Quantum Physics
Stroboscopic Saturation of Multiparameter Quantum Limits in Distributed Quantum Sensing
Berihu Teklu and Victor Montenegro
High-precision sensors that exploit uniquely
quantum phenomena have been shown to surpass the standard
quantum limit of measurement precision. However, in the general scenario where multiple parameters are simultaneously encoded in a
quantum probe, while surpassing the standard
quantum limit is possible, its practical attainability is severely hindered. This difficulty arises due to the fundamental incompatibility among the optimal measurements required for estimating different parameters. A naturally multiparameter sensing scenario emerges when a network of
quantum sensors is spatially distributed, with each individual sensor probing a distinct parameter of interest. The central goal in such a setting is twofold: first, to surpass the standard
quantum limit in estimating global properties of the system – thereby achieving
quantum-enhanced sensitivity for a given network size – and second, to explicitly identify the optimal measurement strategies necessary to practically attain this
quantum advantage. Here, we analytically demonstrate
quantum-enhanced sensitivity for a broad class of distributed
quantum probes, including cases where the precision scales quadratically or quartically with the sensing resources. We construct the corresponding optimal measurement strategies that achieve the ultimate precision limits – namely, saturation of both the Holevo and
quantum Cramér-Rao bounds. We then apply our framework to two concrete scenarios: the simultaneous estimation of multiple gravitational accelerations (gravimetry) and coupling strengths across spatially separated locations. Feasibility analyses indicate that the proposed distributed
quantum-enhanced sensing schemes are within reach of current experimental capabilities.
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Quantum Physics · Cross-listed from math.GR
On the invariants of finite groups arising in a topological quantum field theory
Christopher A. Schroeder and Hung P. Tong-Viet
In this paper, we investigate structural properties of finite groups that are detected by certain group invariants arising from Dijkgraaf–Witten theory, a topological
quantum field theory, in one space and one time dimension. In this setting, each finite group $G$ determines a family of numerical invariants associated with closed orientable surfaces, expressed in terms of the degrees of the complex irreducible characters of $G$. These invariants can be viewed as natural extensions of the commuting probability $d(G)$, which measures the probability that two randomly chosen elements of $G$ commute and has been extensively studied in the literature. By analyzing these higher-genus analogues, we establish new quantitative criteria relating the values of these invariants to key structural features of finite groups, such as commutativity, nilpotency, supersolvability and solvability. Our results generalize several classical
theorems concerning the commuting probability, thereby linking ideas from finite group theory and topological
quantum field theory.
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Quantum Physics
Orders matter: tight bounds on the precision of sequential quantum estimation for multiparameter models
Gabriele Fazio, Jiayu He and Matteo G. A. Paris
In multiparameter
quantum metrology, the ultimate precision of joint estimation is dictated by the Holevo Cramér-Rao bound. In this paper, we discuss and analyze in detail an alternative approach: the stepwise estimation strategy. In this approach, parameters are estimated sequentially, using an optimized fraction of the total available resources allocated to each step. We derive a tight and achievable precision bound for this protocol, the stepwise separable bound, and provide its closed-form analytical expression, revealing a crucial dependence on the chosen measurement ordering. We provide a rigorous comparison with the joint measurement strategy, deriving analytical conditions that determine when the stepwise approach offers superior precision. Through the analysis of several paradigmatic SU(2)
unitary encoding models, we demonstrate that the stepwise strategy can indeed outperform joint measurements, particularly in scenarios characterized by non-optimal probes or models with a high degree of sloppiness. Our findings establish stepwise estimation as a powerful alternative to joint and collective measurements, proving that sequential protocols can provide a genuine metrological advantage, especially in resource-constrained or imperfect experimental settings.
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Quantum Physics
Current fluctuations in nonequilibrium open quantum systems beyond weak coupling: a reaction coordinate approach
Khalak Mahadeviya, Saulo V. Moreira, Sheikh Parvez Mandal et al. (+3 more)
We investigate current fluctuations in open
quantum systems beyond the weak-coupling and Markovian regimes, focusing on a coherently driven
qubit strongly coupled to a structured bosonic environment. By combining full counting statistics with the reaction coordinate mapping, we develop a framework that enables the calculation of steady-state current fluctuations and their temporal correlations in the strong-coupling regime. Our analysis reveals that, unlike in weak coupling, both the average current and its fluctuations exhibit nonmonotonic dependence on the system-environment interaction strength. Notably, we identify a regime where current noise is suppressed below the classical thermodynamic uncertainty bound, coinciding with enhanced anticorrelations in
quantum jump trajectories and faster system relaxation. We further show that these features are linked to nonclassical properties of the reaction coordinate mode, such as non-Gaussianity and
quantum coherence. Our results provide new insights and design principles for controlling current fluctuations in
quantum devices operating beyond the standard weak-coupling paradigm.
