Quantum Physics
Photonic-integrated quantum sensor array for microscale magnetic localisation
Hao-Cheng Weng, John G. Rarity, Krishna C. Balram et al. (+1 more)
Nitrogen-vacancy centres (NVs) are promising solid-state nanoscale
quantum sensors for applications ranging from material science to biotechnology. Using multiple sensors simultaneously offers advantages for probing spatiotemporal correlations of fluctuating fields or the dynamics of point defects. In this work, by integrating NVs with foundry silicon-nitride photonic integrated
circuits, we realise the scalable operation of eight localised NV sensors in an array, with simultaneous, distinct readout of the individual sensors. Using the eight NV sensors and machine-learning methods for multi-point
magnetic field reconstruction, we demonstrate microscale
magnetic localisation of a 30 $\mu$m-sized needle tip. Experimentally, the needle tip can be localised with an error below its dimension and tracked dynamically with high fidelity. We further simulate the feasibility of our platform for monitoring the position and orientation of
magnetic microrobots designed for biological and clinical purposes. Without the complexity of bulk optics, our photonic-integrated multi-sensor platform presents a step towards real-life biomedical applications under out-of-the-lab conditions.
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All authors Hao-Cheng Weng, John G. Rarity, Krishna C. Balram, Joe A. Smith
Quantum Physics · Cross-listed from math.NA
A Quantum Spectral Method for Non-Periodic Boundary Value Problems
Eky Febrianto, Yiren Wang, Burigede Liu et al. (+2 more)
Quantum computing holds the promise of solving computational mechanics problems in polylogarithmic time, meaning computational time scales as $\mathscr{O}((\log N)^c)$, where $N$ is the problem size and $c$ a constant. We propose a
quantum spectral method with polylogarithmic complexity for solving non-periodic boundary value problems with arbitrary Dirichlet boundary conditions. Our method extends the recently proposed approach by Liu et al. (2025), in which periodic problems are discretised using truncated
Fourier series. In such spectral methods, the discretisation of boundary value problems with constant coefficients leads to a set of algebraic equations in the
Fourier space. We implement the respective diagonal solution operator by first approximating it with a
polynomial and then
quantum encoding the
polynomial. The mapping between the physical and
Fourier spaces is accomplished using the
quantum Fourier transform (QFT). To impose zero Dirichlet boundary conditions, we double the domain size and reflect all physical fields antisymmetrically. The respective reflection
matrix defines the
quantum sine transform (QST) by pre- and post-multiplying with the QFT. For non-zero Dirichlet boundary conditions, the solution is decomposed into a boundary-conforming and a homogeneous part. The homogenous part is determined by solving a problem with a suitably modified forcing vector. We illustrate the basic approach with a Dirichlet-Poisson problem and demonstrate its generality by applying it to a fractional
stochastic PDE for modelling spatial random fields. We discuss the
circuit implementation of the proposed approach and provide numerical evidence confirming its polylogarithmic complexity.
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All authors Eky Febrianto, Yiren Wang, Burigede Liu, Michael Ortiz, Fehmi Cirak
Quantum Physics
TrackHHL: A Quantum Computing Algorithm for Track Reconstruction at the LHCb
Xenofon Chiotopoulos, Miriam Lucio Martinez, Davide Nicotra et al. (+4 more)
In the future high-luminosity LHC era, high-energy physics experiments face unprecedented computational challenges for event reconstruction. Employing the LHCb vertex locator as a case study we investigate a novel approach for charged particle track reconstruction. The
algorithm hinges on minimizing an Ising-like
Hamiltonian using
matrix inversion. Solving this
matrix inversion classically achieves reconstruction efficiencies akin to current state-of-the-art
algorithms. Exploiting the Harrow-Hassidim-Lloyd (HHL)
quantum algorithm for linear systems holds the promise of an exponential speedup in the number of input hits over its classical counterpart, contingent on the conditions of efficient
quantum phase estimation (QPE) and effectively reading out the
algorithm's output. This contribution builds on previous work by Nicotra et al and strives to fulfill these conditions and further streamlines the
algorithm's
circuit depth by a factor up to $10^4$. Our version of the HHL
algorithm restricts the QPE precision to one bit, largely reducing
circuit depth and addressing HHL's readout issue. Furthermore, this allows for the implementation of a post-processing
algorithm that reconstructs event Primary Vertices (PVs). The findings presented here aim to further illuminate the potential of harnessing
quantum computing for the future of particle track reconstruction in high-energy physics.
