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Wednesday 17 December

Quantum Physics

Wave-packet dynamics in pseudo-Hermitian lattices: Coexistence of Hermitian and non-Hermitian wavefronts

Alon Beck and Moshe Goldstein

This paper investigates wave-packet dynamics in non-Hermitian lattice systems and reveals a surprising phenomenon: The simultaneous propagation of two distinct wavefronts, one traveling at the non-Hermitian velocity and the other at the Hermitian velocity. We show that this dual-front behavior arises naturally in systems governed by a pseudo-Hermitian Hamiltonian. Using the paradigmatic Hatano-Nelson model as our primary example, we demonstrate that this coexistence is essential for understanding a wide array of unconventional dynamical effects, including abrupt “non-Hermitian reflections”, sudden shifts of Gaussian wave-packets, and disorder-induced emergent packets seeded by the small initial tails. We present analytic predictions that closely match numerical simulations. These results may offer new insight into the topology of non-Hermitian systems and point toward measurable experimental consequences.
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Quantum Physics

Practical Challenges in Executing Shor's Algorithm on Existing Quantum Platforms

Paul Bagourd, Julian Jang-Jaccard, Vincent Lenders et al. (+3 more)

Quantum computers pose a fundamental threat to widely deployed public-key cryptosystems, such as RSA and ECC, by enabling efficient integer factorization using Shor's algorithm. Theoretical resource estimates suggest that 2048-bit RSA keys could be broken using Shor's algorithm with fewer than a million noisy qubits. Although such machines do not yet exist, the availability of smaller, cloud-accessible quantum processors and open-source implementations of Shor's algorithm raises the question of what key sizes can realistically be factored with today's platforms. In this work, we experimentally investigate Shor's algorithm on several cloud-based quantum computers using publicly available implementations. Our results reveal a substantial gap between the capabilities of current quantum hardware and the requirements for factoring cryptographically relevant integers. In particular, we observe that circuit constructions still need to be highly specific for each modulus, and that machine fidelities are unstable, with high and fluctuating error rates.
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All authors Paul Bagourd, Julian Jang-Jaccard, Vincent Lenders, Alain Mermoud, Torsten Hoefler, Cornelius Hempel

Quantum Physics

Continuous-mode analysis for practical continuous-variable quantum key distribution

Yanhao Sun, Jiayu Ma, Xiangyu Wang et al. (+3 more)

Continuous-variable quantum key distribution (CV-QKD) enables two remote parties to establish information-theoretically secure keys and offers high practical feasibility due to its compatibility with mature coherent optical communication technologies. However, as CV-QKD systems progress toward digital implementations, device nonidealities drive the optical field from a single-mode to a continuous-mode region, thereby underscoring the mismatch between theoretical models and practical systems. Here, we introduce temporal modes to construct an entanglement-based scheme that more accurately captures device nonidealities and develop a corresponding secret key rate calculation method applicable to continuous-mode scenarios. We demonstrate that optimizing the pulse-shaping format can significantly improve performance under detector-bandwidth-limited conditions. Experimental results also confirm that the proposed model effectively describes the impact of sampling-time deviations. We further analyze a linear weighted-reconstruction digital signal processing method,which improves the secret key rate by approximately 50% in a 30-km fiber experiment without requiring additional hardware, demonstrating a substantial performance enhancement at metropolitan distances. The proposed theoretical framework accommodates a broader range of experimental conditions and can guide the optimization of digital CV-QKD systems.
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All authors Yanhao Sun, Jiayu Ma, Xiangyu Wang, Song Yu, Ziyang Chen, Hong Guo

Quantum Physics

Decoherence in the Pure Dephasing Spin-Boson Model with Hermitian or Non-Hermitian Bath

Yue-Hong Wu and Ning-Hua Tong

In this paper, we investigate the decoherence of qubit due to its coupling to a Hermitian or a non-Hermitian bath within the pure dephasing spin-boson model. First, using this model, we analytically establish the previously anticipated similarity between the non-equilibrium and the equilibrium correlation functions $P_x(t)$ and $C_x(t)$. Then, in the short/long time asymptotic behaviors of $P_x(t)$, we find singular dependence on $A$ (coupling strength) and $s$ (bath exponent) at their integer values. Finally, we find that the non-Hermitian bath tends to suppress the decoherence of qubit for all values of $A$ and $s$, in contrast to the conclusion of Dey et al. . Our results show the potential of non-Hermitian environment engineering in suppressing the decoherence of qubit.
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Quantum Physics · Cross-listed from cond-mat.quant-gas

