Quantum Physics
Certification and Classification of Linear Quantum Error Mitigation Methods
Zach Blunden-Codd and Mohamed Tamaazousti
Numerous mitigation methods exist for
quantum noise suppression, making it challenging to identify the optimum approach for a specific application; especially as ongoing advances in hardware tuning and error correction are expected to reduce logical error rates. In order to facilitate the future-proof application-dependent comparison of mitigation methods, we develop a set of quantitative metrics that account for continual improvements in logical gate quality. We use these metrics to define qualitative criteria (e.g. scalability, efficiency, and robustness to characterised imperfections in the mitigation implementation), which we combine into application-specific certifications. We then provide a taxonomy of linear mitigation methods, characterising them by their features and requirements. Finally, we use our framework to produce and evaluate a mitigation strategy. A mitigation strategy is a collections of mitigation methods and compilation procedures designed to mitigate all relevant errors for a given piece of characterised hardware. Our example mitigation strategy is targeted at mitigating the outputs of hardware suffering from
stochastic noise and/or rotational errors. We find the most significant determinant of efficient mitigation is accurate and precise characterisation.
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Quantum Physics
JCO: Optimization Framework for Nonlinear Superconducting Circuits Using a Lumped-Element Approach and Harmonic Balance
Emanuele Palumbo, Alessandro Alocco, Andrea Celotto et al. (+4 more)
In this contribution we present JosephsonCircuitsOptimizer.jl (JCO), a simulation and optimization framework based on the JosephsonCircuits.jl library for Julia. It models superconducting
circuits that include Josephson junctions (JJs) and other nonlinear elements within a lumped-element approach, leveraging harmonic balance, a frequency-domain technique that provides a computationally efficient alternative to traditional time-domain simulations. JCO automates the evaluation of optimal
circuit parameters by implementing
Bayesian optimization with Gaussian processes through a device-specific metric and identifying the optimal working point to achieve a defined performance function. This makes it well suited for
circuits with strong nonlinearity and a high-dimensional set of coupled design parameters. To demonstrate its capabilities, we focus on optimizing a Josephson Traveling-Wave Parametric Amplifier (JTWPA) based on Superconducting Nonlinear Asymmetric Inductive eLements (SNAILs), operating in the three-wave mixing regime. The device consists of an array of unit
cells, each containing a loop with multiple JJs, that amplifies weak
quantum signals near the
quantum noise limit. By integrating efficient simulation and optimization strategies, the framework supports the systematic development of superconducting
circuits for a broad range of applications.
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All authors Emanuele Palumbo, Alessandro Alocco, Andrea Celotto, Luca Fasolo, Bernardo Galvano, Patrizia Livreri, Emanuele Enrico
Quantum Physics · Cross-listed from cond-mat.stat-mech
Spin-orbit coupled spin-boson model : A variational analysis
Sudip Sinha, Subhasis Sinha and Sushanta Dattagupta
The
spin-
boson (SB) model is a standard prototype for
quantum dissipation, which we generalize in this work, to explore the dissipative effects on a one-dimensional
spin-orbit (SO) coupled particle in the presence of a sub-ohmic bath. We analyze this model by extending the well-known variational polaron approach, revealing a localization transition accompanied by an intriguing change in the spectrum, for which the doubly degenerate minima evolves to a single minimum at zero momentum as the system-bath coupling increases. For translational invariant system with conserved momentum, a continuous magnetization transition occurs, whereas the ground state changes discontinuously. We further investigate the transition of the ground state in the presence of harmonic confinement, which effectively models a
quantum dot-like nanostructure under the influence of the environment. In both the scenarios, the
entanglement entropy of the
spin-sector can serve as a marker for these transitions. Interestingly, for the trapped system, a cat-like superposition state corresponds to maximum
entanglement entropy below the transition, highlighting the relevance of the present model for studying the effect of decoherence on intra-particle
entanglement in the context of
quantum information processing.
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Quantum Physics
Correlations in a quantum switch-based heat engine with measurements: A proof-of-principle demonstration
Vinicius F. Lisboa, Pedro R. Dieguez, Kyrylo Simonov et al. (+1 more)
Allowing the order of
quantum operations to exist in superposition is known to open new routes for thermodynamic tasks. We investigate a
quantum heat engine where energy exchanges are driven by generalized measurements, and the sequence of these operations is coherently controlled in a superposition of causal orders. Our analysis explores how initial correlations between the working medium and the controller affect the engine's performance. Considering uncorrelated, classically correlated, and entangled initial states, we show that
entanglement enables the superposed causal order to generate coherence in the working medium, thereby enhancing work extraction and efficiency beyond the separable and uncorrelated cases. Finally, we present a proof-of-principle simulation on the IBM
Quantum Experience platform, realizing a
quantum switch of two measurement channels with tunable strengths and experimentally confirming the predicted efficiency enhancement enabled by correlation-assisted superposed causal order.