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All authors Xenofon Chiotopoulos, Miriam Lucio Martinez, Davide Nicotra, Jacco A. de Vries, Kurt Driessens, Marcel Merk, Mark H.M. Winands
Quantum Physics
Photon correlation Fourier spectroscopy of a B center in hBN
Aymeric Delteil, Stéphanie Buil and Jean-Pierre Hermier
The potential of solid-state
quantum emitters for applications critically depends on several key figures of merit. One of the most important is the
quantum coherence of the emitted single
photons, which can be compromised by fast dephasing and spectral
diffusion. In hexagonal boron nitride (hBN), blue-emitting color centers (or B centers) are seen as favorable in this regard, in the light of prior studies mainly based on resonant excitation. Yet, their coherence properties in the more accessible regime of non-resonant excitation (or photoluminescence) has not been extensively characterized. Here, we investigate the coherence and spectral
diffusion of the photoluminescence from a B center in the continuous wave regime using
photon correlation
Fourier spectroscopy. We determine that the emission lineshape consists in a homogeneous contribution, whose linewidth increases with the
laser power, and which is broadened by spectral
diffusion at a timescale of 10 to 100 microseconds. At low power and short time, the emission line is only a factor ~2 above the
Fourier limit, while at long times, the inhomogeneous linewidth increases up to more than a gigahertz. Our work deepens the understanding of decoherence processes of this preeminent family of
quantum emitters in hBN.
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Quantum Physics
Hamiltonian simulation with explicit formulas for Digital-Analog Quantum Computing
Mikel Garcia-de-Andoin, Thorge Müller and Gonzalo Camacho
Digital-analog is a
quantum computational paradigm that employs the natural interaction
Hamiltonian of a system as the entangling resource, combined with single
qubit gates, to implement universal
quantum operations. As in the case of its digital gate-based counterpart, designing digital-analog
circuits that employ optimal
quantum resources often requires an exceedingly large classical computational time. In this work we find a suboptimal solution to this exponentially large problem, showing that it can be solved within
polynomial computational time. In particular, we provide an exact solution for the problem of expressing arbitrary two-body
Hamiltonians as the sum of local
unitary transformations of an arbitrary Ising
Hamiltonian, with the total number of required terms being at most quadratic in system size. This allows us to design a digital-analog simulation protocol that avoids employing numerical optimization over a large parameter space at the preprocessing stage, minimizing computational resources and allowing for further scaling.
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Quantum Physics
Bidimensional measurements of photon statistics within a multimodal temporal framework
C. Hainaut, K. Ouahrouche, A. Rancon et al. (+5 more)
Ultrafast imaging of
photon statistics in two dimensions is a powerful tool for probing non-
equilibrium and transient optical phenomena, yet it remains experimentally challenging due to the simultaneous need for high temporal resolution and statistical fidelity. In this work, we demonstrate spatially resolved single-shot measurements of
photon number distributions using difference-frequency generation (DFG) in a nonlinear BBO
crystal. We show that our platform can discriminate between coherent and thermal
photon statistics across two spatial dimensions with picosecond resolution. At the same time, we find that the retrieved distributions deviate from the ideal ones, a consequence of
vacuum contamination and the
multimodal response of the amplifier. To explain this, we develop a temporal mode decomposition framework that captures the essential physics of signal amplification and fluorescence, and quantitatively reproduces the experimental findings. This establishes a robust approach for measuring two-dimensional
photon statistics while clarifying the fundamental factors that limit the fidelity of such measurements.
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All authors C. Hainaut, K. Ouahrouche, A. Rancon, G. Patera, C. Ouarkoub, M. Le Parquier, P. Suret, A. Amo
Quantum Physics
Variational Quantum Algorithms for Particle Track Reconstruction
Vincenzo Lipardi, Xenofon Chiotopoulos, Jacco A. de Vries et al. (+4 more)
Quantum Computing is a rapidly developing field with the potential to tackle the increasing computational challenges faced in high-energy physics. In this work, we explore the potential and limitations of variational
quantum algorithms in solving the particle track reconstruction problem. We present an analysis of two distinct formulations for identifying straight-line tracks in a multilayer detection system, inspired by the LHCb vertex detector. The first approach is formulated as a ground-state energy problem, while the second approach is formulated as a system of linear equations. This work addresses one of the main challenges when dealing with variational
quantum algorithms on general problems, namely designing an expressive and efficient
quantum ansatz working on tracking events with fixed detector geometry. For this purpose, we employed a
quantum architecture search method based on Monte Carlo Tree Search to design the
quantum circuits for different problem sizes. We provide experimental results to test our approach on both formulations for different problem sizes in terms of performance and computational cost.