Two-Body Kapitza-Dirac Scattering of One-Dimensional Ultracold Atoms

André Becker, Georgios M. Koutentakis and Peter Schmelcher

Kapitza-Dirac scattering, the diffraction of matter waves from a standing light field, is widely utilized in ultracold gases, but its behavior in the strongly interacting regime is an open question. Here we develop a numerically-exact two-body description of Kapitza-Dirac scattering for two contact-interacting atoms in a one-dimensional harmonic trap subjected to a pulsed optical lattice, enabling us to obtain the numerically exact dynamics. We map how interaction strength, lattice depth, lattice wavenumber, and pulse duration reshape the diffraction pattern, leading to an interaction-dependent population redistribution in real and momentum-space. By comparing the exact dynamics to an impulsive sudden-approximation description, we delineate the parameter regimes where it remains accurate and those, notably at strong attraction and small lattice wavenumber, where it fails. Our results provide a controlled few-body benchmark for interacting Kapitza-Dirac scattering and quantitative guidance for Kapitza-Dirac-based probes of ultracold atomic systems.
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Quantum Physics

Quantum Mpemba effect in Local Gauge Symmetry Restoration

Hao-Yue Qi and Wei Zheng

Understanding relaxation in isolated quantum many-body systems remains a central challenge. Recently, the quantum Mpemba effect (QME), a counterintuitive relaxation phenomenon, has attracted considerable attention and has been extensively studied in systems with global symmetries. Here, we study the QME in gauge theories with massive local gauge symmetries. In the lattice Schwinger model, we demonstrate that the gauge structure of the reduced density matrix of a subsystem is entirely determined by the initial state and remain unchanged during the time evolution. We then investigate whether gauge symmetry can be dynamically restored following a symmetric quench. Analytical and numerical results show that when the Maxwell term is zero, gauge symmetry restoration fails due to the emergence of a peculiar conservation law. However, for any finite Maxwell term, subsystem gauge symmetry is restored in the thermodynamic limit. Based on these results, we systematically construct a families of initial states exhibiting the QME. We further explore the QME in the quantum link model-a truncated lattice Schwinger model, which has been realized in experiments. Moreover, we propose an experimentally accessible order parameter that correctly captures the QME. Our work demonstrates the generality of the quantum Mpemba effect even in the local gauge symmetries, and are directly relevant to ongoing quantum simulation experiments of gauge theories.
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Quantum Physics · Cross-listed from physics.bio-ph

Quantum Dynamics of a Nanorotor Driven by a Magnetic Field

V. N. Binhi

A molecular rotor mechanism is proposed to explain weak magnetic field effects in biology. Despite being nanoscale (1 nm), this rotor exhibits quantum superposition and interference. Analytical modeling shows its quantum dynamics are highly sensitive to weak, but not strong, magnetic fields. Due to its enhanced moment of inertia, the rotor maintains quantum coherence relatively long, even in a noisy cellular environment. Operating at the mesoscopic boundary between quantum and classical behavior, such a rotor embedded in cyclical biological processes could exert significant and observable biological influence.
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Quantum Physics

Sharing quantum indistinguishability with multiple parties

Lemieux Wang, Hanwool Lee, Joonwoo Bae et al. (+1 more)

Quantum indistinguishability of non-orthogonal quantum states is a valuable resource in quantum information applications such as cryptography and randomness generation. In this article, we present a sequential state-discrimination scheme that enables multiple parties to share quantum uncertainty, in terms of the max relative entropy, generated by a single party. Our scheme is based upon maximum-confidence measurements and takes advantages of weak measurements to allow a number of parties to perform state discrimination on a single quantum system. We review known sequential state discrimination and show how our scheme would work through a number of examples where ensembles may or may not contain symmetries. Our results will have a role to play in understanding the ultimate limits of sequential information extraction and guide the development of quantum resource sharing in sequential settings.
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All authors Lemieux Wang, Hanwool Lee, Joonwoo Bae, Kieran Flatt

Quantum Physics

Composite N-Q-S: Serial/Parallel Instrument Axioms, Bipartite Order-Effect Bounds, and a Monitored Lindblad Limit

