Quantum Physics
Particle detector in a position-superposed black hole spacetime
Laurens Walleghem and Carlo Cepollaro
We calculate the response of an Unruh–DeWitt detector in a 2+1d spacetime that contains a BTZ black hole in a superposition of locations as viewed in a reference system associated with the detector. Upon performing a
Quantum Reference Frame (QRF) transformation, this can also be seen as a detector in a superposition of locations in a single classical black hole spacetime. We use this to derive the form of the interaction of the detector and scalar field in such a superposition of spacetimes, ignoring backreaction. We define a measurement whose outcome probabilities contain a nonclassical contribution that would be absent for a black hole described by a classical mixture of positions. Finally, we compare our results with a previously studied setup involving a mass-superposed black hole by Foo et al. [Phys. Rev. Lett. 129, 181301 (2022)], and highlight a key difference. We show analytically how this difference arises and find singularities in the mass-superposed spectrum probed by the detector.
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Quantum Physics
Time-Delocalized Local Measurements in an Indefinite Causal Order
Yann Valibouse, Martí Cladera-Rosselló, Michael Antesberger et al. (+3 more)
Processes with indefinite causal order (ICO), such as the
quantum switch, are an emerging resource for
quantum tasks and a fundamental test bed for studies of temporal correlations in
quantum mechanics. A limitation of past photonic implementations of the
quantum switch, however, is their inability to perform measurements inside the switch without either destroying the superposition of causal orders or delaying readout until the after the
quantum switch. Measurements where the results are read out locally are needed for several applications of ICO, but also for a loophole-free verification of ICO. Here, we overcome past limitations by introducing a $\mathit{local}$ measurement scheme and coupling the
photon in the switch to a $\mathit{time-delocalized}$ ancilla system. We experimentally realize this protocol using a photonic
quantum switch with post-selected linear optical logic gates. Our method ensures that the measurement apparatus interacts with the system at two distinct times and yet yields a single outcome. We use a
quantum eraser measurement to preserve the ICO, which we certify by measuring a causal witness and finding a negative value of $\mathcal{C}_W \approx -0.305 (1)$. Furthermore, by explicitly realizing a time-delocalized ancilla system, our protocol not only enables a new class of
quantum switch protocols requiring local readout, but also provides a general method for path-coherence-preserving measurements with broad applications beyond ICO.
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All authors Yann Valibouse, Martí Cladera-Rosselló, Michael Antesberger, Patrick Lima, Philip Walther, Lee A. Rozema
Quantum Physics
Quantum Mpemba effect in chaotic systems with conservation laws
Thomas Martin Müller, Silvia Pappalardi and Rosario Fazio
Closed chaotic
quantum systems relax after a quench into a Gibbs ensemble. At late times, the relaxation speed is determined by their conservation laws and hydrodynamics. As a result, there exist pairs of initial states which thermalize to the same ensemble, yet exhibit drastically different hydrodynamic relaxation. We show in two chaotic
spin chains how this enables a simple and robust realization of the
quantum Mpemba effect: a system initially closer to
equilibrium relaxes slower than one that starts farther away, despite both approaching the same final state.
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Quantum Physics
Quantum Chaos and Eigenstate Thermalization
Rohit Patil and Marcos Rigol
We provide a pedagogical introduction to eigenstate thermalization. This phenomenon, which occurs in generic
quantum many-body systems, allows one to understand why thermalization takes place in isolated systems under
unitary dynamics. We motivate eigenstate thermalization using random
matrix theory and discuss recent complementary results for the volume-law
entanglement entropy of Haar-random states. We discuss numerical results that highlight the corresponding behaviors in
quantum many-body systems.
