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Friday 24 October

Quantum Physics

Obtaining Accurate Ground-State Properties on Near-term Quantum Devices

Qi-Ming Ding, Jiawei Peng, Junxiang Huang et al. (+6 more)

Accurate ground-state calculations on noisy quantum computers are fundamentally limited by restricted ansatz expressivity and unavoidable hardware errors. We introduce a hybrid-quantum classical framework that simultaneously addresses these challenges. Our method systematically purifies noisy two electron reduced density matrices from quantum devices by enforcing N-representability conditions through efficient semidefinite programming, guided by a norm-based distance constraint to the experimental data. To implement this constraint, we develop a hardware efficient calibration protocol based on Clifford circuits. We demonstrate near full configuration interaction accuracy for ground-state energies of H2, LiH, and H4, and compute precise scattering intensities for C6H8 on noisy hardware. This approach surpasses conventional methods by simultaneously overcoming both ansatz limitations and hardware noise, establishing a scalable route to quantum advantage and marking a critical step toward reliable simulations of complex molecularnsystems on noisy devices.
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All authors Qi-Ming Ding, Jiawei Peng, Junxiang Huang, Yukun Zhang, Huiyuan Wang, Xiaosi Xu, Jiajun Ren, Yingjin Ma, Xiao Yuan

Quantum Physics

Scrambling Without Chaos in Random Free-Fermionic Systems

Ali Mollabashi and Mohammad-Javad Vasli

We study the role of randomness in the scrambling of quantum information within integrable free-fermionic systems. Considering quadratic Hamiltonians with varying degrees of randomness, we analyze entanglement-based measures to characterize the scrambling structure. We show that the memory effect in the entanglement of disjoint subsystems of Gaussian states vanishes when the local couplings are random, indicating information delocalization. The tripartite mutual information exhibits negative saturation values similar to those in chaotic systems, albeit with a smaller magnitude, revealing weaker scrambling under integrable quadratic dynamics. Despite integrability, spectral analyses reveal that local random models display a spectral-form-factor ramp and a partial crossover in the single-particle level-spacing ratio from Poisson-like to Wigner–Dyson-like behavior within a certain range of random couplings. These results demonstrate that randomness can act as a minimal ingredient for inducing information scrambling in integrable quadratic fermionic models.
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Quantum Physics · Cross-listed from physics.comp-ph

Fast adaptive discontinuous basis sets for electronic structure

Yulong Pan and Michael Lindsey

We develop a discontinuous Galerkin (DG) framework for automatically constructing adaptive basis sets for electronic structure calculations. By allowing basis functions to be discontinuous across element interfaces, our approach supports flexible combinations of atom-centered and polynomial basis sets, maintains favorable numerical conditioning, and induces structured sparsity of the one- and two-electron integrals, which we compute using specialised numerical integration strategies. In addition, we introduce a simple post-processing procedure to obtain continuous solutions if desired. We also introduce multigrid-preconditioned Poisson solvers that enable fast algorithms for both Hartree-Fock (HF) and density functional theory (DFT) calculations within our DG basis sets. Moreover, these basis sets naturally support adaptive multigrid preconditioning for the linear eigensolvers employed within the self-consistent field iteration for HF and DFT. Numerical experiments for HF and DFT demonstrate that our approach achieves chemical accuracy with modest basis sizes that compare favorably to the sizes of ordinary GTO basis sets achieving similar accuracy, while offering additional structured sparsity and improved computational scalability in the size-extensive limit. The framework thus provides a flexible route toward the construction of systematically improvable and structured adaptive basis sets for electronic structure theory.
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Quantum Physics · Cross-listed from cond-mat.quant-gas

Unveiling the BEC-droplet transition with Rayleigh superradiant scattering

Mithilesh K. Parit, Mingchen Huang, Ziting Chen et al. (+3 more)

Light scattering plays an essential role in uncovering the properties of quantum states through light-matter interactions. Here, we explore the crossover from Bose-Einstein condensate (BEC) to droplets in a dipolar $^{166}$Er gas by employing superradiant light scattering as both a probing and controlling tool. We observe that the efficiency of superradiant scattering exhibits a non-monotonic behavior akin to the rate of sample expansion during the transition, signaling its sensitivity to the initial quantum state, and in turn, revealing the BEC-droplet crossover. Through controlled atom depletion via superradiance, we analyze the sample's expansion dynamics and aspect ratio to identify the BEC-droplet phases distinctly, supported by Gaussian variational ansatz calculations. Finally, using these two approaches, we track how the BEC-droplet crossover points shift under varying magnetic field orientations. Our results show that superradiance can provide a state-sensitive probe and implement rapid atom-number quenches, opening new avenues for studying quantum states in atomic matter.
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All authors Mithilesh K. Parit, Mingchen Huang, Ziting Chen, Yifei He, Haoting Zhen, Gyu-Boong Jo

