Quantum Physics
Quantum Coherence of Rare-Earth Ions in Heterogeneous Photonic Interfaces
Henry C. Hammer, Hassan A. Bukhari, Yogendra Limbu et al. (+6 more)
Harnessing rare-earth ions in
oxides for
quantum networks requires integration with bright emitters in III-V
semiconductors, but local disorder and interfacial noise limit their optical coherence. Here, we investigate the microscopic origins of the ensemble spectrum in Er$^{3+}$:TiO$_2$ epitaxial thin films on GaAs and GaSb substrates. Ab initio calculations combined with noise-
Hamiltonian modeling and Monte Carlo simulations quantify the effects of interfacial and bulk
spin noise and local strain on erbium
crystal-field energies and inhomogeneous linewidths. Photoluminescence excitation spectroscopy reveals that Er$^{3+}$ ions positioned at increasing distances from the III-V/
oxide interface produce a systematic blue shift of the $Y_1\rightarrow Z_1$ transition, consistent with strain relaxation predicted by theory. Thermal annealing produces a compensating
redshift and linewidth narrowing, isolating the roles of oxygen-vacancy and gallium-
diffusion noise. These results provide microscopic insight into disorder-driven decoherence, offering pathways for precise control of hybrid
quantum systems for scalable
quantum technologies.
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All authors Henry C. Hammer, Hassan A. Bukhari, Yogendra Limbu, Brett M. Wasick, Christopher Rouleau, Michael E. Flatté, Durga Paudyal, Denis R. Candido, Ravitej Uppu
Quantum Physics
Entropy Flow and Exceptional-Point Structure in Two-Mode Squeezed-Bath Dynamics
Eric R. Bittner
Squeezed reservoirs provide a powerful means of engineering nonclassical noise and controlling irreversible dynamics in open
quantum systems. Here we develop a comprehensive analysis of two coupled harmonic oscillators driven by independent squeezed baths, focusing on the emergence of coherence-driven
entropy flow and the structure of exceptional points (EPs) in the corresponding Lindblad dynamics. Working entirely within the Gaussian formalism, we derive closed-form
evolution equations for the covariance
matrix and show that squeezing induces
entropy generation only at *second order* in the anomalous correlations, a nonlinear mechanism absent in thermal environments. This
entropy flow is accompanied by a rich non-Hermitian structure: by scanning the squeezing parameters we uncover a characteristic "exceptional-point fan" in the (M1, M2) plane, which separates a narrow PT-unbroken region of oscillatory dynamics from broad PT-broken sectors in which one normal mode becomes purely overdamped. This
geometric organization of EPs reveals that PT
symmetry survives only when the two reservoirs squeeze opposite quadratures, and is generically broken for in-phase squeezing. Our analysis establishes squeezed reservoirs as a natural setting where information-bearing noise drives irreversible behavior through coherent pathways, and lays the groundwork for experimentally accessible probes of
entropy flow and critical mode behavior in more complex open systems.
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Quantum Physics
High-order splitting of non-unitary operators on quantum computers
Peter Brearley and Philipp Pfeffer
Dissipation and irreversibility are central to many physical systems, yet they lead to non-
unitary dynamics that are challenging to realise on
quantum processors. High-order operator splitting is an attractive approach for simulating
unitary dynamics, yet conventional product formulas introduce negative time steps at high orders that are ill-conditioned for dissipative dynamics. We show how block encodings of complex-coefficient product formulas can be constructed by a sequence of simple
Hamiltonian evolutions in real and imaginary time with high-order accuracy. The
unitary substages use positive real coefficients, while the dissipative substages use complex coefficients with positive real parts; the real parts preserve the contractive
evolution, and the imaginary parts are additional
unitary evolutions. We use known formulas of orders 4 and 6 and give a new symmetric formula of order 8 in this restricted class. We apply the approach to the classical problem of lossy mechanical wave propagation in statevector simulations and on a trapped-ion
quantum processor. Orders 4 and 6 require comparable CNOT gates to orders 1 and 2 at large error tolerances, but quickly become more efficient as the tolerance is reduced. On the
quantum hardware, a single step of order 4 achieves lower error than order 1 and comparable error to order 2, while order 6 is noise-limited. Our results show that operator splitting can combine practical
circuit constructions with high-order convergence for non-
unitary dissipative dynamics.
