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Wednesday 6 May

Quantum Physics

Automated Circuit Depth Reduction of Quantum Subroutines via Compilation

Folkert de Ronde, Stephan Wong and Sebastian Feld

Optimizing quantum circuits by reducing circuit depth is essential for improving the efficiency and scalability of quantum algorithms, particularly as quantum hardware continues to evolve. This can be achieved by restructuring quantum algorithms to allow more parallelism. A compiler is needed to automatically detect and apply these optimizations. In this work, we focus on the optimization of two fundamental quantum subroutines: GHZ state creation and CNOT/CZ chain decomposition. Traditional implementations of these subroutines suffer from linearly increasing circuit depth, which limits scalability. We propose a compiler-driven approach that automatically detects and optimizes these two fundamental quantum subroutines. Our approach reduces circuit depth through constant-depth GHZ state creation, constant depth CZ chain decomposition, and logarithmic depth recursive CNOT chain decomposition, which enhance parallel execution. Performance analysis of benchmarked algorithms shows significant reductions in depth. However, our solution also results in an increased gate count, which makes our optimization a trade-off. The gate count for the CNOT chains is doubled, where logarithmic depth reduction is achieved. The reduced circuit depth results in more efficient algorithms by reducing execution time.
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Quantum Physics

Harnessing a 256-qubit Neutral Atom Simulator for Graph Classification

Edoardo Giusto, Gabriele Iurlaro, Bartolomeo Montrucchio et al. (+5 more)

Neutral atom platforms are analogue quantum simulators that offer the possibility to map graphs onto a 2D qubit register using programmable Rubidium atoms arrays, whose valence electrons' energy state is used as qubits, using optical tweezers. This makes it possible to implement algorithms for solving graph combinatorial optimization and Quantum Machine Learning (QML) tasks, such as graph classification. However, the restrictions of real hardware, as well as the very low number of publicly available machines, make such implementation non-trivial. In this work, we manage to compute the Quantum Evolution Kernel (QEK) to extract the features from graphs of the PROTEINS dataset using the 256-qubits Aquila platform (available through AWS) and then we apply classical Machine Learning (ML) techniques for the final classification. The method is benchmarked against classical kernels, resulting in slightly better performance, proving the effectiveness of the method, even in the case of a noisy quantum simulator.
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All authors Edoardo Giusto, Gabriele Iurlaro, Bartolomeo Montrucchio, Alberto Scionti, Olivier Terzo, Chiara Vercellino, Giacomo Vitali, Paolo Viviani

Quantum Physics

Neural-powered unit disk graph embedding: qubits connectivity for some QUBO problems

Chiara Vercellino, Paolo Viviani, Giacomo Vitali et al. (+5 more)

Graph embedding is a recurrent problem in quantum computing, for instance, quantum annealers need to solve a minor graph embedding in order to map a given Quadratic Unconstrained Binary Optimization (QUBO) problem onto their internal connectivity pattern. This work presents a novel approach to constrained unit disk graph embedding, which is encountered when trying to solve combinatorial optimization problems in QUBO form, using quantum hardware based on neutral Rydberg atoms. The qubits, physically represented by the atoms, are excited to the Rydberg state through laser pulses. Whenever qubits pairs are closer together than the blockade radius, entanglement can be reached, thus preventing entangled qubits to be simultaneously in the excited state. Hence, the blockade radius determines the adjacency pattern among qubits, corresponding to a unit disk configuration. Although it is straightforward to compute the adjacency pattern given the qubit coordinates, identifying a feasible unit disk arrangement that matches the desired QUBO matrix is, on the other hand, a much harder task. In the context of quantum optimization, this issue translates into the physical placement of the qubits in the 2D/3D register to match the machine's Ising-like Hamiltonian with the QUBO formulation of the optimization problems. The proposed solution exploits the power of neural networks to transform an initial embedding configuration, which does not match the quantum hardware requirements or does not account for the unit disk property, into a feasible embedding properly representing the target optimization problems. Experimental results show that this new approach overcomes in performance Gurobi solver.
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All authors Chiara Vercellino, Paolo Viviani, Giacomo Vitali, Alberto Scionti, Andrea Scarabosio, Olivier Terzo, Edoardo Giusto, Bartolomeo Montrucchio

Quantum Physics

Finite steps optimise dissipation in stochastically controlled quantum systems

Theodore McKeever, Harry J. D. Miller and Ahsan Nazir

Motivated by the need for precise, energy-efficient, and experimentally realistic quantum control protocols, we investigate the thermodynamic cost of performing quantum step-equilibration processes under the influence of classical stochastic control fields. Whereas purely deterministic protocols exhibit dissipation that scales inversely with the number of steps, we show that weak Gaussian noise in the control variables induces dissipative contributions that grow linearly with the number of steps. Consequently, we derive the finite optimal number of steps and minimal achievable average dissipated work and its variance using the quantum thermodynamic length. These results are demonstrated using two paradigmatic examples: a Landau-Zener sweep of a qubit strongly coupled to a thermal bath and the erasure of a transverse-field Ising model.
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Quantum Physics