Quantum Physics

Quantum Neural Network Architectures for Multivariate Time-Series Forecasting

Sandra Ranilla-Cortina, Diego A. Aranda, Jorge Ballesteros et al. (+4 more)

In this paper, we address the challenge of multivariate time-series forecasting using quantum machine learning techniques. We introduce adaptation strategies that extend variational quantum circuit models, traditionally limited to univariate data, toward the multivariate setting, exploring both purely quantum and hybrid quantum-classical formulations. First, we extend and benchmark several VQC-based and hybrid architectures to systematically evaluate their capacity to model cross-variable dependencies. Second, building upon these foundations, we introduce the iQTransformer, a novel quantum transformer architecture that integrates a quantum self-attention mechanism within the iTransformer framework, enabling a quantum-native representation of inter-variable relationships. Third, we provide a comprehensive empirical evaluation on both synthetic and real-world datasets, showing that quantum-based models may achieve competitive or superior forecasting accuracy with fewer trainable parameters and faster convergence than state-of-the-art classical and quantum baselines in some cases. These contributions highlight the potential of quantum-enhanced architectures as efficient and scalable tools for advancing multivariate time-series forecasting.
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All authors Sandra Ranilla-Cortina, Diego A. Aranda, Jorge Ballesteros, Jesus Bonilla, Nerea Monrio, Elías F. Combarro, Jose Ranilla

Quantum Physics

Role of inefficient measurement in realizing post-selection-based non-Hermitian qubits

Roson Nongthombam, Aman Verma and Amarendra K. Sarma

Post-selecting against quantum jumps into the ground state confines the evolution of the three-level system to the excited states manifold, effectively realizing a PT-symmetric non-Hermitian qubit. In this work, by introducing post-selection efficiencies for both decay channels, the second-excited to first-excited and the first-excited to ground-state transitions, we formulate a hybrid-Liouvillian framework that captures the unmonitored dynamics of the non-Hermitian qubit. We find that the decoherence effects arising from quantum jumps within the second-excited and first-excited manifold also manifest under inefficient post-selection of the second-excited to first-excited transitions, thereby modifying the spectral properties of the Liouvillian and leading to a splitting of the exceptional points. A comparative analysis shows that the trajectory-based approach, obtained by ensemble-averaging stochastic measurement trajectories generated via the Bayesian state update rule, and the Lindblad evolution remain consistent. Our results highlight the fundamental role of measurement inefficiency in realizing post-selection-based non-Hermitian qubits and in shaping the structure of Liouvillian exceptional points. These findings provide new insights into how inefficient measurement processes influence non-Hermitian behavior in open quantum systems.
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Quantum Physics

Access to Klein Tunneling via Space-Time Modulation

Furkan Ok, Amir Bahrami and Christophe Caloz

We show that space-time modulation of electromagnetic potentials enables Klein tunneling far below the static threshold. The derived kinematics reveal oblique transitions that can connect opposite-energy continua without requiring their overlap, yielding a velocity-tunable Klein gap where transmission vanishes within a finite velocity window and reemerges beyond. The associated reduction in energy thresholds – by up to four orders of magnitude – suggests the potential for experimental realization using flying-focus fronts and relativistic electron beams.
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Quantum Physics

Runtime reduction in lattice surgery utilizing time-like soft information

Yutaro Akahoshi, Riki Toshio, Jun Fujisaki et al. (+3 more)

Runtime optimization of the quantum computing within a given computational resource is important to achieve practical quantum advantage. In this paper, we propose a runtime reduction protocol for the lattice surgery, which utilizes the soft information corresponding to the logical measurement error. Our proposal is a simple two-step protocol: operating the lattice surgery with the small number of syndrome measurement cycles, and reexecuting it with full syndrome measurement cycles in cases where the time-like soft information catches logical error symptoms. We firstly discuss basic features of the time-like complementary gap as the concrete example of the time-like soft information based on numerical results. Then, we show that our protocol surpasses the existing runtime reduction protocol called temporally encoded lattice surgery (TELS) for the most cases. In addition, we confirm that the combination of our protocol and the TELS protocol can reduce the runtime further, over 50% in comparison to the naive serial execution of the lattice surgery. The proposed protocol in this paper can be applied to any quantum computing architecture based on the lattice surgery, and we expect that this will be one of the fundamental building blocks of runtime optimization to achieve practical scale quantum computing.
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All authors Yutaro Akahoshi, Riki Toshio, Jun Fujisaki, Hirotaka Oshima, Shintaro Sato, Keisuke Fujii