Kazuyuki Yoshida

We develop a composite operational architecture for sequential quantum measurements that (i) gives a tight bipartite order-effect bound with an explicit equality set characterized on the Halmos two-subspace block, (ii) upgrades Doeblin-type minorization to composite instruments and proves a product lower bound for the operational Doeblin constants, yielding data-driven exponential mixing rates, (iii) derives a diamond-norm commutator bound that quantifies how serial and parallel rearrangements influence observable deviations, and (iv) establishes a monitored Lindblad limit that links discrete look-return loops to continuous-time GKLS dynamics under transparent assumptions. Building on the GKLS framework of Gorini, Kossakowski, Sudarshan, Lindblad, Davies, Spohn, and later work of Fagnola-Rebolledo and Lami et al., we go beyond asymptotic statements by providing finite-sample certificates for the minorization parameter via exact binomial intervals and propagating them to rigorous bounds on the number of interaction steps required to attain a prescribed accuracy. A minimal qubit toy model and CSV-based scripts are supplied for full reproducibility. Our results position order-effect control and operational mixing on a single quantitative axis, from equality windows for pairs of projections to certified network mixing under monitoring. The framework targets readers in quantum information and quantum foundations who need explicit constants that are estimable from data and transferable to device-level guarantees.
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Quantum Physics

Dynamics and steady states of tight-binding chains in presence of isolated defects

Anish Acharya, Luca Giuggioli and Shamik Gupta

Reduced transport and localization in isolated quantum systems are typically attributed to spatially-extended disorder, but may also emerge from the influence of a few controllable defects. We show here how a single defect profoundly reshapes wave-function spreading on a finite and periodic tight-binding lattice. Adapting the defect technique from classical random-walk studies, we obtain exact time-resolved site-occupation probabilities and several observables of interest. Even a single defect induces remarkable nonlinear effects, including non-monotonic suppression of transport, enhanced localization at distant sites, and strong sensitivity to the initial particle position at long times. These results demonstrate that minimal perturbations can generate nontrivial long-time transport signatures, giving rise to a microscopic defect-driven mechanism of quantum localization. Although the main results presented pertain to a single isolated defect, we show that the developed formalism may naturally extend to multiple as well as to a wider class of defects.
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Quantum Physics

Universal Blind Quantum Computation with Recursive Rotation Gates

Mohit Joshi, Manoj Kumar Mishra and S. Karthikeyan

Blind Quantum Computation lets a limited-capability client delegate its complex computation to a remote server without revealing its data or computation. Several such protocols have been proposed under varied quantum computing models. However, these protocols either rely on highly entangled resource states (in measurement-based models) or are based on non-parametric resource sets (in circuit-based models). These restrictions hinder the practical applicability of such an algorithm in the NISQ era, especially concerning the hybrid quantum-classical infrastructure, which depends on parametric gates. We present a protocol for universal blind quantum computation based on recursive decryption of parametric rotation gates, which does not require a highly entangled state at the server side and substantially reduces the communication rounds required for practical prototyping of secure variational algorithms.
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Quantum Physics

Exponential convergence dynamics in Grover's search algorithm

Samuel Cogan, Jonathan Raghoonanan and Tim Byrnes

Grover's search algorithm is the cornerstone of many applications of quantum computing, providing a quadratic speed-up over classical methods. One limitation of the algorithm is that it requires knowledge of the number of solutions to obtain an optimal success probability, due to the oscillatory dynamics between the initial and solution states (the “soufflé problem”). While various methods have been proposed to solve this problem, each has its drawbacks in terms of inefficiency or sensitivity to control errors. Here, we modify Grover's algorithm so that, for suitably chosen parameters, the usual oscillatory dynamics are replaced by an approximately exponential convergence into the solution subspace. The basic idea is to couple the solution states to an engineered ancilla reservoir such that the initial state is nonreflectively absorbed. Trotterizing the continuous algorithm yields a quantum circuit that gives equivalent performance, while preserving the same quadratic quantum speedup as the original algorithm.
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Quantum Physics

