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Monday 3 November

Quantum Physics

GRAPE.jl: Gradient Ascent Pulse Engineering in Julia

Michael H. Goerz, Sebastián C. Carrasco, Alastair Marshall et al. (+1 more)

The GRAPE$.$jl package (https://github.com/JuliaQuantumControl/GRAPE.jl) implements Gradient Ascent Pulse Engineering, a widely used method of quantum optimal control. Its purpose is to find controls that steer a quantum system in a particular way. This is a prerequisite for next-generation quantum technology, such as quantum computing or quantum sensing. GRAPE$.$jl exploits the unique strengths of the Julia programming language to achieve both flexibility and numerical performance. It builds on the QuantumControl$.$jl framework.
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All authors Michael H. Goerz, Sebastián C. Carrasco, Alastair Marshall, Vladimir S. Malinovsky

Quantum Physics

Spatial Incompatibility Witnesses for Quantum Temporal Correlations

Xiangjing Liu, Harshit Verma, Yunlong Xiao et al. (+2 more)

We introduce a witness-based framework for certifying quantum temporal correlations via the pseudo-density matrix (PDM) formalism, which is a spatiotemporal generalization of the density matrix. We define spatial incompatibility (SI) as the minimum distance between a PDM and valid density matrices. For trace-norm distance, we show that this reduces to the PDM's negativity, enabling the construction of experimentally accessible SI witnesses. We derive a tight bound on SI for quantum channels and analyze the respective roles of state and channel coherence in witnessing SI. Our approach, unlike the LG framework, exploits measurements that generate coherence through state disturbance. We further show that channels satisfying the LG inequality for incoherent states can still exhibit detectable SI, demonstrating that measurement disturbance enhances the certification of temporal correlations.
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All authors Xiangjing Liu, Harshit Verma, Yunlong Xiao, Oscar Dahlsten, Mile Gu

Quantum Physics · Cross-listed from cond-mat.quant-gas

Enhanced performance of sudden-quench quantum Otto cycles via multi-parameter control

Raymon S. Watson and Karen V. Kheruntsyan

Advances in experimental control of interacting quantum many-body systems with multiple tunable parameters-such as ultracold atomic gases and trapped ions-are driving rapid progress in quantum thermodynamics and enabling the design of quantum thermal machines. In this work, we utilize a sudden quench approximation as a means to investigate the operation of a quantum thermodynamic Otto cycle in which multiple parameters are simultaneously controllable. The method applies universally to many-body systems where such control is available, and therefore provides general principles for investigating their operation as a working medium in quantum thermal machines. We investigate application of this multi-parameter quench protocol in an experimentally realistic one-dimensional Bose gas, as well as in the transverse-field Ising model. We find that such a multi-parameter Otto cycle, when operating as an engine, outperforms not only its constituent single-parameter Otto cycles in terms of the net work and efficiency, but also the combined net work of its constituent engine cycles when added together independently. We also find that a similar multi-parameter enhancement applies to the coefficient of performance when the Otto cycle operates as a refrigerator.
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Quantum Physics · Cross-listed from physics.chem-ph

Screening in the Heitler-London Model: Revisiting the Bonding and Antibonding States of the Hydrogen Molecule

Washington P. da Silva, Daniel Vieira, Jonas Maziero et al. (+1 more)

The present manuscript revisits one of the earliest approaches to treating molecular systems within the Schrödinger formalism of quantum mechanics: the Heitler-London (HL) model. Originally proposed in 1927 and based on a linear combination of atomic orbitals, the HL model provided a foundational description of covalent bonds and has served as the basis for numerous variational methods. Focusing on the hydrogen molecule, we begin by revisiting the analytical calculations of the original HL model, from which the qualitative physics of bonding and antibonding states can be obtained. Subsequently, we propose including electronic screening effects directly in the original HL wave function. We then compare our proposal with variational quantum Monte Carlo (VQMC) calculations, whose trial wave function allows us to optimize the electronic screening potential as a function of the inter-proton distance. We obtain the bond length, binding energy, and vibrational frequency of the H$_2$ molecule. Beyond revisiting this foundational approach in quantum mechanics, our proposal can serve as improved input for constructing new, but still analytically simple, variational wave functions to describe dissociation or bond formation.
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All authors Washington P. da Silva, Daniel Vieira, Jonas Maziero, Edgard P. M. Amorim