Quantum Physics

Scalable protocol to coherence estimation from scarce data: Theory and experiment

Qi-Ming Ding, Ting Zhang, Hui Li et al. (+1 more)

Key quantum features like coherence are the fundamental resources enabling quantum advantages and ascertaining their presence in quantum systems is crucial for developing quantum technologies. This task, however, faces severe challenges in the noisy intermediate-scale quantum era. On one hand, experimental data are typically scarce, rendering full state reconstruction infeasible. On the other hand, these features are usually quantified by highly nonlinear functionals that elude efficient estimations via existing methods. In this work, we propose a scalable protocol for estimating coherence from scarce data and further experimentally demonstrate its practical utility. The key innovation here is to relax the potentially NP-hard coherence estimation problem into a computationally efficient optimization. This renders the computational cost in our protocol insensitive to the system size, in sharp contrast to the exponential growth in traditional methods. This work opens a novel route toward estimating coherence of large-scale quantum systems under data-scarce conditions.
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All authors Qi-Ming Ding, Ting Zhang, Hui Li, Da-Jian Zhang

Quantum Physics · Cross-listed from physics.optics

Enhancement of femtosecond photon echo signals from an inhomogeneously broadened InAs quantum dot ensemble using chirped pulses

Yuta Kochi, Yutaro Kinoshita, Masanari Watanabe et al. (+2 more)

Photon echo (PE) techniques offer a promising approach to optical quantum memory, yet their implementation in conventional platforms, such as rare-earth-ion-doped crystals, is hindered by limited bandwidths. Semiconductor quantum dot (QD) ensembles, featuring THz-scale inhomogeneous broadening and sub-picosecond dynamics, provide an attractive alternative for ultrafast applications. However, achieving coherent control across such broad spectral ranges remains challenging due to detuning and spatial field inhomogeneities, which reduce PE efficiency. In this work, we experimentally demonstrated adiabatic rapid passage (ARP)-enhanced PE in dense, self-assembled InAs QD ensembles exhibiting THz-scale inhomogeneous broadening and operating at telecom wavelengths, achieving a 3.2-fold increase in echo efficiency. Chirped control pulses designed to satisfy adiabatic conditions across the ensemble enable broadband rephasing. Numerical simulations based on a two-level model reproduce the key experimental observations, including the ARP-induced enhancement, thereby validating the underlying physical picture. These results establish ARP as a robust and scalable approach for coherent control in InAs QD ensembles, with potential applications for ultrafast and broadband optical communication in the THz spectral region.
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All authors Yuta Kochi, Yutaro Kinoshita, Masanari Watanabe, Ryutaro Ide, Junko Ishi-Hayase

Quantum Physics

Myopic Entropy Scheduling for Ramsey Magnetometry

Julian Greentree, William Moran, Rob Evans et al. (+3 more)

This paper presents an entropy based adaptive measurement sequence strategy for quantum sensing of magnetic fields. To physically ground our ideas we consider a sensor employing a nitrogen vacancy center in diamond, however our approach is applicable to other quantum sensor arrangements. The sensitivity and accuracy of these sensors typically rely on long sequences of rapidly occurring measurements. We introduce a new technique for designing these measurement sequences aimed at reducing the number of measurements required for a specified accuracy as measured by entropy, by selecting measurement parameters that optimally reduce entropy at each measurement. We compare, via simulation, the efficiency and sensitivity of our new method with several existing measurement sequence design strategies. Our results show quantifiable improvements in sensing performance. We also show analytically that our entropy reduction approach, reduces, under certain simplified conditions, to a well-known and widely used measurement strategy.
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All authors Julian Greentree, William Moran, Rob Evans, Andrew Melatos, Neel Kanth Kundu, Peter M. Farrell

Quantum Physics

Tunable Asymmetric Delay Attack in Quantum Clock Synchronization

Hui Han, Haotian Teng, Hailong Xu et al. (+7 more)

Quantum clock synchronization underpins modern secure communications and critical infrastructure, yet its fundamental dependence on channel reciprocity introduces an exploitable vulnerability to asymmetric delay attacks. Current attack strategies rely on static delays, limiting their ability to target application-specific stability requirements. Here, we propose a tunable asymmetric delay attack (T-ADA) that dynamically controls delay parameters to induce manipulate synchronization accuracy. Through experimental implementation, we demonstrate how tailored attack trajectories can selectively compromise system stability across different scenarios. This work uncovers key vulnerabilities in synchronization protocols under customizable attacks and provide a foundation for developing secure and resilient quantum clock synchronization systems.
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All authors Hui Han, Haotian Teng, Hailong Xu, Jinquan Huang, Yuanmei Xie, Yichen Zhang, Bo Liu, Wanrong Yu, Baokang Zhao, Shuhui Chen