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Quantum Physics
Shake before use: universal enhancement of quantum thermometry by unitary driving
Emanuele Tumbiolo, Lorenzo Maccone, Chiara Macchiavello et al. (+2 more)
Quantum thermometry aims at determining temperature with ultimate precision in the
quantum regime. Standard
equilibrium approaches, limited by the
Quantum Fisher Information given by static energy fluctuations, lose sensitivity outside a fixed temperature window. Non-
equilibrium strategies have therefore been recently proposed to overcome these limits, but their advantages are typically model-dependent or tailored for a specific purpose. This Letter establishes a general, model-independent result showing that any temperature-dependent
unitary driving applied to a thermalized probe enhances its
quantum Fisher information with respect to its
equilibrium value. Such information gain is expressed analytically through a positive semi-definite kernel of information currents that quantify the flow of statistical distinguishability. Our results, together with an analysis of the relation between information gain and control cost, are benchmarked on a driven
spin-$1/2$ thermometer, furthermore showing that resonant modulations remarkably restore the quadratic-in-time scaling of the Fisher information and allow to shift the sensitivity peak across arbitrary temperature ranges.
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All authors Emanuele Tumbiolo, Lorenzo Maccone, Chiara Macchiavello, Matteo G.A. Paris, Giacomo Guarnieri
Quantum Physics
Quantum Hardware-Efficient Selection of Auxiliary Variables for QUBO Formulations
Damian Rovara, Lukas Burgholzer and Robert Wille
The
Quantum Approximate Optimization
Algorithm (QAOA) requires considered optimization problems to be translated into a compatible format. A popular transformation step in this pipeline involves the quadratization of higher-order binary optimization problems, translating them into Quadratic Unconstrained Binary Optimization (QUBO) formulations through the introduction of auxiliary variables. Conventional
algorithms for the selection of auxiliary variables often aim to minimize the total number of required variables without taking the constraints of the underlying
quantum computer-in particular, the connectivity of its
qubits-into consideration. This quickly results in interaction graphs that are incompatible with the target device, resulting in a substantial compilation overhead even with highly optimized compilers. To address this issue, this work presents a novel approach for the selection of auxiliary variables tailored for architectures with limited connectivity. By specifically constructing an interaction graph with a regular structure and a limited maximal degree of vertices, we find a way to construct QAOA
circuits that can be mapped efficiently to a variety of architectures. We show that, compared to
circuits constructed from a QUBO formulation using conventional auxiliary selection methods, the proposed approach reduces the
circuit depth by almost 40%. An implementation of all proposed methods is publicly available at https://github.com/munich-
quantum-toolkit/problemsolver.
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Quantum Physics
No-go theorems for sequential preparation of two-dimensional chiral states via channel-state correspondence
Ruihua Fan, Yantao Wu, Yimu Bao et al. (+1 more)
We investigate whether sequential
unitary circuits can prepare two-dimensional
chiral states, using a correspondence between sequentially prepared states, isometric tensor network states, and one-dimensional
quantum channel
circuits. We establish two no-go
theorems, one for Gaussian
fermion systems and one for generic interacting systems. In Gaussian
fermion systems, the correspondence relates the defining features of
chiral wave functions in their
entanglement spectrum to the algebraic decaying correlations in the steady state of channel dynamics. We establish the no-go
theorem by proving that local channel dynamics with translational invariance cannot support such correlations. As a direct implication, two-dimensional Gaussian
fermion isometric tensor network states cannot support algebraically decaying correlations in all directions or represent a
chiral state. In generic interacting systems, we establish a no-go
theorem by showing that the state prepared by sequential
circuits cannot host the tripartite
entanglement of a
chiral state due to the constraints from causality.
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All authors Ruihua Fan, Yantao Wu, Yimu Bao, Zhehao Dai
Quantum Physics
Berry's phase on photonic quantum computers
Steven Abel, Iwo Wasek and Simon Williams
We formulate a continuous-variable
quantum computing (CVQC)
algorithm to study Berry's phase on photonic
quantum computers. We demonstrate that CVQC allows the simulation of charged particles with orbital angular momentum under the influence of an adiabatically changing $\vec{B}$ field. Although formulated entirely in the CVQC setting, our construction uses only passive linear-optical operations (beam splitters and phase shifts), which act identically in single-
photon photonic architectures. This enables experimental realisation on the Quandella Ascella platform, where we observe the Berry's phase phenomenon with interferometric measurement. We also generalise the framework to more rapid non-adiabatic
evolution. By concatenating Aharonov-Anandan cycles for opposing
magnetic fields we demonstrate that one can engineer a
circuit in which dynamical phases and leading non-
geometric errors cancel by
symmetry, leaving the intrinsically robust
geometric phase contribution.
