Quantum Physics · Cross-listed from physics.optics
Deterministic quantum dot single-photon sources: operational principles and state-of-the-art specifications
J.C. Loredo, L. Stefan, B. Krogh et al. (+13 more)
Non-classical states of light play a fundamental role in
quantum technology. From photonic
quantum computers and simulators, to
quantum communication and sensing,
quantum states of light enable performing tasks that may outperform their best classical counterparts.
Semiconductor quantum dots embedded in photonic nanostructures offer the most advanced classes of
quantum light sources. Importantly, the underlying physics processes determining device performance are today fully understood, and dedicated engineering projects are currently advancing these sources towards real-world
quantum technology applications. We review the performance of deterministic single-
photon sources based on
quantum dots in photonic
crystal waveguides, the approach with the highest performance specs since it intrinsically combines suppression of leaky modes and Purcell enhancement to slow-light waveguide mode. Furthermore, we present prototype data from sources that today are commercially available and with performance metrics approaching the ideal.
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All authors J.C. Loredo, L. Stefan, B. Krogh, R. Jensen, I. Suleiman, S. Krüger, M. Bergamin, H. Thyrrestrup, S. Budtz, J. Roulund, Z. Liu, X. Zhao, L. Vertchenko, A. Ludwig, O. A.D. Sandberg, P. Lodahl
Quantum Physics · Cross-listed from cond-mat.mes-hall
Controlling Dissipative Topology Through Floquet Driving: From Transient Diagnostics to Boundary States Isolation
Koustav Roy, Shahroze Shahab and Saurabh Basu
Engineering dissipative dynamics in open
quantum systems is under active focus, especially in topological settings where resilient edge modes are expected to exhibit decay rates distinct from the bulk. In this letter, we propose an efficient dynamical scheme to discern such long-lived excitations. Employing a Floquet-Lindblad framework, we explore how periodic driving reshapes the key features of a paradigmatic topological model, namely a Creutz ladder. Our results bear testimony to a drive-induced unipolar-bipolar transition in the Liouvillian skin effect, which gets dynamically manifested as a
chiral-helical damping crossover. Such a transition effectively rescales the bulk localization length, giving rise to a polarization drift that we identify as a new invariant for efficient diagnosis of the nontrivial phases. As the transition becomes more gradual via tuning drive-rescaled parameters, we uncover signatures of a scale-free localization where skin and extended modes co-exist with distinct decay rates. The emergent hierarchy of the decay rates yields two disparate timescales: a
chiral wavefront that rapidly empties the bulk followed by a long-lived regime dominated by robust edge modes. Overall, our results provide convincing evidence that periodic driving serves as a powerful handle to manipulate dissipative topological phases and dynamically isolate the boundary modes.
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Quantum Physics
Nonstabilizerness Estimation using Graph Neural Networks
Vincenzo Lipardi, Domenica Dibenedetto, Georgios Stamoulis et al. (+2 more)
This article proposes a Graph Neural Network (GNN) approach to estimate nonstabilizerness in
quantum circuits, measured by the stabilizer Rényi
entropy (SRE). Nonstabilizerness is a fundamental resource for
quantum advantage, and efficient SRE estimations are highly beneficial in practical applications. We address the nonstabilizerness estimation problem through three supervised learning formulations starting from easier classification tasks to the more challenging regression task. Experimental results show that the proposed GNN manages to capture meaningful features from the graph-based
circuit representation, resulting in robust generalization performances achieved across diverse scenarios. In classification tasks, the GNN is trained on product states and generalizes on
circuits evolved under Clifford operations, entangled states, and
circuits with higher number of
qubits. In the regression task, the GNN significantly improves the SRE estimation on out-of-distribution
circuits with higher number of
qubits and gate counts compared to previous work, for both unstructured random
quantum circuits and structured
circuits derived from the transverse-field Ising model. Moreover, the graph representation of
quantum circuits naturally integrates hardware-specific information. Simulations on noisy
quantum hardware highlight the potential of the proposed GNN to predict the SRE measured on
quantum devices.