Quantum Physics

Stability of Maximum-Entropy Inference in Finite Dimensions

James Tian

We study maximum-entropy inference for finite-dimensional quantum states under linear moment constraints. Given expectation values of finitely many observables, the feasible set of states is convex but typically non-unique. The maximum-entropy principle selects the Gibbs state that agrees with the data while remaining maximally unbiased. We prove that convergence of moments and entropy implies convergence of states in trace norm, derive explicit quantitative bounds linking data and entropy deviations to state distance, and show that these results are stable under unital completely positive maps. The analysis is self-contained and relies on convex duality, relative entropy, and Pinsker-type inequalities, providing a rigorous and unified foundation for finite-dimensional maximum-entropy inference.
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Quantum Physics

A broadband single microwave-photon detector insensitive to the thermal noise

Y. Q. Chai, M. Y. Wang, S. N. Wang et al. (+2 more)

Thermal noise is one of the physical obstacles that constrain the achievable detection sensitivities of various detectors. Indeed, as we showed in a recent paper (PRB 111, 024501 (2025)), the usual Josephson threshold detector (JTD) operated in an equilibrium state can be utilized to implement a weak microwave signal, just approaching (but not arriving at) its energy quantum limit, even though its physical parameters have been optimized. In this letter, we further demonstrate numerically that the phase dynamics of a current-biased Josephson junction (CBJJ) can be insensitive to the always-on thermal noise if the sweep rate of the biased current is significantly high. As a consequence, the JTD can be operated alternatively in a non-equilibrium state. Based on the statistical binary detection criterion, we demonstrate how such a non-equilibrium JTD (NEJTD) can be utilized to implement the weak microwave signal, arriving at its energy quantum limit level. The dynamic range and photon-number resolvability of the proposed NEJTD are also discussed when it serves as a broadband single microwave-photon detector.
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All authors Y. Q. Chai, M. Y. Wang, S. N. Wang, P. H. Ouyang, L. F. Wei

Quantum Physics

Harnessing Intrinsic Noise for Quantum Simulation of Open Quantum Systems

Sameer Dambal, Akira Sone and Yu Zhang

Simulating open quantum systems on quantum computers presents a fundamental challenge: open quantum dynamics are intrinsically nonunitary, whereas quantum computers operate through unitary evolution. Conventional approaches overcome this mismatch by encoding nonunitary processes into unitary circuits, but such methods incur substantial overhead in both qubits and gates. Here, we propose an alternative perspective. Quantum processors are themselves open systems, inherently subject to noise. Instead of correcting all errors and then encoding nonunitary dynamics with unitary logical qubits and gates, we show how noise can be harnessed as a computational resource. We develop a noise-assisted quantum algorithm that selectively preserves physical noise to emulate nonunitary channels, enabling efficient simulation of open quantum dynamics with minimal qubit requirements. Our approach applies both to noisy intermediate-scale quantum (NISQ) devices and future fault-tolerant architectures. By leveraging intrinsic noise, this method circumvents the need to encode nonunitary dynamics into unitary gates and relaxes fidelity requirements on physical qubits, thereby reducing the overhead of quantum error correction. This framework reframes noise from a limitation into a resource, opening new directions for practical quantum simulation of open systems
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Quantum Physics · Cross-listed from cond-mat.mes-hall

The spinterface mechanism for the chiral-induced spin selectivity effect: A Critical Perspective

Subhajit Sarkar, Amos Sharoni, Oliver L. A. Monti et al. (+1 more)

The chiral-induced spin selectivity (CISS) effect, whereby chiral molecules preferentially transmit electrons of one spin orientation, remains one of the most intriguing and debated phenomena at the interface of spintronics, molecular electronics, and quantum materials. Despite extensive experimental observations across diverse platforms - including transport junctions, photoemission, and enantioselective chemistry - a comprehensive theoretical framework is still lacking. In this perspective, we critically examine the spinterface mechanism as a unifying explanation for the CISS effect. The spinterface model, which hypothesizes a feedback interaction between electron motion in chiral molecules and fluctuating surface magnetic moments, is shown to quantitatively reproduce experimental data across various systems and conditions. We contrast it with some existing theoretical models, highlighting key experimental features. Importantly, we also address open questions and criticisms of this model, including the nature of surface magnetism, the role of dissipation, and the applicability of the mechanism to non-helical or electrode-free systems. By offering falsifiable predictions and reconciling theory with experimental raw data, this work aims to sharpen the dialogue surrounding the microscopic origin of CISS and stimulate further experimental and theoretical progress.
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All authors Subhajit Sarkar, Amos Sharoni, Oliver L. A. Monti, Yonatan Dubi