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All authors Vinicius F. Lisboa, Pedro R. Dieguez, Kyrylo Simonov, Roberto M. Serra
Quantum Physics
Super-Heisenberg Scaling Using Nonlinear Quantum Scrambling
Dong Xie and Chunling Xu
Super-Heisenberg scaling, which scales as $N^{-\beta}$ with $\beta>1$ in terms of the number of particles $N$ or $T^{-\beta}$ in terms of the
evolution time $T$, is better than Heisenberg scaling in
quantum metrology. It has been proven that super-Heisenberg scaling can be achieved when the
Hamiltonian of the system involves many-body interactions or the time-dependent terms. We demonstrate that nonlinear
quantum scrambling facilitates the achievement of super-Heisenberg scaling $T^{-\beta}$ when the generator of the parameter is time-independent. More importantly, in dissipative systems, we can still obtain super-Heisenberg scaling in the friction model. In the optical cavity system, an exponential improvement in measurement precision over time can be achieved by combining injected external squeezing and intracavity squeezing. Our work provides an optimal method for leveraging nonlinear resources to enhance the measurement precision of the driving field.
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Quantum Physics
Reusability of Quantum Catalysts
Haitao Ma, Yantong Li, Yingchun Kang et al. (+4 more)
Quantum catalysts enable transformations that otherwise would be forbidden, offering a pathway to surpass conventional limits in
quantum information processing. Among them, embezzling catalysts stand out for achieving near-perfect performance while tolerating only minimal disturbance, bridging the gap between ideal and practical catalysis. Yet, this superior capability comes at a cost: Each use slightly degrades the catalyst, leading to an inevitable accumulation of imperfection. This gradual decay defines their most distinctive property – reusability – which, despite its fundamental importance, remains largely unexplored. Here, we establish a quantitative framework to characterize the operational lifetime of embezzling catalysts, focusing on their role in
entanglement distillation and extending the analysis to
quantum teleportation. We show that the catalytic advantage inevitably diminishes with repeated use, deriving bounds on the maximum effective reuse rounds for a desired performance gain. Our results uncover the finite reusability of catalysts in
quantum processes and point toward sustainable strategies for
quantum communication.
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All authors Haitao Ma, Yantong Li, Yingchun Kang, Bing Yu, Junjing Xing, Zhaobing Fan, Yunlong Xiao
Quantum Physics
Network nonlocality breaking channels
Kaushiki Mukherjee and Nirman Ganguly
Network nonlocality, a recently noted form of nonlocality has been shown to have distinctive features, marking a significant departure from the notion of standard Bell nonlocality in the context of
quantum correlations. On a pragmatic front, it has gained significant importance as researchers worldwide actively engage in the study on
quantum networks. However, as typical to any
quantum resource, network nonlocality is also vulnerable to environmental noise, which sometimes prove to be detrimental. Environmental interactions are modeled in terms of
quantum channels. In the present study, we introduce and characterize network nonlocality breaking channels. Network nonlocality breaking channels model environmental influences which results in the loss of resource, i.e., the system loses its nonlocal resource due to such interactions. The study is done in the ambit of some suitably chosen inequalities in (i) linear networks and (ii)
star-shaped networks. Further, the loss in full network nonlocality is also studied. Furthermore, we also characterize
quantum channels according to their ability in preserving
quantum resources, i.e., they do not break network nonlocality, which enables one to identify useful
quantum channels in networks. The study is vindicated by illustrations from various noise models like depolarizing and dephasing channels.