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

Multistate iterative qubit coupled cluster (MS-iQCC): a quantum-inspired, state-averaged approach to ground- and excited-state energies

Robert A. Lang, Shashank G. Mehendale, Ilya G. Ryabinkin et al. (+1 more)

We introduce the multistate iterative qubit coupled cluster (MS-iQCC) method, a quantum-inspired algorithm that runs efficiently on classical hardware and is designed to predict both ground and excited electronic states of molecules. Accurate excited-state energetics are essential for interpreting spectroscopy and chemical reactivity, but standard electronic structure methods are either too computationally expensive for larger systems or lose reliability in the presence of strong electron correlation. MS-iQCC addresses this challenge by simultaneously optimizing multiple electronic states in a single, state-averaged procedure that treats ground and excited states on equal footing. This removes the energetic bias that is introduced when excited states are computed one at a time and constrained to remain orthogonal to previously optimized states. The approach supports multireference electronic structure by allowing multideterminantal initial guesses and by adaptively building a compact exponential ansatz from a pool of qubit excitation generators. We apply MS-iQCC to H$_4$, H$_2$O, N$_2$, and C$_2$, including strongly correlated geometries, and observe robust convergence of all targeted state energies to chemically meaningful accuracy across their potential energy surfaces.
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All authors Robert A. Lang, Shashank G. Mehendale, Ilya G. Ryabinkin, Artur F. Izmaylov

Sunday 2 November

Quantum Physics · Cross-listed from cs.CL

Hybrid Quantum Transformer for Language Generation

Desheng Kong, Xiangshuo Cui, Jiaying Jin et al. (+2 more)

Although quantum computing has been increasingly applied to replace classical computation, most existing quantum or hybrid models remain confined to simple tasks, with no successful application to large-scale natural language generation to date. In this work, we present the first hybrid quantum-classical large language model (LLM) for natural language generation, HyQuT, capable of performing coherent and context-aware dialogue. The proposed architecture integrates variational quantum circuits (VQCs) into the Transformer framework at both 8M and 150M parameter scales. Experimental results show that a minimal number of qubits (10 qubits with 80 quantum gates) can replace about 10% of the classical parameters in the 150M-parameter model, while achieving comparable convergence stability and generation quality. This study provides an early demonstration of the feasibility of integrating quantum computing to large-scale generative language models.
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All authors Desheng Kong, Xiangshuo Cui, Jiaying Jin, Jing Xu, Donglin Wang

Quantum Physics

The electron double-slit experiment from an ISP perspective

David LeBlond

This paper presents a pedagogical model, and accompanying R code, of the electron double-slit experiment using the perspective of indivisible stochastic processes. The approach offers an alternative lens on quantum probability and coherence phenomena, emphasizing a statistical rather than purely wave-mechanical interpretation.
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Quantum Physics

EPR Revisited: Context-Indexed Elements of Reality and Operational Completeness

Mikołaj Sienicki and Krzysztof Sienicki

We reframe the EPR argument through an operational lens, replacing the notion of fixed "elements of reality" with context-indexed conditional states - what's often referred to as a measurement assemblage. This move deliberately sidesteps the assumption of context-independent values for incompatible observables. Our updated version of the Reality Criterion works like this: if Alice measures observable x and obtains outcome a, then Bob's system must adopt a conditional state that ensures the corresponding outcome for that specific context. Crucially, we also assume operational completeness - a condition that quantum mechanics satisfies when we're dealing with quantum-reachable assemblages. Now, in any theory where one party cannot signal to the other (so-called one-sided no-signaling theories), perfect predictions do support drawing context-indexed inferences. But - and this is key - they don't legitimize assigning fixed values across all contexts. We rigorously demonstrate this distinction. To ground the argument, we offer examples: the qubit singlet scenario using Pauli settings and CJWR thresholds, a continuous-variable case based on the Reid criteria, and a counterexample in the spirit of the PR box, which highlights the boundaries of what quantum theory can actually reach.
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Quantum Physics

Characterizing QUBO Reformulations of the Max-k-Cut Problem for Quantum Computing

Adrian Harkness, Hamidreza Validi, Ramin Fakhimi et al. (+4 more)