Thursday 23 October

Quantum Physics · Cross-listed from cond-mat.supr-con

Imaging magnetic flux trapping in lanthanum hydride using diamond quantum sensors

Yang Chen, Junyan Wen, Ze-Xu He et al. (+7 more)

Lanthanum hydride has attracted significant attention in recent years due to its signatures of superconductivity at around 250 K (1, 2). However, the megabar pressures required for synthesize and maintain its state present extraordinary challenges for experiments, particularly in characterizing its Meissner effect (3, 4). The nitrogen-vacancy (NV) center in diamond has emerged as a promising quantum probe to address this problem (5-8), but a gap remains between its working pressure and the pressure required to study the superconducting state of lanthanum hydride (9-12). In this work, using neon gas as the pressure transmitting medium, the working pressure of NV centers is extended to nearly 200 GPa. This quantum probe is then applied to study the Meissner effect of a LaH$_{9.6}$ sample, synthesized by laser heating ammonia borane and lanthanum. A strong magnetic shielding effect is observed, with the transition temperature beginning at around 180 K and completing at 220 K. In addition, magnetic field imaging after field cooling reveals strong flux trapping and significant inhomogeneities within the sample. Our work provides compelling evidence for superconductivity in lanthanum hydride and highlights the importance of spatially resolved techniques in characterizing samples under ultrahigh pressure conditions.
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All authors Yang Chen, Junyan Wen, Ze-Xu He, Jing-Wei Fan, Xin-Yu Pan, Cheng Ji, Huiyang Gou, Xiaohui Yu, Liucheng Chen, Gang-Qin Liu

Quantum Physics · Cross-listed from cs.IT

Overlapped-repetition Shor codes achieving fourfold asymptotic rate

En-Jui Chang

Introducing controlled overlap among a few repetition blocks yields a fourfold asymptotic rate improvement while preserving an average stabilizer weight of \(4\). Substituting the overlapped outer layer with an LDPC code further produces a family of constructions with asymptotic rate \(2/d\). We also describe a constant-excitation variant that suppresses collective coherent errors without additional overhead, as well as a bosonic generalization that extends the framework to oscillator encodings. The resulting family achieves a code rate intermediate between that of the rotated surface code (average stabilizer weight \(4\)) and the BB code (average stabilizer weight \(6\)), while remaining free of the performance degradation typical of iterative decoders.
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Quantum Physics · Cross-listed from cond-mat.mes-hall

Characterizing Neon Thin Film Growth with an NbTiN Superconducting Resonator Array

Kyle Matkovic, Patrick Russell, Andrew Palmer et al. (+6 more)

Electrons levitating above the surface of solid neon have recently emerged as a promising platform for high-quality qubits. The morphology and uniformity of the neon growth in these systems is crucial for qubit performance in a scalable architecture. Here we report on the controlled growth and characterization of thin solid neon films using multiplexed superconducting microwave resonators. By monitoring changes in the resonant frequency and internal quality factor ($Q_i$) of an array of frequency multiplexed quarter-wave coplanar waveguide resonators, we quantify the spatial uniformity of the film. A pulsed gas deposition protocol near the neon triple point results in repeatable film formation, generating measurable shifts in frequency and variations in $Q_i$ across the resonator array. Notably, introducing a post-deposition anneal at 12 K for one hour improves the film homogeneity, as shown by the reduced resonator-to-resonator variance in frequency and $Q_i$, consistent with enhanced wetting. These results demonstrate resonator-based metrology as an in-situ tool for characterising neon film growth, directly supporting the development of electron on inert quantum solid qubit platforms.
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All authors Kyle Matkovic, Patrick Russell, Andrew Palmer, Eric Helgemo, Lukas Delventhal, Kun Zuo, Kundan Surse, Rajib Rahman, Maja C. Cassidy