Distributed Quantum Error Correction with Bivariate Bicycle Codes in a Modular Architecture

Nitish Kumar Chandra, Eneet Kaur, Reza Nejabati et al. (+1 more)

Quantum low density parity check (qLDPC) codes, particularly bivariate bicycle (BB) codes, achieve competitive fault tolerance thresholds while offering substantially higher encoding rates than planar surface codes. However, their intrinsically long-range stabilizer structure makes them difficult to implement on monolithic devices with nearest neighbor connectivity and limited qubit capacity. In this work, we study the realization of a BB code in a modular multiprocessor architecture, where quantum processors are interconnected through shared Bell pairs. We consider processors with all to all internal connectivity, which is feasible on trapped ion and neutral atom platforms, enabling flexible local gate execution while inter-processor (nonlocal) gates are mediated by shared entanglement. We describe a star network architecture that can realize this distributed setting. We partition the qubits of the [[144,12,12]] BB code across 4, 6, and 12 quantum processors and analyze the resulting logical error rates and pseudo-threshold performance under circuit level noise by varying the number of processors and a scaling factor that captures the additional noise associated with nonlocal operations. We use Monte Carlo simulations with BP+OSD decoding and extend the previously known BB code ansatz to the distributed setting. Our results provide architectural insight and design considerations for distributed BB codes in modular quantum computing architectures.
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All authors Nitish Kumar Chandra, Eneet Kaur, Reza Nejabati, Kaushik P. Seshadreesan

Quantum Physics

Efficient Multi-Controlled Gate Implementation in Trapped-Ion Systems

Minhyeok Kang, Taejin Kim, Jungsoo Hong et al. (+1 more)

Multi-controlled gates are essential primitives in quantum algorithms, yet implementing them via standard gate-level decompositions remains resource-intensive. We develop efficient pulse-level implementations of multi-controlled gates in trapped-ion systems using the Cirac-Zoller scheme. We first show that the Cirac-Zoller construction admits a freedom in the sign choice of red-sideband (RSB) pulses, which leaves the logical operation invariant up to a local Pauli-$Z$ correction. By exploiting this freedom, we construct equivalent realizations of multi-controlled gates and develop pulse cancellation for more efficient implementations of successive gates. We perform numerical simulations and show that pulse cancellation reduces the gate time and improves the state fidelity. Furthermore, we propose ancilla-free circuits for general $N$-controlled gates that use a single-controlled gate primitive and $\mathcal{O}(N)$ RSB pulses. As a key application, we apply our pulse cancellation to the linear combination of unitaries (LCU) method for block encoding. We show that the RSB-pulse cost of the select operator over $L$ unitaries can be reduced from $\mathcal{O}(L\log L)$ to $\mathcal{O}(L)$, which improves the efficiency and scalability of LCU-based quantum circuits.
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All authors Minhyeok Kang, Taejin Kim, Jungsoo Hong, Joonsuk Huh

Quantum Physics

Unconditional Authentication in Quantum Key Distribution via Hybrid Entangled Physical Unclonable Functions

Nicolas Laurent-Puig, Mina Doosti, Adriano Innocenzi et al. (+1 more)

Quantum Key Distribution (QKD) enables Information-Theoretically Secure (ITS) key exchange, robust even against future quantum computing threats. However, a fundamental limitation of QKD is the requirement for an authenticated classical channel, which necessitates a pre-shared secret key. In this work, we address this challenge by adopting a Hybrid Entangled Physical Unclonable Function (PUF) protocol for authentication. We demonstrate that this PUF-based method generates an ITS initial key under minimal explicit hardware assumptions. This approach allows us to experimentally perform a fully ITS-authenticated entanglement-based QKD protocol that relies solely on such assumptions, effectively eliminating the need for pre-shared secrets. This represents a significant step towards the practical realization of quantum network protocols using lightweight, readily available hardware assumptions, without weakening security guarantees.
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All authors Nicolas Laurent-Puig, Mina Doosti, Adriano Innocenzi, Eleni Diamanti

Quantum Physics

Neural network modeling of many-body super- and sub-radiant dynamics

Gianluca Lagnese, Laurin Brunner, Lorenzo Rossi et al. (+3 more)

There is significant interest in exploring novel phenomena in quantum light-matter interfaces, which are driven by the combination of structured dissipation and long-range interactions that are typical in such systems. To this end, it is important to develop new general numerical simulation techniques, which can access large system sizes and are not based on semi-classical approaches. Here, we report the first application of neural quantum states to obtain the dissipative dynamics of light-matter-coupled systems beyond what is accessible with exact and tensor-network calculations. We specifically apply this method to simulate the many-body emission dynamics of approximately 40 atoms, arranged in dense arrays in one and two dimensions. These systems have been chosen because they can support prominent subradiant dynamics at late times and could be realized with cold atomic quantum simulators.
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All authors Gianluca Lagnese, Laurin Brunner, Lorenzo Rossi, Darrick Chang, Markus Schmitt, Zala Lenarčič