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All authors Vincenzo Lipardi, Domenica Dibenedetto, Georgios Stamoulis, Evert van Nieuwenburg, Mark H.M. Winands
Quantum Physics · Cross-listed from cond-mat.stat-mech
Refinements of the Eigenstate Thermalization Hypothesis under Local Rotational Invariance via Free Probability
Elisa Vallini, Laura Foini and Silvia Pappalardi
The Eigenstate Thermalization Hypothesis (ETH) was developed as a framework for understanding how the principles of statistical mechanics emerge in the long-time limit of isolated
quantum many-body systems. Since then, ETH has shifted the
attention towards the study of
matrix elements of physical observables in the energy eigenbasis. In this work, we revisit recent developments leading to the formulation of full ETH, a generalization of the original ETH ansatz that accounts for multi-point correlation functions. Using tools from free probability, we explore the implications of local rotational invariance, a property that emerges from the statistical invariance of observables under random basis transformations induced by small perturbations of the
Hamiltonian. This approach allows us to make quantitative predictions and derive an analytical characterization of subleading corrections to
matrix-element correlations, thereby refining the ETH ansatz. Moreover, our analysis links the statistical properties of
matrix elements under random basis changes to the empirical averages over energy windows that are usually considered when dealing with a single instance of the ensemble. We validate our analytical predictions through comparison with numerical simulations in non-integrable Floquet systems.
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Quantum Physics
Quantum spectroscopy of topological dynamics via a supersymmetric Hamiltonian
Hiroshi Yamauchi, Satoshi Kanno, Yuki Sato et al. (+4 more)
Topological data analysis (TDA) characterizes complex dynamics through global invariants, but classical computation becomes prohibitive for high-dimensional data. We reinterpret time-domain dynamics as the
eigenvalue spectrum of a supersymmetric (SUSY)
Hamiltonian and thereby estimate topological descriptors through
quantum spectroscopy. While zero modes correspond to Betti numbers, we show that low-lying excited states quantify the stability of topological features. Using a Takens
embedding of the Lorenz system together with a resource-efficient
quantum phase estimation implemented on IBM
quantum hardware, we observe that the spectral gap of the SUSY
Laplacian tracks the persistence of homological structures. Notably, the minimum of this spectral gap coincides with the onset of chaos, whereas its reopening reflects the
geometric maturation of the attractor. Validated on small complexes yet offering an exponential advantage over classical diagonalization (from $O(N^3)$ to $\mathrm{poly}(\log N)$), this framework suggests that
quantum hardware can function as a spectrometer for data
topologies beyond classical reach.
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All authors Hiroshi Yamauchi, Satoshi Kanno, Yuki Sato, Hiroyuki Tezuka, Yoshi-aki Shimada, Eriko Kaminishi, Naoki Yamamoto
Quantum Physics
Entanglement and Minimal Hilbert Space in the Classical Dual States of Quantum Theory
Diego J. Cirilo-Lombardo and Norma G. Sanchez
A precise physical description and understanding of the classical dual content of
quantum theory is necessary in many disciplines today: from concepts and interpretation to
quantum technologies and computation. In this paper we investigate
Quantum Entanglement with the new approach APL
Quantum 2, 016104 (2025) on dual Classicalization. Thus, the results of this paper are twofold:
Entanglement and Classicalization and the relationship between them. Classicalization truly occurs only under the action of the Metaplectic group Mp(n) (Minimal Representation group, double covering of the
Symplectic group). Some of the results of this paper involves the computation and analysis of the
entanglement for different types of coherent (coset and non coset) states and
topologies: in the circle and the cylinder. We project the entangled wave functions onto the even (+) and odd (-) irreducible
Hilbert Mp(n) subspaces, and compute their square norms:
Entanglement Probabilities P++, P–, P+-, (eg in the same or in the different subspaces), and the Total sum of them, and more. These theoretical and conceptual results can be of experimental and practical real-world interest.