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Quantum Physics
Entanglement certification in bulk nonlinear crystals for degenerate and non-degenerate SPDC: spectral filter effects on transverse spatial correlations
Hashir Kuniyil, Asad Ali and Saif Al-Kuwari
Spatial correlations of
photon pairs from spontaneous parametric down-conversion (SPDC) underpin
quantum imaging and
entanglement certification. We present the first systematic study of spectral filter bandwidth effects on transverse spatial correlations in bulk Type-I BBO for degenerate and non-degenerate configurations. In the far field, the degenerate conditional momentum width is pump-limited and filter-invariant, while non-degenerate configurations exhibit monotonic growth in both marginal and conditional momentum widths – with the walk-off axis $\approx 100$ times more sensitive than the non-walk-off axis. In the near field, we identify a previously unreported flat-dip-rise profile: the conditional position width narrows by $\approx 10\%$ at an optimal bandwidth $\Delta_\mathrm{dip} \approx 1.35\,\Delta\lambda_\mathrm{SPDC}$ before rising due to
geometric displacement. When the filter is placed on the idler arm, the dip shifts by the exact factor $(\lambda_i/\lambda_s)^2$. Both results are universal for any non-degenerate SPDC source, requiring only a finite
crystal length, $d\theta/d\lambda \neq 0$, and incoherent spectral averaging. The Reid EPR uncertainty product is consistently smaller on the walk-off axis – a structural advantage of bulk birefringent geometry absent in quasi-phase-matched sources. The optimal filter bandwidth $\Delta_F = \Delta_\mathrm{dip}$ is determined entirely by the intrinsic phase-matching bandwidth of the
crystal and is directly readable from the X-
entanglement spectral width of the source.
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Quantum Physics
Quantum Random Number Generator with Internal Consistency Check and Public Verification
Rodrigo Piera, Gianluca De Santis, Agustin Sanchez et al. (+2 more)
Quantum Random Number Generators provide true physical randomness based on
quantum processes, essential for cryptographic and scientific applications. However, practical implementations face challenges in robustness and verifiability: ensuring that the
entropy source remains secure and stable over time, and enabling independent confirmation of randomness quality without compromising security. We present a system based on a simple looped beam splitter architecture that uses only passive optical components. The device features an intrinsic self-testing mechanism derived from the stability of detection-probability ratios, allowing continuous validation of correct operation. In addition, the same physical process generates two independent random sequences with identical
entropy: a private sequence, used for secure applications, and a public one, enabling external statistical verification with zero mutual information between them. This approach demonstrates that robust, self-testing, and publicly verifiable
quantum randomness can be achieved with minimal optical complexity without jeopardizing security.
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All authors Rodrigo Piera, Gianluca De Santis, Agustin Sanchez, Yury Kurochkin, James A. Grieve
Quantum Physics
Generation and detection of squeezed states via a synchronously pumped optical parametric oscillator
Edoardo Suerra, Samuele Altilia, Stefano Olivares et al. (+7 more)
A synchronously pumped optical parametric oscillator (SPOPO) operating at 93 MHz is used to generate squeezed states at 1035 nm. The system features a counter-propagating beam at the same wavelength as the
quantum state, which simultaneously actively stabilizes the cavity and, after transmission, acts as the local oscillator for homodyne detection. By deriving the local oscillator directly from the SPOPO cavity, the setup establishes an intrinsically excellent spatial mode overlap and high interference visibility, forming a distinctive self-referenced architecture. Two spatial light modulators enable precise spectral shaping of both the pump and the local oscillator in amplitude and phase, allowing investigation of the spectral properties of the generated states. The versatility of the setup further allows exploration of different SPOPO configurations, including regimes with varied finesse and escape efficiency. Representative measurements, including homodyne traces and squeezing levels as functions of pump power and local oscillator bandwidth, demonstrate the performance of the system. Theoretical simulations based on a multimode singular-value-decomposition model reproduce well the measured dependence of squeezing on pump power and LO bandwidth, confirming the accuracy of the description and the robustness of the setup. Measured squeezing levels up to -3.3 dB are achieved, corresponding to -5.7 dB at SPOPO output, evidencing the robustness and versatility of this platform for stable pulsed squeezed-light generation and advanced
quantum optical applications.
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All authors Edoardo Suerra, Samuele Altilia, Stefano Olivares, Alessandro Ferraro, Francesco Canella, Dario Giannotti, Gianluca Galzerano, Sebastiano Corli, Enrico Prati, Simone Cialdi
Quantum Physics
Feynman path sum approach for simulation of linear optics
Wagner F. Balthazar, Quinn M. B. Palmer, Alex. E. Jones et al. (+2 more)
The Feynman path integral formalism has inspired the development of
memory-efficient and parallelizable classical
algorithms for simulating
quantum computers. We adapt this approach for the calculation of probability amplitudes of linear-optical
boson sampling experiments, which involve Fock-state inputs, linear optical
circuits, and photo-detection at the output. We describe this simulation method and compare it with alternative approaches. Additionally, we implement a Linear-Optical Feynman Path simulator in open-source C code, enhancing its performance using tensor contraction techniques. Our method is benchmarked for low-depth linear optical
circuits, where it offers advantages in runtime and
memory efficiency.
