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Wednesday 3 June

Quantum Physics · Cross-listed from cond-mat.mtrl-sci

Electron-Ion Path Integral Monte Carlo with Hard Core

Riccardo Fantoni

We performed numerical (restricted) path integral Monte Carlo experiments on metallic Hydrogen from first principles. We study a quantum two component plasma where one component is made of pointwise particles of negative unitary charge and the other is made of charged hard spheres of positive unitary charge. We study both the additive mixture and a nonadditive mixture where we only keep a hard core between unlike species. We specialize to the case of the electron-proton plasma with a 1:1 ratios between the molar fraction of the two species. We measured thermodynamic and structural properties of the plasma. From an analysis of the structure we see a transition from a metallic Hydrogen phase, to a molecular Hydrogen phase as the temperature is lowered. As expected at high density the correlations are diminished.
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Quantum Physics

Nonreciprocal Dispersive Coupling for Quantum Sensing

Dong Xie and Chunling Xu

Dispersive coupling is widely utilized for quantum information readout. Most prior studies have concentrated on reciprocal dispersive coupling. Here, we further construct nonreciprocal dispersive coupling and apply it to quantum sensing. For cavity photon number measurement, nonreciprocal dispersive coupling delivers higher precision than its reciprocal counterpart, and this advantage grows more pronounced with an increase in photon number. When directly measuring the single-photon driving strength, however, nonreciprocal dispersive coupling shows no superiority over reciprocal dispersive coupling. By converting the information of driving strength into cavity photon numbers via our proposed strategy, nonreciprocal dispersive coupling again outperforms reciprocal dispersive coupling in precision, with the advantage becoming increasingly significant at larger driving strength. This work presents a novel method to boost quantum sensing and enable the fabrication of ultra-precise quantum sensors.
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Quantum Physics

Circuit-Level Noise Estimation via Shuttling in Plaquette Circuits

Huyen Do and Alexandru Paler

We present a method for estimating QEC circuit-level noise levels assuming that only single-shot measurements are available (e.g. measurements are slow and performed in a zoned/parallel fashion), and that lower level quantum hardware calibration is not possible (e.g. cloud access) or not feasible (e.g. large scale computing). We develop and run surface code plaquette experiments using two syndrome qubit configurations: FRESH, involving fresh qubits for each plaquette repetition, and RECYCLE, reusing qubits. To validate our approach, we compile plaquettes to ion-trap (IonQ Aria1) native gate set and apply hardware-aware rewrite templates to reduce circuit depth and execution time. We also run the experiments on a non-shuttling, superconducting processor (IBM Torino). We estimate circuit-level noise rates from the resulting single-shot plaquette measurement statistics, and conclude numerically about the viability of low-depth QEC experiments.
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Quantum Physics

Extremely slow scaling of minimal Hamming distance in quantum sampling data

P. S. Golubev, I. A. Iakovlev and V. V. Mazurenko

Quantum data can be obtained from a diverse range of sources, including direct measurements from noisy quantum processors, cold-atom simulators, and classical approximations such as variational neural-network states. However, our ability to characterize these systems is fundamentally limited, as the available measurement data are often sparse compared to the exponentially large Hilbert space of the system. To address this, we propose using the expected minimal Hamming distance calculated for a set of unique bitstrings as a robust metric revealing a distinct power-law behaviour. Crucially, we have established a direct connection between the empirical power-law parameters and the intrinsic dimension of the quantum measurement outcomes. Through various examples of real experiments and simulations, we show that the power-law parameters reliably characterize the underlying geometric structure of measurement outcomes and identify quantum phase transitions from limited quantum information, without the need for accumulating extensive statistics or explicitly calculating physical observables. This enables the analysis of completely different quantum experiments within a single framework. Furthermore, we demonstrate the versatility of our approach on classical high-dimensional data, showing that the power-law parameters can successfully discriminate different classes of handwritten digits from the MNIST dataset.
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Quantum Physics

Distributed Variational Quantum Optimisation by Entanglement-Selective Transport

Edric Matwiejew, Pascal Elahi and Ugo Varetto

Distributed quantum optimisation is challenging because computing the problem cost function across multiple quantum processors requires non-local gates, which can incur overhead in latency and fidelity. Here we introduce QESTO, a distributed variational ansatz for graph-based discrete optimisation that requires only persistent pre-shared Bell pairs for remote operations. Using local operations, it encodes local constraint information in the Bell pairs that is leveraged to produce amplitude transfer towards globally valid distributed solution states. QESTO requires one Bell pair per distributed edge of the problem graph and, after initialisation of the Bell states, uses no non-local gates. On two bounded weighted Wang tile-matching problem ensembles, QESTO achieves stronger convergence to low-cost tilings than equivalently partitioned QAOA with no distributed gates at ansatz depths of two or higher, and exceeds the mean performance of monolithic QAOA at the deepest studied depth in both ensembles. These results suggest that persistent entanglement can support useful variational communication while reducing per-layer non-local gate overhead.
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Quantum Physics · Cross-listed from cond-mat.mes-hall