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Quantum Physics
Holographic duality between bulk topological order and boundary mixed-state order
Tsung-Cheng Lu, Yu-Jie Liu, Sarang Gopalakrishnan et al. (+1 more)
We introduce a
holographic framework for analyzing the steady states of repeated
quantum channels with strong
symmetries. Using channel-state duality, we show that the steady state of a $d$-dimensional
quantum channel is holographically mapped to the boundary reduced density
matrix of a $(d+1)$-dimensional wavefunction generated by a sequential
unitary circuit. From this perspective, strong-to-weak spontaneous
symmetry breaking (SWSSB) in the steady state arises from the anyon condensation on the boundary of a topological order in one higher dimension. The conditional mutual information (CMI) associated with SWSSB is then inherited from the bulk topological
entanglement entropy. We make this duality explicit using isometric tensor network states (isoTNS) by identifying the channel's time
evolution with the transfer
matrix of a higher-dimensional isoTNS. Built on isoTNS, we further construct continuously tunable
quantum channels that exhibit distinct mixed-state phases and transitions in the steady states.
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All authors Tsung-Cheng Lu, Yu-Jie Liu, Sarang Gopalakrishnan, Yizhi You
Quantum Physics · Cross-listed from cond-mat.str-el
Topological BF Theory construction of twisted dihedral quantum double phases from spontaneous symmetry breaking
Zhi-Qiang Gao, Chunxiao Liu and Joel E. Moore
Nonabelian topological orders host exotic anyons central to
quantum computing, yet established realizations rely on case-by-case constructions that are often conceptually involved. In this work, we present a systematic construction of nonabelian dihedral
quantum double phases based on a continuous $O(2)$ gauge field. We first formulate a topological $S[O(2)\times O(2)]$ BF theory, and by identifying the Wilson loops and twist operators of this theory with anyons, we show that our topological BF theory reproduces the complete anyon data, and can incorporate all Dijkgraaf–Witten twists. Building on this correspondence, we present a microscopic model with $O(2)$
lattice gauge field coupled to Ising and rotor matter whose Higgsing yields the desired dihedral
quantum double phase. A perturbative renormalization group analysis further suggests a direct transition from this phase to a $U(1)$ Coulomb or
chiral topological phase at a stable multicritical point with emergent $O(3)$
symmetry. Our proposal offers an alternative route to nonabelian topological order with promising prospects in synthetic gauge field platforms.
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Quantum Physics
Monogamy of Mutual Information in Graph States
Jesus Fuentes, Cynthia Keeler, William Munizzi et al. (+1 more)
The monogamy of mutual information (MMI) is a
quantum entropy inequality that enforces the non-positivity of tripartite information. We investigate the failure of MMI in graph states as a forbidden-subgraph phenomenon, conjecturing that every MMI-violating graph state is local-Clifford equivalent to one whose graph contains a four-
star subgraph. We construct a family of
star-like graphs whose states fail a specific class of MMI instances, and extend this analysis to general
star topologies. Deriving adjacency
matrix constraints that fix the MMI evaluation for these instances and interpreting them physically, we prove the forbidden-subgraph
conjecture for this family of graphs. Finally, through an exhaustive search over graph representatives for all $8$-
qubit stabilizer
entropy vectors, we establish that MMI failure is not reducible to the cases within our scope.
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All authors Jesus Fuentes, Cynthia Keeler, William Munizzi, Jason Pollack
Quantum Physics
Modelling and experimental verification of photoelectrical response of NV diamond spin centres
Josef Soucek, Michael Petrov, Michal Gulka et al. (+2 more)
We report on a mathematical model of the photoelectric response of NV colour centres in diamond, that can be employed for sensing and
quantum science information applications. Although the model applies to NV centre in diamond, it can be applied with small modifications to other semiconducting solid state
qubits. In our model, we include the drift and collection of charge carriers as well as the presence of other defects via generation and recombination dynamics. Though the photoluminescence readout and the associated dynamics of the NV defect has been extensively studied experimentally and theoretically, so far, there has been no precise model for photocurrent readout, including these effects. In our description, we use a multilevel-level system including mS=0, mS=+-1 ground and excited states, singlet state and the NV0 neutral state. Also, the presence of substitutional nitrogen (NS), which for example determines the
spin coherence via the paramagnetic
spin bath, is discussed together with presence of acceptor defects. We model the time-dependent occupation of all electronic sublevels and also consider the electronic charge transport from the Boltzmann transport equation, leading to information about the charge state transitions and recombination dynamics. ODMR and PDMR response as well as their
quantum efficiencies, are calculated. On this basis, we determine an optimal parameter space for
qubit operations, including the highest
spin contrast and especially relate those to NS presence. The model is confirmed experimentally and can become a useful tool for optimisation of the performance of NV
qubit photoelectric readout.