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All authors Wagner F. Balthazar, Quinn M. B. Palmer, Alex. E. Jones, Jake F. F. Bulmer, Ernesto. F. Galvão
Quantum Physics
Engineered Kerr Nonlinearities for Precise Quantum Control of Fock States
Gabriella G. Damas, Ciro Micheletti Diniz, Norton G. de Almeida et al. (+2 more)
We present a practical design framework for high-fidelity
quantum control in coupled Kerr-nonlinear oscillators, directly addressing the challenge of spectral crowding. We show that systematic spectral degeneracies, which hinder selective addressing, are a direct consequence of rational Kerr-nonlinearity ratios ($K_1/K_2$). Our solution is a universal architectural principle: engineer this ratio to be a complex rational value, approximating an incommensurate number to systematically eliminate parasitic resonances. Using a Magnus expansion, we derive a complete effective
Hamiltonian, including all Stark-shift corrections, to accurately target transitions. We numerically validate this framework by demonstrating protocols for the deterministic synthesis of NOON states, and high-
photon-number Fock states (e.g., $n=4$), achieving ideal fidelities exceeding $\mathcal{F}>99.9\%$. The protocols are shown to be robust against environmental decay and thermal effects. This work provides an architectural blueprint for bosonic processors in
circuit QED and establishes foundational principles that could inform future designs of multi-mode
quantum systems.
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All authors Gabriella G. Damas, Ciro Micheletti Diniz, Norton G. de Almeida, Celso J. Villas-Bôas, G. D. de Moraes Neto
Quantum Physics
Quadratic Quantum Speedup for Finding Independent Set of a Graph
Xianjue Zhao, Peiyun Ge, Li You et al. (+1 more)
A quadratic speedup of the
quantum adiabatic
algorithm (QAA) for finding independent sets (ISs) in a graph is proven analytically. In comparison to the best classical
algorithm with $O(n^2)$ scaling, where $n$ is the number of vertexes, our
quantum algorithm achieves a time complexity of $O(n^2)$ for finding a large IS, which reduces to $O(n)$ for identifying a size-2 IS. The complexity bounds we obtain are confirmed numerically for a specific case with the $O(n^2)$
quantum algorithm outperforming the classical greedy
algorithm, that also runs in $O(n^2)$. The definitive analytical and numerical evidence for the quadratic
quantum speedup benefited from an analytical framework based on the Magnus expansion in the interaction picture (MEIP), which overcomes the dependence on the ground state degeneracy encountered in conventional energy gap analysis. In addition, our analysis links the performance of QAA to the spectral structure of the median graph, bridging algorithmic complexity, graph theory, and experimentally realizable Rydberg
Hamiltonians. The understanding gained provides practical guidance for optimizing near-term Rydberg atom experiments by revealing the significant impact of detuning on blockade violations.
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All authors Xianjue Zhao, Peiyun Ge, Li You, Biao Wu
Quantum Physics
Enhancing the reachability of variational quantum algorithms via input-state design
Shaojun Wu, Shan Jin, Abolfazl Bayat et al. (+1 more)
Variational
quantum algorithms (VQAs) face an inherent trade-off between expressivity and trainability: deeper
circuits can represent richer states but suffer from noise accumulation and barren plateaus, while shallow
circuits remain trainable and implementable but lack expressive power. Here, we propose a general framework to address this challenge by enhancing the VQA performance with a specially designed input state constructed using a linear combination technique. This approach systematically modified the set of states reachable by the original
circuit, enhancing accuracy while preserving efficiency. We provide a rigorous proof that such framework increases the expressive capacity of any given VQA ansatz, and demonstrate its broad applicability across different ansatz families. As applications, we apply the method to ground-state preparation of the transverse-field Ising, cluster-Ising, and
Fermi-Hubbard models, achieving consistently higher accuracy under the same gate budget compared with standard VQAs. These results highlight input-state design as a powerful complement to
circuit design in realizing VQAs that are both expressive and trainable.