Probing PbTe-Pb nanowire devices with radio-frequency reflectometry

Xin-Yi Tang, Lin Li, Zezhou Xia et al. (+10 more)

We report the implementation of radio-frequency (rf) reflectometry on selective-area-grown PbTe-Pb nanowire devices on a CdTe substrate. These nanowires are predicted to host Majorana zero modes. We demonstrate the compatibility of the rf technique, including both resistive and capacitive sensing, with these nanowires. The effect of dielectric loss from the CdTe substrate is quantitatively characterized. Furthermore, the feasibility of rf reflectometry is verified under finite magnetic fields where zero-energy modes can emerge. Our results establish the fast control of PbTe quantum devices, paving the way for their applications in topological quantum computation.
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All authors Xin-Yi Tang, Lin Li, Zezhou Xia, Jierong Huo, Wenyu Song, Lining Yang, Zonglin Li, Jiaye Xu, Peilin Li, Runan Shang, Qi-Kun Xue, Ke He, Hao Zhang

Quantum Physics

Arbitrary manipulation of nuclear spins in hexagonal boron nitride

Fattah Sakuldee and Mehdi Abdi

Due to its localized nature and controllability, the negatively charged boron vacancy centers (V$_\text{B}^-$) in hexagonal boron nitride (hBN) are a promising spin platform for accessing its neighboring nuclei with potential for performing quantum computational tasks. However, the methods of utilizing and manipulating the nuclear spins are still lacking. In this work, we propose a protocol for the preparation of single- and multi-qubit gates on the nuclear spins, utilizing the electron spin as an auxiliary qubit. By applying a background magnetic field and a multi-tone continuous drive, we show that the electron spin coupling to the nuclei can be efficiently engineered. This allows for suppressing the undesired electron-nuclear interactions through the Hahn echo pulse sequence. The target gates are then implemented by employing proper RF drives. Our numerical results for realistic parameters show gate fidelities as high as $99\%$ for single-qubit and $95\%$ for multi-qubit gates. With the gate execution durations being less than $300$ ns, our protocol evades electron spin decoherence effects. Therefore, our scheme sets the stage for the practical application of V$_\text{B}^-$ in hBN for quantum computation purposes.
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Quantum Physics

Anisotropic Rabi Model as a Noise Biased Qubit

Jia-Wen Yu, Ke-Xiong Yan, Yuan Qiu et al. (+7 more)

We present the quantum anisotropic Rabi model as a potential resource for a noise biased qubit. The system-environment coupling can be biased by tuning the relative strengths of the rotating-wave and counter-rotating-wave interactions, characterized by the anisotropy parameter $\eta$. This anisotropy selectively suppresses dominant decoherence pathways, thereby enabling the construction of a protected logical qubit in the ultrastrong and deep-strong coupling regimes. The logical states (formed by the ground and first excited states of the anisotropic Rabi model) possess coherence times that are enhanced compared to the isotropic case. Moreover, we construct a set of universal gate operations within the logical-state subspace and demonstrate that the gate operations associated with different values of $\eta$ exhibit robustness against external noise. These findings are expected to inspire applications and research directions for the anisotropic Rabi model with promising potential impacts.
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All authors Jia-Wen Yu, Ke-Xiong Yan, Yuan Qiu, Yiming Yu, Yexiong Zeng, Adam Miranowicz, Zhi-Cheng Shi, Ye-Hong Chen, Yan Xia, Franco Nori

Quantum Physics · Cross-listed from hep-th

Multi-entropy in random tensor networks

Miao Hu, Simon Lin and Ion Nechita

We study the evaluation of Rényi multi-entropies $S^{(q)}_n$ in Random Tensor Network (RTN) states in the large bond-dimension limit. For the case of Rényi index $n=2$ and arbitrary number of parties $q$, we prove that that multi-entropies are determined by minimal multiway cuts through the network. When the minimal multiway cut is degenerate, we characterize the full minimizer set via compatible families of minimal cuts and give a criterion for all minimizers to come from ordinary cut partitions. For $n=2$, this gives a natural generalization of the minimal cut description of bipartite entanglement to multipartite systems with arbitrarily many parties. For the case of integer $n>2$, we show that the minimal multiway cut conjecture is in general not true by providing explicit counter examples for both the single random tensor and for the network built from isometric tilings. We discuss the implication for our results on the multipartite entanglement structures in RTN and holography.
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Quantum Physics · Cross-listed from physics.atom-ph