Quantum computing offers significant potential for solving NP-hard combinatorial (optimization) problems that are beyond the reach of classical computers. One way to tap into this potential is by reformulating combinatorial problems as a quadratic unconstrained binary optimization (QUBO) problem. The solution of the QUBO reformulation can then be addressed using adiabatic quantum computing devices or appropriate quantum computing algorithms on gate-based quantum computing devices. In general, QUBO reformulations of combinatorial problems can be readily obtained by properly penalizing the violation of the problem's constraints in the original problem's objective. However, characterizing tight (i.e., minimal but sufficient) penalty coefficients for this purpose is important and non-trivial for enabling the solution of the resulting QUBO in current and near-term quantum computing devices. Along these lines, we present closed-form characterizations of tight penalty coefficients for two distinct QUBO reformulations of the max $k$-cut problem whose values depend on the (weighted) degree of the vertices of the graph defining the problem. These findings contribute to the ongoing effort to make quantum computing a viable tool for solving combinatorial problems at scale. We support our theoretical results with illustrative examples and simple numerical results.
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All authors Adrian Harkness, Hamidreza Validi, Ramin Fakhimi, Illya V. Hicks, Samuel Stein, Tamás Terlaky, Luis F. Zuluaga

Quantum Physics

Attosecond quantum optical interferometry

Javier Rivera-Dean, Lidija Petrovic, Maciej Lewenstein et al. (+1 more)

In this work, we explore the scheme of attosecond quantum interferometry (AQI), the quantum optical version of classical attosecond interferometry, which allows to measure quantum optical properties on the attosecond time-scale. We develop how the scheme of AQI can be used for engineering the phase-space and photon statistics properties of the emitted harmonics, using the relative phase of a two-color driving field as a control, and further enables to manipulate the field correlations as well as their entanglement characteristics. In addition, this scheme allows us to learn properties of the phase-space distribution of the harmonic quantum state, by means of measuring an attosecond quantum tomography trace. This serves as a new type of protocol for in situ attosecond measurements of quantum optical observables. With this, we achieve to further connect all-optical attosecond measurement schemes with quantum optics, allowing for a rich manifold of observations.
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All authors Javier Rivera-Dean, Lidija Petrovic, Maciej Lewenstein, Philipp Stammer

2511.01097 · 2 Nov · Acknowledgments section have been updated in v3. Additional discussion and theoretical analysis have been added to the main text and Supplementary, respectively, with further analysis on the performance of the AQT technique. The text now consists of 21 pages (12 main text + 9 Supplementary Material), 12 figures (7 main text + 5 Supplementary Material). Comments are welcome

Abstract PDF $QNTM ×8$ENTG ×1$MNFD ×1$PHOT ×1 +1

Quantum Physics

Robust Quantum State Generation in Symmetric Spin Networks

Andre Luiz P. de Lima, Luke S. Baker, Anatoly Zlotnik et al. (+3 more)

In this work, we consider a parameterized Ising model with long-range symmetric pairwise interactions on a network of spin $\frac{1}{2}$ particles. The system is designed with symmetric dynamics, allowing for the reduction of the state space to a subspace defined by the set of Dicke states. We propose a method for designing robust electromagnetic amplitude pulses based on a moment quantization approach. The introduced parameter accounts for uncertainties in the electromagnetic field, resulting in a family of distinct Hamiltonians. By employing a discretized moment-based quantization technique, we design a control pulse capable of simultaneously steering an infinite collection of dynamical systems to compensate for parameter variations. This approach benefits from the duality between the infinite-dimensional parameterized system and its finite-dimensional trucnated moment dynamics. Simulation results demonstrate the efficacy of this method in achieving states of significant interest in quantum sensing, including the GHZ and W states.
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All authors Andre Luiz P. de Lima, Luke S. Baker, Anatoly Zlotnik, Andrew K. Harter, Michael J. Martin, Jr-Shin Li

Quantum Physics

In situ calibration of unitary operations during quantum error correction

Jonathan Kunjummen and Jacob M. Taylor

Quantum error correction uses the measurement of syndromes and classical decoding algorithms to estimate the location and type of errors while protecting the encoded quantum bits. Here we consider how prior information and Bayesian updates can play a critical role in improving the performance of QEC in the scenario of a particularly noisy qubit. This allows for leveraging even distance codes, which typically are less valued in QEC, to handle the noisy qubit, changing the power-law scaling of the logical error rate with the baseline physical error rate. A crucial component of this is updating the prior by real time feeding of decoder outputs into a approximate Kalman filter. Thus our approach provides a bootstrap to the actual error rates. We show this via simulation of the full closed-loop system: starting from uniform priors, the update procedure gradually learns site-specific error rates, enabling the decoder to outperform a fixed-prior baseline. In turn, we show that this enables in situ calibration of unitary operations via injection of gate set tomography operations with only moderate overhead in the more typical scenario of low noise qubits.
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Quantum Physics · Cross-listed from cs.NI