Quantum data hiding with two-qubit separable states

Donghoon Ha and Jeong San Kim

We consider the discrimination of two-party quantum states and provide a quantum data-hiding scheme using two-qubit separable states. We first provide a bound on the optimal local discrimination of two-party quantum states, and establish a sufficient condition under which a two-party quantum state ensemble can be used to construct a data-hiding scheme. We illustrate this condition with examples of two-qubit state ensembles consisting of two orthogonal separable states. As our data-hiding scheme can be implemented with separable states of the lowest possible dimension, its practical realization becomes significantly more attainable.
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Quantum Physics

Coherent transfer via parametric control of normal-mode splitting in a superconducting multimode resonator

Kai-I Chu, Xiao-Cheng Lu, Hsin Chang et al. (+5 more)

Microwave storage and retrieval are essential capabilities for superconducting quantum circuits. Here, we demonstrate an on-chip multimode resonator in which strong parametric modulation induces a large and tunable normal-mode splitting that enables microwave storage. When the spectral bandwidth of a short microwave pulse covers the two dressed-state absorption peaks, part of the pulse is absorbed and undergoes coherent energy exchange between the modes, producing a clear time-domain beating signal. By switching off the modulation before the beating arrives, we realize on-demand storage and retrieval, demonstrating an alternative approach to microwave photonic quantum memory. This parametric-normal-mode-splitting protocol offers a practical route toward a controllable quantum-memory mechanism in superconducting circuits.
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All authors Kai-I Chu, Xiao-Cheng Lu, Hsin Chang, Wei-Cheng Hung, Jing-Yang Chang, Jeng-Chung Chen, Chii-Dong Chen, Yung-Fu Chen

Quantum Physics

Quantum batteries in coherent Ising machine

Jin-Tian Zhang, Shuang-Quan Ma, Jing-Yi-Ran Jin et al. (+2 more)

With intensive studies of quantum thermodynamics, quantum batteries (QBs) have been proposed to store and transfer energy via quantum effects. Despite many theoretical models, decoherence remains a severe challenge and practical platforms are still rare. Here, we propose a QB based on the coherent Ising machine, in which the signal field acts as the core energy-storage unit. To clarify the role of quantum coherence in resisting dissipation, we decompose the ergotropy, i.e., the maximum extractable work from the QB, into its coherent and incoherent components. We find that the coherent part decays at a rate roughly half that of the incoherent part, exhibiting much stronger robustness against decoherence. More importantly, the coherent ergotropy and the average charging power reach their respective maxima at essentially the same moment, which defines the optimal instant to switch off the pump field. Finally, by coupling the QB to a two-level system as the load, we demonstrate an efficient energy discharge process of the proposed QB. Our work establishes a realistic and immediately-implementable QB architecture on a mature optical platform, laying a foundation for experimental exploration of quantum energy storage.
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All authors Jin-Tian Zhang, Shuang-Quan Ma, Jing-Yi-Ran Jin, Tao Liu, Qing Ai

Quantum Physics

Bosonic quantum computing with near-term devices and beyond

Timo Hillmann

(Abridged.) This thesis investigates scalable fault-tolerant quantum computation through the development of bosonic quantum codes, quantum LDPC codes, and decoding protocols that connect continuous-variable and discrete-variable error correction. We investigate superconducting microwave implementations of continuous-variable quantum computing, including the deterministic generation of cubic phase states, and introduce the dissipatively stabilized squeezed cat qubit, a noise-biased bosonic encoding with enhanced error suppression and faster gates. The performance of rotation-symmetric and GKP codes is analyzed under realistic noise and measurement models, revealing key trade-offs in measurement-based schemes. To integrate bosonic codes into larger architectures, we develop decoding methods that exploit analog syndrome information, enabling quasi-single-shot decoding in concatenated systems. On the discrete-variable side, we introduce localized statistics decoding, a highly parallelizable decoder for quantum LDPC codes, and propose quantum radial codes, a new family of single-shot LDPC codes with low overhead and strong circuit-level performance. Finally, we present fault complexes, a homological framework for analyzing faults in dynamic quantum error correction protocols. Extending the role of homology in static CSS codes, fault complexes provide a general language for the design and analysis of fault-tolerant schemes.
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Quantum Physics

Microscopic model for a spatial multimode generation based on Multi-pump Four Wave Mixing in hot vapours