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Quantum Physics
Efficient Identification of Permutation Symmetries in Many-Body Hamiltonians via Graph Theory
Saumya Shah and Patrick Rebentrost
The computational cost of simulating
quantum many-body systems can often be reduced by taking advantage of physical
symmetries. While methods exist for specific
symmetry classes, a general
algorithm to find the full permutation
symmetry group of an arbitrary Pauli
Hamiltonian is notably lacking. This paper introduces a new method that identifies this
symmetry group by establishing an isomorphism between the
Hamiltonian's permutation
symmetry group and the
automorphism group of a coloured bipartite graph constructed from the
Hamiltonian. We formally prove this isomorphism and show that for physical
Hamiltonians with bounded locality and interaction degree, the resulting graph has a bounded degree, reducing the computational problem of finding the
automorphism group to
polynomial time. The
algorithm's validity is empirically confirmed on various physical models with known
symmetries. We further show that the problem of deciding whether two
Hamiltonians are permutation-equivalent is
polynomial-time reducible to the graph isomorphism problem using our graph representation. This work provides a general, structurally exact tool for algorithmic
symmetry finding, enabling the scalable application of these
symmetries to
Hamiltonian simulation problems.
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Quantum Physics · Cross-listed from cond-mat.supr-con
Nonequilibrium Quasiparticle Dynamics in a MoRe-Based Superconducting Resonator under IR Excitation
O. A. Kalenyuk, S. I. Futimsky, I. A. Martynenko et al. (+5 more)
The response of a MoRe-based superconducting resonator operating near 5 K to pulsed infrared irradiation is investigated, and the underlying physical mechanisms are analyzed. The device exhibits a pronounced nonlinear response dominated by nonequilibrium quasiparticle dynamics rather than uniform thermal heating. Infrared pulses produce strong distortions of the resonance curve and a transient decrease in the resonance frequency, consistent with increased kinetic inductance caused by quasiparticle generation. The frequency shift scales approximately linearly with absorbed power, whereas the dissipation response saturates at higher powers, indicating the formation of a nonequilibrium steady-state quasiparticle population. These observations demonstrate a transition from a linear pair-breaking regime to a saturated dissipation regime, likely associated with a quasiparticle relaxation bottleneck or partial suppression of the smaller superconducting gap in MoRe. The results highlight the relevance of nonequilibrium processes in MoRe and confirm its potential for microwave kinetic-inductance detector applications.
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All authors O. A. Kalenyuk, S. I. Futimsky, I. A. Martynenko, A. P. Shapovalov, O. O. Boliasova, V. I. Shnyrkov, A. L. Kasatkin, A. A. Kordyuk
Quantum Physics
Algebraic power scaling in a slowly-quenched bosonic quantum battery
Donny Dwiputra, Ahmad R. T. Nugraha, Sasfan A. Wella et al. (+1 more)
Bosonic modes provide a promising platform for
quantum batteries as a result of their unbounded energy spectrum. However, the energy that can be stored during a coherent charging process is limited due to coherent oscillations between the charger and battery. In this work, we show that by introducing a slow quench in the interaction between a coherently driven charger mode and a quadratic oscillator battery, the maximum stored energy and maximum battery power scale algebraically with the quench duration, with exponents controlled by the ramp profile. This finding implies that, quite counterintuitively, slower quenches lead to faster charging. Such a quench suppresses coherent energy oscillations between the battery and the charger, allowing an unbounded increase in power. We further show that, in the ideal closed protocol, the stored energy is fully extractable as ergotropy, while charger dissipation converts the algebraic enhancement into a finite-time scaling window with an optimal quench duration. We also show that the temporal-extensive scaling occurs in a broader context by mapping the system to a coherently driven Tavis-Cummings battery. Finally, we discuss experimentally accessible signatures in superconducting
circuit quantum electrodynamics and organic microcavity platforms.
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All authors Donny Dwiputra, Ahmad R. T. Nugraha, Sasfan A. Wella, Freddy Permana Zen
Quantum Physics · Cross-listed from cond-mat.mes-hall
Irina Heinz, Jeroen Danon and Guido Burkard
Spin qubits have proven to be a feasible candidate for
quantum computation, and some realizations of
spin qubits already benefit from advanced device manufacturing in the
semiconductor industry. Compared to superconducting platforms,
spin qubits can operate at higher temperatures from tens of millikelvin up to a few kelvin. However, recent experiments show a non-trivial and often non-monotonic dependence of the
spin qubit frequency on the temperature, featuring a region of decreased sensitivity to temperature fluctuations. In this work, we aim to gain insight into the physics behind such temperature shifts in the low-temperature limit. Investigating the
spin qubits' interaction with
phonon modes of the host material, we can explain some of the key features of the observed behavior and estimate the temperature sweet spot for the
qubit frequency shift.