Quantum Physics

Quantum Interference and the Limits of Separability

Sebastian Horvat

Quantum theory implies, and empirical evidence confirms, that while particles $\textit{can}$ exhibit wave-like behavior in interferometric experiments, this behavior is so limited as $\textit{not}$ to allow for third- and higher-order interference. The article at hand shows that this possibility-impossibility structure suggests the universal validity of a principle that regulates statistical correlations between spatiotemporally localized events, $\textit{independently}$ of the nature of the objects that may or may not partake in these events. Roughly, the said principle mandates that $\textit{any}$ joint influence of $m$ mutually spacelike separated events on $\textit{another}$ event, be such, that it can be separated by $\textit{at least}$ $\lceil \frac{m}{2} \rceil$ mediating events, and in some cases, by $\textit{no more}$ than $\lceil \frac{m}{2} \rceil$ mediating events. The structure of quantum interference thus teaches us that events can influence each other in a non-separable fashion, but that this non-separability has a certain exactly quantifiable limit.
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Quantum Physics

Certifying Randomness or its Lack Thereof for General Network Scenarios

Maria Ciudad Alañón, Daniel Centeno, Andrew Watford et al. (+1 more)

The certification of intrinsic randomness is foundational to quantum information theory and central in many practical applications thereof, such as in the generation of unquestionably random numbers and in cryptographic protocols. Device-independent randomness certification based on violations of Bell inequalities has been thoroughly investigated within the standard Bell scenario. In this work, we aim to extend this line of research by exploring randomness certification in more general causal structures, namely, network scenarios. To address this task, we demonstrate how the computational tool known as the inflation technique can be adapted. As proof of concept, we use inflation to certify randomness relative to a beyond-quantum adversary for sample probability distributions obtained in the bilocality and triangle scenarios. Complementarily, we also provide computational methods for the problem of certifying an absence of randomness, which should not be conflated with certifying the classicality of a given probability distribution. We conclude with a discussion of conceptual subtleties regarding randomness certification in networks, highlighting important open problems in this nascent research field.
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All authors Maria Ciudad Alañón, Daniel Centeno, Andrew Watford, Elie Wolfe

Quantum Physics

Absence of gravitationally induced entanglement in certain semi-classical theories of gravity

Ward Struyve

Bose et al. and Marletto and Vedral proposed an experiment to test whether gravity can induce entanglement between massive systems, arguing that the capacity to do so would imply the quantum nature of gravity. In this work, a class of semi-classical models is examined that treat gravity classically, through some potential in the Schrödinger equation, and it is shown that these models do not generate entanglement. This class includes the Newton-Schrödinger model, where gravity is sourced by the wave function, the Bohmian analogue, where gravity is sourced by actual point-particles, and an interpolating model proposed by Döner and Grossardt. These models are analyzed in the context of the proposed experiment and contrasted with the standard Newtonian potential, which does generate entanglement.
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Quantum Physics

No-broadcasting of non-Gaussian states

Kaustav Chatterjee and Ulrik Lund Andersen

Gaussian states are of fundamental importance in the physics of continuous-variable quantum systems. They are appealing for the experimental ease with which they can be produced, and for their compact and an elegant mathematical description. Nevertheless, many proposed quantum technologies require us to go beyond the realm of Gaussian states and introduce non-Gaussian elements. In terms of quantum resource theory, we can then recognize non-Gaussian states as resources and Gaussian operations and states as free, which can be used and prepared easily. Given such a structure of resource theory, the task of broadcasting the resource is to determine if the resource content of a state can be cloned in a meaningful way, which, if possible, provides a strong operation for manipulation of the resource. In this work, we prove that broadcasting of non-Gaussian states via Gaussian operations is not possible. For this, we first show that the relative entropy of non- Gaussianity is not super-additive, which rules it out as a prime candidate in the analysis of such no-go results. Our proof is then based on understanding fixed points of Gaussian operations and relates to the theory of control systems. The no-go theorem also states that if two initially uncorrelated systems interact by Gaussian dynamics and non-Gaussianity is created at one subsystem, then the non-Gaussianity of the other subsystem must be reduced. Further, keeping the set of free operations fixed to Gaussian operations, we can also comment on the broadcasting of Wigner negativity and genuine quantum non-Gaussianity.
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Quantum Physics

Thermodynamic decoupling in the deep-strong coupling regime

S. Palafox, M. Salado-Mejía, M. Santiago-García et al. (+1 more)

In the deep-strong coupling (DSC) regime, the interaction between light and matter exceeds their bare frequencies, leading to an effective decoupling. Theoretical and experimental evidence for this behavior has relied solely on measurements of local observables at equilibrium. However, such a local approach is insufficient to accurately describe energy fluxes in critical and nonequilibrium phenomena. Here, we use a two-terminal quantum junction to derive a thermodynamically consistent global master equation. We demonstrate that the associated heat current, a key nonlocal observable in any quantum thermal machine, also approaches zero in this extreme coupling scenario, underscoring the role of virtual photons in the vacuum ground state. Our results indicate that the decoupling is a more general feature of the DSC regime, with implications for quantum thermotronics.
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All authors S. Palafox, M. Salado-Mejía, M. Santiago-García, R. Román-Ancheyta