H.M. Florez

Multipartite entanglement is an important resource for quantum information processing. It has been shown that it is possible to employ alkali atoms to implement single device multipartite entanglement by using nonlinear processes with spatial modes. This work presents the first microscopic description of such multi-mode generation with two-pump four wave mixing (4WM) in dense atomic media. We implement an extension of a double $\Lambda$ model for a single pump 4WM in order to describe the multi-mode generation with a two-pump configuration. We propose a Floquet expansion to solve the multimode gain amplification and noise properties. The model describes the angle and the two-photon dependency of the multimode generation and the quantum correlations among the modes. We investigate the entanglement properties of the system, describing the main properties of previous experimental observations. Such a microscopic description can be used to predict the gain distribution of modes and the quantum correlation within a typical range of experimental parameters.
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Quantum Physics

Graph-theoretical search for integrable multistate Landau-Zener models

Zixuan Li and Chen Sun

The search for exactly solvable models is an evergreen topic in theoretical physics. In the context of multistate Landau-Zener models – $N$-state quantum systems with linearly time-dependent Hamiltonians – the theory of integrability provides a framework for identifying new solvable cases. In particular, it was proved that the integrability of a specific class known as the multitime Landau-Zener (MTLZ) models guarantees their exact solvability. A key finding was that an $N$-state MTLZ model can be represented by data defined on an $N$-vertex graph. While known host graphs for MTLZ models include hypercubes, fans, and their Cartesian products, no other families have been discovered, leading to the conjecture that these are the only possibilities. In this work, we conduct a systematic graph-theoretical search for integrable models within the MTLZ class. By first identifying minimal structures that a graph must contain to host an MTLZ model, we formulate an efficient algorithm to systematically search for candidate graphs for MTLZ models. Implementing this algorithm using computational software, we enumerate all candidate graphs with up to $N = 13$ vertices and perform an in-depth analysis of those with $N \le 11$. Our results corroborate the aforementioned conjecture for graphs up to $11$ vertices. For even larger graphs, we propose a specific family, termed descendants of “$(0,2)$-graphs”, as promising candidates that may violate the conjecture above. Our work can serve as a guideline to identify new exactly solvable multistate Landau-Zener models in the future.
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Quantum Physics

Characterizing entanglement shareability and distribution in $N$-partite systems

Hui Li, Ting Gao and Fengli Yan

Exploring the shareability and distribution of entanglement possesses fundamental significance in quantum information tasks. In this paper, we demonstrate that the square of bipartite entanglement measures $G_q$-concurrence, which is the generalization of concurrence, follows a set of hierarchical monogamy relations for any $N$-qubit quantum state. On the basis of these monogamy inequalities, we render two kinds of hierarchical indicators that exhibit evident advantages in the capacity of witnessing entanglement. Moreover, we show an analytical relation between $G_q$-concurrence and concurrence in $2\otimes d$ systems. Furthermore, we rigorously prove that the monogamy property of squared $G_q$-concurrence is superior to that of squared concurrence in $2\otimes d_2\otimes d_3\otimes\cdots\otimes d_N$ systems. In addition, several concrete examples are provided to illustrate that for multilevel systems, the squared $G_q$-concurrence satisfies the monogamy relation, even if the squared concurrence does not. These results better reveal the intriguing characteristic of multilevel entanglement and provide critical insights into the entanglement distribution within multipartite quantum systems.
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Quantum Physics

Enabling Technologies for Scalable Superconducting Quantum Computing

Xanthe Croot, Kasra Nowrouzi, Christopher Spitzer et al. (+21 more)

Experiments with superconducting quantum processors have successfully demonstrated the basic functions needed for quantum computation and evidence of utility, albeit without a sizable array of error-corrected qubits. The realization of the full potential of quantum computing centers on achieving large scale fault-tolerant quantum computers. Science, engineering and industry advances are needed to robustly generate, sustain, and efficiently manipulate an exponentially large computational (Hilbert) space as well as supply the number and quality components needed for such a scaled system. In this article, we suggest critical areas of quantum system and ecosystem development, with respect to the handling and transmission of quantum information within and out of a cryogenic environment, that would accelerate the development of quantum computers based on superconducting circuits.
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All authors Xanthe Croot, Kasra Nowrouzi, Christopher Spitzer, Carmen G. Almudever, Alexandre Blais, Malcolm Carroll, Jerry Chow, Daniel Friedman, Masao Tokunari, Edoardo Charbon, Vivek Chidambaram, Andrew N. Cleland, David Danovitch, Joseph Emerson, David Gunnarsson, Raymond Laflamme, John Martinis, Robert McDermott, William D. Oliver, Michel Pioro-Ladriere, Yoshiaki Sato, Hidenori Ohata, Kouichi Semba, Irfan Siddiqi