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All authors Josef Soucek, Michael Petrov, Michal Gulka, Emilie Bourgeois, Milos Nesladek
Quantum Physics
SPARTA: $\chi^2$-calibrated, risk-controlled exploration-exploitation for variational quantum algorithms
Mikhail Zubarev
Variational
quantum algorithms face a fundamental trainability crisis: barren plateaus render optimization exponentially difficult as system size grows. While recent Lie algebraic theory precisely characterizes when and why these plateaus occur, no practical optimization method exists with finite-sample guarantees for navigating them. We present the sequential plateau-adaptive regime-testing
algorithm (SPARTA), the first measurement-frugal scheduler that provides explicit, anytime-valid risk control for
quantum optimization. Our approach integrates three components with rigorous statistical foundations: (i) a $\chi^2$-calibrated sequential test that distinguishes barren plateaus from informative regions using likelihood-ratio supermartingales; (ii) a probabilistic trust-region exploration strategy with one-sided acceptance to prevent false improvements under shot noise; and (iii) a theoretically-optimal exploitation phase that achieves the best attainable convergence rate. We prove
geometric bounds on plateau exit times, linear convergence in informative basins, and show how Lie-algebraic variance proxies enhance test power without compromising statistical calibration.
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Quantum Physics · Cross-listed from physics.app-ph
Robotic chip-scale nanofabrication for superior consistency
Felix M. Mayor, Wenyan Guan, Erik Szakiel et al. (+2 more)
Unlike the rigid, high-volume automation found in industry, academic research requires process flexibility that has historically relied on variable manual operations. This hinders the fabrication of advanced, complex devices. We propose to address this gap by automating these low-volume, high-stakes tasks using a robotic arm to improve process control and consistency. As a proof of concept, we deploy this system for the resist development of Josephson junction devices. A statistical comparison of the process repeatability shows the robotic process achieves a resistance spread across chips close to 2%, a significant improvement over the ~7% spread observed from human operators, validating robotics as a solution to eliminate operator-dependent variability and a path towards industrial-level consistency in a research setting.
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All authors Felix M. Mayor, Wenyan Guan, Erik Szakiel, Amir H. Safavi-Naeini, Samuel Gyger
Quantum Physics
Entanglement-limited linear response in fermionic systems
Hadi Cheraghi, Ali G. Moghaddam and Teemu Ojanen
We propose a general connection between
entanglement-
entropy scaling laws and the linear response functions of particle-conserving fermionic systems in their ground state. Specifically, we show that the response to perturbations coupled to the particle number within a finite region exhibits the same size scaling as the
entanglement entropy of that region. We explicitly verify this scaling in free-
fermion systems that display area-law, volume-law, and critical forms of
entanglement. The resulting
entanglement-governed scaling of response functions leads to unexpected physical consequences. For instance, contrary to conventional expectations, the energy absorption rate and particle-number fluctuations in gapped systems scale with the boundary of the perturbed region rather than with its volume. Our work thus establishes a direct link between linear-response properties and many-body
entanglement.
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Quantum Physics · Cross-listed from math.AP
Wigner and Gabor phase-space analysis of propagators for evolution equations
Elena Cordero, Gianluca Giacchi and Luigi Rodino
We study the Wigner kernel and the Gabor
matrix associated with the propagators of a broad class of linear
evolution equations, including the complex heat, wave, and Hermite equations. Within the framework of time-frequency analysis, we derive explicit expressions for the Wigner kernels of
Fourier multipliers and establish quantitative decay estimates for the corresponding Gabor
matrices. These results are obtained under symbol regularity conditions formulated in the Gelfand-Shilov scale and ensure exponential off-diagonal decay or quasi-diagonality of the
matrix representation. We believe this approach can be extended to more general symbols in the pseudodifferential setting, improving the existing results in terms of their Gabor
matrix decay. For the complex heat equation, we obtain closed-form formulas exhibiting both dissipative and oscillatory behavior governed respectively by the real and imaginary parts of the
diffusion parameter. The modulus of the Gabor
matrix is shown to display Gaussian decay and temporal spreading consistent with
diffusion phenomena. In contrast, the complex Hermite equation is analyzed via Hörmander's metaplectic
semigroup, where the propagator decomposes as the product of a real Hermite
semigroup and a fractional
Fourier transform. In this setting, the Gabor
matrix retains its Gaussian shape while undergoing a pure rotation on the time-frequency plane, reflecting the
symplectic structure of the underlying flow. The analysis provides a unified operator-theoretic and phase-space perspective on
parabolic and
hyperbolic evolution equations, linking the geometry of their symbols with the sparsity and localization properties of their Gabor representations. Explicit formulas are given in a form suitable for numerical computation and visualization of phase-space dynamics.