Ramsey Atom Interferometry with Transverse Optical Modes

Ryan Husband, Ryan J. Thomas, Yosri Ben-Aïcha et al. (+10 more)

We experimentally demonstrate atom interferometry using the transverse phase profile of an optical mode. As proof-of-principle, we use the helical phase windings of Hypergeometric Gaussian beams for Ramsey interferometry with ensembles of ballistically-expanding cold Rb87 atoms, and we show that the interferometer can measure rotations induced by a motor with a sensitivity that scales linearly with orbital angular momentum and interferometer time. We characterize the thermal decoherence of the interferometer, deriving and experimentally confirming a closed-form expression for the spatially-varying interferometer visibility arising near the singularity of the helical phase winding, motivating the use of condensed atoms in ring-shaped traps.
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All authors Ryan Husband, Ryan J. Thomas, Yosri Ben-Aïcha, Rhys H. Eagle, Jessica Eastman, John E. Debs, Patrick J. Everitt, Michael Larsen, Eric Imhof, Charles A. Sackett, John D. Close, Simon A. Haine, Samuel Legge

Quantum Physics

Leggett-Garg test inequality with spin and flavour neutrino oscillations in a constant magnetic field

I. A. Monroy and S. D. Madrid

The Leggett-Garg inequality (LGI), an analogue of Bellś inequality involving correlations of measurements of one observable on a system at different times, stands as one of the hallmark tests of quantum mechanics against classical predictions. In this work, we investigate its implications in the context of neutrino flavour ($\nu_{e}^{L}\leftrightarrow\nu_{\mu}^{L}$) and spin ($\nu_{e}^{L}\leftrightarrow\nu_{e}^{R}$) oscillations in the presence of a constant transverse magnetic field. For systems with strong magnetic fields, we show that, for both cases, there are length regions $\Delta L$ where the LGI is violated, as quantified by the correlator functions $K_{3}$ and $K_{4}$.
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Quantum Physics

Optimizing the Sensitivity-Noise Trade-off in Non-Hermitian Sensing via Off-Exceptional-Deficiency Operation

Shangxuan Li and Bin Guo

A central challenge in non-Hermitian sensing is that spectral singularities simultaneously amplify both the signal and environmental noise. We address this predicament in a double-chain Hatano-Nelson model featuring unidirectional interlayer coupling. At the exceptional deficiency (ED) limit, the system exhibits a macroscopically degenerate complex spectrum and a pronounced non-Hermitian skin effect (NHSE), yielding a sensitivity that scales exponentially with lattice size $N$ while remaining robust across a six-order-of-magnitude detuning range. By introducing diagonal spatial disorder, we demonstrate that the NHSE is progressively suppressed, whith eigenspace cosine similarity analysis quantifying a well-defined fault-tolerance threshold. To reconcile the sensitivity-noise trade-off, we delineate "At-ED" and "Off-ED" operating regimes. While the At-ED configuration imposes fractional-order noise amplification (SNR $\propto \delta^{-1/2}$) that saturates at a suboptimal plateau, migrating to the Off-ED regime eliminates this geometric singularity and restores a linear scaling law (SNR $\propto \delta^{-1}$), achieving an SNR enhancement of several orders of magnitude. Crucially, this improvement is achieved while fully preserving the exponential sensitivity scaling, albeit at a slightly reduced absolute sensitivity compared to the strict At-ED limit. Our findings establish the Off-ED framework as a concrete paradigm for next-generation topological sensors that reconcile extreme sensitivity with robust noise immunity.
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Quantum Physics

Robust Steerability Classification via Key Feature Extraction and Matrix Structure Preservation

Yutao Xin, Huixian Meng, Zhongyan Li et al. (+1 more)