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Quantum Physics · Cross-listed from cond-mat.quant-gas
Three-body interactions in Rydberg lattices
Rhine Samajdar, Mikhail D. Lukin and Valentin Walther
Programmable arrays of neutral Rydberg atoms are one of the leading platforms today for scalable
quantum simulation and computation. In these systems, the dipole-dipole interactions between the individual atoms, or
qubits, typically result in binary – i.e., two-body – couplings. In this work, we develop an experimentally accessible scheme for engineering three-body interactions in Rydberg
lattices. Such strong three-body couplings can fundamentally modify the underlying physics compared to systems with only two-body interactions: we demonstrate this, in particular, by systematically investigating the effective many-body
Hamiltonian and its emergent
quantum phases. This capability paves the way for the
quantum simulation of a broader class of correlated models of condensed matter and high-energy physics.
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Quantum Physics
Spectral-angular parametrization of open qudit dynamics: gap coordinates, Cartan structure, and GKLS decoupling
Jean-Pierre Gazeau, Kaoutar El Bachiri, Zakaria Bouameur et al. (+1 more)
Every $n$-level density
matrix can be diagonalized as $\rho=U\,\mathrm{diag}(p_1,\ldots,p_n)U^\dagger$, splitting it into an
eigenvalue vector $(p_1,\ldots,p_n)$ and a
unitary eigenbasis $U$. We introduce a new coordinate system on the
eigenvalue vector alone: the gap coordinates $r_a:=p_a-p_{a+1}\ge0$, $a=1,\ldots,n-1$. We show that $(r_1,\ldots,r_{n-1})$ are precisely the simple-root coordinates of the
eigenvalue vector in the Cartan subalgebra of $A_{n-1}=\mathfrak{sl}(n)$, so that the spectral diagonal expands in the fundamental-coweight basis, $\mathsf D(\mathbf r)=\sum_a r_a\,\omega_a^\vee$, and the $n-1$
eigenvalue-ordering inequalities collapse into the single linear constraint $\sum_a a\,r_a\le1$ defining a weighted simplex $R_{n-1}$. This identification yields closed-form expressions for the Fisher–Rao and Bures metrics at the maximally mixed state in terms of the inverse Cartan
matrix of $A_{n-1}$, and for a piecewise-linear alternative to the standard definition of purity. On the angular side we give an explicit Tilma–Sudarshan-type coordinatization of the flag
manifold $F_n\simeq\mathrm{SU}(n)/\mathbb T^{n-1}$ and a global coherent-state resolution of the identity on $F_n$, enabling an $\mathrm{SU}(n)$-covariant integral quantization of the flag variety. Under GKLS dynamics, the pair (gap coordinates, flag angles) exhibits a partial decoupling: the
eigenvalue gaps evolve under dissipation alone, while the flag angles are driven by both the
Hamiltonian and the dissipator, which we derive directly in these coordinates, including an explicit illustration on the real qutrit sector.
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All authors Jean-Pierre Gazeau, Kaoutar El Bachiri, Zakaria Bouameur, Yassine Hassouni
Quantum Physics
From Symmetry and Reduction to Physically Meaningful Relational Observables in Many-Body Quantum Theory
Ville J. Härkönen
We consider
symmetries and reduction in non-relativistic many-body
quantum mechanics, with the aim of identifying physically meaningful observables in systems such as molecules and crystalline solids. To this end, we propose a unified framework based on two additional postulates supplementing the standard
quantum-mechanical formalism. For stable systems, the physically relevant states are normalizable stationary states, while physically meaningful observables are required to be invariant under a selected subgroup of the
symmetry group and under Galilean boosts. In addition, we postulate the existence of a map from the set of all observables allowed by
quantum mechanics to the corresponding invariant physically meaningful observables. The originality of the present work does not lie in specific reductions, but in the unified framework that connects
symmetry reduction and relational many-body
quantum theory. We interpret entities like superselection rules and
quantum reference frames as important parts of the postulated process of obtaining the physically meaningful relational description. In particular, the requirement of Galilean-boost invariance added strengthens the criterion for physical observability by excluding quantities that depend on the choice of inertial frame. An important consequence of the postulates is that in the considered cases every physically meaningful observable necessarily depends on more than one non-invariant observable, the latter being typically associated with degrees of freedom assigned to a single particle. The postulates thus lead to theories that are well aligned with the literature on reduction and the description of molecules, while at the same time being consistent with the relational interpretation of
quantum mechanics, according to which the complete physical description of a system is defined only relative to other systems.