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Quantum Physics · Cross-listed from cs.LG
Neural surrogates for designing gravitational wave detectors
Carlos Ruiz-Gonzalez, Sören Arlt, Sebastian Lehner et al. (+5 more)
Physics simulators are essential in science and engineering, enabling the analysis, control, and design of complex systems. In experimental sciences, they are increasingly used to automate experimental design, often via combinatorial search and optimization. However, as the setups grow more complex, the computational cost of traditional, CPU-based simulators becomes a major limitation. Here, we show how neural surrogate models can significantly reduce reliance on such slow simulators while preserving accuracy. Taking the design of interferometric gravitational wave detectors as a representative example, we train a neural network to surrogate the gravitational wave physics simulator Finesse, which was developed by the LIGO community. Despite that small changes in physical parameters can change the output by orders of magnitudes, the model rapidly predicts the quality and feasibility of candidate designs, allowing an efficient exploration of large design spaces. Our
algorithm loops between training the surrogate, inverse designing new experiments, and verifying their properties with the slow simulator for further training. Assisted by auto-differentiation and GPU parallelism, our method proposes high-quality experiments much faster than direct optimization. Solutions that our
algorithm finds within hours outperform designs that take five days for the optimizer to reach. Though shown in the context of gravitational wave detectors, our framework is broadly applicable to other domains where simulator bottlenecks hinder optimization and discovery.
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All authors Carlos Ruiz-Gonzalez, Sören Arlt, Sebastian Lehner, Arturs Berzins, Yehonathan Drori, Rana X Adhikari, Johannes Brandstetter, Mario Krenn
Quantum Physics
Simulating dynamics of the two-dimensional transverse-field Ising model: a comparative study of large-scale classical numerics
Joseph Vovrosh, Sergi Julià-Farré, Wladislaw Krinitsin et al. (+11 more)
The
quantum dynamics of many-
qubit systems is an outstanding problem that has recently driven significant advances in both numerical methods and programmable
quantum processing units. In this work, we employ a comprehensive toolbox of state-of-the-art numerical approaches to classically simulate the dynamics of the two-dimensional transverse field Ising model. Our methods include three different tensor network techniques –
matrix product states, tree-tensor networks, and two-dimensional tensor-networks under the belief propagation approximation – as well as time-dependent variational Monte Carlo with Neural
Quantum States. We focus on two paradigmatic dynamical protocols: (i)
quantum annealing through a critical point and (ii) post-quench dynamics. Our extensive results show the quantitative predictions of various state-of-the-art numerical methods providing a
benchmark for future numerical investigations and experimental studies with the aim to push the limitations on classical and QPUs. In particular, our work connects classical simulability to different regimes associated with
quantum dynamics in Rydberg arrays - namely, quasi-adiabatic dynamics, the Kibble-Zurek mechanism, and
quantum quenches.
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All authors Joseph Vovrosh, Sergi Julià-Farré, Wladislaw Krinitsin, Michael Kaicher, Fergus Hayes, Emmanuel Gottlob, Augustine Kshetrimayum, Kemal Bidzhiev, Simon B. Jäger, Markus Schmitt, Joseph Tindall, Constantin Dalyac, Tiago Mendes-Santos, Alexandre Dauphin
Quantum Physics
Quantitative and Optimal Device-Independent Lower Bounds on Detection Efficiency
Arkaprabha Ghosal, Soumyadip Patra and Peter Bierhorst
This paper examines a quantitative and optimal lower bound on the detector efficiency in a (2,2,2) Bell experiment within a fully device-independent framework, whereby the detectors used in the experiment are uncharacterized. We provide a tight lower bound on the minimum efficiency required to observe a desired Bell-CHSH violation using the Navascués-Pironio-Acín (NPA) hierarchy, confirming tightness up to four decimal places with numerical optimization over explicit
quantum realizations. We then introduce the effect of dark counts and demonstrate how to quantify the minimum required efficiency to observe a desired CHSH violation with an increasing dark count error. Finally, to obtain an analytical closed-form expression of the minimum efficiency, we consider the set of no-signaling behaviors that satisfy the Tsirelson bound, which are easier to characterize than the
quantum set. Using such behaviors, we find a simple closed-form expression for a lower bound on the minimum efficiency which is monotonically increasing with the CHSH violation, though the analytically obtained lower bounds are meaningfully below the numerically tight lower bound.