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All authors Shaojun Wu, Shan Jin, Abolfazl Bayat, Xiaoting Wang
Quantum Physics
Entanglement and Dynamical Scaling Laws in Quantum Superabsorption
Juan David Álvarez-Cuartas and John H. Reina
Quantum batteries (QBs) exploit collective
quantum resources to surpass the limits of classical energy storage and power delivery. We analyze $N$-
qubit cavity-coupled QBs governed by Dicke and Tavis–Cummings models under Gaussian driving and open-system dynamics. Finite-size scaling laws $\mathcal{O}(N)\!\sim\!N^{\alpha}$ demonstrate an optimal region of relaxation and dephasing where coherent driving stabilizes
entanglement entropy growth for thermodynamic observables (maximum energy $E_{\mathrm{max}}$, charging time $\tau$, and maximum power $\bar{P}_{\mathrm{max}}$) and for
qubit and cavity
entanglement entropies. The Dicke model exhibits
entropy-suppressed extensive behavior, while the Tavis–Cummings model achieves super-extensive scaling with $\alpha_{E_{\mathrm{max}}}\!\in\![1.08,1.26]$, $\alpha_{\tau}\!\approx\!-0.49$, $\alpha_{\bar{P}_{\mathrm{max}}}\!\in\![1.57,1.73]$, supported by
qubit-cavity
entanglement. We demonstrate that dissipation can act as a stabilizer source, yielding scaling
benchmarks that are relevant to several experimental platforms. Our findings connect
entanglement, dissipation-enhanced scaling laws and superabsorption, outlining a pathway towards scalable
quantum batteries offering practical
quantum advantage.
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Quantum Physics
Quantum dynamics of spin-J particles in static and rotating magnetic fields: Entanglement resonances and kinks
Nargis Sultana, Siddharth Seetharaman and Rejish Nath
We examine the
quantum dynamics of both a single
spin-J particle and a pair of
spin-J particles in the presence of static and rotating
magnetic fields, which can be important for qudit-based
quantum technologies. Notably, we find resonant, periodic oscillations between two maximally stretched states, irrespective of the value of J. Additionally, we observe periodic transitions between sublevels with
magnetic quantum numbers of opposite signs. The dynamics also exhibit a periodic transfer of the
spin to the maximally stretched state, starting from the ground state of the initial
Hamiltonian. For a pair of
spins, we derive various resonance conditions and further analyze the
entanglement generated by dipole-dipole interactions. In the case of two
spin-1/2 particles, the
entanglement dynamics reveal resonances and kinks in the maximum
entanglement, and their criteria can be obtained from the energy spectrum. Strikingly, we show that the kink can be exploited to engineer the
entanglement dynamics. Finally, we briefly discuss the regime of weak dipolar interactions, which are relevant for dipolar Bose-Einstein condensates.
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Quantum Physics
Quantum Nonlocality under Latency Constraints
Dawei Ding, Zhengfeng Ji, Pierre Pocreau et al. (+2 more)
Bell inequalities are bounds on the correlations between different parties obeying a local hidden variable theory. Here, "local" refers to spacetime locality: the parties cannot communicate their inputs because they must produce their outputs faster than the speed-of-light delay between them. In other words, the parties must satisfy a certain latency constraint. In this work, we explicitly incorporate spacetime locality into the formulation of Bell inequalities by imposing such a latency constraint. When the latency constraint is sufficiently tight such that no parties can communicate, this becomes a standard Bell scenario. When the latency constraint is relaxed such that a subset of the parties can communicate, we no longer have a Bell scenario, but we can again find a divide between classical and
quantum behaviors. Hence, we observe that the classical-
quantum gap should actually be a function of time. To study these more general scenarios, we introduce the mathematical framework of latency-constrained games, which models time-evolving input and output processes for spatially separated parties subject to finite communication speeds. This framework allows us to systematically study the weirdness of
quantum mechanics in the "low-latency regime" where the speed-of-light delay is non-negligible. Latency-constrained games can describe real-time decision-making in real-world settings that are latency-sensitive, such as high-frequency trading and distributed systems, and can reveal the utility of
quantum correlations in these settings.
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All authors Dawei Ding, Zhengfeng Ji, Pierre Pocreau, Mingze Xu, Xinyu Xu
Quantum Physics
Extended Coherent States
Z.M. McIntyre, A. Kasman and R. Milson
Using the formalism of Maya diagrams and ladder operators, we describe the
algebra of annihilating operators for the class of rational extensions of the harmonic oscillator. This allows us to construct the corresponding coherent state in the sense of Barut and Girardello. The resulting time-dependent function is an exact solution of the time-dependent Schrödinger equation and a joint eigenfunction of the
algebra of annihilators. Using an argument based on Schur functions, we also show that the newly exhibited coherent states asymptotically minimize position-momentum uncertainty.