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All authors Khalak Mahadeviya, Saulo V. Moreira, Sheikh Parvez Mandal, Mahasweta Pandit, Javier Prior, Mark T. Mitchison
Quantum Physics
Decoherence-Aware Entangling and Swapping Strategy Optimization for Entanglement Routing in Quantum Networks
Shao-Min Huang, Cheng-Yang Cheng, Ming-Huang Chien et al. (+2 more)
Quantum teleportation enables high-security communications through end-to-end
quantum entangled pairs. End-to-end entangled pairs are created by using swapping processes to consume short entangled pairs and generate long pairs. However, due to environmental interference, entangled pairs decohere over time, resulting in low fidelity. Thus, generating entangled pairs at the right time is crucial. Moreover, the swapping process also causes additional fidelity loss. To this end, this paper presents a short time slot protocol, where a time slot can only accommodate a process. It has a more flexible arrangement of entangling and swapping processes than the traditional long time slot protocol. It raises a new optimization problem TETRIS for finding strategies of entangling and swapping for each request to maximize the fidelity sum of all accepted requests. To solve the TETRIS, we design two novel
algorithms with different optimization techniques. Finally, the simulation results manifest that our
algorithms can outperform the existing methods by up to 60 ~ 78% in general, and by 20 ~ 75% even under low entangling probabilities.
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All authors Shao-Min Huang, Cheng-Yang Cheng, Ming-Huang Chien, Jian-Jhih Kuo, Chih-Yu Wang
Quantum Physics
Quantum circuit model for continuous-time quantum walks on random graphs
Sabyasachi Chakraborty, Rohit Sarma Sarkar, Sonjoy Majumder et al. (+1 more)
Quantum-
circuit implementations of continuous-time
quantum walks (CTQWs) can provide an efficient route to model graph-based
algorithms. However, constructing
circuits that faithfully reproduce CTQW dynamics across arbitrary graphs remains a major challenge. In this work, we introduce a
Laplacian partitioning
algorithm (LPA) that enables an efficient and scalable
quantum-
circuit realization of CTQWs on random graphs. A common
algorithm to simulate a general graph (of size $N = 2^n$ for $n$
qubits) on a
quantum circuit is based on Pauli decomposition of the graph
Hamiltonian, which can yield $O(4^n)$ terms, and require $O(N^2\log N)$ time for coefficient computation. In contrast, our LPA uses $O(2^n)$ terms, in $O(N^2)$ time. Our
circuit provides a graph-agnostic framework for CTQWs, implemented via a Trotter-Suzuki product formula and confirming error scaling consistent with theoretical Trotter error bounds. To further test the
circuit performance, we study the localization behavior of the CTQW. In our case, localization originates from
Laplacian spectral degeneracies rather than disorder (Anderson-type), and our
circuit faithfully reproduces these localization phenomena and spectral structure for a random graphs with high accuracy.
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All authors Sabyasachi Chakraborty, Rohit Sarma Sarkar, Sonjoy Majumder, Rohit Kishan Ray
Quantum Physics
Forecasting Quantum Observables: A Compressed Sensing Approach with Performance Guarantees
Víctor Valls, Albert Akhriev, Olatz Sanz Larrarte et al. (+5 more)
Data-driven extrapolation methods aim to extend the dynamics of
quantum observables from measurements, but they often lack guarantees on prediction accuracy. We introduce a framework based on atomic norm minimization that can certify whether the spectral model learned by a
forecasting algorithm – i.e., Bohr frequencies and amplitudes – is consistent with
unitary quantum time
evolution. Certification holds when the dynamics are governed by a small number of well-separated Bohr frequencies. We validate the approach on multiple
forecasting algorithms applied to
spin-chain
Hamiltonians with 8–20 sites. Comparing with exact diagonalization, certified models yield an average
forecasting error below 0.1 (observable range $[-1, 1]$) in 97% of cases and below 0.05 in 91–99% of cases. Even in the presence of noise, certified models remain robust at the 0.1 error threshold.
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All authors Víctor Valls, Albert Akhriev, Olatz Sanz Larrarte, Javier Oliva del Moral, Štěpán Šmíd, Josu Etxezarreta Martinez, Sergiy Zhuk, Dmytro Mishagli
Quantum Physics
Fast and fault-tolerant logical measurements: Auxiliary hypergraphs and transversal surgery
Alexander Cowtan, Zhiyang He, Dominic J. Williamson et al. (+1 more)
Quantum code surgery is a promising technique to perform fault-tolerant computation on
quantum low-density parity-check codes. Recent developments have significantly reduced the space overhead of surgery. However, generic surgery operations still require $O(d)$ rounds of repeated syndrome extraction to be made fault-tolerant. In this work, we focus on reducing the time overhead of surgery. We first present a general set of conditions that ensure fault-tolerant surgery operations can be performed with constant time overhead. This fast surgery necessarily makes use of an auxiliary complex described by a hypergraph rather than a graph. We then introduce a concrete scheme called block reading, which performs transversal surgery across multiple code blocks. We further investigate surgery operations with intermediate time overhead, between $O(1)$ and $O(d)$, which apply to
quantum locally testable codes. Finally, we establish a
circuit equivalence between homomorphic measurement and hypergraph surgery and derive bounds on the time overhead of generic logical measurement schemes. Overall, our results demonstrate that reducing the time cost of code surgery is not reliant on the
quantum memory being single-shot. Instead it is chiefly the connectivity between a code and its measurement ancilla system that determines the achievable measurement time overhead.