Generalization ability is essential for assessing the robustness of quantum steerability classifiers. In this work, we investigate robust steerability classification from the perspective of key feature extraction and matrix structure preservation. The dataset introduced in Phys. Rev. A 100, 022314 (2019) provides the training basis for the present work. With strictly unsteerable random states, T-diagonal states, and All-Versus-Nothing (AVN) states, we evaluate the generalization performance of support vector machines (SVMs), multilayer perceptrons (MLPs), and deep perceptron control classifiers(DPs) trained on full-information features. None of these classifiers perform consistently on T-diagonal or AVN states. Given that stochastic local operations and classical communication and local unitary transformations preserve steerability, we introduce a key feature that determines steerability. SVMs trained on this feature overcome the instability on T-diagonal states but still fail on AVN states. Moreover, this feature alone is insufficient for training robust neural-network-based steerability classifiers. Recognizing that flattening quantum states into one-dimensional vectors may destroy their intrinsic matrix structure, we introduce matrix versions of both features and train convolutional neural networks on them. The most robust overall performance among the tested classifiers is achieved only when the matrix structure is preserved and key features are extracted simultaneously. Finally, as an application, we employ the most robust classifiers to predict the number of projective measurements required to detect the steerability of axially symmetric states
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All authors Yutao Xin, Huixian Meng, Zhongyan Li, Pu Wang

Quantum Physics · Cross-listed from physics.atom-ph

Photon shot-noise-limited Rydberg-EIT electrometry

Gyeongmin Ju, Ye Jin Yu, Heewoo Kim et al. (+4 more)

Rydberg-atom electrometry is a core technique in the development of highly sensitive quantum electric-field sensors. Its sensitivity based on atom-photon interaction is typically limited by photon shot-noise (PSN) and spectral broadenings. Here, we experimentally demonstrate a near PSN-limited Rydberg electrometry from a 85Rb atomic vapor cell. By engineering atomic coherence through control of residual magnetic fields and laser frequency noise, we achieve the Rydberg electromagnetically induced transparency (EIT) with the narrow linewidth of 1.6 MHz, yielding an enhanced spectral slope for high-sensitivity Rydberg-EIT electrometry. Under optimized superheterodyne detection conditions, we obtain an electric-field sensitivity of 12.5(8) nV cm^-1 Hz^-1/2 at 37 GHz, in close agreement with the calculated PSN limit. These results provide direct experimental evidence of the high-sensitive quantum electrometry and establish a practical route toward quantum-noise-limited Rydberg electrometry.
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All authors Gyeongmin Ju, Ye Jin Yu, Heewoo Kim, Hansol Jeong, Jinhyuk Bae, Changhoon Baek, Han Seb Moon

Quantum Physics

Spectral Fusion for Identifying Early State Exclusion in Symmetric Quantum Spin Chains

Mia Escobar, Valentin Garcia and Anastasiia Minenkova

Perfect state transfer (PST) in one-dimensional quantum spin chains provides a natural setting in which quantum information transport can be analyzed using spectral methods. In the single-excitation subspace, the dynamics of a chain with nearest-neighbor interactions are governed by a Jacobi matrix, allowing questions of state transfer to be formulated in terms of eigenvalue distributions and symmetry properties of eigenvectors. In this work, we investigate the phenomenon of early state exclusion (ESE), whereby the overlap of the time-evolved state with the initial state vanishes at a time strictly earlier than the first occurrence of perfect state transfer. Building on earlier constructions of Hamiltonians exhibiting PST with and without ESE, we provide explicit Jacobi matrix realizations for arbitrary odd-length chains and establish general conditions under which ESE occurs or does not occur. We propose the process of spectral fusion (SF) to build infinite families of such Hamiltonians. These results broaden the known class of spin chains displaying early state exclusion and further clarify the role of spectral structure of the Hamiltonians.
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Quantum Physics

Characterization of errors in photon-heralded quantum operations between non-interacting quantum emitters

Mahsa Karimi, Samuel Mister, Christoph Simon et al. (+1 more)

We develop an analytic perturbative framework that enables the analysis of small Markovian errors in probabilistic, photon-heralded quantum operations between non-interacting emitters. Building on and extending the Zero-Photon-Generation (ZPG) framework, we derive closed-form perturbative solutions that capture both ideal (zero-order) and noisy (low-order) gate dynamics conditioned on time-integrated photon counting. Our framework provides analytic solutions to process matrices and Pauli error weights up to leading order, bridging the gap between detailed physical imperfections of a system and its corresponding abstract Pauli noise models. Moreover, our framework captures imperfections across the full physical system stack, from photon generation to optical manipulation. We benchmark the resulting perturbative predictions on a repeat-until-success CZ gate against numerical simulations, demonstrating accurate modeling of source-induced noise, and then apply the same framework to analyze coherent phase-shifter miscalibrations as a representative example of optical-manipulation errors. The methods developed in this work enable physics-informed parameter tuning to optimize gate designs and develop tailored quantum error correction protocols toward fault-tolerant quantum computing using hybrid light–matter quantum systems.
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All authors Mahsa Karimi, Samuel Mister, Christoph Simon, Stephen C. Wein