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Quantum Physics
Tunable dual-band atomic mirror based on subwavelength atomic arrays under electromagnetically induced transparency
Shiwen Sun, Yi-Xin Wang, Xiao Liu et al. (+1 more)
Subwavelength atomic arrays offer a powerful platform for engineering cooperative light-matter interactions and enabling
quantum metasurfaces. We demonstrate that a two-dimensional array of three-level atoms operating under electromagnetically induced transparency can function as a tunable dual-band atomic mirror, where two independently controllable reflection bands emerge from the collective optical responses mediated by dipole-dipole interactions. These resonances yield dual reflection bands with asymmetric linewidths, whose spectral positions and bandwidths can be tuned through the control-field parameters, dipole orientation, incident geometry, and
lattice constant. We further identify the conditions under which additional diffraction orders emerge, which delineate the operational and tunable range of the atomic mirror via its collective-mode structure. This scheme provides a fully tunable dual-band atomic mirror operating across broad frequency and angular ranges, offering a practical and experimentally accessible pathway toward reconfigurable photonic elements in atomic-array platforms at low energy levels.
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All authors Shiwen Sun, Yi-Xin Wang, Xiao Liu, Yan Zhang
Quantum Physics
No-Go Theorem for Norm-Based Nonclassicality Certification with Linear Functionals
Soumyakanti Bose, Yong-Siah Teo, Hyukjoon Kwon et al. (+1 more)
Despite various approaches to encode nonclassical light, most existing formulations either suffer from limited practicality or rely on optimization procedures that are computationally demanding. Here, we develop a framework for quantifying optical nonclassicality without invoking any optimization, using generic classicalization channels, p-norms and linear functionals generated by displaced rotationally-invariant operators. However, for a subset of such measures, involving s-ordered distributions and a Gaussian classicalization channel, we analytically establish a no-go
theorem demonstrating that no such universal measure can exist. We further substantiate our theoretical result through explicit examples involving both Gaussian and non-Gaussian states, followed by a generic criterion for a no-go
theorem, whose the existence remains to be established.
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All authors Soumyakanti Bose, Yong-Siah Teo, Hyukjoon Kwon, Hyunseok Jeong
Quantum Physics
Secret Entanglement, Public Geometry. Quantum Cryptography from a Geometric Perspective
Loris Di Cairano
Can a secret be hidden not in which
quantum state is prepared, but in the way that state moves through its space of possibilities? Motivated by this question, we propose an essential
geometric perspective on
quantum cryptography in which projective
Hilbert space and its
entanglement foliations play a central role. The basic ingredients are: (a) the Fubini-Study metric on the
manifold of pure states, (b) a family of
entanglement measures viewed as scalar functions on this
manifold, and (c) controlled trajectories generated by
unitary operations. The
geometric structure – state
manifold, metric, and allowed moves – is fully public, as is the functional form of the
entanglement family. What remains secret is the choice of parameter $\theta$ that selects a specific
entanglement functional $E_\theta$ and the corresponding foliation into constant-
entanglement hypersurfaces. In this setting, classical messages are encoded not only in the sequence of states but also in the pattern of upward, downward, or tangential steps with respect to the hidden foliation. We formalize this idea in terms of
geometric entanglement codes and illustrate it with two toy constructions in which incompatible foliations play the role of mutually unbiased bases.