Quantum Physics

Trade-off relations and enhancement protocol of quantum battery capacities in multipartite systems

Yiding Wang, Xiaofen Huang, Shao-Ming Fei et al. (+1 more)

First, we investigate the trade-off relations of quantum battery capacities in two-qubit system. We find that the sum of subsystem battery capacity is governed by the total system capacity, with this trade-off relation persisting for a class of Hamiltonians, including Ising, XX, XXZ and XXX models. Then building on this relation, we define residual battery capacity for general quantum states and establish coherent/incoherent components of subsystem battery capacity. Furthermore, we introduce the protocol to guide the selection of appropriate incoherent unitary operations for enhancing subsystem battery capacity in specific scenarios, along with a sufficient condition for achieving subsystem capacity gain through unitary operation. Numerical examples validate the feasibility of the incoherent operation protocol. Additionally, for the three-qubit system, we also established a set of theories and results parallel to those for two-qubit case. Finally, we determine the minimum time required to enhance subsystem battery capacity via a single incoherent operation in our protocol. Our findings contribute to the development of quantum battery theory and quantum energy storage systems.
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All authors Yiding Wang, Xiaofen Huang, Shao-Ming Fei, Tinggui Zhang

Quantum Physics

High efficiency controlled quantum secure direct communication with 4D qudits and Grover search algorithm

Ni-Shi Lu and Ping Zhou

Currently, the progress of quantum secure direct communication (QSDC) is impeded by a fundamental trade off among control efficiency, security, and scalability. This study proposes an innovative controlled QSDC protocol based on a collaborative unitary sequence decoding paradigm to break this deadlock.Leveraging four dimensional single particle states, the protocol's core innovation lies in its three party decoding mechanism. The controller's authorization unlocks a specific unitary operation sequence, enabling the receiver to directly decode exclusively via quantum operations, eliminating the need for classical computational algorithms in conventional protocols. This tailored sequence underpins its high efficiency.The protocol also seamlessly incorporates decoy photon authentication, creating a multi layer defense against both external and internal attacks. Consequently, it achieves a remarkable qudit efficiency of 66.7%, offering a significant performance improvement over existing schemes and an efficient, highly secure solution for future quantum networks.
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Tuesday 16 December

Quantum Physics

A quantum advection-diffusion solver using the quantum singular value transform

Gard Olav Helle, Tommaso Benacchio, Anna Bomme Ousager et al. (+1 more)

We present a quantum algorithm for the simulation of the linear advection-diffusion equation based on block encodings of high order finite-difference operators and the quantum singular value transform. Our complexity analysis shows that the higher order methods significantly reduce the number of gates and qubits required to reach a given accuracy. The theoretical results are supported by numerical simulations of one- and two-dimensional benchmarks.
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All authors Gard Olav Helle, Tommaso Benacchio, Anna Bomme Ousager, Jørgen Ellegaard Andersen

Quantum Physics · Cross-listed from physics.optics

Self-referenced nonlinear interferometry for chromatic dispersion sensing across multiple length scales

Romain Dalidet, Sébastien Tanzilli, Gregory Sauder et al. (+2 more)

Chromatic dispersion critically impacts the performance of numerous applications ranging from telecommunication links to ultrafast optics and nonlinear devices, yet fast and precise measurements are challenging, especially for short length-dispersion products. We present a fully fiber-integrated nonlinear Sagnac interferometer that exploits cascaded second-order processes to generate frequency-anticorrelated idler light and achieve odd-order dispersion cancellation without active stabilization. The measurement is intrinsically self-referenced, as the dispersion-induced phase is extracted from the interference between counter-propagating nonlinear processes within the same Sagnac loop, eliminating the need for an external reference arm or prior calibration. Operating entirely at telecom wavelengths and read out on a standard optical spectrum analyzer, the device produces instantaneous, high-visibility fringes and calibration-free spectra using dual-port normalization. We demonstrate chromatic dispersion measurements on fiber samples ranging from 25 cm to 4 km, spanning short fiber segments to long-haul links. This architecture combines self-stability, broadband compatibility, and rapid acquisition, offering a practical metrology tool for both research and industry.
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All authors Romain Dalidet, Sébastien Tanzilli, Gregory Sauder, Laurent Labonté, Anthony Martin