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Quantum Physics
Efficient Equivalent of Shallow Quantum Hashing
Ilnar Zinnatullin and Alexander Vasiliev
Quantum hashing is a widely used technique in
quantum computation that allows us to design space-efficient
algorithms and protocols. Recently, Vasiliev has shown that the phase form of shallow
quantum hashing can be implemented by a
circuit of depth 2. In this paper, we establish a connection between shallow
quantum hashing and single-
qubit quantum hashing for the amplitude form. For a shallow
circuit, we propose a
circuit of depth 1 that achieves the same collision resistance.
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Quantum Physics
TorchQuantumDistributed
Oliver Knitter, Jonathan Mei, Masako Yamada et al. (+1 more)
TorchQuantumDistributed (tqd) is a PyTorch-based [Paszke et al., 2019] library for accelerator-agnostic differentiable
quantum state vector simulation at scale. This enables studying the behavior of learnable parameterized near-term and fault- tolerant
quantum circuits with high
qubit counts.
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All authors Oliver Knitter, Jonathan Mei, Masako Yamada, Martin Roetteler
Quantum Physics
Performance Guarantees for Quantum Neural Estimation of Entropies
Sreejith Sreekumar, Ziv Goldfeld and Mark M. Wilde
Estimating
quantum entropies and divergences is an important problem in
quantum physics, information theory, and machine learning.
Quantum neural
estimators (QNEs), which utilize a hybrid classical-
quantum architecture, have recently emerged as an appealing computational framework for estimating these measures. Such
estimators combine classical neural networks with parametrized
quantum circuits, and their deployment typically entails tedious tuning of hyperparameters controlling the sample size, network architecture, and
circuit topology. This work initiates the study of formal guarantees for QNEs of measured (Rényi) relative
entropies in the form of non-asymptotic error risk bounds. We further establish exponential tail bounds showing that the error is sub-Gaussian and thus sharply concentrates about the ground truth value. For an appropriate sub-class of density operator pairs on a space of dimension $d$ with bounded Thompson metric, our theory establishes a copy complexity of $O(|\Theta(\mathcal{U})|d/\epsilon^2)$ for QNE with a
quantum circuit parameter set $\Theta(\mathcal{U})$, which has minimax optimal dependence on the accuracy $\epsilon$. Additionally, if the density operator pairs are permutation invariant, we improve the dimension dependence above to $O(|\Theta(\mathcal{U})|\mathrm{polylog}(d)/\epsilon^2)$. Our theory aims to facilitate principled implementation of QNEs for measured relative
entropies and guide hyperparameter tuning in practice.
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Quantum Physics
Decoupling local classicality from classical explainability: A noncontextual model for bilocal classical theory and a locally-classical but contextual theory
Sina Soltani, Marco Erba, David Schmid et al. (+1 more)
We construct an ontological model for the theory known as bilocal classical theory doi.org/10.1103/PhysRevA.102.052216. To our knowledge, this is only the second time that an ontological model has been constructed for an entire theory, rather than just for some particular scenarios within a theory. This result refutes a
conjecture from doi.org/10.1103/PhysRevA.102.052216 which suggested that there might be no local-realist ontological model for bilocal classical theory. Moreover, it is the first time that an ontological model has been constructed for a theory that fails to be locally tomographic, showing that the assumption of local
tomography underpinning the structure
theorem in doi.org/10.22331/q-2024-03-14-1283 is a genuine limitation of the
theorem. This demonstrates that in general there is no tension between failures of local
tomography and classical explainability (i.e., generalised noncontextuality). In fact, bilocal classical theory is in many ways more simply understood via the underlying ontological model than it is within its original formulation (much as how odd-dimensional stabiliser subtheories can be more simply understood via Spekkens' toy theory). Furthermore, this result naturally leads to the question, does every locally-classical theory admit of an ontological model? By constructing a concrete counterexample, we show that this is not the case. Our findings demonstrate that there is no straightforward relationship between theories being locally-classical, and them being classically-explainable. This shows that the fundamental status of compositional properties (such as local
tomography) is not a technical side-issue, but a central and unavoidable question for a coherent understanding even of classicality itself.