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All authors Vincenzo Lipardi, Xenofon Chiotopoulos, Jacco A. de Vries, Domenica Dibenedetto, Kurt Driessens, Marcel Merk, Mark H.M. Winands
Quantum Physics · Cross-listed from gr-qc
Molecular analogue for scalar dynamics in an AII metric
Davi de Moura Esposti Moreira, Matheus Elias Pereira and Alexandre Grezzi de Miranda Schmidt
Tachyons are hypothetical particles that propagate faster than light, yet they have never been observed in nature or in the laboratory. In this work, we introduce the $H_2^+$ molecule as an analogue for the dynamics of a spinless test particle interacting with the gravitational field generated by a tachyon. The tachyonic spacetime is modeled using an AII metric, and the problem is analyzed through the Klein–Gordon equation for a scalar field in this background. We compute the quasi-normal modes and the Hawking radiation spectrum associated with the system. By introducing a specific external potential — defined precisely for this purpose and fine–tuned through a careful comparison of system constants — we demonstrate that both the radial and angular components of a test particle's wave function can be effectively reproduced by the electronic dynamics within $H_2^+$. We thus propose a mathematical framework for studying a molecular analog model of an extreme gravitational system.
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Quantum Physics
Subradiant Decay in 2D and 3D Atomic Arrays
Nicola Piovella and Romain Bachelard
Subradiance is a phenomenon where coupled emitters radiate light at a slower rate than independent ones. While its observation was first reported in disordered cold atom clouds, ordered subwavelength arrays of emitters have emerged as promising platforms to design highly cooperative optical properties based on dipolar interactions. In this work we characterize the eigenmodes of 2D and 3D regular arrays, using a method which can be used for both infinite and very large systems. In particular, we show how finite-size effects impact the lifetimes of these large arrays. Our results may have interesting applications for
quantum memories and topological effects in ordered atomic arrays.
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Quantum Physics
Lorentz Transformation in Quantum Mechanics
Marcello Baldo
The compatibility of special relativity and
Quantum Mechanics has been questioned by several authors. The origin of this tension can be traced back mainly to the introduction of the measurement processes and the corresponding wave function reduction, which play a crucial role in
Quantum Mechanics. We approach this problem with the help of a recent proposal for a model of
Quantum Mechanics, where the measurement is explicitly described as a specific
stochastic process. This implements ordinary
Quantum Mechanics, where measurement and reduction are treated as phenomenological events of unknown origin without any physical justification. To state clearly the question in general, we first discuss and establish the effect of a Lorentz transformation on a generic wave function in space-time. Alongside the analysis we formulate the relativistic version of the model. We then consider few thought experiments in order to analyze to what extent
Quantum Mechanics follows relativistic invariance and find the specific critical points where non invariance possibly occurs. The analysis can shade light to the interpretation of the existing experimental observations.
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Quantum Physics · Cross-listed from cond-mat.stat-mech
Scaling of free cumulants in closed system-bath setups
Merlin Füllgraf, Jochen Gemmer and Jiaozi Wang
The Eigenstate Thermalization Hypothesis (ETH) has been established as a cornerstone for understanding thermalization in
quantum many-body systems. Recently, there has been growing interest in the full ETH, which extends the framework of the conventional ETH and postulates a smooth function to describe the multi-point correlations among
matrix elements. Within this framework, free cumulants play a central role, and most previous studies have primarily focused on closed systems. In this paper, we extend the analysis to a system-bath setup, considering both an idealized case with a random-
matrix bath and a more realistic scenario where the bath is modeled as a defect Ising chain. In both cases, we uncover a universal scaling of the microcanonical free cumulants of observables associated with the central system
Hamiltonian with respect to the interaction strength. Furthermore we establish a connection between this scaling behavior and the thermalization dynamics of the thermal free cumulants of corresponding observables.
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Quantum Physics
Quantum limit cycles and synchronization from a measurement perspective
Tobias Nadolny and Christoph Bruder
Limit-cycle oscillators are the basic building blocks for synchronization; yet, the notion of a
quantum limit cycle has remained unclear. Here, we study
quantum limit cycles and synchronization in the presence of continuous heterodyne measurement. The resulting
quantum trajectories, i.e., time evolutions of the
quantum state conditioned on the measurement outcome, make the
quantum limit cycles apparent. We focus on the paradigmatic model of the
quantum van der Pol oscillator and on two-level systems. Our work provides insights into limit cycles in
quantum systems, emphasizing their similarity to classical limit cycles subject to noise. Additionally, we connect theoretical measures of
quantum synchronization to quantities experimentally accessible via heterodyne detection.