Quantum Network Tomography for General Topology with SPAM Errors

Xuchuang Wang, Matheus Guedes De Andrade, Guus Avis et al. (+3 more)

The goal of quantum network tomography (QNT) is the characterization of internal quantum channels in a quantum network from external peripheral operations. Prior research has primarily focused on star networks featuring bit-flip and depolarizing channels, leaving the broader problem – such as QNT for networks with arbitrary topologies and general Pauli channels – largely unexplored. Moreover, establishing channel identifiability remains a significant challenge even in simplified quantum star networks. In the first part of this paper, we introduce a novel network tomography method, termed Mergecast, in quantum networks. We demonstrate that Mergecast, together with a progressive etching procedure, enables the unique identification of all internal quantum channels in networks characterized by arbitrary topologies and Pauli channels. As a side contribution, we introduce a subclass of Pauli channels, termed bypassable Pauli channels, and propose a more efficient unicast-based tomography method, called BypassUnicast, for networks exclusively comprising these channels. In the second part, we extend our investigation to a more realistic QNT scenario that incorporates state preparation and measurement (SPAM) errors. We rigorously formulate SPAM errors in QNT, propose estimation protocols for such errors within QNT, and subsequently adapt our Mergecast approaches to handle networks affected by SPAM errors. Lastly, we conduct NetSquid-based simulations to corroborate the effectiveness of our proposed protocols in identifying internal quantum channels and estimating SPAM errors in quantum networks. In particular, we demonstrate that Mergecast maintains good performance under realistic conditions, such as photon loss and quantum memory decoherence.
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All authors Xuchuang Wang, Matheus Guedes De Andrade, Guus Avis, Yu-zhen Janice Chen, Mohammad Hajiesmaili, Don Towsley

Quantum Physics

ECCentric: An Empirical Analysis of Quantum Error Correction Codes

Aleksandra Świerkowska, Jannik Pflieger, Emmanouil Giortamis et al. (+1 more)

Quantum Error Correction (QEC) is essential for building scalable quantum computers, but a lack of systematic, end-to-end evaluation methods makes it difficult to assess how different QEC codes perform under realistic conditions. The vast diversity of codes, an expansive experimental search space, and the absence of a standardized framework prevent a thorough, holistic analysis. To address this, we introduce ECCentric, an end-to-end benchmarking framework designed to systematically evaluate QEC codes across the full quantum computing stack. ECCentric is designed to be modular, extensible, and general, allowing for a comprehensive analysis of QEC code families under varying hardware topologies, noise models, and compilation strategies. Using ECCentric, we conduct the first systematic benchmarking of major QEC code families against realistic, mid-term quantum device parameters. Our empirical analysis reveals that intra-QPU execution significantly outperforms distributed methods, that qubit connectivity is a far more critical factor for reducing logical errors than increasing code distance, and that compiler overhead remains a major source of error. Furthermore, our findings suggest that trapped-ion architectures with qubit shuttling are the most promising near-term platforms and that on noisy devices, a strategic and selective application of QEC is necessary to avoid introducing more errors than are corrected. This study provides crucial, actionable insights for both hardware designers and practitioners, guiding the development of fault-tolerant quantum systems.
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All authors Aleksandra Świerkowska, Jannik Pflieger, Emmanouil Giortamis, Pramod Bhatotia

Quantum Physics

Pseudo quantum advantages in perceptron storage capacity

Fabio Benatti, Masoud Gharahi, Giovanni Gramegna et al. (+2 more)

We investigate a generalized quantum perceptron architecture characterized by an oscillating activation function with a tunable frequency ranging from zero to infinity. Employing analytical techniques from statistical mechanics, we derive the optimal storage capacity and demonstrate that the classical result is recovered in the limit of vanishing frequency. As the frequency increases, however, the architecture exhibits enhanced quantum storage capabilities. Notably, this improvement stems solely from the specific form of the activation function and, in principle, could be emulated within a classical framework. Accordingly, we refer to this enhancement as a pseudo quantum advantage.
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All authors Fabio Benatti, Masoud Gharahi, Giovanni Gramegna, Stefano Mancini, Vincenzo Parisi