Tuesday 2 June

Quantum Physics

Quantum digital simulations of time-domain semiconductor spectroscopy in the semi-classical approximation

Mykhailo Klymenko, Bahar Goldozian, Thong Hoang et al. (+2 more)

We present a digital quantum simulation framework for ultrafast optical spectroscopy of semiconductor materials. The framework is based on Brillouin-zone discretization and is designed as a quantum alternative to classical simulations based on the semiconductor Bloch equations. Its current capabilities include quantum simulations of linear absorption and optical gain, incorporating Lorentzian broadening, finite-temperature band-filling effects, and reduced-dimensionality effects. Comparison with classical simulations of GaAs within the single-particle approximation demonstrates quantitative agreement in the noiseless limit. The inclusion of realistic hardware noise characteristic of NISQ-era quantum computers effectively manifests as an additional source of scattering, resulting in increased spectral broadening. We also show that the linear optical response, including many-body interactions treated within the Hartree-Fock approximation, can be mapped onto a system of coupled classical oscillators. Under certain assumptions about the query complexity of the oscillator couplings, this system exhibits a provable quantum advantage, as demonstrated in [Phys. Rev. X 13, 041041 (2023)]. Beyond the Hartree-Fock approximation, classical simulations based on many-body quantum kinetic equations face the so-called hierarchy problem, whereas the algorithmic complexity of the quantum simulations remains unchanged, offering a promising approach to overcoming this challenge.
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All authors Mykhailo Klymenko, Bahar Goldozian, Thong Hoang, Jared H. Cole, Muhammad Usman

Quantum Physics · Cross-listed from cs.LG

Derivative Informed Learning of Exchange-Correlation Functionals

Eike S. Eberhard, Luca A. Thiede, Abdul Aldossary et al. (+5 more)

Machine-learned (ML) exchange-correlation (XC) functionals aim to replace human-designed density functional approximations by learning directly from reference data, but they still do not consistently outperform traditional $\mathcal{O}(N^4)$-scaling hybrid functionals. We study a hybrid-distillation setting in which $\mathcal{O}(N^3)$-scaling ML-XC functionals are trained to reproduce B3LYP/def2-SVP targets. We introduce Derivative Informed XC-Loss (DI-Loss), a loss that incorporates additional information from the reference hybrid functional by supervising first and second derivatives of the energy on the Grassmannian of admissible density matrices. Rather than only matching the self-consistent fixed point, DI-Loss aligns the local first- and second-order response of the learned functional with that of the target functional. Across four evaluated architectures, DI-Loss consistently improves the main energy metrics. Averaged uniformly across architectures, the total-energy MAE decreases by 66% relative to energy and density supervision alone. The density-sensitive mean-field energy metric $E_\rho$ improves from $1.2$ to $0.8$ mEh on average, while dipole and $\mathcal{L}_2$ density errors do not improve uniformly. We further show that densities from the distilled functionals reduce hybrid-functional SCF iterations by up to 50%. In downstream TDDFT calculations, Hessian supervision improves excited-state predictions, with XCdiff reducing the mean excitation-energy MAE by 19 - 35%.
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All authors Eike S. Eberhard, Luca A. Thiede, Abdul Aldossary, Andreas Burger, Nicholas Gao, Vignesh Bhethanabotla, Alán Aspuru-Guzik, Stephan Günnemann

Quantum Physics

Continuous-Variable Quantum State Tomography Enabled by Quantum Mirrors

Mariano Uria, Amaru Moya, Carla Hermann-Avigliano et al. (+2 more)

In quantum technologies, continuous-variable systems offer advantages over their discrete counterparts. However, continuous-variable tomography suffers from exponentially growing sample complexity. We propose protocols using quantum mirrors to transfer the complete information of incident photonic states onto a control atomic system. This enables full photonic state characterization through measurements on the control atom alone, realized via kernel functions, direct wavefunction reconstruction, and pointwise Wigner function measurements. Our approach overcomes the limitations of conventional photon counting, statistical inference, and inverse transformation, providing a robust framework for benchmarking and verifying non-Gaussian states in continuous-variable quantum optics.
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All authors Mariano Uria, Amaru Moya, Carla Hermann-Avigliano, Pablo Solano, Aldo Delgado

Quantum Physics · Cross-listed from physics.chem-ph

Spin dynamics and ortho-para conversion in H$_{2}$O during the phase transition from gas to solid in external magnetic fields

Chrysovalantis S. Kannis, Ralf Engels, Nicolas Faatz et al. (+2 more)