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Quantum Physics
Benchmarking quantum key distribution by mixing single photons and laser light
Yann Portella, Petr Steindl, Juan Rafael Álvarez et al. (+8 more)
Quantum key distribution is a key application of
quantum mechanics, shaping the future of
privacy and secure communications. Many protocols require single
photons, often approximated by strongly attenuated
laser pulses. Here, we harness the emission of a
quantum dot embedded in a micropillar and explore a hybrid approach where the information is encoded on a mixture of single
photons and
laser pulses. We derive a phenomenological analysis of the configuration where both sources of light are mixed incoherently to perform the BB84 protocol, showing nearly perfect matching between theory and experiment. This provides a flexible technology compensating limited collected brightnesses of single-
photon sources as well as a thorough investigation of single-
photon statistics advantage scenarios over Poisson-distributed statistics. Explicitly, our model highlights an efficiency threshold for unconditional advantage of single
photons over
laser along with insights on the interplay between single-
photon purity and collected brightness in the performances of BB84.
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All authors Yann Portella, Petr Steindl, Juan Rafael Álvarez, Tim Hebenstreit, Aristide Lemaître, Martina Morassi, Niccolo Somaschi, Loïc Lanco, Filip Rozpędek, Pascale Senellart, Dario A. Fioretto
Quantum Physics · Cross-listed from physics.optics
Dinosaur Photonic Crystal Cavity Interfaces for Color Center Coupling to Triangular Nanostructures
Julian M. Bopp, Lucca Valerius and Tim Schröder
Waveguide-coupled photonic
crystal cavities with a triangular cross section fabricated by angled etching are suitable to interface embedded color centers with flying photonic
qubits in
quantum information applications. Moreover, their fabrication requires fewer processing steps compared to nanostructures produced by quasi-isotropic undercutting. As an alternative to established hole-based photonic
crystal cavities, we introduce corrugated triangular 'Dinosaur' photonic
crystal cavities, and develop a tapered, quasi loss-free cavity-waveguide interface to adiabatically interconvert Bloch and waveguide modes. We optimize the cavity-waveguide interface to minimize
photon losses and demonstrate that its adjustment allows precise tuning of the light-matter interaction.
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Quantum Physics · Cross-listed from math-ph
Strong Kantorovich duality for quantum optimal transport with generic cost and optimal couplings on quantum bits
Gergely Bunth, József Pitrik, Tamás Titkos et al. (+1 more)
We prove Kantorovich duality for a linearized version of a recently proposed non-quadratic
quantum optimal transport problem, where
quantum channels realize the transport. As an application, we determine optimal solutions of both the primal and the dual problem using this duality in the case of
quantum bits and distinguished cost operators, with certain restrictions on the states involved. Finally, keeping the same restrictions regarding the states involved, we use this information on optimal solutions to give an analytical proof of the triangle inequality even for the square of the induced
quantum Wasserstein divergences.
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All authors Gergely Bunth, József Pitrik, Tamás Titkos, Dániel Virosztek
Quantum Physics · Cross-listed from cond-mat.stat-mech
Weak-Memory Dynamics in Discrete Time
Hugues Meyer and Kay Brandner
Discrete dynamics arise naturally in systems with broken temporal translation
symmetry and are typically described by first-order recurrence relations representing classical or
quantum Markov chains. When
memory effects induced by hidden degrees of freedom are relevant, however, higher-order discrete
evolution equations are generally required. Focusing on linear dynamics, we identify a well-delineated weak-
memory regime where such equations can, on an intermediate time scale, be systematically reduced to a unique first-order counterpart acting on the same state space. We formulate our results as a mathematical
theorem and work out two examples showing how they can be applied to
stochastic Floquet dynamics under coarse-grained and
quantum collisional models.
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Quantum Physics
Twin-Field Quantum Key Distribution: Protocols, Security, and Open Problems
Syed M. Arslan, Syed Shahmir, Noureldin Mohammad et al. (+2 more)
Twin-Field
Quantum Key Distribution (TF-QKD) has emerged as a potential protocol for long distance secure communication, overcoming the rate-distance limitations of conventional
quantum key distribution without requiring trusted repeaters. By having two parties transmit phase encoded weak coherent pulses (WCP) to an untrusted central node, the TF-QKD exploits single-
photon interference to achieve secret key rates scaling as square-root of channel length, enabling
quantum-secured communication over unprecedented distances. This survey provides a comprehensive survey of TF-QKD, covering the original protocol, its fundamental principles, and key-rate derivation. We discuss major TF-QKD variants, including Phase-Matching QKD and Sending-or-Not-Sending QKD, with various improved versions. We compare their performance, implementation trade-offs, protocol-specific vulnerabilities, and countermeasures. The survey summarizes security proofs ranging from asymptotic decoy-state analyses to finite-key composable frameworks, experimental milestones, technological enablers, and practical deployment challenges. Finally, we outline open problems in the field and present a roadmap for integrating TF-QKD into scalable
quantum networks, underscoring its central role in the future
quantum internet.