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Quantum Physics
Strengthening the quantum data processing inequality for maximal $f$-divergences via unraveling
Marcos Ruibal Ortigueira, Robert de Keijzer, Luke Visser et al. (+2 more)
Maximal $f$-divergences, among them the Belavkin–Staszewski relative
entropy, are non-increasing under completely positive trace-preserving maps, which is the
quantum data processing inequality (DPI). We quantify this decrease for Lindblad evolutions with Hermitian jump operators by lifting the problem to a
stochastic unraveling, in which the two states become measures on pure states evolving under a classical Fokker–Planck equation. The lift rests on the identity that the infimum of the classical $f$-divergence over ensembles realizing two states is equal to their maximal $f$-divergence. This infimum is attained on a common basis of pure states, which is admissible initial data for the unraveling. The result is a strengthened DPI, with the loss bounded below by the time integral of a relative $f$-Fisher information. Given a two-sided bound on the unraveling's transition kernel, we derive two exponential decay estimates. For bracket-generating jump operators, the rate reaches twice the spectral gap of the symmetrized generator after an explicit delay. Without bracket generation, the kernel bound alone gives any rate below twice the spectral gap of the full generator.
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All authors Marcos Ruibal Ortigueira, Robert de Keijzer, Luke Visser, Oliver Tse, Servaas Kokkelmans
Quantum Physics
Benchmarking neutral atom-based quantum processors at scale
Andrea B. Rava, Kristel Michielsen and J. A. Montanez-Barrera
In recent years, neutral atom-based
quantum computation has been established as a competing alternative for the realization of fault-tolerant
quantum computation. However, as with other
quantum technologies, various sources of noise limit their performance. With processors continuing to scale up, new techniques are needed to characterize and compare them in order to track their progress. In this work, we present two systematic
benchmarks that evaluate these
quantum processors at scale. We use the
quantum adiabatic
algorithm (QAA) and the
quantum approximate optimization
algorithm (QAOA) to solve maximal independent set (MIS) instances of random unit-disk graphs. These
benchmarks are scalable, relying not on prior knowledge of the system's
evolution but on the quality of the MIS solutions obtained. Rather than isolating individual sources of noise, they provide an application-level figure of merit: improvements in a QPU and its implementation of the protocols should be reflected in higher-quality MIS solutions. We
benchmark quera_aquila and pasqal_fresnel on problem sizes up to 102 and 85
qubits, respectively. Overall, quera_aquila performs better on QAOA and QAA instances. Finally, we generate MIS instances of up to 1000
qubits, providing scalable
benchmarks for evaluating future, larger processors as they become available. The proposed protocols can therefore serve as a common reference for comparisons, allowing future work to assess whether advances in hardware translate into measurable improvements in MIS solution quality.
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Quantum Physics · Cross-listed from cond-mat.stat-mech
Generation of concurrence in a generalized central spin model with a three-spin interacting environment
Adithya A. Vasista, Anushka Agrawal and Tanay Nag
We consider the three-
spin Ising model to study the effect of three-
spin interacting term on bi-partitie
entanglement between adjacent
spins. The three-dominated disordered region has tri-partite
entanglement causing a vanishingly small concurrence, while it acquires maximum value around the critical points. Considering the above model as an environment, we construct a generalized central
spin model where two central
spins, initially in an unentangled pure state, are coupled locally to two distinct sites of the environmental
spin chain. We study the generation of mixed state
entanglement between the central
spins when the transverse field of the environment is kept fixed, and suddenly quenched, referring to
equilibrium and non-
equilibrium dynamics of the central
spins, respectively. For the critical environment in the
equilibrium, the concurrence shows a dip-revival structure governed by quasi-particle movement. In the non-
equilibrium study, we find an initial growth of concurrence followed by a two-stage fall for the inter-phase quench which is governed by dynamic decoherence channels. The central
spins are maximally entangled for a quench in the vicinity of a multicritical point, which arises due to three-
spin interaction only. The concurrence becomes long-lived for an intra-phase quench, and this sustainability depends on the strength of the three-
spin interaction. Therefore, the three-
spin interaction indeed helps in generating bi-partite
entanglement in the central
spins.