Quantum Physics · Cross-listed from cond-mat.mes-hall

Landau Polarons as Generators of Quantum-Coherent States

Arnab Ghosh, Patrick Brosseau, Dmitry N. Dirin et al. (+3 more)

Since Landau's theory, polarons have been understood as quasiparticles in which charges are dressed by the lattice field, yet decades of transport and spectroscopic studies have yielded only static indirect renormalizations. Whether such dressing can dynamically reorganize electronic spectra to generate new quantum-coherent states has remained unresolved. Here we use femtosecond coherent multidimensional spectroscopy on size and composition controlled perovskite quantum dots to track polaronic field-induced dynamics in real time, revealing their consequences. We observe a delayed condensation into a confined spectrum of coherent states on 50-150 fs timescales, with couplings between these states evolving dynamically on the same timescale. The splittings are robust, exhibit anomalous linear size dependence, exceed single-particle splittings and manifest at 300 K. A Raman-constrained spin-boson Hamiltonian captures both the anomalous scaling and dynamical onset, establishing polarons as generators of coherent manifolds that enable collective quantum phenomena including superradiance, superfluorescence and superabsorption.
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All authors Arnab Ghosh, Patrick Brosseau, Dmitry N. Dirin, Rui Tao, Maksym V. Kovalenko, Patanjali Kambhampati

Quantum Physics

Fragmentation of Virtual Orbitals for Quantum Computing: Reducing Qubit Requirements through Many-Body Expansion

Federico Zahariev, Vassiliki-Alexandra Glezakou and Mark S. Gordon

We introduce quantum virtual-orbital fragmentation (Q-FVO), a systematic method for reducing the largest active space in correlated quantum-chemistry calculations. The complete occupied space is retained, the localized virtual space is partitioned into chemically motivated fragments, and the correlation energy is recovered through an inclusion-exclusion many-body expansion. Across six molecular benchmarks, the largest one-body Q-FVO calculations reduce the qubit requirement by 46 to 66 percent, while two-body calculations reduce it by approximately 31 to 42 percent relative to the corresponding unfragmented spaces. Two-body expansions recover most of the correlation energy, with errors of 0.9 to 7.5 kcal/mol; three-body expansions are below 1 kcal/mol for all CCSD tests and remain below 2 kcal/mol at CCSD(T). Illustrative statevector UCCSD calculations also reduce implementation-reported circuit depth while retaining accuracy below 1 kcal/mol. Q-FVO can be nested inside Q-EFMO real-space fragmentation and, in turn, the resulting cluster can be embedded in a Q-EFP environment. The hierarchy therefore reduces quantum-resource growth along three complementary dimensions: environment, molecular fragments, and virtual-orbital space.
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Quantum Physics · Cross-listed from math-ph

The generalized adiabatic theorem for extended lattice systems

Lennart Becker, Stefan Teufel and Marius Wesle

We prove an adiabatic theorem for infinitely extended lattice fermion systems with gapped ground states, allowing perturbations that may close the gap. The Heisenberg dynamics on the CAR-algebra is generated by a time dependent two-parameter family of Hamiltonians $H^{\varepsilon,\eta}_t=\eta^{-1}(H_t+\varepsilon(H^1_t+V_t))$, where $H_t$ is assumed to have a gapped ground state $\omega_t$, $\eta \in (0,1]$ is the adiabatic parameter and $ \varepsilon \in [0,1]$ controls the strength of the perturbation. We construct a quasi-local dressing transformation $\beta^{\varepsilon,\eta}_t=\exp(i \mathcal{L}_{S^{\varepsilon,\eta}_t})$ that yields super-adiabatic states $\omega^{\varepsilon,\eta}_t =\omega_t \circ \beta^{\varepsilon,\eta}_t$ which, when tested against local observables, solve the corresponding time-dependent Schrödinger equation up to errors asymptotically smaller than any power of $\eta$ and $\varepsilon$. The construction is local in space and time, does not assume uniqueness of the ground state, and works under super-polynomial decay of the interactions $H_t$ and $H_t^1$ rather than exponential decay. If the Hamiltonian is time-independent on an interval, the dressed state is $\eta$-independent and forms a non-equilibrium almost-stationary state with lifetime of order $\varepsilon^{-\infty}$. The result provides a rigorous basis for linear response to macroscopic changes in gapped systems, including a proof of Ohm's law for macroscopic Hall currents.
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Quantum Physics

Local-to-Global Entanglement Dynamics by Periodically Driving Impurities

Zhi-Xing Lin, Abhinav Prem, Shinsei Ryu et al. (+1 more)