The spin dynamics of water ice in the presence of external magnetic fields are investigated. The employed model is based on the approach introduced by Buntkowsky et al. [Z. Phys. Chem. 222, 1049 (2008)], which considers two nearest-neighbor water molecules and yields a four-spin system, as the abundant oxygen isotope has zero nuclear spin. The model is extended to include coupling to external magnetic fields, allowing us to analyze the interplay between magnetic dipole-dipole interactions and magnetic field coupling. Two types of configurations are examined: (i) static, homogeneous fields, corresponding to a time-independent interaction, and (ii) spatially varying sinusoidal fields in relative motion with the molecules, leading to a time-dependent interaction. All computations are performed within the density operator formalism. The ortho/para populations and the total spin projections are evaluated during the first tens of milliseconds following the gas-to-solid phase transition. For static homogeneous fields, we show that increasing field strength suppresses dipolar-induced depolarization. Assuming that all molecules are initially in the para state, we show that static homogeneous fields can drive the ortho population up to approximately $50\%$, whereas suitably chosen sinusoidal-field configurations can increase it beyond $90\%$. These results are relevant for schemes aiming to preserve or manipulate nuclear-spin polarization during deposition.
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All authors Chrysovalantis S. Kannis, Ralf Engels, Nicolas Faatz, Simon J. Pütz, Markus Büscher

Quantum Physics

High-Dimensional Quantum Key Distribution via full Core-mode Encoding over Deployed Multicore Fibers

G. H. dos Santos, K. B. Sawada, N. Villalba et al. (+11 more)

Quantum key distribution (QKD) provides information-theoretic security rooted in quantum physics, while high-dimensional (HD) encoding increases both noise tolerance and secret-key yield. Multicore fibers (MCFs), a leading platform for next-generation telecom networks, are a natural substrate for HD-QKD. Field demonstrations over deployed MCFs have so far relied on a hybrid qudit encoding strategy that combines two path (core modes) with the time-bin photonic degree of freedom, rather than exploiting the full set of available core modes. Although practical, this approach incurs intrinsic efficiency penalties that grow with dimension. Here we implement a four-dimensional ($d=4$) QKD protocol that directly exploits the full set of core modes of a four-core MCF, operating over an installed MCF network across the Universidad de Concepción campus under continuous environmental perturbations. We further benchmark the scheme using superconducting nanowire detectors at $10\,$dB channel loss, achieving a composable finite-key rate of $R = 6.19\times 10^{-3}\,$bits/pulse, the highest per-pulse rate reported to date for HD-QKD at comparable loss. This result establishes core-mode encoding as a viable architecture for realistic, high-rate quantum-secure communications.
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All authors G. H. dos Santos, K. B. Sawada, N. Villalba, C. Jara, N. Guerrero, C. Melo, M. H. Magiotto, D. Martínez, G. B. Xavier, J. Cariñe, G. Saavedra, E. S. Gómez, S. P. Walborn, G. Lima

Quantum Physics · Cross-listed from cond-mat.mtrl-sci

Emergence of Macroscopic Quantum Order via Translational Zero Modes

Kenan Gundogdu

Macroscopic quantum coherence in solids, such as in superfluids, superconductors, and condensates, is generally limited to low temperatures because order forms within a fixed excitation spectrum whose competing states become thermally populated as temperature rises. Here, we show that strong coupling between electronic excitations and a deformable lattice enables a different route. Above a critical density, this coupling nucleates self generated confining potentials that trap the very excitations generating them. Unlike rigid external traps, these potentials can translate through the host lattice without changing their internal structure, defining a translational zero mode. Coupling to this zero mode provides a shared dynamical coordinate that lowers and isolates a single collective many body configuration, opening a density dependent gap that suppresses thermal occupation of competing states and supports off diagonal long range order at elevated temperatures. As a concrete realization, we identify high-temperature superfluorescence in lead halide perovskites as the radiative instability of this zero mode dressed ordered excitonic state. More broadly, this establishes a general route to macroscopic quantum order: not cooling within a fixed spectrum, nor pairing instabilities, but a self generated mobile confining structure whose translational zero mode reconstructs the many-body spectrum to protect coherence.
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Quantum Physics

Quantum Information Harvesting with the Parallel Quantum Flow Algorithm

Nicholas P. Bauman, Ajay Panyala, Chenxu Liu et al. (+3 more)