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Quantum Physics
Evidence for unexpectedly low quasiparticle generation rates across Josephson junctions of driven superconducting qubits
Byoung-moo Ann, Sang-Jun Choi, Hee Chul Park et al. (+6 more)
Recent studies find that even drives far below the superconducting gap frequency may cause drive-induced quasiparticle generation (QPG) across Josephson junctions (JJs) of superconducting
qubits (SCQs), posing a serious concern for fault-tolerant superconducting
quantum computing (FTSQC). Nonetheless, quantitative experimental estimation on QPG rates has remained vague. Here, we investigate QPG using strongly driven SCQs, reaching
qubit drive amplitudes up to $2\pi\times$300 GHz by applying intense drive fields through the readout resonators. The resonator nonlinear responses enable quantification of the energy loss at SCQs, including the contribution from QPG. Surprisingly, the estimated total energy loss rates are far lower than those expected by the Floquet-Markov formalism with QPG as the sole loss mechanism. Meanwhile, calculations that incorporate high-frequency cutoffs (HFCs) in the QPG conductance at approximately 17-20 GHz effectively explain the experimental observations. These results suggest limitations in either the QPG conductance model or the Markovian treatment of the QPG processes. Both possibilities possess crucial implications for handling QPG problems toward FTSQC and for a more deeper understanding of Josephson junctions.
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All authors Byoung-moo Ann, Sang-Jun Choi, Hee Chul Park, Sercan Deve, Robin Dekker, Gary A. Steele, Jaseung Ku, Seung-Bo Shim, Junho Suh
Quantum Physics
CO-QLink: Cryogenic Optical Link for Scalable Quantum Computing Systems and High-Performance Cryogenic Computing Systems
Zheng Chang, Siqi Zhang, Wenqiang Huang et al. (+8 more)
Cryogenic systems necessitate extensive data transmission between room-temperature and cryogenic environments, as well as within the cryogenic temperature domain. High-speed, low-power data transmission is pivotal to enabling the deployment of larger-scale cryogenic systems, including the scalable
quantum computing systems and the high-performance cryogenic computing systems fully immersed in
liquid nitrogen. In contrast to wireline and microwave links, optical communication links are emerging as a solution characterized by high data rates, high energy efficiency, low signal attenuation, absence of thermal conduction, and superior scalability. In this work, a 4K heat-insulated high-speed (56Gbps) low-power (1.6pJ/b) transceiver (TRX) that achieves a complete link between 4K systems and room temperature (RT) equipment is presented. Copackaged with a PIN photodiode (PD), the RX uses an inverter-based analog front-end and an analog half-rate clock data recovery loop. Connecting to a Mach-Zehnder modulator (MZM), the TX contains a voltage-mode driver with current-mode injection for low-power output-swing-boosting and 3-tap feed-forward equalization (FFE). This link has been demonstrated in the control and readout of a complete superconducting
quantum computing system.
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All authors Zheng Chang, Siqi Zhang, Wenqiang Huang, Tian Tian, Qichun Liu, Tiefu Li, Nan Qi, Yuanjin Zheng, Zhihua Wang, Yanshu Guo, Hanjun Jiang
Quantum Physics
Algorithmic Quantum Simulations of Quantum Thermodynamics
Yangsen Ye, Jue Nan, Dong Chen et al. (+27 more)
Characterizing
quantum phases-of-matter at finite-temperature is essential for understanding complex materials and large-scale thermodynamic phenomena. Here, we develop algorithmic protocols for simulating
quantum thermodynamics on
quantum hardware through
quantum kernel function expansion (QKFE), producing the free energy as an analytic function of temperature with uniform convergence. These protocols are demonstrated by simulating transverse field Ising and XY models with superconducting
qubits. In both analogue and digital implementations of the QKFE
algorithms, we exhibit quantitative agreement of our
quantum simulation experiments with the exact results. Our approach provides a general framework for computing thermodynamic potentials on programmable
quantum devices, granting access to key thermodynamic properties such as
entropy, heat capacity and criticality, with far-reaching implications for material design and drug development.