Quantum Physics

Enhancing Kerr-Cat Qubit Coherence with Controlled Dissipation

Francesco Adinolfi, Daniel Z. Haxell, Alessandro Bruno et al. (+4 more)

Quantum computing crucially relies on maintaining quantum coherence for the duration of a calculation. Bosonic quantum error correction protects this coherence by encoding qubits into superpositions of noise-resilient oscillator states. In the case of the Kerr-cat qubit (KCQ), these states derive their stability from being the quasi-degenerate ground states of an engineered Hamiltonian in a driven nonlinear oscillator. KCQs are experimentally compatible with on-chip architectures and high-fidelity operations, making them promising candidates for a scalable bosonic quantum processor. However, their bit-flip time must increase further to fully leverage these advantages. Here, we present direct evidence that the bit-flip time in a KCQ is limited by leakage out of the qubit manifold and experimentally mitigate this process. We coherently control the leakage population and measure it to be > 9%, twelve times higher than in the undriven system. We then cool this population back into the KCQ manifold with engineered dissipation, identify conditions under which this suppresses bit-flips, and demonstrate increased bit-flip times up to 3.6 milliseconds. By employing both Hamiltonian confinement and engineered dissipation, our experiment combines two paradigms for Schrödinger-cat qubit stabilization. Our results elucidate the interplay between these stabilization processes and indicate a path towards fully realizing the potential of these qubits for quantum error correction.
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All authors Francesco Adinolfi, Daniel Z. Haxell, Alessandro Bruno, Laurent Michaud, Venus Hasanuzzaman Kamrul, Preeti Pandey, Alexander Grimm

Quantum Physics

The adiabatic theorem for non-Hermitian quantum systems with real eigenvalues and the complex geometric phase

Minyi Huang and Ray-Kuang Lee

The adiabatic theorem is one of the most interesting and significant theorems in quantum mechanics. However, the adiabatic theorem can fail for general non-Hermitian quantum systems. In this paper, by utilizing the complex geometric phase, the functional calculus for biorthogonal systems and the Grönwall inequality, we prove rigorously that the adiabatic theorem is still valid for diagonalizable non-Hermitian systems with real eigenvalues. The proof also justifies the definition of a complex Berry phase for non-Hermitian systems, in both Abelian and non-Abelian cases.
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Quantum Physics · Cross-listed from cond-mat.str-el

Exploring the limit of the Lattice-Bisognano-Wichmann form describing the Entanglement Hamiltonian: A quantum Monte Carlo study

Siyi Yang, Yi-Ming Ding and Zheng Yan

As a powerful theoretical construct, the entanglement Hamiltonian (EH) encapsulates the essential entanglement properties of a quantum many-body system. From the EH, one can extract a variety of entanglement quantities, such as entanglement entropies, negativity, and the entanglement spectrum. However, its general analytical form remains largely unknown. While the Bisognano-Wichmann theorem gives an exact EH form for Lorentz-invariant field theories, its validity on lattice systems is limited, especially when Lorentz invariance is absent. In this work, we propose a general scheme based on the lattice-Bisognano-Wichmann (LBW) ansatz and multi-replica-trick quantum Monte Carlo methods to numerically reconstruct the entanglement Hamiltonian in two-dimensional systems and systematically explore its applicability to systems without translational invariance, going beyond the original scope of the primordial Bisognano-Wichmann theorem. Various quantum phases–including gapped and gapless phases, critical points, and phases with either discrete or continuous symmetry breaking–are investigated, demonstrating the versatility of our method in reconstructing entanglement Hamiltonians. Furthermore, we find that when the entanglement boundary of a system is ordinary (i.e., free from surface anomalies), the LBW ansatz provides an accurate approximation well beyond Lorentz-invariant cases. Our work thus establishes a general framework for investigating the analytical structure of entanglement in the complex quantum many-body systems.
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Quantum Physics

On entropy production of repeated quantum measurements III. Quantum detailed balance

Tristan Benoist, Noé Cuneo, Vojkan Jakšić et al. (+1 more)