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All authors Syed M. Arslan, Syed Shahmir, Noureldin Mohammad, Saif Al-Kuwari, Muataz Alhussein
Quantum Physics · Cross-listed from cond-mat.mtrl-sci
High-temperature plasma in Casimir physics
Suman Kumar Panja and Mathias Boström
We present a short review of an unusual but important application for a high-temperature charged
plasma. The unorthodox proposition was made by Ninham concerning a contribution from Casimir forces across high-temperature electron-positron
plasma in
nuclear interactions. The key message in the current work is how high temperatures ($\sim10^{11}$ \,K) pop out as essential. Clearly, classical, semi-classical, and
quantum considerations for the background media impact both the Casimir effect and the physics of
stars and the Universe.
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Quantum Physics
Fermionic dynamics on a trapped-ion quantum computer beyond exact classical simulation
Faisal Alam, Jan Lukas Bosse, Ieva Čepaitė et al. (+37 more)
Simulation of the time-dynamics of fermionic many-body systems has long been predicted to be one of the key applications of
quantum computers. Such simulations – for which classical methods are often inaccurate – are critical to advancing our knowledge and understanding of
quantum chemistry and materials, underpinning a wide range of fields, from biochemistry to clean-energy technologies and chemical synthesis. However, the performance of all previous digital
quantum simulations of
fermions has been matched by classical methods, and it has thus far remained unclear whether near-term, intermediate-scale
quantum hardware could offer any computational advantage in this area. Here, we implement an efficient
quantum simulation
algorithm on Quantinuum's System Model H2 trapped-ion
quantum computer for the time dynamics of a 56-
qubit system that is too complex for exact classical simulation. We focus on the periodic spinful 2D
Fermi-Hubbard model and present evidence of
spin-charge separation, where the elementary electron's charge and
spin decouple. In the limited cases where ground truth is available through exact classical simulation, we find that it agrees with the results we obtain from the
quantum device. Employing long-range Wilson operators to study deconfinement of the effective gauge field between spinons and the effective potential between charge carriers, we find behaviour that differs from predictions made by classical tensor network methods. Our results herald the use of
quantum computing for simulating strongly correlated electronic systems beyond the capacity of classical computing.
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All authors Faisal Alam, Jan Lukas Bosse, Ieva Čepaitė, Adrian Chapman, Laura Clinton, Marcos Crichigno, Elizabeth Crosson, Toby Cubitt, Charles Derby, Oliver Dowinton, Norhan Eassa, Paul K. Faehrmann, Steve Flammia, Brian Flynn, Filippo Maria Gambetta, Raúl García-Patrón, Max Hunter-Gordon, Glenn Jones, Abhishek Khedkar, Joel Klassen, Michael Kreshchuk, Edward Harry McMullan, Lana Mineh, Ashley Montanaro, Caterina Mora, John J. L. Morton, Alberto Nocera, Dhrumil Patel, Pete Rolph, Raul A. Santos, James R. Seddon, Evan Sheridan, Wilfrid Somogyi, Marika Svensson, Niam Vaishnav, Sabrina Yue Wang, Gethin Wright, Eli Chertkov, Henrik Dreyer, Michael Foss-Feig
Quantum Physics
Quantum predator-prey cycles in dissipative Rydberg array
Ya-Xin Xiang, Weibin Li, Zhengyang Bai et al. (+1 more)
The predator-prey cycle is a paradigmatic example of self-organized population oscillations in far-from-
equilibrium systems, yet testing its underlying mechanism in natural ecosystems is often precluded by uncontrollable microscopic parameters. Here, we propose a
quantum analogue of predator-prey dynamics using a tunable two-dimensional Rydberg atom array. Through mean-field analysis and large-scale numerical simulations based on the open-system discrete truncated Wigner approximation, we demonstrate stable predator-prey cycles of Rydberg excitations on microsecond timescales. We show that nonperturbative
quantum coherence drives spontaneous time-translation
symmetry breaking, leading to globally synchronized oscillations under short-range interactions. Even under desynchronization caused by
quantum jumps, locally synchronized predator-prey cycles persist, with amplitude scaling inversely with the square root of the system size. Our work extends the study of predator-prey models to the
quantum realm and advances
quantum simulation strategies that leverage engineered many-body nonequilibrium effects.