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

Women in Theoretical Quantum Physics in Brazil:demographics, career profiles, recognition, and leadership

Tatiana Pauletti, Paula Homem de Mello, Thereza Paiva et al. (+1 more)

Gender imbalance in Physics remains a persistent global challenge, and Brazil is no exception. While women account for only 24% of Physics faculty in the country, their representation in Quantum Physics is even smaller. In this work, we provide the first comprehensive overview of women working in Theoretical Quantum Physics in Brazil, here referred to as the SheQ (She + Quantum) community. Using data from the CNPq Lattes platform, we identify 93 researchers and analyze their geographic distribution, academic trajectories, scientific productivity, international experience, recognition through awards and fellowships, and engagement with initiatives promoting gender equity. Our results reveal both progress and persistent disparities: SheQ researchers have a strong scientific output, leadership roles, and international training; yet, their recognition through productivity fellowships remains modest, and their involvement in gender-related initiatives, although increasing among younger generations, remains limited. By combining quantitative indicators with institutional perspectives, we highlight structural barriers as well as opportunities for fostering a more inclusive environment in Quantum Physics. his study thus contributes to a broader reflection on how diversity not only promotes fairness but also strengthens creativity, innovation, and scientific progress.
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All authors Tatiana Pauletti, Paula Homem de Mello, Thereza Paiva, Vivian V.França

Quantum Physics

Geometric Latent Space Tomography with Metric-Preserving Autoencoders

S.M. Yousuf Iqbal Tomal and Abdullah Al Shafin

Quantum state tomography faces exponential scaling with system size, while recent neural network approaches achieve polynomial scaling at the cost of losing the geometric structure of quantum state space. We introduce geometric latent space tomography, combining classical neural encoders with parameterized quantum circuit decoders trained via a metric-preservation loss that enforces proportionality between latent Euclidean distances and quantum Bures geodesics. On two-qubit mixed states with purity 0.85–0.95 representing NISQ-era decoherence, we achieve high-fidelity reconstruction (mean fidelity $F = 0.942 \pm 0.03$) with an interpretable 20-dimensional latent structure. Critically, latent geodesics exhibit strong linear correlation with Bures distances (Pearson $r = 0.88$, $R^2 = 0.78$), preserving 78% of quantum metric structure. Geometric analysis reveals intrinsic manifold dimension 6.35 versus 20 ambient dimensions and measurable local curvature ($\kappa = 0.011 \pm 0.006$), confirming non-trivial Riemannian geometry with $O(d^2)$ computational advantage over $O(4^n)$ density matrix operations. Unlike prior neural tomography, our geometry-aware latent space enables direct state discrimination, fidelity estimation from Euclidean distances, and interpretable error manifolds for quantum error mitigation without repeated full tomography, providing critical capabilities for NISQ devices with limited coherence times.
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Quantum Physics · Cross-listed from cond-mat.quant-gas

Localization from Infinitesimal Kinetic Grading: Finite-size Scaling, Kibble-Zurek Dynamics and Applications in Sensing

Argha Debnath, Ayan Sahoo and Debraj Rakshit

We study a one-dimensional lattice model with site-dependent nearest-neighbor hopping amplitudes that follow a power-law profile. The hopping variation is controlled by a grading exponent, $|alpha|$, which serves as the tuning parameter of the system. In the thermodynamic limit, the ground state becomes localized in the limit $|alpha| \to 0$, signaling the presence of a critical point characterized by a diverging localization length. Using exact diagonalization methods, we perform finite-size scaling analysis, and extract the associated critical exponent governing the near-critical behavior. To further characterize the criticality, we analyze inverse participation ratio (IPR), energy gap between the ground and first excited state, and fidelity-susceptibility. We also investigate the nonequilibrium dynamics by linearly ramping the hopping profile at various rates and tracking the evolution of the localization length and the IPR. The Kibble-Zurek mechanism successfully explains the resulting dynamics of the system via the critical exponents obtained from static scaling analysis. Beyond its fundamental significance, the kinetic-grading-induced localization transition provides a natural platform for quantum sensing. Using the critical enhancement of the quantum Fisher information (QFI), we demonstrate that the system enables quantum-enhanced parameter estimation of the grading exponent. We propose both adiabatic and dynamical quantum critical sensors and demonstrate that they exhibit enhanced scaling of the QFI. Our results therefore establish graded kinetic systems not only as a new setting for localization physics, but also as a potential resource for designing quantum-enhanced sensing devices.
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Quantum Physics