In light of the dynamical-systems approach to entropy production in repeated quantum measurements, proposed and illustrated in Commun. Math. Phys. 357, 77-123 (2018) [arXiv:1607.00162] and J. Stat. Phys. 182, 44 (2021) [arXiv:2012.03885], we characterize the KMS quantum detailed balance condition for quantum channels via time-reversal invariance and the vanishing of the entropy production for the associated informationally complete quantum instruments.
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All authors Tristan Benoist, Noé Cuneo, Vojkan Jakšić, Claude-Alain Pillet

Quantum Physics · Cross-listed from hep-th

Symmetry-resolved genuine multi-entropy: Haar random and graph states

Norihiro Iizuka and Simon Lin

We study the symmetry-resolved genuine multi-entropy, a measure that captures genuine multi-partite entanglement, in Haar random states and random graph states in the presence of a conserved quantity. For Haar random states, we derive explicit formulae for the genuine multi-entropy under a global $U(1)$ symmetry in the thermodynamic limit, and find that its dependence on subsystem sizes closely resembles that of fully Haar random states without a conserved charge. We also perform numerical analyses, focusing on spin systems for both Haar random and graph states. For random graph states, our numerical analyses reveal distinctive features of their multi-partite entanglement structure and we contrast them with the Haar random case.
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Quantum Physics · Cross-listed from physics.optics

Hyperentanglement in Nanophotonic Systems with Discrete Rotational Symmetry

Lior Fridman, Amit Kam, Amir Sivan et al. (+3 more)

We propose a scheme to generate hyperentanglement between photons carrying angular momentum in nanophotonic systems with discrete rotational symmetry. Coupling free-space photons into surface plasmon polaritons by a polygonal-shaped grating restricts the basis of the generated near-field modes to a finite set, thus creating a new mechanism for spatial mode entanglement. By encoding the incoming photons with spin and orbital angular momenta, we find that the system preserves the high-dimensional Hilbert space, in contrast to rotationally symmetric nanophotonic platforms, where the inseparability of spin and orbital degrees of freedom results in loss of information. We further show that by properly engineering the phase of the photons to conform to the polygonal boundary conditions, we achieve a new scheme for generating hyperentangled states, utilizing both the vector-field nature of the nanophotonic modes and the finite basis of states in polygonal boundary conditions. Our approach paves the way for on-chip quantum communication by expanding the Hilbert space used in computation.
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All authors Lior Fridman, Amit Kam, Amir Sivan, Guy Sayer, Stav Lotan, Guy Bartal

Quantum Physics

Optimizing magnetic coupling in lumped element superconducting resonators for molecular spin qubits

Marcos Rubín-Osanz, David Rodriguez, Ignacio Gimeno et al. (+18 more)

We engineer lumped-element superconducting resonators that maximize magnetic coupling to molecular spin qubits, achieving record single-spin couplings up to $100$ kHz and collective couplings exceeding $10$ MHz. The resonators interact with PTMr organic free radicals, model spin systems with $S=1/2$ and a quasi-isotropic $g \simeq 2$, dispersed in polymer matrices. The highest collective spin-photon coupling strengths are attained with resonators having large inductors, which therefore interact with most spins in the molecular ensemble. By contrast, the coupling of each individual spin $G_{1}$ is maximized in resonators having a minimum size inductor, made of a single wire. The same platform has been used to study spin relaxation and spin coherent dynamics in the dispersive regime, when spins are energetically detuned from the resonator. We find evidences for the Purcell effect, i.e. the photon induced relaxation of those spins that are most strongly coupled to the circuit. The rate of this process gives access to the distribution of single spin photon couplings in a given device. For resonators with a $50$ nm wide constriction at the inductor center, single maximum $G_{1}$ values reach $\sim 100$ kHz. Pumping the spins with strong pulses fed through an independent transmission line induces coherent Rabi oscillations. The spin excitation then proceeds via either direct resonant processes induced by the main pulse frequency or, in the case of square-shaped pulses, via the excitation of the cavity by sideband frequency components. The latter process measures the cavity mode hybridization with the spins and can be eliminated by using Gaussian shaped pulses. These results establish a scalable route toward integrated molecular-spin quantum processors.
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All authors Marcos Rubín-Osanz, David Rodriguez, Ignacio Gimeno, Wenzel Kersten, Nerea González-Prato, María C. Pallarés, Sebastián Roca-Jerat, Marina C. de Ory, Marta Mas-Torrent, J. Alejandro de Sousa, Lorenzo Tesi, Daniel Granados, Jaume Veciana, David Zueco, Anabel Lostao, Jörg Schmiedmayer, Imma Ratera, Joris van Slageren, Núria Crivillers, Alicia Gomez, Fernando Luis