The Quantum Flow (QFlow) algorithm provides a resource-efficient framework for describing correlated many-body systems on hybrid quantum-classical architectures. By enabling parallel utilization of quantum and classical resources, QFlow offers a scalable pathway toward simulations of realistic systems. In this Letter, we report a high-performance computing (HPC) implementation of the QFlow formalism based on a singles-and-doubles model. We demonstrate its performance for target spaces comprising 82 and 114 orbitals, where the flow includes all 6 active electrons in 6 active orbitals type active spaces. In the largest QFlow simulations, we optimize 1.17 million wave function parameters using the equivalent of 12 qubits. Despite the modest qubit requirements of the underlying active-space problems, the method recovers over $95\%$ of the total correlation energy obtained with the coupled cluster singles and doubles (CCSD) approach for systems dominated by dynamical correlation effects, which remain challenging for existing quantum algorithms. We further show that the QFlow formalism retains high accuracy in extended basis sets with diffuse functions, highlighting its potential for realistic large-scale quantum chemistry simulations.
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All authors Nicholas P. Bauman, Ajay Panyala, Chenxu Liu, Muqing Zheng, Meng Wang, Karol Kowalski

Quantum Physics · Cross-listed from gr-qc

Gravitationally Induced Quantum Decoherence of Macroscopic Objects

Hiroki Takeda, Shogo Tomizuka and Takahiro Tanaka

We formulate the gravitationally induced quantum decoherence of a massive object prepared in a spatial superposition. Starting from linearized gravity coupled to a massive system particle and an environmental scalar field, we derive a closed-time-path influence functional governing the reduced system dynamics. In the nonrelativistic and quasi-static regime, the decoherence exponent can be written as a bilinear functional of the difference of the system stress-energy tensors and an effective noise kernel obtained by dressing the environmental stress-energy tensor correlator with graviton propagators. We then apply this framework to the Newtonian long-range gravitational interaction and evaluate the resulting decoherence function for a dilute nonrelativistic gas modeled by finite wave packets and coarse-grained in time and space. By performing controlled approximations, we obtain analytic expressions for the cumulative decoherence function and show that the dominant contribution is accumulated logarithmically over a broad range of distances, while remaining subdominant to conventional collisional decoherence under realistic conditions.
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Quantum Physics

Better Pauli Channel Learning with Maximum Likelihood Estimation

Daniel Belkin, Faisal Alam, Matthew Thibodeau et al. (+3 more)

Error mitigation in a noisy quantum device requires a very good estimate of the noise channel. The accuracy of probabilistic error cancellation is often limited by the high sample complexity of channel tomography. In principle, optimal sample complexity is attained by maximum likelihood estimation (MLE), but MLE is computationally challenging. We show that MLE can be made computationally tractable in certain cases of interest. For the common case of a 1D-local sparse Pauli-Lindblad channel, the likelihood function reduces to an efficiently-evaluable Bayesian network. We show that the resulting computation leads to substantially improved tomography. In addition, we demonstrate by simulation that this can lead to meaningful improvements to the overhead of error mitigation. We also discuss possible extensions of our algorithm to more general settings, such as non-1D circuits and non-Pauli errors.
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All authors Daniel Belkin, Faisal Alam, Matthew Thibodeau, Alireza Seif, Ewout van den Berg, Bryan K. Clark

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

Quantum String Interactions Revealed by Full Counting Statistics

Chang-Yan Wang and Xue-Feng Zhang

How quantum strings interact is a basic question for extended objects in quantum many-body physics. Even the simplest hard-core constraint (no crossing), can generate a nontrivial effective potential, whose microscopic form is difficult to determine because the relative distance between the strings is intrinsically nonlocal. Here we show that this nonlocality is naturally captured by full counting statistics (FCS). For two hard-core quantum strings, we derive an analytic FCS expression for the emergent interaction by identifying the virtual process in which the two strings touch and hop back. Using the FCS–entanglement relation, we find the effective potential has the entanglement-controlled asymptotic form $\ln\Delta E(r)\sim -\pi^2 r^2/(12 S_\ell)$ up to subleading terms, where $S_\ell$ is the entanglement entropy between the two halves of a quantum string. We confirm the theory using high-precision numerical calculations and finite-size FCS estimates. Our results reveal FCS as a direct route to effective interactions between quantum topological line-defects, which may also be extended to higher-form charge.
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Quantum Physics