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All authors Yangsen Ye, Jue Nan, Dong Chen, Torsten V. Zache, Qingling Zhu, Yiming Zhang, Yuan Li, Xiawei Chen, Chong Ying, Chen Zha, Sirui Cao, Shaowei Li, Shaojun Guo, Haoran Qian, Hao Rong, Yulin Wu, Kai Yan, Feifan Su, Hui Deng, Yu Xu, Jin Lin, Ming Gong, Fusheng Chen, Gang Wu, Yong-Heng Huo, Chao-Yang Lu, Cheng-Zhi Peng, Xiaobo Zhu, Xiaopeng Li, Jian-Wei Pan
Quantum Physics
Which-crystal information and wave-particle duality in induced-coherence interferometry
L. Theerthagiri
We provide an operational reinterpretation of wave-particle complementarity in the low-gain Zou-Wang-Mandel (ZWM) induced-coherence interferometer. In the low gain limit, each
photon pair is emitted by either one of two nonlinear
crystals. Preparing nonorthogonal conditional idler states that encode which-
crystal information. While previous studies inferred distinguishability indirectly from signal visibility with undetected idler
photons. We show that the idler states naturally define a binary
quantum hypothesis-testing problem. By performing optimal measurements on the idler, we analyze this task using both zero-error measurement unambiguous discrimination (Ivanovic-Dieks-Peres (IDP)) and minimum-error discrimination (Helstrom bound). We show that the signal visibility equals the optimal inconclusive probability of unambiguous discrimination. The Helstrom bound gives the optimal probability of identifying the emitting
crystal. While signal visibility is an ensemble-averaged expectation value, the IDP and Helstrom strategies correspond to optimal single-
photon decision measurements on the idler. The decision problem concerns inferring a past source event from a present measurement outcome This establishes wave-particle duality in induced coherence as a manifestation of optimal
quantum decision strategies rather than a purely
geometric constraint. We further extend the analysis to the presence of thermal
photons introduced in the object arm, which render the conditional idler states mixed. In this case, both the visibility and the achievable distinguishability are reduced, reflecting the fundamental limitations imposed by mixed-state discrimination. The approach is model-independent and applies to general two-path interferometers with markers.
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Quantum Physics
Escaping Barren Plateaus in Variational Quantum Algorithms Using Negative Learning Rate in Quantum Internet of Things
Ratun Rahman and Dinh C. Nguyen
Variational
Quantum Algorithms (VQAs) are becoming the primary computational primitive for next-generation
quantum computers, particularly those embedded as resource-constrained accelerators in the emerging
Quantum Internet of Things (QIoT). However, under such device-constrained execution conditions, the scalability of learning is severely limited by barren plateaus, where gradients collapse to zero and training stalls. This poses a practical challenge to delivering VQA-enabled intelligence on QIoT endpoints, which often have few
qubits, constrained shot budgets, and strict latency requirements. In this paper, we present a novel approach for escaping barren plateaus by including negative learning rates into the optimization process in QIoT devices. Our method introduces controlled instability into model training by switching between positive and negative learning phases, allowing recovery of significant gradients and exploring flatter areas in the loss landscape. We theoretically evaluate the effect of negative learning on gradient variance and propose conditions under which it helps escape from barren zones. The experimental findings on typical VQA
benchmarks show consistent improvements in both convergence and simulation results over traditional optimizers. By escaping barren plateaus, our approach leads to a novel pathway for robust optimization in
quantum-classical hybrid models.
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Quantum Physics · Cross-listed from math.CO
Algebraic Obstructions and the Collapse of Elementary Structure in the Kronecker Problem
Soong Kyum Lee
While Kronecker coefficients $g(\lambda,\mu,\nu)$ with bounded rows are
polynomial-time computable via
lattice-point methods, no explicit closed-form formulas have been obtained for genuinely three-row cases in the 87 years since Murnaghan's foundational work. This paper provides such formulas for the first time and identifies a universal structural boundary at parameter value 5 where elementary combinatorial patterns collapse. We analyze two independent families of genuinely three-row coefficients and establish that for $k \leq 4$, the formulas exhibit elementary structure: oscillation bounds follow the triangular-Hogben pattern, and
polynomial expressions factor completely over $\mathbb{Z}$. At the critical threshold $k=5$, this structure collapses: the triangular pattern fails, and algebraic obstructions – irreducible quadratic factors with negative discriminant – emerge. We develop integer forcing, a proof technique exploiting the tension between continuous asymptotics and discrete integrality. As concrete results, we prove that $g((n,n,1)^3) = 2 - (n \mod 2)$ for all $n \geq 3$ – the first explicit formula for a genuinely three-row Kronecker coefficient – derive five explicit
polynomial formulas for staircase-hook coefficients, and verify Saxl's
conjecture for 132 three-row partitions.