Quantum Physics

Intelligent Optimal Control of Rydberg Gates with Incremental-Update Deep Reinforcement Learning

Yue Cai, Hanlin Zhang, Keye Zhang et al. (+1 more)

Deep reinforcement learning (DRL), acting as a novel and powerful paradigm for quantum optimal control, offers transformative opportunities for advancing neutral-atom quantum computing. In this work, we theoretically demonstrate a DRL-based framework for realizing Rydberg controlled-NOT gates that achieve both high speed and high fidelity through the synchronous modulation of multiple pulse parameters without any prior heuristic ansatz. By introducing an incremental-update learning policy, our framework effectively regularizes the exploration of the control landscape, ensuring the generation of smooth, experimentally feasible pulse profiles while significantly reducing computational overhead compared to conventional schemes. Crucially, the framework autonomously discovers an early-cutoff policy by optimally reconciling operation speed with high-precision coherent control. Our optimized protocol achieves a peak average fidelity of 0.9991, significantly outperforming conventional methods and surpassing the critical fault-tolerant threshold. This work establishes a generalizable, AI-driven pathway for designing high-performance quantum gates and provides a robust paradigm for autonomous control field optimization across diverse qubit platforms.
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All authors Yue Cai, Hanlin Zhang, Keye Zhang, Jing Qian

Quantum Physics

Generative Quantum-inspired Kolmogorov-Arnold Eigensolver

Yu-Cheng Lin, Yu-Chao Hsu, I-Shan Tsai et al. (+9 more)

High-performance computing (HPC) is increasingly important for scalable quantum chemistry workflows that couple classical generative models, quantum circuit simulation, and selected configuration interaction postprocessing. We present the generative quantum-inspired Kolmogorov-Arnold eigensolver (GQKAE), a parameter-efficient extension of the generative quantum eigensolver (GQE) for quantum chemistry. GQKAE replaces the parameter-heavy feed-forward network components in GPT-style generative eigensolvers with hybrid quantum-inspired Kolmogorov-Arnold network modules, forming a compact HQKANsformer backbone. The method preserves autoregressive operator selection and the quantum-selected configuration interaction evaluation pipeline, while using single-qubit DatA Re-Uploading ActivatioN modules to provide expressive nonlinear mappings. Numerical benchmarks on H4, N2, LiH, C2H6, H2O, and the H2O dimer show that GQKAE achieves chemical accuracy comparable to the GPT-based GQE architecture, while reducing trainable parameters and memory by approximately 66% and improving wall-time performance. For strongly correlated systems such as N2 and LiH, GQKAE also improves convergence behavior and final energy errors. These results indicate that quantum-inspired Kolmogorov-Arnold networks can reduce classical-side overhead while preserving circuit-generation quality, offering a scalable route for HPC-quantum co-design on near-term quantum platforms.
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All authors Yu-Cheng Lin, Yu-Chao Hsu, I-Shan Tsai, Chun-Hua Lin, Kuo-Chung Peng, Jiun-Cheng Jiang, Yun-Yuan Wang, Tzung-Chi Huang, Tai-Yue Li, Kuan-Cheng Chen, Samuel Yen-Chi Chen, Nan-Yow Chen

Quantum Physics

Two-site Bose-Hubbard hopping and Schrödinger cat states

Madeline Berezowski, Artur Sowa and Jonas Fransson

The Bose-Hubbard Hamiltonian can be simplified to have only two lattice sites, in which case the system being described is referred to as a dimer. Due to its structure, the hopping term of the dimer Hamiltonian enjoys invariance in a family of subspaces indexed by a whole number $k$, each subspace corresponding to a system of only $k$ particles. We have invented an inductive argument using the bosonic canonical commutation relations to find the eigenvalues and eigenvectors of the dimer hopping Hamiltonian in its $k$-particle subspaces. In particular, this Hamiltonian, when restricted to one of the $k$-particle subspaces, is exactly the spin projection operator along the $x$-axis, where the number of particles $k$ in the dimer system yields the projection matrix for spin quantum number $s=k/2$. Thus, a new method for computing the eigenvalues and eigenvectors of the $x$-axis spin projector has been unearthed. We use the explicit construction to study the dynamics of coherent states induced by the square of the dimer hopping hamiltonian. We find that it generates Schrödinger cat states in the two-site setting.
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Quantum Physics

Single-photon scattering by a giant molecule asymmetrically coupled to parallel waveguides

Ze-Quan Zhang, Guang-Zheng Ye, Wei-Xin Chen et al. (+2 more)