We study the entanglement dynamics of one-dimensional fermionic chains subject to a local Floquet drive of a two-site impurity, and uncover a sharp transition in the entanglement dynamics set by the driving period $T$. For large periods, the entanglement entropy (EE) grows linearly in time, signaling a heating phase with volume-law entanglement; below a critical period $T_\ast$, the EE instead grows subextensively, characteristic of a local quantum quench. We establish this dichotomy in two complementary settings: a gapless nearest-neighbor hopping chain, where a single transition separates logarithmic from volume-law growth, and a gapped Su-Schrieffer-Heeger (SSH) chain, whose two-band structure yields a richer phase diagram with multiple area-to-volume-law transitions. In the noninteracting limit, we trace these transitions analytically to quasienergy folding in the single-particle Floquet spectrum: a single $\pi$-gap closure for the NN chain, and a sequence of foldings at both 0- and $\pi$-gaps for the SSH chain, yielding the alternating pattern of heating and non-heating phases. We further show that the so-called “average energy" operator furnishes a many-body diagnostic of the transition, remaining local in the non-heating phase but developing non-local couplings in the heating phase. For the gapless chain, using extensive matrix-product-state simulations, we demonstrate that the non-heating phase and its subextensive entanglement growth survive weak interactions over numerically accessible timescales. Our results establish local Floquet engineering as a route to emergent bulk phenomena, offering a new perspective on energy localization and thermalization in driven many-body systems.
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All authors Zhi-Xing Lin, Abhinav Prem, Shinsei Ryu, Bastien Lapierre

Quantum Physics · Cross-listed from physics.optics

Electrical-control of third-order nonlinearity via Fano interference

Deniz Eren Mol, İbrahim Asr{\i}n Üzgüç, Ulaş Eyüpoğlu et al. (+6 more)

Programmable photonic computers necessitate the integration of electrically-tunable compact components into the photonic devices. In the state-of-the-art photonic quantum computers~(PQCs), phase-shift and displacement gates can be implemented in an electrically-programmable way. An efficient PQC, however, necessitates also the tuning of third or higher order nonlinearity for implementing continuous-variable~(CV) gates at a shorter sequence. Here, we demonstrate that such an optical component can be designed using Fano interference and Stark effect in a nonlinear nano-plasmonic system. We study the coupling of a broadband bright plasmon mode to a narrow linewidth quantum object(s), QO(s). We show that by shifting the level-spacing of the QO via Stark effect, one can continuously tune the third-order nonlinearity gate within a picosecond response time. We also present finite-difference time domain~(FDTD) simulations that take the retardation effects into account. In addition, we also show that enhancement due to Fano interference degrades if the QOs are positioned randomly as each QO introduces different phases. This reveals the importance of the spatial extent of the QO-ensemble to be employed in the experiments.
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All authors Deniz Eren Mol, İbrahim Asr{\i}n Üzgüç, Ulaş Eyüpoğlu, Kübra Atar, Sena Taşk{\i}ran, Taner Tarik Aytas, Rasim Volga Ovali, Ramazan Sahin, Mehmet Emre Tasgin

Quantum Physics · Cross-listed from cond-mat.str-el

$\mathbb{Z}_2$ lattice gauge theories: fermionic gauging, transmutation, and Kramers-Wannier dualities

Lei Su

We generalize the gauging of $\mathbb{Z}_2$ symmetries by inserting Majorana fermions, establishing parallel duality correspondences for bosonic and fermionic lattice systems. Using this fermionic gauging, we construct fermionic analogs of $\mathbb{Z}_2$ gauge theories dual to the transverse-field Ising model, interpretable as Majorana stabilizer codes. We demonstrate a unitary equivalence between the $\mathbb{Z}_2$ gauge theory obtained by gauging the fermion parity of a free fermionic system and the conventional $\mathbb{Z}_2$ gauge theory with potentially nonlocal terms on the square lattice with toroidal geometry. This equivalence is implemented by a linear-depth local unitary circuit, connecting the bosonic and fermionic toric codes through a direction-dependent anyonic transmutation. The gauge theory obtained by gauging fermion parity is further shown to be equivalent to a folded Ising chain obtained via the Jordan–Wigner transformation. We clarify the distinction between the recently proposed Kramers–Wannier dualities and those obtained by gauging the $\mathbb{Z}_2$ symmetry along a space-covering path. Our results extend naturally to higher-dimensional $\mathbb{Z}_2$ lattice gauge theories, providing a unified framework for bosonic and fermionic dualities and offering new insights for quantum computation and simulation.
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