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Quantum Physics · Cross-listed from math-ph
Solving a Nonlinear Eigenvalue Equation in Quantum Information Theory: A Hybrid Approach to Entanglement Quantification
Abrar Ahmed Naqash, Fardeen Ahmad Sofi, Mohammad Haris Khan et al. (+1 more)
Nonlinear
eigenvalue equations arise naturally in
quantum information theory, particularly in the variational quantification of
entanglement. In this work, we present a hybrid analytical and numerical framework for evaluating the
geometric measure of
entanglement. The method combines a Gauss Seidel fixed point iteration with a controlled perturbative correction scheme. We make the coupled nonlinear eigenstructure explicit by proving the equal multiplier stationarity identity, which states that at the optimum all block Lagrange multipliers coincide with the squared fidelity between the target state and its closest separable approximation. A normalization-preserving linearization is then derived by projecting the dynamics onto the local tangent spaces, yielding a well-defined first order correction and an explicit scalar shift in the
eigenvalue. Furthermore, we establish a monotonic block ascent property the squared overlap between the evolving product state and the target state increases at every iteration, remains bounded by unity, and converges to a stationary value. The resulting hybrid solver reproduces the exact optimum for standard three
qubit benchmarks, obtaining squared-overlap values of one-half for the Greenberger Horne Zeilinger (GHZ\(_3\)) state and four-ninths for the W\(_3\) state, with smooth monotonic convergence.
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All authors Abrar Ahmed Naqash, Fardeen Ahmad Sofi, Mohammad Haris Khan, Sundus Abdi
Quantum Physics · Cross-listed from cond-mat.mes-hall
Topological states and flat bands in exactly solvable decorated Cayley trees
Wanda P. Duss, Askar Iliasov and Tomáš Bzdušek
We derive the full spectrum of decorated Cayley trees that constitute tree analogs of selected two-dimensional Euclidean
lattices; namely of the Lieb, the double Lieb, the kagome, and the
star lattice. The common feature of these Euclidean
lattices is that their nearest-neighbor models give rise to flat energy bands interpretable through compact localized states. We find that the tree analogs exhibit similar flat or nearly flat energy bands at the corresponding energies. Interestingly, such flat bands in the decorated Cayley trees acquire an interpretation that is absent in their Euclidean counterparts: as edge states localized to the inner or the outer boundary of the tree branches. In particular, we establish an exact correspondence between the Lieb-Cayley tree and an ensemble of one-dimensional Su-Schrieffer-Heeger chains, which maps topological edge states on one side of the chains to flat-band states localized in the bulk of the tree, furnishing the flat energy band with a topological stability. Similar mapping to topological edge states or to states bound to edge defects in one-dimensional chains is shown for flat-band states in all the considered tree decorations. We finally show that the persistence of exact flat bands on infinite decorated trees (i.e., Bethe
lattices) arises naturally from a covering interpretation of tree graphs. Our findings reveal a rich landscape of flat-band and topological phenomena in non-Euclidean systems, where geometry alone can generate and stabilize unconventional
quantum states.
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Quantum Physics
Hyperpolarized Molecular Nuclear Spins Achieve Magnetic Amplification
Shengbang Zhou, Qing Li, Yi Ren et al. (+6 more)
The use of
nuclear spins as physical sensing systems is disadvantaged by their low signal responsivity, particularly when compared to sensing techniques based on electron
spins. This primarily results from the small
nuclear gyromagnetic ratio and the difficulties in achieving high
spin polarization. Here we develop a new approach to investigating the response of hyperpolarized molecular
nuclear spins to
magnetic fields and demonstrate orders-of-magnitude enhanced
magnetic responsivity over state-of-the-art
proton and Overhauser magnetometers. Using hyperpolarized molecules with
proton spins, we report the realization of
magnetic amplification in linear and nonlinear types. We further extend this amplification to hyperpolarized scalar-coupled multi-
spin molecules and observe substantial
magnetic amplification exceeding 10%. Moreover, we observe an anomalous amplification with dispersive frequency dependence that originates from
magnetic interference effects. Our work highlights the potential of hyperpolarized molecular
nuclear spins for use in a new class of
quantum sensors, with promising applications in both applied and fundamental physics, including highly accurate absolute magnetometry and the exploration of
axion-nucleon exotic interactions.