We investigate single-photon scattering in a waveguide-QED setup, where a giant molecule composed of two frequency-detuned giant atoms is coupled to two parallel waveguides via multiple connection points. The competition between coherent atom–atom coupling and the effective decay rates dictates the splitting of a single resonance into a doublet in the transmission (reflection) spectra. By tailoring the asymmetry of the decay rates and the atomic detuning, one can engineer photon-path interference to optimize the transfer between waveguides; under chiral coupling conditions, this interference can be further harnessed to realize fully deterministic routing. In the non-Markovian regime, retardation effects can reshape the spectra and actively drive transitions between the weak- and strong-coupling regimes, converting an unsplit Markovian resonance into a clearly separated doublet, or conversely merging a split doublet back into a single resonance. For sufficiently long time delays, it further generates multiple resonances and avoided crossings, enriching the spectral response. Our results demonstrate how atomic detuning, decay-rate asymmetry, and non-Markovian retardation cooperate to provide versatile, interference-based control over single-photon routing in multi-port quantum networks.
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All authors Ze-Quan Zhang, Guang-Zheng Ye, Wei-Xin Chen, Yong Li, Huaizhi Wu

Quantum Physics

Fundamental Limitations of Post-Quantum Cryptographic Architectures

Jiho Jung, Donghwa Ji, Mingyu Lee et al. (+1 more)

Modern lattice-based cryptography, particularly the learning with errors paradigm, relies on injecting artificial noise to secure data against quantum adversaries. This study systematically examines the theoretical and physical boundaries of this noise-reliant model across four interconnected domains: computational complexity, information-theoretic thermodynamics, quantum error correction, and quantum learning theory. Starting from the algorithmic foundation, our analysis notes that these frameworks rely on provisional complexity-theoretic assumptions that remain vulnerable to future quantum algorithmic advancements. Furthermore, by translating this cryptographic mechanism into physical thermodynamics, we illustrate that intentionally injected discrete Gaussian noise does not equate to the permanent erasure of information. Because the structural integrity of the cryptographic secret remains preserved within the ciphertext, advanced quantum error correction protocols and quantum learning models can efficiently extract the underlying mathematical kernel. Ultimately, we suggest that while lattice-based cryptography provides a robust transitional alternative, definitively classifying these frameworks as unconditionally post-quantum represents a premature classification relying on transient physical bottlenecks rather than impenetrable theoretical boundaries.
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All authors Jiho Jung, Donghwa Ji, Mingyu Lee, Kabgyun Jeong

Quantum Physics

Causal-Order Identification of Memoryless Sequential Quantum Processes from Restricted Projective Data

Masahito Hayashi

Identifying causal order from restricted projective data is generally nontrivial. When two quantum players interact only through an unobserved environment, the available local measurement statistics are typically not tomographically complete, so the underlying process cannot in general be reconstructed exactly from the observed distribution. As a result, causal direction can be statistically identifiable in some cases but fundamentally indistinguishable in others. In this work, we determine necessary and sufficient conditions for deciding when an observed distribution is compatible with a memoryless sequential quantum process in a fixed direction. We show that directional conditional-independence structure and the positivity criterion based on the pseudo-density matrix, as developed in recent work by We show that directional conditional-independence structure and PDM-based positivity criteria are not sufficient by themselves. We then specialize to the two-qubit Pauli setting, where the problem remains non-tomographic but becomes explicitly tractable. In this regime, we characterize when the two sequential directions are statistically indistinguishable, and we show by example that positivity alone does not exclude more general memoryful strategies, whereas the additional algebraic consistency requirement does.
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Quantum Physics

Measurement-Device-Independent Entanglement Quantification in a Fully Connected Time-Bin Quantum Network

Lu Liu, Ling-Xuan Kong, Ze-Yang Lu et al. (+3 more)

Fully connected quantum networks enable scalable quantum communication, yet reliable entanglement characterization without trusting measurement devices remains challenging. Here we experimentally demonstrate measurement-device-independent (MDI) entanglement verification and quantification in a time-bin-encoded fully connected quantum network. Using a broadband periodically poled lithium niobate on insulator source combined with dense wavelength-division multiplexing, we distribute all six pairwise entangled links among four users over 20-km fiber channels, preserving high-fidelity entanglement without active stabilization of the long-distance fiber links. We show that conventional entanglement witnesses can fail under untrusted measurement conditions. By encoding trusted input states in the polarization degree of freedom of the same photons, we realize MDI measurements without ancillary photons or additional experimental resources. Both entanglement verification and quantification are obtained from the same measurement dataset. Our results establish a practical and scalable approach for reliable entanglement characterization in quantum networks.
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All authors Lu Liu, Ling-Xuan Kong, Ze-Yang Lu, Xu-Jie Peng, Xiao-Xu Fang, He Lu

Quantum Physics

Hierarchical entanglement transitions and hidden area-law sectors in quantum many-body dynamics