Quantum Physics

No, classical gravity does not entangle quantized matter fields

Lajos Diósi

In their recent work, Nature, 646, 813 (2025), Aziz and Howl claim that classical (unquantized) gravity can generate entanglement of quantized matter if matter is treated within quantum field theory which is, no doubt, our ultimate theory to use. We show that the perturbative result of Aziz and Howl in interaction picture is inconsistent with our exact and simple non-perturbative derivation in Heisenberg picture, that fundamentally precludes the claimed entanglement.
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Quantum Physics

Kostant relation in filtered randomized benchmarking for passive bosonic devices

David Amaro-Alcalá

We aim to reduce the cost of the current bosonic randomized benchmarking proposal. To do this, we introduce two filter functions: one uses immanants, the other uses characters of the special unitary group. These filters avoid computing Clebsch-Gordan coefficients and yield simple variance expressions. The character filter is not only efficient to compute, but also has a constant, low variance. Our filters rely on the same data as the original proposal. We also discuss an example with photon loss and gain. Our numerical evidence shows that a scheme using weak coherent states and intensity measurements can yield estimates close to those obtained without loss or gain. Our work could support simpler platform characterization and streamline data analysis.
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Quantum Physics · Cross-listed from cond-mat.mes-hall

Exchange operation of Majorana zero modes in topological insulator-based Josephson trijunctions

Yunxiao Zhang, Zhaozheng Lyu, Xiang Wang et al. (+19 more)

Majorana zero modes are anyons obeying non-Abelian exchange statistics distinct from fermions or bosons. While significant progresses have been achieved in the past two decades in searching for these exotic excitations in solid-state systems, their non-Abelian nature remains unverified, as definitive proof requires braiding operations. Here, we report preliminarily experimental advances in creating, manipulating, and exchanging the presumed Majorana zero modes in an envelope-shaped Josephson device composed of multiple trijunctions on a topological insulator surface. We observed the signatures of in-gap states migration consistent with the expectations of the Fu-Kane model, supporting the realization of an exchange operation. This work would establish a critical pathway toward ultimately braiding Majorana zero modes in the Fu-Kane scheme of topological quantum computation.
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All authors Yunxiao Zhang, Zhaozheng Lyu, Xiang Wang, Yukun Shi, Duolin Wang, Xiaozhou Yang, Enna Zhuo, Bing Li, Yuyang Huang, Zenan Shi, Anqi Wang, Heng Zhang, Fucong Fei, Xiaohui Song, Peiling Li, Bingbing Tong, Ziwei Dou, Jie Shen, Guangtong Liu, Fanming Qu, Fengqi Song, Li Lu

Quantum Physics · Cross-listed from cond-mat.dis-nn

Correspondence Between Ising Machines and Neural Networks

Andrew G. Moore

Computation with the Ising model is central to future computing technologies like quantum annealing, adiabatic quantum computing, and thermodynamic classical computing. Traditionally, computed values have been equated with ground states. This paper generalizes computation with ground states to computation with spin averages, allowing computations to take place at high temperatures. It then introduces a systematic correspondence between Ising devices and neural networks and a simple method to run trained feed-forward neural networks on Ising-type hardware. Finally, a mathematical proof is offered that these implementations are always successful.
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Saturday 1 November

Quantum Physics · Cross-listed from cs.LG

Superpositional Gradient Descent: Harnessing Quantum Principles for Model Training

Ahmet Erdem Pamuk, Emir Kaan Özdemir and Şuayp Talha Kocabay

Large language models (LLMs) are increasingly trained with classical optimization techniques like AdamW to improve convergence and generalization. However, the mechanisms by which quantum-inspired methods enhance classical training remain underexplored. We introduce Superpositional Gradient Descent (SGD), a novel optimizer linking gradient updates with quantum superposition by injecting quantum circuit perturbations. We present a mathematical framework and implement hybrid quantum-classical circuits in PyTorch and Qiskit. On synthetic sequence classification and large-scale LLM fine-tuning, SGD converges faster and yields lower final loss than AdamW. Despite promising results, scalability and hardware constraints limit adoption. Overall, this work provides new insights into the intersection of quantum computing and deep learning, suggesting practical pathways for leveraging quantum principles to control and enhance model behavior.
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2511.01918 · 1 Nov · Accepted at 2025 IEEE International Conference on Quantum Artificial Intelligence (IEEE QAI 2025). This is the accepted version of the paper. The final published version will appear in the IEEE proceedings. o̧pyright} 2025 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses

Abstract PDF $QNTM ×7$CRCT ×2$LANG ×1

Quantum Physics

Diffusion Minimization via Optimal Smearing in Collapse and Hybrid Classical-Quantum Gravitational Models

Nicolò Piccione

Spontaneous diffusion (i.e., non-conservation of energy) is a prominent, testable prediction of collapse and hybrid classical-quantum gravitational models. Without smearing of the mass density operator, the associated heating (or energy increase) rate diverges, yet the smearing distribution is arbitrary and, on scales much larger than the smearing length $r_C$, much of the phenomenology is expected to be insensitive to this choice. We propose to resolve this arbitrariness as follows: for a fixed $r_C$, select the distribution that minimizes the heating rate. Conceptually, this should identify the minimal deviation from standard quantum mechanics and provide models that, once experimentally refuted, would strongly disfavor all variants with different distributions. We apply this approach to the most investigated collapse models: GRW (for Ghirardi-Rimini-Weber), CSL (for Continuous Spontaneous Localization), and DP (for Diósi-Penrose). Notably, the Gaussian is optimal only for the GRW case. Finally, we apply it to the Tilloy-Diósi hybrid classical-quantum model of Newtonian gravity, leading to the minimally deviating variant of it. This version of the model is entirely determined by only one free parameter $r_C$ and, if experimentally refuted, would strongly disfavor any other version of it.
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Quantum Physics · Cross-listed from eess.SY

Towards Quantum Algorithms for the Optimization of Spanning Trees: The Power Distribution Grids Use Case

Carsten Hartmann, Nil Rodellas-Gràcia, Christian Wallisch et al. (+5 more)

Optimizing the topology of networks is an important challenge across engineering disciplines. In energy systems, network reconfiguration can substantially reduce losses and costs and thus support the energy transition. Unfortunately, many related optimization problems are NP hard, restricting practical applications. In this article, we address the problem of minimizing losses in radial networks, a problem that routinely arises in distribution grid operation. We show that even the computation of approximate solutions is computationally hard and propose quantum optimization as a promising alternative. We derive two quantum algorithmic primitives based on the Quantum Alternating Operator Ansatz (QAOA) that differ in the sampling of network topologies: a tailored sampling of radial topologies and simple sampling with penalty terms to suppress non-radial topologies. We show how to apply these algorithmic primitives to distribution grid reconfiguration and quantify the necessary quantum resources.
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All authors Carsten Hartmann, Nil Rodellas-Gràcia, Christian Wallisch, Thiemo Pesch, Frank K. Wilhelm, Dirk Witthaut, Tobias Stollenwerk, Andrea Benigni

Quantum Physics

Quantum dynamics in lattices in presence of bulk dephasing and a localized source

Tamoghna Ray, Katha Ganguly, Dario Poletti et al. (+2 more)

The aim of this work is to study the dynamics of quantum systems subjected to a localized fermionic source in the presence of bulk dephasing. We consider two classes of one-dimensional lattice systems: (i) a non-interacting lattice with nearest-neighbor and beyond, i.e., long-ranged (power-law) hopping, and (ii) a lattice that is interacting via short-range interactions modeled by a fermionic quartic Hamiltonian. We study the evolution of the local density profile $n_i(t)$ within the system and the growth of the total particle number $N(t)$ in it. For case (i), we provide analytical insights into the dynamics of the nearest-neighbor model using an adiabatic approximation, which relies on assuming faster relaxation of coherences of the single particle density matrix. For case (ii), we perform numerical computations using the time-evolving block decimation (TEBD) algorithm and analyze the density profile and the growth exponent in $N(t)$. Our detailed study reveals an interesting interplay between Hamiltonian dynamics and various environmentally induced mechanisms in open quantum systems, such as local source and bulk dephasing. It brings out rich dynamics, including universal dynamical scaling and anomalous behavior across various time scales and is of relevance to various quantum simulation platforms.
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All authors Tamoghna Ray, Katha Ganguly, Dario Poletti, Manas Kulkarni, Bijay Kumar Agarwalla