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All authors Shengbang Zhou, Qing Li, Yi Ren, Jingyan Xu, Raphael Kircher, Danila A. Barskiy, Dmitry Budker, Min Jiang, Xinhua Peng
Quantum Physics
Efficient circuits for leaf-separable state preparation
Sunil Vittal, Anthony Wilkie, Nika Rastegari et al. (+2 more)
Efficient state preparation is a challenging and important problem in
quantum computing. In this work, we present a recursive state preparation
algorithm that combines logarithmic-depth Dicke state
circuits with Hamming weight encoders for efficiently preparing “leaf-separable"
quantum states. The
algorithm is built on binary partition trees, generalized weight distribution blocks (gWDBs), and leaf-level encoders. We evaluate the performance of the
algorithm by numerically simulating it on randomly generated target states with between 4 and 15
qubits. Compared to general state preparation approaches which require $O(2^n)$ CX gates, our
algorithm achieves a
circuit depth of $O(k\log\frac{n}{k} + 2^k)$ and uses $O(n(k+2^k))$ two-
qubit gates, where $k < n$ denotes the subtree size. We also compare implementations of the
algorithm with and without the use of ancilla
qubits, providing a detailed analysis of the trade-offs in
circuit depth and two-
qubit gate counts. These results contribute to scalable state preparation for
quantum algorithms that require structured inputs such as Dicke or near-Dicke states.
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All authors Sunil Vittal, Anthony Wilkie, Nika Rastegari, Mostafa Atallah, Rebekah Herrman
Quantum Physics
Finite relative entropy for locally squeezed states
Daniela Cadamuro, Markus B. Fröb, Dimitrios Katsinis et al. (+1 more)
Relative
entropy serves as a fundamental measure of state distinguishability in both
quantum information theory and relativistic
quantum field theory. Despite its conceptual importance, however, explicit computations of relative
entropy remain notoriously difficult. Thus far, results in closed form have only been obtained for ground states, coherent states, and, more recently, single-mode squeezed states. In this work, we extend the analysis to multi-mode squeezed states, imposing that the squeezing generators be local either in space or in spacetime, which results in a continuum of squeezed modes. We provide a detailed and self-contained analysis of such states for a free scalar
quantum field on Minkowski spacetime, connecting also with older results on the essential self-adjointness of the Wick square, and showing that they lie in the folium of the Minkowski
vacuum representation. We uncover that local-in-space squeezing leads to physically unreasonable states which have a divergent energy density and relative
entropy, while local-in-spacetime squeezing provides a physically reasonable class of states with finite relative
entropy.
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All authors Daniela Cadamuro, Markus B. Fröb, Dimitrios Katsinis, Jan Mandrysch
Quantum Physics
Ultrafast quantum gates with fully quantized free-electron quantum optics
Yongcheng Ding
Free-electron
quantum optics provides a versatile platform for manipulating electrons at the
quantum level with potential applications in
quantum information technologies. We propose a grating-based architecture for fully quantized free-electron
quantum optics, in which
photon-electron interactions map onto Jaynes-Cummings and Tavis-Cummings models via Bloch-Floquet analysis. Within this framework, we design ultrafast single- and two-
qubit gates with cavity-free flying electrons, enabling universal
quantum computing in experimentally accessible setups. More broadly, this framework establishes a platform for probing free-electron
quantum optics and advancing
quantum technologies in simulation, sensing, and information processing.
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Quantum Physics
The Riemann Hypothesis Emerges in Dynamical Quantum Phase Transitions
ShiJie Wei, Yue Zhai, Quanfeng Lu et al. (+7 more)
The Riemann Hypothesis (RH), one of the most profound unsolved problems in mathematics, concerns the nontrivial zeros of the Riemann
zeta function. Establishing connections between the RH and physical phenomena could offer new perspectives on its physical origin and verification. Here, we establish a direct correspondence between the nontrivial zeros of the
zeta function and dynamical
quantum phase transitions (DQPTs) in two realizable
quantum systems, characterized by the averaged accumulated phase factor and the Loschmidt amplitude, respectively. This precise correspondence reveals that the RH can be viewed as the emergence of DQPTs at a specific temperature. We experimentally demonstrate this correspondence on a five-
qubit spin-based system and further propose an universal
quantum simulation framework for efficiently realizing both systems with
polynomial resources, offering a
quantum advantage for numerical verification of the RH. These findings uncover an intrinsic link between nonequilibrium critical dynamics and the RH, positioning
quantum computing as a powerful platform for exploring one of mathematics' most enduring
conjectures and beyond.