Tarun Grover

Chaotic many-body dynamics typically generates volume-law entanglement from initially low-entangled states. We reveal an intricate, hierarchical entanglement structure in local quantum quenches, both in the canonical purification of locally quenched Gibbs states and in a companion pure-state circuit model. In either setting, the full state exhibits a Renyi-index-tuned transition: at long times, $S_{\alpha>1}$ obeys an area law, while $S_{\alpha\le 1}$ is volume-law. More strikingly, the response linear in the quench strength is carried by only an O(1)-dimensional dominant Schmidt sector; the corresponding states exhibit their own area-to-volume-law transitions at critical indices $\alpha_c<1$, implying polynomial-bond-dimension approximability in one dimension. We provide evidence that this hierarchy persists recursively: upon bipartitioning the dominant Schmidt states, their leading Schmidt sectors exhibit analogous structure. We derive the mechanism analytically in the circuit model, prove the $S_{\alpha>1}$ area law for locally quenched Gibbs states, and support the hierarchy by exact diagonalization of random circuits and locally quenched Gibbs states of chaotic spin chains.
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Quantum Physics

Online Riemannian Gradient Descent for Quantum State Tomography with Matrix Product Operators

Jian-Feng Cai, Jingyang Li, Xiaoqun Zhang et al. (+1 more)

Matrix product operators (MPOs) provide a scalable approach for quantum state tomography (QST) by offering a compact representation of many-body mixed states with limited entanglement, using only a number of parameters that scales polynomially with the system size. In this paper, we study QST for quantum density matrices that can be represented by MPOs. We first derive an equivalent characterization of Hermiticity in terms of the MPO core tensors and show that the coefficient tensor of an MPO under the Pauli or generalized Gell-Mann basis admits a real-valued low tensor-train (TT) rank structure. This establishes an explicit connection between MPO-based QST and noisy low-rank tensor completion. Motivated by this formulation, we develop an online Riemannian gradient descent (oRGD) algorithm that sequentially incorporates measurement data during the reconstruction process. With a proper initialization, we prove that oRGD converges linearly to the target MPO and succeeds with a number of distinct measurement settings that scales quadratically with the system size. As a byproduct, our analysis also yields a significantly improved sample complexity bound for the low TT rank tensor completion task. Furthermore, we propose a tailored spectral initialization method and establish its theoretical guarantee. Numerical experiments on several classes of quantum states validate the effectiveness and scalability of the proposed method.
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All authors Jian-Feng Cai, Jingyang Li, Xiaoqun Zhang, Yuanwei Zhang

Quantum Physics · Cross-listed from cond-mat.stat-mech

Finite-size scaling properties of classical random walk on various two-dimensional lattices

Nimish Sharma and Tanay Nag

We consider various two-dimensional lattices such as square, Kagome, Lieb, honeycomb, dice lattices of finite extent, to study the effect of lattice profile in terms of the number of nearest neighbour and connectivity patterns on the classical random walk in the unbiased scenario. We find that the standard deviation of distance travelled by the walker is insensitive to the non-uniformity of the lattice profile leading to diffusive transport even in the finite size lattices. Our study indicates that the mass fractal dimension varies within a window $1.50\pm 0.03$ for all finite-size lattices. A weak ordering within the above window, correlated with the average coordination number, is observed, while Lieb and square lattices yielding the minimum and maximum values, respectively. However, confidence intervals reveal substantial statistical overlap for several lattice pairs even though the lattice profiles vary as far as the average number of connecting bonds and directionality of bonds are concerned. We also study the scaling complexity of the circumference of the closed curve traced by the walker while investigating the hull dimension. We find similar trend for hull fractal dimension as well and that was found to within the window $1.37\pm 0.03$ for finite-size lattices. Within the above window, the ordering remains qualitatively unaltered as compared to mass dimension while the confidence interval rectifies the order quantitatively. The square lattice clearly exhibits the upper bound for hull fractal dimension and the remaining lattices show extensive statistical overlap within the above window. We exhibit a tendency of the mass and hull fractal dimension to reach their thermodynamic values given by Brownian motion when we allow more number of steps within the finite size of the lattice, as confirmed by a data collapse analysis.
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Quantum Physics

Confidence uncertainty: position and momentum can be jointly determined with a guaranteed probability

Jia-Yi Lin, Xin-Yu Li, Wei Wang et al. (+1 more)

Standard-deviation and entropic formulations of uncertainty principle capture the spread of the probability distribution but say little about the probability itself contained in a small region. We introduce the confidence uncertainty $\Delta^{c}x(\theta_x)$ as the minimal Lebesgue measure of the support set in which the particle is found with probability at least $\theta_x$, and the companion interval confidence uncertainty $\Delta^{I}x(\theta_x)$ which restricts the support to a single interval. We prove two complementary uncertainty inequalities. (i) For $\theta_x+\theta_p\le 1$ both confidence uncertainties can be made arbitrarily small simultaneously, so that no nontrivial product bound holds; in particular, position and momentum can be jointly localised with probability at least~$50\%$. (ii) For $\theta_x+\theta_p>1$ a lower bound holds: combining Lenard's projection inequality with the Donoho–Stark operator-norm bound we obtain $\Delta^{c}x\,\Delta^{c}p\geq 2\pi\hbar\bigl(\sqrt{\theta_x\theta_p}-\sqrt{(1-\theta_x)(1-\theta_p)}\bigr)^{\!2}$, and for the interval version we obtain the sharp implicit Landau–Pollak bound $\Delta^{I}x\,\Delta^{I}p\geq 4\hbar\,\lambda_{0}^{-1}\!\bigl((\sqrt{\theta_x\theta_p}-\sqrt{(1-\theta_x)(1-\theta_p)})^{2}\bigr)$, where $\lambda_{0}(c)$ is the largest prolate-spheroidal eigenvalue. We support the analytical bounds with numerical evaluation of $\lambda_{0}(c)$, provide closed-form small-$c$ and large-$c$ asymptotics, compute the optimal Slepian-superposition states that saturate the interval bound, and compare the resulting product against the variance Heisenberg–Kennard, the Białynicki-Birula–Mycielski entropic, and the Donoho–Stark concentration bounds. The unified picture provides a complete phase diagram on $(\theta_x,\theta_p)\in[0,1]^{2}$.
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All authors Jia-Yi Lin, Xin-Yu Li, Wei Wang, Shengjun Wu