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All authors Alexander Cowtan, Zhiyang He, Dominic J. Williamson, Theodore J. Yoder
Quantum Physics
Ruelle-Pollicott Decay of Out-of-Time-Order Correlators in Many-Body Systems
Jerónimo Duarte, Ignacio García-Mata and Diego A. Wisniacki
The out-of-time-order correlator (OTOC) quantifies information scrambling in
quantum systems and serves as a key diagnostic of
quantum chaos. In one-body systems with a classical counterpart, the relaxation of the OTOC is governed by Ruelle-Pollicott resonances. For many-body systems lacking a semiclassical limit, recent studies have identified an analogous role played by the Liouvillian spectrum of weakly open extensions of the dynamics, where the slowest decay rate – the Liouvillian gap – encodes relaxation. Here we study the kicked Ising
spin chain and show that the long-time exponential decay of the OTOC in the isolated system occurs at a rate equal to twice this intrinsic gap. This correspondence is demonstrated across parameter regions exhibiting distinct level spacing statistics, indicating that the Liouvillian spectrum provides a robust framework for characterizing relaxation and irreversibility in closed many-body
quantum systems.
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Quantum Physics
Signatures of Topological Symmetries on a Noisy Quantum Simulator
Christopher Lamb, Robert M. Konik, Hubert Saleur et al. (+1 more)
Topological
symmetries, invertible and otherwise, play a fundamental role in the investigation of
quantum field theories. Despite their ubiquitous importance across a multitude of disciplines ranging from string theory to condensed matter physics, controlled realizations of models exhibiting these
symmetries in physical systems are rare.
Quantum simulators based on engineered solid-state devices provide a novel alternative to conventional condensed matter systems for realizing these models. In this work, eigenstates of
impurity Hamiltonians and loop operators associated with the topological
symmetries for the Ising conformal field theory in two space-time dimensions are realized on IBM's Kingston simulator. The relevant states are created on the
quantum device using a hybrid
quantum-classical
algorithm. The latter is based on a variation of the
quantum approximate optimization
algorithm ansatz combined with the
quantum natural gradient optimization method. Signatures of the topological
symmetry are captured by measuring correlation functions of different
qubit operators with results obtained from the
quantum device in reasonable agreement with those obtained from classical computations. The current work demonstrates the viability of noisy
quantum simulators as platforms for investigating low-dimensional
quantum field theories with direct access to observables that are often difficult to probe in conventional condensed matter experiments.
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All authors Christopher Lamb, Robert M. Konik, Hubert Saleur, Ananda Roy
Quantum Physics · Cross-listed from cond-mat.str-el
Quantum Fisher Information as a Thermal Probe in Frustrated Magnets through Insights from Quantum Spin Ice
Chengkang Zhou, Zhengbang Zhou, Félix Desrochers et al. (+2 more)
Quantum Fisher information (QFI) is a measure of multipartite
entanglement accessible via inelastic
neutron scattering. Here we demonstrate that QFI reveals thermal and dynamical properties of
quantum spin ice (QSI), a three-dimensional
quantum spin liquid with fractionalized excitations. By developing a multi-directed loop update
quantum Monte Carlo
algorithm, along with exact diagonalization and gauge mean-field theory, we compute the QFI for the pyrochlore
lattice. The temperature and momentum dependence of QFI maps the phase diagram, distinguishing the
ferromagnetic ordered phase, its critical region, the zero-flux QSI, and the $\pi$-flux QSI. QFI also captures two crossover scales: from trivial paramagnet to classical
spin ice, then to QSI. We discuss the $\pi$-flux QSI in light of experiments on cerium-based pyrochlores. Our results suggest that QFI not only detects
entanglement but also serves as a sensitive thermal and dynamical probe for frustrated
quantum magnets.