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All authors ShiJie Wei, Yue Zhai, Quanfeng Lu, Wentao Yang, Pan Gao, Chao Wei, Junda Song, Franco Nori, Tao Xin, GuiLu Long
Quantum Physics
Electrical thermography via centimetre-scale fiber-based distributed temperature sensing
Victor Cochet, Axel Faccio, Georgios Stoikos et al. (+4 more)
We present a Raman-based Distributed Temperature Sensor (RDTS) with centimetre-scale resolution for thermographic analysis of electronic
circuits. Temperature is measured along a single-mode fiber routed across a custom printed
circuit board (PCB) with 1 cm$^2$ heating elements, using optical time-domain reflectometry of Raman signals detected by superconducting nanowire single-
photon detectors (SNSPDs). This approach enables two-dimensional thermal mapping of the PCB under heating configurations with multiple hotspots. A spatial resolution of 3 cm and a temperature accuracy of 2 {\deg}C are achieved with an integration time of 5 minutes. Thermography can be performed down to 77 K, revealing that the PCB thermal resistance decreases by nearly an order of magnitude compared to room temperature, due to enhanced convective cooling in
liquid nitrogen. These results establish centimetre-scale RDTS as a robust technique for real-time, spatially resolved thermography of electronic
circuits, particularly in regimes where infrared imaging is ineffective, such as at low temperatures or within volumetric electronic architectures.
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All authors Victor Cochet, Axel Faccio, Georgios Stoikos, Towsif Taher, Rob Thew, Jérôme Extermann, Enrico Pomarico
Quantum Physics · Cross-listed from gr-qc
Quantum Electron Clouds near Black Holes: Black Atoms and Molecules
Hinako Iseki, Shin Sasaki and Kenta Shiozawa
We study
quantum mechanical wavefunctions near highly curved spaces, i.e., black holes. By utilizing the formalism developed by DeWitt, we derive the Schrödinger equations in the vicinity of the Schwarzschild and the Reissner-Nordström black hole geometries. The
quantum electron cloud for the "black hydrogen atom" - an electron trapped by black holes - is particularly studied. We solve the equations and find that black holes generally attract the wavefunctions, localizing them near the horizon where the electrons are most likely to be trapped. These results imply that not only classical objects but also the
quantum material and even the chemical properties of the atoms are affected by strong
gravity. We also discuss black hydrogen molecules composed of multi-centered Majumdar-Papapetrou black holes.
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Quantum Physics · Cross-listed from physics.optics
Perovskite Nanocrystals as Emerging Single-Photon Emitters: Progress, Challenges, and Opportunities
Jehyeok Ryu, Victor Krivenkov, Adam Olejniczak et al. (+2 more)
Metal-halide perovskite nanocrystals (PNCs) have emerged as leading candidates for next-generation
quantum emitters, offering a unique combination of high photoluminescence
quantum yield, tunable emission, short radiative lifetimes, and record-high single-
photon purity under ambient conditions. These properties, together with low-cost and scalable solution-phase fabrication, position PNCs as attractive alternatives to traditional epitaxial and colloidal
quantum dots. In this Review, we outline the physical parameters that define
quantum emission in PNCs, compare their performance to other established and emerging
quantum emitters, and assess the key figures of merit, including photostability, single-
photon purity, and
photon indistinguishability, required for practical
quantum applications. We discuss underlying mechanisms affecting PNC emission behavior and highlight recent advances in improving their
quantum emitting properties through synthetic and photonic engineering approaches. While challenges related to environmental stability and
photon indistinguishability remain, emerging strategies, such as surface passivation, metal ion doping, and coupling with electromagnetic nano- and micro-cavities, are steadily closing the gap between PNCs and ideal
quantum light sources.