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Quantum Physics
Noise-Robustness for Delegated Quantum Computation in the Circuit Model
Anne Broadbent and Joshua Nevin
Cloud-based
quantum computing, coupled with the rapid progress in
quantum algorithms, brings to the forefront the question of verifiability in delegated
quantum computations. In the current landscape of noisy
quantum devices, this question must be addressed alongside noise tolerance. In this work, we revisit the
circuit-based framework for verifiable
quantum computation introduced by Broadbent [Theory of Computing, 2018], and extend it to the setting of server-side noise. Our contribution is an improved upper bound on the noise-tolerance threshold, achieved through a protocol that interleaves computation and test rounds in an indistinguishable manner. This structure enables a concise security proof against arbitrary deviations by the server, while ensuring robustness to realistic noise.
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Quantum Physics
On-Demand Control of Input-State-Dependent Single-Photon Scattering in Multi-Mode Waveguides
Yan Liu, Qing-Ao Xiang, Xin-Yuan Yang et al. (+4 more)
Precise control of a single
photon transport in broadband, multi-mode waveguides is a fundamental challenge for scalable
quantum networks. We propose a theoretical scheme for on-demand control of single-
photon scattering using a driven $\Lambda$-type emitter coupled to a rectangular waveguide. By employing the Lippmann-Schwinger formalism, we derive the exact analytical scattering
matrix and reveal two key interference mechanisms: electromagnetically induced transparency for complete transmission and Fano resonance for complete reflection. We demonstrate that the single-
photon scattering is dynamically engineered by the driving field, enabling a switch between complete transmission and dual-frequency complete reflection. Crucially, in the multi-mode regime, we show that the scattering is governed by
quantum interference between modes, making it critically dependent on the input photonic state. By preparing the
photon in a specific coherent superposition state, the multi-mode interference is harnessed to achieve Fano resonance-mediated complete reflection. Conversely, a single-mode input suppresses complete reflection. This input-state-dependent scattering establishes a general framework for multi-mode
quantum photonics, paving the way for broadband dual-frequency filters, multi-mode
quantum routers, and on-chip spectrometers.
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All authors Yan Liu, Qing-Ao Xiang, Xin-Yuan Yang, Ji-Bing Yuan, Shi-Qing Tang, Xin-Wen Wang, Ya-Ju Song
Quantum Physics
Nonreciprocal transmission in a cavity-magnon system by rotational Sagnac effect
Zhe-Qi Yang, Si-Qi Lin and Zhi-Rong Zhong
Ultrahigh nonreciprocal transmission has been achieved in a cavity-
magnon system, which consists of two whispering gallery modes (WGMs) and a single
magnon mode within a
magnetic insulator yttrium iron garnet sphere. The nonreciprocal frequency shift induced by the Sagnac effect enables unidirectional transmission of an input field, while suppressing propagation in the opposite direction, thereby facilitating nonreciprocal optical transmission. Within experimentally accessible parameter regimes, the optical isolation ratio can exceed 40 dB, representing the highest isolation ratio reported to date. Furthermore, applying squeezing to the
magnon mode further enhances this isolation performance. Additionally, the directionality of light isolation can be reversed simply by modifying the rotation of the WGM cavity. These findings offer promising prospects for developing high-performance, tunable, and compact optical nonreciprocal devices.
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Quantum Physics
Delayed Choice Quantum Eraser Experiment Revisited: Causality and Informational Coherence
Taku Ohwada
An operationally well-defined delayed-choice
quantum-eraser experiment is proposed, realizing a genuine delayed choice within presently available
quantum-optical technology. A multimode
quantum memory supplies a controlled and verifiable delay, ensuring that the choice operation is applied strictly after the observation event. Electronic single-
photon interference detection measurements furnish a direct statistical discriminator between the causal and informational coherence hypotheses, based solely on marginal detection statistics and without any post-selection.
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