest. We fulfill the need for estimates on performing noisy quantum state preparation, verification, and observation. To do
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Measurement-efficient quantum Krylov subspace diagonalisation Quantum (IF 5.1) Pub Date : 2024-08-13 Zongkang Zhang, Anbang Wang, Xiaosi Xu, Ying Li
The Krylov subspace methods, being one category of the most important classical numerical methods for linear algebra problems, can be much more powerful when generalised to quantum computing. However, quantum Krylov subspace algorithms are prone to errors due to inevitable statistical fluctuations in quantum measurements. To address this problem, we develop a general theoretical framework to analyse
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A learning theory for quantum photonic processors and beyond Quantum (IF 5.1) Pub Date : 2024-08-08 Matteo Rosati
We consider the tasks of learning quantum states, measurements and channels generated by continuous-variable (CV) quantum circuits. This family of circuits is suited to describe optical quantum technologies and in particular it includes state-of-the-art photonic processors capable of showing quantum advantage. We define classes of functions that map classical variables, encoded into the CV circuit
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Hayden-Preskill recovery in chaotic and integrable unitary circuit dynamics Quantum (IF 5.1) Pub Date : 2024-08-08 Michael A. Rampp, Pieter W. Claeys
The Hayden-Preskill protocol probes the capability of information recovery from local subsystems after unitary dynamics. As such it resolves the capability of quantum many-body systems to dynamically implement a quantum error-correcting code. The transition to coding behavior has been mostly discussed using effective approaches, such as entanglement membrane theory. Here, we present exact results on
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Resource-Efficient Real-Time Polarization Compensation for MDI-QKD with Rejected Data Quantum (IF 5.1) Pub Date : 2024-08-08 Olinka Bedroya, Chenyang Li, Wenyuan Wang, Jianyong Hu, Hoi-Kwong Lo, Li Qian
Measurement-device-independent quantum key distribution (MDI-QKD) closes all the security loopholes in the detection system and is a promising solution for secret key sharing. Polarization encoding is the most common QKD encoding scheme, as it is straightforward to prepare and measure. However, implementing polarization encoding in MDI QKD imposes extra challenges, as polarization alignment must be
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Entanglement spectrum of matchgate circuits with universal and non-universal resources Quantum (IF 5.1) Pub Date : 2024-08-07 Andrew M. Projansky, Joshuah T. Heath, James D. Whitfield
The entanglement level statistics of a quantum state have recently been proposed to be a signature of universality in the underlying quantum circuit. This is a consequence of level repulsion in the entanglement spectra being tied to the integrability of entanglement generated. However, such studies of the level-spacing statistics in the entanglement spectrum have thus far been limited to the output
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Improved Pairwise Measurement-Based Surface Code Quantum (IF 5.1) Pub Date : 2024-08-02 Linnea Grans-Samuelsson, Ryan V. Mishmash, David Aasen, Christina Knapp, Bela Bauer, Brad Lackey, Marcus P. da Silva, Parsa Bonderson
We devise a new realization of the surface code on a rectangular lattice of qubits utilizing single-qubit and nearest-neighbor two-qubit Pauli measurements and three auxiliary qubits per plaquette. This realization gains substantial advantages over prior pairwise measurement-based realizations of the surface code. It has a short operation period of 4 steps and our performance analysis for a standard
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Stabilization of symmetry-protected long-range entanglement in stochastic quantum circuits Quantum (IF 5.1) Pub Date : 2024-08-02 Iosifina Angelidi, Marcin Szyniszewski, Arijeet Pal
Long-range entangled states are vital for quantum information processing and quantum metrology. Preparing such states by combining measurements with unitary gates opened new possibilities for efficient protocols with finite-depth quantum circuits. The complexity of these algorithms is crucial for the resource requirements on a large-scale noisy quantum device, while their stability to perturbations
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Long-lived collective Rydberg excitations in atomic gas achieved via ac-Stark lattice modulation Quantum (IF 5.1) Pub Date : 2024-08-02 Stanisław Kurzyna, Bartosz Niewelt, Mateusz Mazelanik, Wojciech Wasilewski, Michał Parniak
Collective Rydberg excitations provide promising applications ranging from quantum information processing, and quantum computing to ultra-sensitive electrometry. However, their short lifetime is an immense obstacle in real-life scenarios. The state-of-the-art methods of prolonging the lifetime were mainly implemented for ground-state quantum memories and would require a redesign to effectively work
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Universal framework for simultaneous tomography of quantum states and SPAM noise Quantum (IF 5.1) Pub Date : 2024-07-30 Abhijith Jayakumar, Stefano Chessa, Carleton Coffrin, Andrey Y. Lokhov, Marc Vuffray, Sidhant Misra
We present a general denoising algorithm for performing $\textit{simultaneous tomography}$ of quantum states and measurement noise. This algorithm allows us to fully characterize state preparation and measurement (SPAM) errors present in any quantum system. Our method is based on the analysis of the properties of the linear operator space induced by unitary operations. Given any quantum system with
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Single-shot Quantum Signal Processing Interferometry Quantum (IF 5.1) Pub Date : 2024-07-30 Jasmine Sinanan-Singh, Gabriel L. Mintzer, Isaac L. Chuang, Yuan Liu
Quantum systems of infinite dimension, such as bosonic oscillators, provide vast resources for quantum sensing. Yet, a general theory on how to manipulate such bosonic modes for sensing beyond parameter estimation is unknown. We present a general algorithmic framework, quantum signal processing interferometry (QSPI), for quantum sensing at the fundamental limits of quantum mechanics by generalizing
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Adiabatic quantum trajectories in engineered reservoirs Quantum (IF 5.1) Pub Date : 2024-07-30 Emma C. King, Luigi Giannelli, Raphaël Menu, Johannes N. Kriel, Giovanna Morigi
We analyze the efficiency of protocols for adiabatic quantum state transfer assisted by an engineered reservoir. The target dynamics is a quantum trajectory in the Hilbert space and is a fixed point of a time-dependent master equation in the limit of adiabatic dynamics. We specialize to quantum state transfer in a qubit and determine the optimal schedule for a class of time-dependent Lindblad equations
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On Strong Bounds for Trotter and Zeno Product Formulas with Bosonic Applications Quantum (IF 5.1) Pub Date : 2024-07-25 Tim Möbus
The Trotter product formula and the quantum Zeno effect are both indispensable tools for constructing time-evolutions using experimentally feasible building blocks. In this work, we discuss assumptions under which quantitative bounds can be proven in the strong operator topology on Banach spaces and provide natural bosonic examples. Specially, we assume the existence of a continuously embedded Banach