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All authors Jehyeok Ryu, Victor Krivenkov, Adam Olejniczak, Alexey Y. Nikitin, Yury Rakovich
Quantum Physics
Magnetic flux and its topological effects in Aharonov-Bohm effect
Manvendra Somvanshi and D. Jaffino Stargen
The Aharonov-Bohm effect is a physical phenomenon in which the
quantum state of a charged particle acquires a phase shift that is directly proportional to the
magnetic flux, $\Phi$, due to a (classical)
magnetic field, ${\mathbf B}$, which is confined in a spatial region from which the
magnetic field cannot escape. Even though the charged particle is not allowed to interact with the
magnetic field, it accumulates a phase shift that affects the interference pattern produced. Not surprisingly, this apparent nonlocality is puzzling and counter intuitive. In this work, we provide an explanation that explains the physics underlying this apparent nonlocality. We find that the role of the confined
magnetic field is to impart a puncture in the configuration space, $\mathbb{R}^2$, of the charge. Therefore, the
quantum state corresponding to the charged
quantum particle acquires the phase shift due to its response to the modified
topology of the configuration space, $\mathbb{R}^2-\{0\}$, corresponding to the charge.
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Quantum Physics · Cross-listed from hep-th
Generalizing quantum dimensions: Symmetry-based classification of local pseudo-Hermitian systems and the corresponding domain walls
Yoshiki Fukusumi and Taishi Kawamoto
We study conformal field theories (CFTs) and their classifications from a modern perspective based on the abstract algebraic formalism of
symmetries or conserved charges, known as
symmetry topological field theories (SymTFTs). By studying the algebraic structure of the SymTFTs in detail, we found a natural generalization of the
quantum dimensions associated with (pseudo-)Hermitian systems and (non)-
unitary CFTs. These generalized data of SymTFTs provide classifications of massless and massive renormalization group flows, which will describe the
quantum phase transitions of the corresponding pseudo-Hermitian systems. Moreover, our discussions straightforwardly enable one to relate a general class of coset constructions or level-rank dualities to domain wall problems between topological
quantum field theories (or a series of corresponding
quantum phase transitions related to the
Higgs mechanism). Our work provides a systematic reduction and classification of algebraic data,
symmetries, for pseudo-Hermitian systems based on ideas from established mathematical fields, linear
algebra and ring theory.
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Quantum Physics
High-speed $R_{ZZ}$ gates in Kerr-cat qubits via fast-forward scaling
Takaaki Aoki and Shumpei Masuda
Kerr parametric oscillators can encode Kerr-cat
qubits, whose biased-noise nature can reduce the hardware overhead required for fault-tolerant
quantum computation. In a recently proposed $R_{ZZ}$-gate scheme for Kerr-cat
qubits, a tunable coupler must be displaced while avoiding nonadiabatic excitation. To address this challenge, we propose and theoretically analyze a protocol that applies fast-forward scaling to the coupler displacement. The protocol suppresses nonadiabatic excitation of the coupler and enables high speed $R_{ZZ}$ gates.
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Quantum Physics
Unconditional and exponentially large violation of classicality
Marcello Benedetti, Gabriel Marin-Sanchez, Jordi Weggemans et al. (+2 more)
Testing the predictions of
quantum mechanics has been one of the main experimental endeavors for decades. Recent advancements in technology led to a number of demonstrations which test non-classicality via specific computational tasks. Limitations of these experiments include dependence on complexity theory assumptions, susceptibility to hardware noise and inefficient verification, raising questions about their scalability. We propose to test non-classicality using a game based on complement sampling, an efficiently verifiable problem that achieves the largest possible separation between
quantum and classical computation when both input and output represent samples from probability distributions. When restricting the input to instances inspired by the Bernstein-Vazirani problem, our game admits an exponentially large violation of classicality unconditionally, i.e. without relying on computational hardness assumptions. We demonstrate the game on Quantinuum System Model H2 trapped-ion
quantum computers, with experiments consisting of thousands of different
circuits on up to 55
qubits. The observed scores can be explained by a systematic adoption of a
quantum strategy, further corroborating the
quantum nature of the hardware in an efficient and scalable way.
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All authors Marcello Benedetti, Gabriel Marin-Sanchez, Jordi Weggemans, Matthias Rosenkranz, Harry Buhrman
Quantum Physics
Memory-Assisted Nonlocal Interferometer Towards Long-Baseline Telescopes
Bin Wang, Xi-Yu Luo, Bo-Feng Gao et al. (+12 more)
Quantum networks and remote
quantum entanglement serve as vital future
quantum communication resources with broad applicability. A key direction lies in extending the baseline of optical interferometers to enhance angular resolution in interferometric imaging. Here, by measuring a simulated thermal light field, we report the demonstration of a
memory-assisted nonlocal interferometer achieving a fiber-link baseline up to 20 km while simultaneously showing its capability to compensate for a
geometric delay equivalent to 1.5 km. This result demonstrates potential for enhancing the angular resolution of interferometric imaging in the optical band with delocalized single-
photon entanglement, and paves the way for future application of
quantum memories in astronomical observation.