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All authors Chengkang Zhou, Zhengbang Zhou, Félix Desrochers, Yong Baek Kim, Zi Yang Meng
Quantum Physics
Efficient adaptive control strategy for multi-parameter quantum metrology in two-dimensional systems
Qifei Wei and Shengshi Pang
Quantum metrology leverages
quantum resources such as
entanglement and squeezing to enhance parameter estimation precision beyond classical limits. While optimal
quantum control strategies can assist to reach or even surpass the Heisenberg limit, their practical implementation often requires the knowledge of the parameters to be estimated, necessitating adaptive control methods with feedback. Such adaptive control methods have been considered in single-parameter
quantum metrology, but not much in multi-parameter
quantum metrology so far. In this work, we bridge this gap by proposing an efficient adaptive control strategy for multi-parameter
quantum metrology in two-dimensional systems. By eliminating the trade-offs among optimal measurements, initial states, and control
Hamiltonians through a system extension scheme, we derive an explicit relation between the
estimator variance and
evolution time. Through a reparameterization technique, the optimization of
evolution times in adaptive iterations are obtained, and a recursive relation is established to characterize the precision improvement across the iterations. The proposed strategy achieves the optimal performance up to an overall factor of constant order with only a few iterations and demonstrates strong robustness against deviations in the errors of control parameters at individual iterations. Further analysis shows the effectiveness of this strategy for
Hamiltonians with arbitrary parameter dependence. This work provides a practical approach for multi-parameter
quantum metrology with adaptive
Hamiltonian control in realistic scenarios.
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Quantum Physics
ParaToric 1.0: Continuous-time quantum Monte Carlo for the toric code in a parallel field
Simon M. Linsel and Lode Pollet
We introduce ParaToric, a C++ package for simulating the toric code in a parallel field (i.e., $X$- and $Z$-fields) at finite temperature. We implement and extend the continuous-time
quantum Monte Carlo
algorithm of Wu, Deng, and Prokof'ev on the square, triangular, honeycomb, and cubic
lattices with either periodic or smooth open boundaries. The package is expandable to arbitrary
lattice geometries and custom observables diagonal in either the $X$- or $Z$-basis. ParaToric also supports snapshot extraction in both bases, making it ideal for generating training/benchmarking data for other methods, such as
lattice gauge theories, cold atom or other
quantum simulators,
quantum spin liquids, artificial intelligence, and
quantum error correction. The software provides bindings to C/C++ and Python, and is thus almost universally integrable into other software projects.
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Quantum Physics · Cross-listed from physics.chem-ph
Herman-Kluk-Like Semi-Classical Initial-Value Representation for Boltzmann Operator
Binhao Wang, Fan Yang, Chen Xu et al. (+1 more)
The coherent-state initial-value representation (IVR) for the semi-classical real-time propagator of a
quantum system, developed by Herman and Kluk (HK), is widely used in computational studies of chemical dynamics. On the other hand, the Boltzmann operator $e^{-\hat{H}/(k_B T)}$, with $\hat{H}$,$k_B$, and $T$ representing the
Hamiltonian, Boltzmann constant, and temperature, respectively, plays a crucial role in chemical physics and other branches of
quantum physics. One might naturally assume that a semi-classical IVR for the
matrix element of this operator in the coordinate representation (i.e., $ \langle \tilde{x} | e^{-\hat{H}/(k_B T)} | x \rangle$, or the imaginary-time propagator) could be derived via a straightforward “real-time $\rightarrow$ imaginary-time transformation” from the HK IVR of the real-time propagator. However, this is not the case, as such a transformation results in a divergence in the high-temperature limit $(T \rightarrow \infty)$. In this work, we solve this problem and develop a reasonable HK-like semi-classical IVR for $ \langle \tilde{x} | e^{-\hat{H}/(k_B T)} | x \rangle$ specifically for systems where either the gradient of the potential energy (i.e., the force intensity) has a finite upper bound, or the potential becomes harmonic in the long-range limit. The integrand in this IVR is a real Gaussian function of the positions $x$ and $\tilde{x}$, which facilitates its application to realistic problems. Our HK-like IVR is exact for free particles and harmonic oscillators, and its effectiveness for other systems is demonstrated through numerical examples.
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All authors Binhao Wang, Fan Yang, Chen Xu, Peng Zhang
Quantum Physics · Cross-listed from physics.atom-ph
Impact of rotation on a cold atom interferometer and compensation strategy
Noémie Marquet, Yannick Bidel, Malo Cadoret et al. (+8 more)
Rotations play a detrimental role in achieving ultra-high-performance inertial measurements with an atom interferometer, leading potentially to a total loss of interference contrast and the emergence of dominant phase shift biases. This becomes particularly significant when considering operation in dynamic conditions such as those encountered in Earth orbiting satellites in the perspective of future space
gravity missions on-boarding a cold atom accelerometer. We study in this context the impact of rotation on the phase shift and contrast of an atom interferometer and investigate mitigation strategies. An analytical model is derived and compared to experimental demonstrations carried out using an original setup in which the well-controlled proof-mass of a space electrostatic accelerometer is used as the retro-reflection mirror of a cold atom gravimeter. By properly counter-rotating the electrostatic proof-mass, we demonstrate for instance the possibility of recovering the interferometer contrast, otherwise equal to zero, to a level better than 90%, in both cases of constant angular velocities or in presence of angular accelerations. Our results demonstrate the possibility to perform high performance inertial measurements with a cold atom interferometer in a challenging environments.