Roadmap: 2D Materials for Quantum Technologies

Qimin Yan, Tongcang Li, Xingyu Gao et al. (+29 more)

Two-dimensional (2D) materials have emerged as a versatile and powerful platform for quantum technologies, offering atomic-scale control, strong quantum confinement, and seamless integration into heterogeneous device architectures. Their reduced dimensionality enables unique quantum phenomena, including optically addressable spin defects, tunable single-photon emitters, low-dimensional magnetism, gate-controlled superconductivity, and correlated states in Moiré superlattices. This Roadmap provides a comprehensive overview of recent progress and future directions in exploiting 2D materials for quantum sensing, computation, communication, and simulation. We survey advances spanning spin defects and quantum sensing, quantum emitters and nonlinear photonics, computational theory and data-driven discovery of quantum defects, spintronic and magnonic devices, cavity-engineered quantum materials, superconducting and hybrid quantum circuits, quantum dots, Moiré quantum simulators, and quantum communication platforms. Across these themes, we identify common challenges in defect control, coherence preservation, interfacial engineering, and scalable integration, alongside emerging opportunities driven by machine$-$learning$-$assisted design and integrated experiment$-$theory feedback loops. By connecting microscopic quantum states to mesoscopic excitations and macroscopic device architectures, this Roadmap outlines a materials-centric framework for integrating coherent quantum functionalities and positions 2D materials as foundational building blocks for next-generation quantum technologies.
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All authors Qimin Yan, Tongcang Li, Xingyu Gao, Sumukh Vaidya, Saakshi Dikshit, Yue Luo, Stefan Strauf, Reda Moukaouine, Anton Pershin, Adam Gali, Zhenyao Fang, Harvey Stanfield, Ivan J. Vera-Marun, Michael Newburger, Simranjeet Singh, Tiancong Zhu, Mauro Brotons-Gisbert, Klaus D. Jöns, Brian D. Gerardot, Brian S. Y. Kim, John R. Schaibley, Kyle L. Seyler, Jesse Balgley, James Hone, Kin Chung Fong, Lin Wang, Guido Burkard, Yihang Zeng, Tobias Heindel, Serkan Ateş, Tobias Vogl, Igor Aharonovich

Quantum Physics

Pulsed single-photon spectroscopy of an emitter with vibrational coupling

Sourav Das, Aiman Khan, Elnaz Darsheshdar et al. (+2 more)

We analytically derive the quantum state of a single-photon pulse scattered from a single quantum two-level emitter interacting with a vibrational bath. This solution for the quadripartite system enables an information-theoretic characterization of vibrational effects in quantum light spectroscopy. We show that vibration-induced dephasing reduces the quantum Fisher information (QFI) for estimating the emitter's linewidth, largely reflecting the Franck-Condon suppression of light-matter coupling. Comparing time- and frequency-resolved photodetection, we find the latter to be more informative in estimating the emitter's linewidth for stronger vibrational coupling.
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All authors Sourav Das, Aiman Khan, Elnaz Darsheshdar, Francesco Albarelli, Animesh Datta

Quantum Physics

Quantum Radiometric Calibration

Leif Albers, Jan-Malte Michaelsen and Roman Schnabel

Optical quantum computing, as well as sensing technology based on quantum correlations are in preparation. These require photodiodes with close to perfect quantum efficiency for the detection of about 10^16 to 10^18 photons per second. Already the radiometric calibration is a challenge. Here, we provide the proof of concept of the quantum radiometric calibration (QRC) method, which is based on Heisenberg's uncertainty principle, derive the formula for its precision, and exclude the potential sources of systematic error. As an example, we calibrate a pair of the most efficient commercial photodiode at 1550 nm to the previously unknown system detection efficiency of (97.20 +/- 0.37)% using 10-dB-squeezed vacuum states. This value is unexpectedly low, too low for planned gravitational wave detectors and for continuous-variable optical quantum computing. With further improved precision, our work opens up the second true end-user application of the advantage provided by quantum correlations.
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