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All authors Bin Wang, Xi-Yu Luo, Bo-Feng Gao, Jian-Long Liu, Chao-Yang Wang, Zi Yan, Qiao-Mu Ke, Da Teng, Ming-Yang Zheng, Yuan Cao, Jun Li, Cheng-Zhi Peng, Qiang Zhang, Xiao-Hui Bao, Jian-Wei Pan
Quantum Physics
Towards Global Quantum Key Distribution
Haoran Zhang, Haotao Zhu, Ruihua He et al. (+4 more)
Quantum Key Distribution (QKD) supports the negotiation and sharing of private keys with unconditional security between authorized parties. Over the years, theoretical advances and experimental demonstrations have successfully transitioned QKD from laboratory research to commercial applications. As QKD expands its reach globally, it encounters challenges such as performance limitations, cost, and practical security concerns. Nonetheless, innovations in satellite-based QKD and the development of new protocols are paving the way towards a worldwide network. In this review, we provide an overview of QKD implementations, with a focus on protocols, devices, and
quantum channels. We discuss the challenges of practical QKD and explore long-haul QKD. Additionally, we highlight the future research directions that are expected to significantly advance the realization of a global QKD network.
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All authors Haoran Zhang, Haotao Zhu, Ruihua He, Yan Zhang, Chao Ding, Lajos Hanzo, Weibo Gao
Quantum Physics
Maximizing the nondemolition nature of a quantum measurement via an adaptive readout protocol
Arjen Vaartjes, Rocky Yue Su, Laura A. O'Neill et al. (+15 more)
Quantum error correction (QEC) requires non-invasive measurements for fault tolerant
quantum computing. Deviations from ideal
quantum non-demolition (QND) measurements can disturb the encoded information. To address this challenge, we develop a readout protocol for a $D-$dimensional system that, after a single positive outcome, switches to probing only the $D{-}1$ remaining subspace. This adaptive switching strategy minimizes measurement-induced errors by relying on negative-result measurement results that do not perturb the
Hamiltonian. We apply the protocol on an 8-dimensional $^{123}{\rm Sb}$
nuclear qudit in silicon, and achieve an increase in the readout fidelity from $(98.93\pm0.07)\%$ to $(99.61\pm0.04)\%$, while reducing threefold the overall readout time. To highlight the broader relevance of measurement-induced errors, we study a 10-dimensional $^{73}{\rm Ge}$
nuclear spin read out through Pauli
spin blockade, revealing
nuclear spin flips arising from hyperfine and quadrupole interactions. These results unveil the effect of non-ideal QND readout across diverse platforms, and introduce an efficient readout protocol that can be implemented with minimal FPGA logic on existing hardware.
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All authors Arjen Vaartjes, Rocky Yue Su, Laura A. O'Neill, Paul Steinacker, Gauri Goenka, Mark R. van Blankenstein, Xi Yu, Benjamin Wilhelm, Alexander M. Jakob, Fay E. Hudson, Kohei M. Itoh, Chih Hwan Yang, Andrew S. Dzurak, David N. Jamieson, Martin Nurizzo, Danielle Holmes, Arne Laucht, Andrea Morello
Quantum Physics · Cross-listed from cs.DS
Cycle Basis Algorithms for Reducing Maximum Edge Participation
Fan Wang and Sandy Irani
We study the problem of constructing cycle bases of graphs with low maximum edge participation, defined as the maximum number of basis cycles that share any single edge. This quantity, though less studied than total weight or length, plays a critical role in
quantum fault tolerance because it directly impacts the overhead of
lattice surgery procedures used to implement an almost universal
quantum gate set. Building on a recursive
algorithm of Freedman and Hastings, we introduce a family of load-aware heuristics that adaptively select vertices and edges to minimize edge participation throughout the cycle basis construction. Our approach improves empirical performance on random regular graphs and on graphs derived from small
quantum codes. We further analyze a simplified balls-into-bins process to establish lower bounds on edge participation. While the model differs from the cycle basis
algorithm on real graphs, it captures what can be proven for our heuristics without using complex graph theoretic properties related to the distribution of cycles in the graph. Our analysis suggests that the maximum load of our heuristics grows on the order of (log n)^2. Our results indicate that careful cycle basis construction can yield significant practical benefits in the design of fault-tolerant
quantum systems. This question also carries theoretical interest, as it is essentially identical to the basis number of a graph, defined as the minimum possible maximum edge participation over all cycle bases.
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