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All authors Noémie Marquet, Yannick Bidel, Malo Cadoret, Alexis Bonnin, Sylvain Schwartz, Phuong-Anh Huynh, Alexandre Bresson, Antoine Godard, Franck Pereira Dos Santos, Olivier Carraz, Nassim Zahzam
Quantum Physics
Quantum remeshing and efficient encoding for fracture mechanics
Ulysse Remond, Pierre-Emmanuel Emeriau, Liam Lysaght et al. (+3 more)
We present a variational
quantum algorithm for structural mechanical problems, specifically addressing crack opening simulations that traditionally require extensive computational resources. Our approach provides an alternative solution for a relevant 2D case by implementing a parametrized
quantum circuit that stores nodal displacements as
quantum amplitudes and efficiently extracts critical observables. The
algorithm achieves optimal nodal displacements by minimizing the elastic energy obtained from finite element method. The energy is computed with only a polylogarithmic number of measurements. Extracting relevant scalar observables such as the stress intensity factor is then done efficiently on the converged solution. To validate the scalability of our approach, we develop a warm start strategy based on a remeshing technique that uses coarse solutions to circumvent barren plateaus in the optimization landscape of the more refined problems. Our method has been experimentally validated on Quandela's photonic
quantum processor Ascella and comprehensive numerical simulations demonstrate its scalability across increasingly complex
quantum systems.
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All authors Ulysse Remond, Pierre-Emmanuel Emeriau, Liam Lysaght, Jean Ruel, Joseph Mikael, Kyryl Kazymyrenko
Quantum Physics
Purified phase estimation samples spectra efficiently
Stefano Scali, Josh Kirsopp, Antonio Márquez Romero et al. (+1 more)
Quantum phase estimation (QPE) is a cornerstone
algorithm for extracting
Hamiltonian eigenvalues, but its standard, eigenstate-centric form relies on carefully prepared coherent inputs that are costly or impractical for many strongly correlated systems. We overcome this bottleneck via DOS-QPE, an incoherent, purification-based variant of QPE that works directly with mixed-state probes and estimates the density of states (DOS) of the
Hamiltonian. By adding a purification register and simple entangling layers, we turn standard QPE into an ensemble-based DOS sampler without modifying the core phase-estimation block. Conceptually, this purification closely aligns with the recent random purification channel framework from
quantum learning theory, but instantiated here as a concrete phase-estimation
circuit. We further equip DOS-QPE with
symmetry-adapted input ensembles and a compressed-sensing reconstruction pipeline, and demonstrate on fermionic and
nuclear Hamiltonians that a single experimental setup can recover rich spectral information relevant to thermodynamics, spectroscopy, and many-body structure.
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All authors Stefano Scali, Josh Kirsopp, Antonio Márquez Romero, Michał Krompiec
Quantum Physics
Unsupervised Learning to Recognize Quantum Phases of Matter
Mehran Khosrojerdi, Alessandro Cuccoli, Paola Verrucchi et al. (+1 more)
Drawing the
quantum phase diagram of a many-body system in the parameter space of its
Hamiltonian can be seen as a learning problem, which implies labelling the corresponding ground states according to some classification criterium that defines the phases. In this work we adopt unsupervised learning, where the
algorithm has no access to any priorly labeled states, as a tool for determining
quantum phase diagrams of many-body systems. The
algorithm directly works with
quantum states: given the ground-state configurations for different values of the
Hamiltonian parameters, the process uncovers the most significant way of grouping them based on a similarity criterion that refers to the fidelity between
quantum states, that can be easily estimated, even experimentally. We
benchmark our method with two specific
spin-$\frac{1}{2}$ chains, with states determined via tensor network techniques. We find that unsupervised learning
algorithms based on spectral clustering, combined with “silhouette” and “elbow” methods for determining the optimal number of phases, can accurately reproduce the phase diagrams. Our results show how unsupervised learning can autonomously recognize and possibly unveil novel phases of
quantum matter.
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All authors Mehran Khosrojerdi, Alessandro Cuccoli, Paola Verrucchi, Leonardo Banchi
Quantum Physics · Cross-listed from hep-th
On Krylov Complexity as a Probe of the Quantum Mpemba Effect
Mohsen Alishahiha and Mohammad Javad Vasli
We investigate Krylov state complexity as a probe of the
quantum Mpemba effect in
quantum spin chains. For models without global $U(1)$
symmetry, Krylov complexity exhibits clear Mpemba-like crossings, consistent with conventional diagnostics such as the trace distance, while offering a complementary interpretation in terms of
Hilbert-space exploration and dynamical delocalization. In $U(1)$-symmetric systems, we confirm that the recently proposed symmetric component of Krylov complexity serves as a robust and reliable indicator of the QME, capturing anomalous relaxation even in cases where the total complexity fails to do so.