Quantum Physics

Floquet quantum multiparameter estimation with periodic-driving-induced topological phase transition

Yu Yang, Yuyang Tang, Pei Zhang et al. (+1 more)

Periodically driven systems provide a powerful platform for quantum multiparameter estimation. Constructing a static effective Hamiltonian in a proper rotating frame is commonly employed to assess the attainable precision. However, such an approach becomes nonfeasible for more general time-periodically driven systems. To tackle this dilemma, we develop a quantum multiparameter estimation strategy in the Floquet theory framework. The contributions of Floquet eigenmodes, quasienergies, and multi-photon processes to the quantum Fisher information matrix and measurement incompatibility are determined, respectively. Moreover, this approach is applied to a ring-shaped Rashba spin-orbit interferometer model exhibiting the topological phase transition (TPT). In the vicinity of the TPT boundary, we reveal a pronounced enhancement in the estimation precision of multiple parameters with the Heisenberg limit scaling and even higher. Meanwhile, the measurement incompatibility vanishes in an oscillatory manner, and the stroboscopic projective measurement enables the highest estimation precision achievable. This work provides a complete Floquet picture for time-dependent critical quantum multiparameter estimation.
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All authors Yu Yang, Yuyang Tang, Pei Zhang, Fuli Li

Quantum Physics

Triage: An Adaptive Parallel Window Decoding Scheduler for Real-time Fault-Tolerant Quantum Computation

Jiahan Chen, Chenghong Zhu, Ge Bai et al. (+1 more)

Fault-tolerant quantum computation (FTQC) critically depends on real-time classical decoding, which is rapidly emerging as a system bottleneck. As quantum systems scale, decoding latency and throughput limitations lead to exponential syndrome backlogs and logical operation stalls. While hardware accelerators and parallel windowing offer pathways to speed up decoding, dynamically deploying a finite pool of decoders across a vast quantum error correction architecture remains an unresolved resource allocation problem. To address this, we formulate FTQC decoding as a constrained dynamic scheduling problem by utilizing a spatio-temporal framework based on slices. We propose Triage, a dual-mode architecture that mitigates operation stalls by adaptively combining a cost-efficient heuristic scheduler with a priority-aware emergency mode to rapidly resolve the causal cone of critical operations. Our evaluation shows that Triage maintains low algorithm stalls and logical error rates even under scarce classical resource constraints. Across various benchmarks, Triage achieves an average logical error rate reduction of 52.6% compared to standard temporal parallelism, enabling an efficient classical control plane for scalable FTQC architectures.
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All authors Jiahan Chen, Chenghong Zhu, Ge Bai, Xin Wang

Quantum Physics

Hamiltonian-Generated Dynamics and Quantum Resource Allocation in a 4-Qubit Isotropic Heisenberg Spin Ring with Adjustable Next-Nearest-Neighbor Interactions

Seyed Mohsen Moosavi Khansari

This investigation delivers a fully analytical solution for the unitary evolution of a four-qubit isotropic Heisenberg XXX ring with periodic boundary conditions and a tunable next-nearest-neighbor exchange parameter \(\alpha\). Adopting a Bell-type product state as the initial condition, we obtain closed-form expressions for the square-root fidelity \(F(\rho(0),\rho(t))=|\cos(\phi/2)|\), the global \(l_1\)-norm coherence \(C_{l_1}(\rho(t))=\sin^2(\phi/2)\), and the bipartite entanglement of formation \(E_F(t)\) for the reduced pairs \((1,2)\) and \((3,4)\). These quantities are dictated entirely by the single phase \(\phi=(\alpha+1)t\). The fidelity shows oscillatory behavior with amplitude \(|\cos(\phi/2)|\) and reaches a quiescent dynamical regime at \(\alpha=-1\), characterized by \(F\equiv 1\) for all times. Meanwhile, the coherence follows \(C_{l_1}(\rho(t))=\sin^2(\phi/2)\), with a response sensitivity proportional to \(|\alpha+1|\), and fully extinguishes at the stabilization point \(\alpha=-1\). The entanglement of formation \(E_F(t)\), formulated as an entropic function of \(\phi\), undergoes striped periodic modulations and likewise freezes at the same parameter value. The unification of the phase ties together all observables, showing that larger \(|\alpha+1|\) drives faster evolution, with peak susceptibility occurring when \((\alpha+1)t=\pi/4+k\pi/2\). This complete analytical architecture supplies precise reference data suited for small-scale quantum hardware and charts a clear route for incorporating decoherence, thermal effects, and generalizations to larger spin assemblies.
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Quantum Physics