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All authors Sina Soltani, Marco Erba, David Schmid, John H.Selby
Quantum Physics
Neural Architecture Search for Quantum Autoencoders
Hibah Agha, Samuel Yen-Chi Chen, Huan-Hsin Tseng et al. (+1 more)
In recent years, machine learning and deep learning have driven advances in domains such as image classification,
speech recognition, and anomaly detection by leveraging multi-layer neural networks to model complex data. Simultaneously,
quantum computing (QC) promises to address classically intractable problems via
quantum parallelism, motivating research in
quantum machine learning (QML). Among QML techniques,
quantum autoencoders show promise for compressing high-dimensional
quantum and classical data. However, designing effective
quantum circuit architectures for
quantum autoencoders remains challenging due to the complexity of selecting gates, arranging
circuit layers, and tuning parameters. This paper proposes a neural architecture search (NAS) framework that automates the design of
quantum autoencoders using a genetic
algorithm (GA). By systematically evolving variational
quantum circuit (VQC) configurations, our method seeks to identify high-performing hybrid
quantum-classical autoencoders for data reconstruction without becoming trapped in local minima. We demonstrate effectiveness on image
datasets, highlighting the potential of
quantum autoencoders for efficient feature extraction within a noise-prone, near-term
quantum era. Our approach lays a foundation for broader application of genetic
algorithms to
quantum architecture search, aiming for a robust, automated method that can adapt to varied data and hardware constraints.
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All authors Hibah Agha, Samuel Yen-Chi Chen, Huan-Hsin Tseng, Shinjae Yoo
Quantum Physics
Longitudinal Pulsed Dynamic Nuclear Polarization Transfer via Periodic Optimal Control
José P. Carvalho, Anders Bodholt Nielsen, David L. Goodwin et al. (+2 more)
Taking inspiration from NMR spectroscopy, periodic irradiation schemes have recently shown remarkable performance when implemented into pulsed dynamic
nuclear polarization (DNP) sequences. This has prompted considerable interest in development of broadband pulsed DNP sequences utilizing such schemes. On this background, most efforts have focused on solid-state NMR like transverse
spin-locked pulse sequences whose performance in DNP applications may be compromised by the broadband capabilities of the initial excitation pulse. Leveraging the flexibility and robustness of optimal control theory combined with underlying insights from effective
Hamiltonian theory, we present a new family of broadband DNP pulse sequences, termed LOOP (Longitudinally Optimized with Overarching Periodicity), that alleviates the excitation-pulse challenge by accomplishing longitudinal polarization transfer. These sequences define robust single-
spin effective $z$ rotations, with impressive compensation towards microwave field inhomogeneity, and are capable of delivering DNP transfer with bandwidths exceeding 100 MHz, while employing a peak microwave field amplitude of only 32 MHz, at an external
magnetic field of 0.35 T.
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All authors José P. Carvalho, Anders Bodholt Nielsen, David L. Goodwin, Nino Wili, Niels Chr. Nielsen
Quantum Physics
A demonstration that classical gravity does not produce entanglement
Mike D. Schneider, Nick Huggett and Niels Linnemann
Once again, dispute has arisen over the interpretation of proposed
quantum information theory experiments to probe the
quantum nature of
gravity by testing for gravitationally induced
entanglement (GIE) between two spatially separated massive particles ([2] vs. [16, 17]; further contributions in [11, 13]). The confusion appears to reside in interpreting applications of a
Hamiltonian formalism. But classical
gravity cannot mediate
entanglement on independent grounds. A Newton-Cartan analysis shows that if
gravity is classical, a mediator, and
entanglement is observed as an outcome of performing a GIE experiment, something other than
gravity must have supplied the (virtual) force needed during the experiment to produce the effect.
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Quantum Physics
Entropic Dynamics approach to Quantum Electrodynamics
Ariel Caticha
Entropic dynamics (ED) is a framework that allows one to derive
quantum theory as a Hamilton-Killing flow on the cotangent bundle of a statistical
manifold. These flows are such that they preserve the
symplectic and the (information) metric geometries; they explain the linearity of
quantum mechanics and the appearance of complex numbers. In this paper the ED framework is extended to deal with local gauge
symmetries. More specifically, on the basis of maximum
entropy methods and information geometry, for an appropriate choice of ontic variables and constraints, we derive the
quantum electrodynamics of radiation fields interacting with charged particles. As a test that despite its unorthodox foundation the ED approach is empirically successful we derive the Maxwell equations.