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Quantum Physics
Multiparameter quantum-enhanced adaptive metrology with squeezed light
Giorgio Minati, Enrico Urbani, Nicolò Spagnolo et al. (+2 more)
Squeezed light enables
quantum-enhanced phase estimation, with crucial applications in both fundamental physics and emerging technologies. To fully exploit the advantage provided by this approach, estimation protocols must remain optimal across the entire parameter range and resilient to instabilities in the probe state. In this context, strategies that rely on pre-calibrated squeezing levels are vulnerable to degradation over time and become sub-optimal when experimental conditions fluctuate. Here, we develop an adaptive multiparameter estimation strategy for ab-initio phase estimation, achieving sub-standard
quantum limit precision in the full periodicity interval $[0,\pi)$, without relying on prior knowledge of the squeezing parameter. Our approach employs real-time feedback to jointly estimate both the optical phase and the squeezing level, ensuring robustness against experimental drifts and calibration errors. This self-calibrating scheme establishes a reliable
quantum-enhanced sensing framework, opening new routes for practical scenarios and scalable distributed sensor networks using squeezed light.
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All authors Giorgio Minati, Enrico Urbani, Nicolò Spagnolo, Valeria Cimini, Fabio Sciarrino
Quantum Physics · Cross-listed from cond-mat.quant-gas
Nonlinear Landau levels in the almost-bosonic anyon gas
Alireza Ataei, Ask Ellingsen, Filippa Getzner et al. (+3 more)
We consider the quantitative description of a many-particle gas of interacting abelian anyons in the plane, confined in a trapping potential. If the anyons are modeled as
bosons with a
magnetic flux attachment, and if the total
magnetic flux is small compared to the number of particles, then an average-field description becomes appropriate for the low-energy collective state of the gas. Namely, by means of a Hartree-Jastrow ansatz, we derive a two-parameter Chern-Simons-Schrödinger energy functional which extends the well-known Gross-Pitaevskii / nonlinear Schrödinger density functional theory to the
magnetic (anyonic) self-interaction. One parameter determines the total number of self-generated
magnetic flux units in the system, and the other the effective strength of
spin-orbit self-interaction. This latter interaction can be either attractive/focusing or repulsive/defocusing, and depends both on the intrinsic
spin-orbit interaction and the relative length scale of the flux profile of the anyons. Densities and energies of ground and excited states are studied analytically and numerically for a wide range of the parameters and align well with a sequence of exact nonlinear Landau levels describing Jackiw-Pi self-dual
solitons. With increasing flux, counter-rotating
vortices are formed, enhancing the stability of the gas against collapse. Apart from clarifying the relations between various different anyon models that have appeared in the literature, our analysis sheds new light on the many-anyon spectral problem, and also exemplifies a novel supersymmetry-breaking phenomenon.
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All authors Alireza Ataei, Ask Ellingsen, Filippa Getzner, Théotime Girardot, Douglas Lundholm, Dinh-Thi Nguyen
Quantum Physics
Single-shot antidistinguishability of unitary operations
Satyaki Manna and Anandamay Das Bhowmik
The notion of antidistinguishability captures the possibility of ruling out certain alternatives in a
quantum experiment without identifying the actual outcome. Although extensively studied for
quantum states, the antidistinguishability of
quantum channels remains largely unexplored. In this work, we investigate the single-shot antidistinguishability of
unitary operations. We analyse two scenarios: antidistinguishability with single-system probes and with entangled probes. For sets of three
unitaries, we first prove that all maximally entangled states are equivalent in their performance as probe. In the
qubit case, we further establish that maximally entangled probes are always sufficient: if a set of three
qubit unitaries is antidistinguishable with either a single-system or non-maximally entangled probe, then it is also antidistinguishable with a maximally entangled one. However, in higher dimension, this equivalence fails. In dimension 3, there exists a set of
unitaries that are antidistinguishable with non-maximally entangled probe or single-system probe but not with maximally entangled probe. We also establish that union of two antidistinguishable sets of three
qubit unitaries also forms a set of antidistinguishable
unitaries. Lastly, we provide methods to construct antidistinguishable
unitaries from non-antidistinguishable ones.