SpinTune: Improving the Reliability of Quantum Sensor Networks for Practical Quantum-Classical Utility

Jason Ludmir, Nicholas S. DiBrita, Jason Han et al. (+1 more)

Emerging quantum sensors are increasingly envisioned as components of hybrid quantum-classical high-performance computing, enabling new capabilities in scientific, cyber-physical, and machine-learning pipelines. However, their practical utility is limited by environmental decoherence, which degrades sensing reliability. While dynamical decoupling (DD) pulse sequences can mitigate this, standard methods are often suboptimal in the presence of realistic noise. We present SpinTune, a reinforcement learning software approach that autonomously discovers adaptive, piecewise DD sequences tailored to specific environments. Using a simulation model of a Carbon-13 spin bath, we show that SpinTune significantly outperforms standard DD sequences in preserving coherence.
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All authors Jason Ludmir, Nicholas S. DiBrita, Jason Han, Tirthak Patel

Quantum Physics · Cross-listed from math.CO

Uniform Mixing in Chiral Quantum Walks

Luke Levine, Jessy Jacob Mesapam, Benjamin Mustico et al. (+3 more)

This paper studies uniform mixing in continuous-time quantum walks. We show that for some unitary signing $\sigma$, the complete graph $K^\sigma_n$ has probabilistic uniform mixing. In contrast, Ahmadi \etal (2003) proved that no complete graph has uniform mixing except for $K_2$, $K_3$, and $K_4$. Our technique is based on a stopping rule for quantum walks which reduces global to local uniform mixing. As a corollary, we found an orientation of $H(n,4)$ that mixes to uniform faster than any other Hamming graphs, which improves a result of Godsil and Zhan (2019). We also show that there are infinite families of oriented circulants with average uniform mixing. This is a chiral violation of a No-Go theorem due to Godsil (2013) which states that no graph has average uniform mixing except for $K_2$.
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All authors Luke Levine, Jessy Jacob Mesapam, Benjamin Mustico, Christino Tamon, Gabriel Tucker, Hanmeng Zhan

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

Imaging GHz surface acoustic wave modes in electrostricted LaAlO$_3$/SrTiO$_3$ heterostructures

Ranjani Ramachandran, Sayanwita Biswas, Prithwijit Mandal et al. (+6 more)

The LaAlO$_3$/SrTiO$_3$ (LAO/STO) interface hosts a gate-tunable superconducting two-dimensional electron gas (2DEG) which can be programmed to create quantum devices such as ballistic electron waveguides and quantum dots. To fully exploit this platform for quantum transport, a key requirement is the ability to shuttle single electrons, electron pairs, and other exotic states between spatially separated devices with precision. Surface acoustic waves (SAWs), which travel along the surface of a solid, offer a powerful route to achieve this through their moving electrical potential that captures and transfers electrons. %acoustoelectric coupling. In particular, SAWs in the GHz regime enable fast, controlled transport of individual quantum particles. Although this approach is well-explored in GaAs-based 2DEG, SAW generation in STO remains largely unexplored due to the lack of intrinsic piezoelectricity at room temperature. Here, we investigate room-temperature SAWs in LAO/STO and observe SAW modes up to 2.2 GHz with very low propagation loss of the order $10^{-3}$ dB per wavelength. To directly visualize these modes, we employ Atomic Acoustic Force Microscopy (AAFM), achieving sub-micron resolution imaging of the SAW wave forms, providing insight into the electrostriction-induced SAW generation mechanism. Our measurements indicate a shear horizontal-type mode, which provides the ability to couple to in-plane degrees of freedom for future acoustoelectric and quantum device applications. This work studies the fundamentals of SAW excitation and propagation on STO, a widely used and commercially available substrate, enabling straightforward coupling of SAWs to a broad range of materials that can be grown or transferred onto STO.
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All authors Ranjani Ramachandran, Sayanwita Biswas, Prithwijit Mandal, Kyoungjun Lee, Madeleine Msall, Chang-Beom Eom, Patrick Irvin, Jeremy Levy, Mingyun Yuan