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All authors Ya-Xin Xiang, Weibin Li, Zhengyang Bai, Yu-Qiang Ma
Quantum Physics
Rui Zhang, Yue-Yang Fei, Zhenhuan Liu et al. (+9 more)
In
quantum networks, after passing through noisy channels or information processing, residual states may lack sufficient
entanglement for further tasks, yet they may retain hidden
quantum resources that can be recycled. Efficiently recycling these states to extract
entanglement resources such as genuine multipartite
entanglement or Einstein-Podolsky-Rosen pairs is essential for optimizing network performance. Here, we develop a tripartite
entanglement distillation scheme using an eight-
photon quantum platform, demonstrating
entanglement superactivation phenomena which are unique to multipartite systems. We successfully generate a three-
photon genuinely entangled state from two bi-separable states via local operations and classical communication, demonstrating superactivation of genuine multipartite
entanglement. Furthermore, we extend our scheme to generate a three-
photon state capable of extracting an Einstein-Podolsky-Rosen pair from two initial states lacking this capability, revealing a previously unobserved
entanglement superactivation phenomenon. Our methods and findings offer not only practical applications for
quantum networks, but also lead to a deeper understanding of multipartite
entanglement structures.
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All authors Rui Zhang, Yue-Yang Fei, Zhenhuan Liu, Xingjian Zhang, Xu-Fei Yin, Yingqiu Mao, Li Li, Nai-Le Liu, Otfried Gühne, Xiongfeng Ma, Yu-Ao Chen, Jian-Wei Pan
Quantum Physics
Usefulness of $d\otimes d$ dimensional pure entangled states for antidiscrimination of quantum measurements when $d$ is even
Satyaki Manna
The usefulness of
entanglement in
quantum channel discrimination is a central topic in
quantum information theory. A landmark result in this direction was established by Piani and Watrous [$Phys. Rev. Lett.102, 250501 (2009)$] who proved that all entangled states are useful for discrimination of
quantum channels. We pose the same question in the context of antidiscrimination of
quantum channels. We partially answer this by showing that for every pure entangled state of $\mathbbm{C}^d\otimes\mathbbm{C}^d$ (with even $d$), there exist three projective measurements which are antidiscriminable (but not discriminable) with that input state but those three measurements are not antidiscriminable with the product probe.
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Quantum Physics
Limitation of Quantum Walk Approach to the Maximum Matching Problem
Alcides Gomes Andrade Júnior and Akira Matsubayashi
The Maximum Matching problem has a
quantum query complexity lower bound of $\Omega(n^{3/2})$ for graphs on $n$ vertices represented by an adjacency
matrix. The current best
quantum algorithm has the query complexity $O(n^{7/4})$, which is an improvement over the trivial bound $O(n^2)$. Constructing a
quantum algorithm for this problem with a query complexity improving the upper bound $O(n^{7/4})$ is an open problem. The
quantum walk technique is a general framework for constructing
quantum algorithms by transforming a classical random walk search into a
quantum search, and has been successfully applied to constructing an
algorithm with a tight query complexity for another problem. In this work we show that the
quantum walk technique fails to produce a fast
algorithm improving the known (or even the trivial) upper bound on the query complexity. Specifically, if a
quantum walk
algorithm designed with the known technique solves the Maximum Matching problem using $O(n^{2-\epsilon})$ queries with any constant $\epsilon>0$, and if the underlying classical random walk is independent of an input graph, then the guaranteed time complexity is larger than any
polynomial of $n$.
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Quantum Physics · Cross-listed from cond-mat.quant-gas
Thermal Casimir effect in the spin-orbit coupled Bose gas
Marek Napiórkowski and Pawel Jakubczyk
We study the thermal Casimir effect in ideal Bose gases with
spin-orbit (S-O) coupling of Rashba type below the critical temperature for Bose-Einstein condensation. In contrast to the standard situation involving no S-O coupling, the system exhibits long-ranged Casimir forces both in two and three dimensions ($d=2$ and $d=3$). We identify the relevant scaling variable involving the ratio $D/\nu$ of the separation between the confining walls $D$ and the S-O coupling magnitude $\nu$. We derive and discuss the corresponding scaling functions for the Casimir energy. In all the considered cases the resulting Casimir force is attractive and the S-O coupling $\nu$ has impact on its magnitude. In $d=3$ the exponent governing the decay of the Casimir force becomes modified by the presence of the S-O coupling, and its value depends on the orientation of the confining walls relative to the plane defined by the Rashba coupling. In $d=2$ the obtained Casimir force displays singular behavior in the limit of vanishing $\nu$
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