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Quantum Physics
Quantum Reinforcement Learning: Recent Advances and Future Directions
Jawaher Kaldari, Shehbaz Tariq, Saif Al-Kuwari et al. (+3 more)
As
quantum machine learning continues to evolve, reinforcement learning stands out as a particularly promising yet underexplored frontier. In this survey, we investigate the recent advances in QRL to assess its potential in various applications. While QRL has generally received less
attention than other
quantum machine learning approaches, recent research reveals its distinct advantages and transversal applicability in both
quantum and classical domains. We present a comprehensive analysis of the QRL framework, including its
algorithms, architectures, and supporting SDK, as well as its applications in diverse fields. Additionally, we discuss the challenges and opportunities that QRL can unfold, highlighting promising use cases that may drive innovation in
quantum-inspired reinforcement learning and catalyze its adoption in various interdisciplinary contexts.
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All authors Jawaher Kaldari, Shehbaz Tariq, Saif Al-Kuwari, Samuel Yen-Chi Chen, Symeon Chatzinotas, Hyundong Shin
Quantum Physics · Cross-listed from cond-mat.str-el
Interplay of ferromagnetism, nematicity and Fermi surface nesting in kagome flat band
Yuman He, Wentao Jiang, Siqi Wu et al. (+4 more)
Recent experiment on Fe-doped CoSn has uncovered a series of correlated phases upon hole doping of the kagome flat bands. Among the phases observed, a nematic phase with a six- to two-fold rotation
symmetry breaking is found to prevail over a wide doping and temperature range. Motivated by these observations, we investigate the interaction-driven phases realized in a kagome model with partially filled, weakly dispersing flat bands. Density-density interactions up to second-nearest neighbors are considered. We identify a close competition between
ferromagnetic and nematic phases in our self-consistent Hartree-Fock calculations: while on-site interaction favors ferromagnetism, the sizable inter-sublattice interactions stabilize nematicity over a wide doping window. Competition from translational-
symmetry-breaking phases is also considered. Overall, our results show that nematicity is a generic outcome of partially filled kagome flat bands and establish a minimal framework for understanding correlated flat-band phases.
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All authors Yuman He, Wentao Jiang, Siqi Wu, Xuzhe Ying, Berthold Jack, Xi Dai, Hoi Chun Po
Quantum Physics
Quantization of Polaritons Confined in Dielectric Structures
Amir Rahmani, Dogyun Ko, Maciej Dems et al. (+2 more)
Light-matter interaction in the regime of strong
quantum coupling is usually treated within the framework of the Hopfield model. However, the picture of coupling well-defined modes of light and matter is correct only as long as the shapes of these eigenmodes are not substantially modified by the interaction. Moreover, parameters of theoretical models are usually obtained by fitting to experimental data. To date, there is no straightforward method to determine a
quantum master equation corresponding to a system with specific dielectric structure, which may lead to incompatibility of theoretical descriptions and physical realizations. In this work, a recipe for obtaining a
quantum model in the polariton eigenmode basis is presented, based on Bogoliubov transformation in the conservative case and third quantization technique in the dissipative case. It is shown how this method can be used for boosting interaction strength and engineering nonlocal many-body interactions in carefully designed nanostructures, resulting in strongly nonclassical correlations of emitted light.
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All authors Amir Rahmani, Dogyun Ko, Maciej Dems, Andrzej Opala, Michał Matuszewski
Quantum Physics
Diagnosing Simulation and Hardware Barriers to Cross-Size Transfer in Equivariant Quantum Reinforcement Learning
Monit Sharma and Hoong Chuin Lau
Equivariant
quantum circuits (EQCs) parameterise reinforcement-learning policies for combinatorial optimisation with a size-independent parameter count, suggesting policies trained on small instances may transfer to larger ones. Whether such transfer survives realistic execution has not been measured end-to-end. We train EQC policies on Euclidean Travelling Salesman instances and evaluate identical checkpoints across statevector simulation,
matrix-product-state simulation, noisy simulation, a protocol-matched noiseless emulator, and trapped-ion hardware. Within the validated regime, zero-shot five-to-ten-city transfer beats target-size training in all six evaluations. Beyond it, three barriers emerge: bond-dimension truncation destroys policy quality even without transfer; larger size jumps degrade performance consistently with a conditional diagnostic bound; and finite-shot execution inflates the transfer gap from ${\sim}5\%$ to $31.3\%$ (sampling noise alone) to $45.3\%$ hardware), because action margins lie below the shot-noise floor and collapse as $n^{-2.1}$. A cross-platform campaign across four hardware vendors confirms the penalty is set by native two-
qubit gate count and error mitigation, not shot budget. A shot-complexity bound formalises the obstruction. We claim no
quantum advantage; we provide the diagnostic standard such claims should meet.