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

Kitaev chain in synthetic dimension with cavity-controlled Majorana modes

Adel Ali and Alexey Belyanin

We introduce a tunable synthetic-dimension platform for realizing Kitaev-chain physics with high degree of control over Majorana zero modes. It is based on a generic Landau-quantized two dimensional electron system coupled to the magnetic flux of a superconducting LC circuit. The structured vector potential of a superconducting LC inductor induces attractive interactions between electron angular-momentum states at the lowest Landau level. These states serve as a synthetic dimension for the coveted fermionic Kitaev chain, with Majorana zero modes existing at the boundaries of the angular-momentum lattice. The crucial advantage of this proposal is the possibility of a robust, nonlocal readout and control of the Majorana states by a LC resonator. The platform relies on mature circuit QED and semiconductor technologies and provides a promising pathway to topological quantum computing.
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Tuesday 5 May

Quantum Physics

Graphs on chip: a silicon photonics platform

H. Girin, X. Chécoury, B. Odouard et al. (+5 more)

We present a versatile photonic waveguide network platform implementing quantum (wave) graphs, proposed by Kottos & Smilansky [Phys. Rev. Lett. 79, 4794 (1997)] to investigate ray-wave correspondence and quantum chaos. Realized on a silicon-on-insulator chip at telecom wavelengths, it enables a unique capability: the direct, non-invasive imaging of individual optical wave functions with unprecedented resolution via third-harmonic generation in silicon, which we use to study the localization of intensity distributions. Furthermore, by investigating two graphs with contrasting classical dynamics – one strongly chaotic, the other one ergodic, but non-mixing – we reveal strikingly different spectral statistics, in quantitative agreement with random matrix theory and a minimal unitary quantum-map model. This establishes silicon photonics networks as a versatile and scalable platform for investigating quantum chaos and non-linear graphs, and paves the way for optical quantum computing in complex networks.
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All authors H. Girin, X. Chécoury, B. Odouard, S. Bittner, J.-R. Coudevylle, B. Dietz, C. Lafargue, M. Lebental

Quantum Physics · Cross-listed from physics.optics

Scattering-Induced Loss in Ferroelectric Photonic Devices

Jonah Townsend, Enzo Conceição Picinini and Rogério de Sousa

Ferroelectric materials have colossal optical nonlinearities, but their integration into quantum photonic chips is made challenging by the additional loss mechanisms that they introduce. Here we present a perturbative theory that expresses non-absorptive (elastic) photon scattering-induced loss as a functional of a general spectral density for spatial fluctuations of electric permittivity. We apply the theory to calculations of attenuation coefficients $\alpha$ in slab waveguides in order to compare two distinct loss mechanisms: Interface roughness and ferroelectric domain disorder. Our theory can account for realistic roughness without special symmetry considerations, and it demonstrates how to use electron microscopy images of ferroelectric domains to obtain explicit numerical predictions for $\alpha$. Loss is maximum when the mean domain length is comparable to the wavelength of light (Mie regime), indicating that, for telecom wavelengths, sub-micron domains (Rayleigh regime) or single domain waveguides provide equivalent strategies for reducing loss.
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Quantum Physics

Hidden Prime-Factor Subgroups in Molecular and Condensed-Phase Systems

Srinivasan S. Iyengar and Amr Sabry

We describe a group theoretic analysis of Shor's algorithm and other related hidden subgroup problems in mathematics and relate these to symmetries of molecular and condensed phase assemblies. By recasting Shor's algorithm through the lens of group theory, we expose the possibility that physical systems such as molecular orbitals, condensed phase assemblies and optical beams may be designed such that these contain information pertaining to the solution to hard mathematical problems such as prime-factoring. We discuss real molecular systems, whose orbitals are constructed from symmetry-adapted linear combinations of atomic orbitals, and show that these contain information pertaining to the prime-factors of corresponding integers. Due to the broad significance of prime-factoring towards a variety of encryption problems in cyber-security, we believe this novel and fundamental approach may have broad impact.
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Quantum Physics

Robust certification of high-dimensional quantum devices

Javier Fernández, Albert Rico, David Viedma et al. (+6 more)

Certifying quantum behavior from classically accessible data is essential for secure communication and scalable quantum technologies. While powerful certification methods such as Bell nonlocality and quantum steering exist, their implementation typically requires entanglement or additional assumptions, and experimental demonstrations mainly focus on low-dimensional systems. In minimal prepare-and-measure scenarios, where a sender encodes information into quantum states and a receiver performs a single measurement, robust certification becomes particularly challenging, especially in the presence of noise and in higher-dimensional Hilbert spaces. Here, we propose, design, and experimentally implement a protocol that certifies quantumness between two distant parties without the need for preshared resources or measurement incompatibility. The experiments are carried out using the orbital angular momentum degrees of freedom of single photons, chosen for providing increased dimensionality that is scalable. We demonstrate the robustness of the protocol through rank-stability analysis of the observed correlations, which enables the certification of non-classicality even in the presence of noise. Our results provide a practical route to validate high-dimensional quantum communication systems and open new possibilities for secure and dimension-efficient quantum information processing.
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All authors Javier Fernández, Albert Rico, David Viedma, Evelyn A. Ortega, Valerio Pruneri, Adam Vallés, Verònica Ahufinger, Anna Sanpera, Some S. Bhattacharya