Essential Unitarity for Higher-Order Quantum Computation

Samson Abramsky and Radha Jagadeesan

We develop a boundary-centric semantic framework for higher-order quantum computation, building on the Kelly-Laplaza description of compact closure and Abramsky's execution account. In the semantic carrier Perm(C), morphisms are complex-linear combinations of polarized boundary linkings, composed by execution. Finite-family addresses provide coherent control over finite-level quantum registers (qudits) while retaining the multiplicative boundary structure. We identify essential unitarity, a boundary condition extending ordinary unitarity to higher-order interfaces. On positive qudit registers it coincides with ordinary matrix unitarity; at higher order it expresses preservation of information across the full polarized boundary. We define a unit-free coherent quantum core generated by multiplicative wiring, unitary gates on positive qudit registers, and contextual coherent control, and prove that every one of its morphisms is essentially unitary. The framework realizes an applied coherent quantum switch and the unitary stages of equal-ratio one-slot supermap dilations with explicit memory. An extended abstract of this work was accepted for QPL 2026 and is forthcoming in its proceedings.
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Quantum Physics

Quantum error correction with the toric code

Atom Computing and Collaborators

Quantum computing platforms based on arrays of tweezer-confined neutral atoms have recently emerged as a competitive modality thanks to a direct path toward high qubit count, rapidly advancing operation fidelities, and their ability to execute circuits with arbitrary qubit connectivity. These features will enable the use of efficient error correction schemes with high encoding-rates, time-efficient decoding, and resource-efficient architectures based on transversal gates. With these goals in mind, recent state of the art neutral atom demonstrations focus on the transition from the use of physical qubits to error-corrected logical qubits, but to date there has been no demonstration of repeated error correction scalable to arbitrary depth. Here, we demonstrate many cycles of syndrome extraction in a toric quantum error correcting code, using mid-circuit measurement and replacement of lost qubits, including reloading of a qubit reservoir for indefinite coherent operation. We characterize the logical error rate after up to 90 cycles, showing that logical information can be preserved through multiple rounds of qubit reloading. Comparing two distances of the code up to 8 rounds of syndrome extraction shows a lower absolute logical error rate for the larger distance code.
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Quantum Physics

Quantum circuit partition as a maze: emerging percolation transition via path finding

P. Zentilini, M. Guatto, F. Preti et al. (+4 more)

In quantum circuit optimization, circuit partitioning enables the optimization process to be parallelized across multiple devices. Each device is responsible for either reducing the number of selected gates or simplifying the local circuit structure. Most existing approaches to circuit partitioning are quantum-distribution-oriented and rely on splitting CNOT gates by introducing mid-circuit measurements and qubit resets. Currently, there is no criterion to determine how a circuit can be optimally partitioned without removing the CNOT gates for circuit optimization purposes. To address this challenge, we formalize the partition problem as a cutting path through a maze, where the CNOT gates represent the walls. We show that the existence of such a path separates quantum circuits into two classes through a percolation phase transition. In particular, it distinguishes a partitionable regime from a nonpartitionable one, arising from qubit permutations. Such permutations are generated by simulated annealing. We analyze its effect on the CNOT cluster from the perspective of network science and distribution analysis. Our results show that partitioning into two CNOT clusters is possible when the number of CNOTs is almost equal to the number of qubits. Based on this observation, we provide a scalable and practical criterion for identifying whether such a partition exists. Overall, our framework provides theoretical and numerical insight into circuit partitioning within quantum circuit optimization, forming the basis for algorithmic development.
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All authors P. Zentilini, M. Guatto, F. Preti, D. Arya, F. A. Cárdenas-López, F. Motzoi, E. Prati

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

Multiparametric Quantum Sensing of Liquids Using NV Centres and Tethered Magnetic Nanoparticles

Johannes Fiedler, Martin Møller Greve and Justas Zalieckas

We propose a new concept for non-invasive, multiparametric liquid analysis based on nitrogen-vacancy (NV) centre magnetometry, relaxometry and surface-tethered magnetic nanoparticles. Magnetic nanoparticles are anchored to a diamond surface via DNA strands, forming nanoscale mechanical oscillators whose thermally driven motion is strongly influenced by the surrounding liquid environment. The resulting time-dependent magnetic fields couple to near-surface NV centres and are detected via optically detected magnetic resonance or changes in spin coherence time. By spatially patterning the diamond surface with regions functionalised by DNA tethers of different lengths, sequences, or chemical modifications, a single liquid is mapped onto a high-dimensional quantum response vector rather than a single scalar observable. Changes in viscosity, molecular adsorption, or chemical interactions modify the dynamics of magnetic nanoparticles in a region-specific manner, enabling differential sensing across the surface. We outline the physical transduction mechanism, discuss relevant scaling relations, and assess experimental feasibility using established wide-field NV magnetometry and relaxometry methods. The proposed platform combines quantum sensing with surface heterogeneity, offering a versatile route toward parallel, label-free liquid characterisation.
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