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Quantum Physics · Cross-listed from cond-mat.mtrl-sci
Enhanced Secondary Electron Detection of Single Ion Implants in Silicon Through Thin SiO2 Layers
Ella B Schneider, Oscar G Lloyd-Willard, Kristian Stockbridge et al. (+7 more)
Deterministic placement of single dopants is essential for scalable
quantum devices based on group-V donors in silicon. We demonstrate a non-destructive, high-efficiency method for detecting individual ion implantation events using secondary electrons (SEs) in a focused ion beam (FIB) system. Using low-energy Sb ions implanted into undoped silicon, we achieve up to 98% single-ion detection efficiency, verified by calibrated ion-current measurements before and after implantation. The technique attains ~30 nm spatial resolution without requiring electrical contacts or device fabrication, in contrast to ion-beam-induced-current (IBIC) methods. We find that introducing a controlled SiO2 capping layer significantly enhances SE yield, consistent with an increased electron mean free path in the
oxide, while maintaining high probability of successful ion deposition in the underlying substrate. The yield appears to scale with ion velocity, so higher projectile mass (e.g. Yb, Bi etc) requires increased energy to maintain detection efficiency. Our approach provides a robust and scalable route to precise donor placement and extends deterministic implantation strategies to a broad range of material systems and
quantum device architectures.
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All authors Ella B Schneider, Oscar G Lloyd-Willard, Kristian Stockbridge, Mark Ludlow, Sam Eserin, Luke Antwis, David C Cox, Roger P Webb, Ben N Murdin, Steve K Clowes
Quantum Physics
Offline dedicated quantum attacks on block cipher constructions based on two parallel permutation-based pseudorandom functions
Xiao-Fan Zhen, Zhen-Qiang Li, Jia-Cheng Fan et al. (+2 more)
Quantum cryptanalysis is essential for evaluating the security of cryptographic systems against the threat of
quantum computing. Recently, Shi et al. introduced a dedicated
quantum attack on block cipher constructions based on XOR-type functions, which greatly reduces the required resources (including
circuit depth, width, and the number of gates) compared to the parallel Grover-meets-Simon
algorithm. Here, our contribution is in two aspects. On the one hand, we discover new cryptographic structures amenable to this attack: PolyMAC and constructions based on two parallel permutation-based pseudorandom functions (TPP-PRFs), including XopEM, SoEM22, SUMPIP, and DS-SoEM, thereby answering Shi et al.' s open question. On the other hand, for constructions based on TPP-PRFs, we break the obstacle that this attack relies on online query by constructing decoupled XOR-type functions, then propose an offline
quantum attack on them. Compared to previous results, our offline attack exhibits significantly reduced query complexity. Specifically, the number of queries to the encryption oracle is reduced from $O(2^{(n+t)/2}\cdot (n-t))$ to $O(2^{t}\cdot (n-t))$ in the
quantum query model, where $0<t<n$, $t$ is a truncation parameter, and $n$ is the input length of constructions. Further, we enable its implementation in the classical query model, optimizing both the classical query complexity and time complexity from $\tilde O(2^{2n/3})$ to $\tilde O(2^{(2n-t)/3})$ for $0<t \leq n/2$.
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All authors Xiao-Fan Zhen, Zhen-Qiang Li, Jia-Cheng Fan, Su-Juan Qin, Fei Gao
Quantum Physics · Cross-listed from math.AP
Small-time approximate controllability of the logarithmic Schr\”dinger equation
Karine Beauchard, Rémi Carles and Eugenio Pozzoli
We consider Schrödinger equations with logarithmic nonlinearity and bilinear controls, posed on $\mathbb{T}^d$ or $\mathbb{R}^d$. We prove their small-time global $L^2$-approximate controllability. The proof consists in extending to this nonlinear framework the approach introduced by the first and third authors in \cite{beauchard-pozzoli2} to control the linear equation: it combines the small-time controllability of phases and gradient flows. Due to the nonlinearity, the required estimates are more difficult to establish than in the linear case. The proof here is inspired by WKB analysis. This is the first result of (small-time) global approximate controllability, for nonlinear Schrödinger equations, with bilinear controls.
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Quantum Physics
Quantifiers of Noise Reducibility Under Restricted Control
Graeme D. Berk, Kavan Modi and Simon Milz
The correlation structure of multitime
quantum processes - succinctly described by
quantum combs - is an important resource for many
quantum information protocols and control tasks. Inspired by approaches for
quantum states, we introduce quantifiers of the practical utility of
quantum processes that satisfy monotonicity properties, thus overcoming shortcomings in previous state-motivated approaches. Applying these quantifiers to the problem of noise reduction of a
quantum process under open-loop control, they are shown to represent the largest amount of temporal mutual information that a process can possibly exhibit. In addition, we study their resource composition behaviour and connect them to the recently introduced notion of generalised comb divergences. Finally, in light of these new quantifiers, we re-interpret the numerical findings of npj
Quantum Information 9, 104 (2023) on the relationship of dynamical decoupling and non-Markovian
memory, which were based on insufficient resource quantifiers, and show that its main conclusion - the interpretation of dynamical decoupling as a resource
distillation - still holds.
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