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Quantum Physics
Synchronized Aharonov-Bohm Motifs via Engineered Dissipation
Christopher W. Wächtler and Gloria Platero
The interplay between external gauge fields and
lattice geometry can induce extreme localization dynamics through complete destructive interference. We show that combining this flux-induced localization with engineered dissipation leads to robust
spin synchronization in rotationally symmetric
spin geometries, referred to as Aharonov-Bohm motifs, with cyclic
symmetries of any order. The synchronized dynamics is independent of initial conditions and features
entanglement among
spins within each motif. We further demonstrate that multiple motifs can fully synchronize when coupled, which is achieved by applying additional collective dissipation acting on all intra-motif
spins. These results reveal a direct connection between flux-induced localization, dissipative engineering, and collective
quantum synchronization.
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Quantum Physics · Cross-listed from cond-mat.supr-con
YBa$_2$Cu$_3$O$_7$ nano-constriction Josephson junctions and SQUIDs fabricated by focused helium-ion-beam irradiation
Christoph Schmid, Christopher Buckreus, David Haas et al. (+9 more)
By focused $30\,\mathrm{keV}$ He ion beam irradiation, epitaxially grown YBa$_2$Cu$_3$O$_7$ (YBCO) thin films can be driven from the superconducting to the insulating state with increasing irradiation dose. A properly chosen dose suppresses superconductivity down to $4\,\mathrm{K}$, while crystallinity is still preserved. With this approach we create areas of normal-conducting YBCO that can be used to define resistively shunted constriction-type Josephson junctions (cJJs) on the nanometer scale. We also demonstrate that the fabricated cJJs can be incorporated in direct current superconducting
quantum interference devices and can be used as detector junctions in THz
antennas.
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All authors Christoph Schmid, Christopher Buckreus, David Haas, Max Pröpper, Robin Hutt, César Magén, Dominik Hanisch, Max Karrer, Meinhard Schilling, Dieter Koelle, Reinhold Kleiner, Edward Goldobin
Quantum Physics
Flexible Genetic Algorithm for Quantum Support Vector Machines
Nguyen Minh Duc, Vu Tuan Hai, Le Bin Ho et al. (+1 more)
Quantum Support Vector Machines (QSVM) is one of the most promising frameworks in
quantum machine learning, yet their performance depends on the design of the feature map. Conventional approaches rely on fixed
quantum circuits, which often fail to generalize across
datasets. To address this limitation, we propose GA-QSVM, a hybrid framework that employs Genetic
Algorithms (GA) to automatically optimize feature maps. The proposed method introduces a configurable framework that flexibly defines the evolutionary parameters, enabling the construction of adaptive
circuits. Experimental evaluation of
datasets, including Digits, Fashion, Wine, and Breast Cancer, demonstrates that GA-QSVMs achieve a comparable accuracy compared to classical SVMs and standard QSVMs. Furthermore, transfer learning results indicate that GA-QSVM's
circuits generalize effectively across
datasets. These findings highlight the potential of evolutionary strategies to automate and enhance kernel design for future
quantum machine learning applications.
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All authors Nguyen Minh Duc, Vu Tuan Hai, Le Bin Ho, Tran Nguyen Lan
Quantum Physics
Feature Ranking in Credit-Risk with Qudit-Based Networks
Georgios Maragkopoulos, Lazaros Chavatzoglou, Aikaterini Mandilara et al. (+1 more)
In finance, predictive models must balance accuracy and interpretability, particularly in credit risk assessment, where model decisions carry material consequences. We present a
quantum neural network (QNN) based on a single qudit, in which both data features and trainable parameters are co-encoded within a unified
unitary evolution generated by the full Lie
algebra. This design explores the entire
Hilbert space while enabling interpretability through the magnitudes of the learned coefficients. We
benchmark our model on a real-world, imbalanced credit-risk
dataset from Taiwan. The proposed QNN consistently outperforms LR and reaches the results of random forest models in macro-F1 score while preserving a transparent correspondence between learned parameters and input feature importance. To quantify the interpretability of the proposed model, we introduce two complementary metrics: (i) the edit distance between the model's feature ranking and that of LR, and (ii) a feature-poisoning test where selected features are replaced with noise. Results indicate that the proposed
quantum model achieves competitive performance while offering a tractable path toward interpretable
quantum learning.
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All authors Georgios Maragkopoulos, Lazaros Chavatzoglou, Aikaterini Mandilara, Dimitris Syvridis