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Quantum Physics
Blind Catalytic Quantum Error Correction: Target-State Estimation and Fidelity Recovery Without A Priori Knowledge
Hikaru Wakaura
Catalytic
quantum error correction (CQEC) amplifies residual coherence with a reusable catalyst, giving threshold-free recovery whenever the target coherent modes survive in the noisy state; its original protocol, however, requires complete knowledge of the ideal target, which fails for variational and iterative
algorithms whose output is unknown to the correction module. Here we show that this requirement can be removed by estimating the target from the noisy output alone, in a two-stage protocol we call blind CQEC. At the density-
matrix level studied here the recovery map is the mode-inclusion-restricted projection of the estimate, so recovery fidelity obeys F_rec >= 1 - 2||rho_est - rho_target||_1 - 2 Delta_mode: the design of blind CQEC reduces to a classical estimation problem under a recovery ceiling set by mode survival. We
benchmark five estimation strategies across three noise channels, four
quantum algorithms (d = 4-64), Haar-random states, and mixed targets, assuming oracle access to the noisy density
matrix. With exactly calibrated noise, channel inversion coincides with the oracle and both are capped by the mode-survival ceiling (F_rec = 0.77 at d = 64 with the 10^-10 mode threshold); noise-model-free coherence maximization matches the ceiling to within 1.5% at d <= 16; the choice between them is set by calibration accuracy, with the dephasing rate exponentially dominant. Unlike error-mitigation methods, blind CQEC returns the state itself rather than corrected expectation values. A noisy-VQE demonstration for H2 yields a 3.4x energy-error reduction. These results chart the
estimator design space for blind, threshold-free recovery and identify the two open problems, an operational measurement model and a
circuit-level catalytic map, that remain before deployment.
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Quantum Physics · Cross-listed from cond-mat.quant-gas
Localization with Hopping Disorder in a Quasiperiodic Synthetic Momentum Lattice
Joel M. Sunil, J. Bharathi Kannan, Monu Bhartiya et al. (+5 more)
Quasiperiodicity is easily realized with ultracold atoms in optical
lattices and has been used to simulate the delocalization-localization transition. Random local potentials can also be implemented by spatial light modulators. Programmable hopping disorder, however, remains difficult to realize in conventional optical
lattices. Momentum-space
lattice (MSL) offers a platform to address this. We implement the MSL using an $^{87}$Rb Bose-Einstein condensate via multiple Bragg diffraction and
benchmark the platform by simulating wavepacket dynamics with hopping disorder on top of the generalized Aubry-André (GAA) model. We test programmable hopping disorder added to localized/delocalized backgrounds tunable by the Aubry-André potential strength, as well as systems with mobility edges. Uncorrelated hopping disorder smooths the AA transition into a crossover between weakly (large localization lengths) and strongly localized regimes; the resulting enhancement in localization suppresses wavepacket spreading. We also implement spatially correlated hopping disorder and compare its dynamics with uncorrelated disorder of the same final width, demonstrating a correlation-induced enhancement in spreading. Measured dynamics agrees with trends from ideal tight-binding simulations. Trends in non-universal features depending on microscopic structure and short-time dynamics as functions of quasiperiodic potential strength, hopping-disorder strength, and GAA deformation also match numerical results, with better agreement at larger hopping-disorder strengths. Numerical simulations of the MSL dynamics provide insights into sources of corrections. Our results demonstrate that MSL provides a versatile platform for realizing general disordered
quantum systems with programmable hopping amplitudes beyond quasiperiodic models.
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All authors Joel M. Sunil, J. Bharathi Kannan, Monu Bhartiya, Rayees A S, Shuvarati Roy, G. J. Sreejith, M. S. Santhanam, Umakant Rapol
Quantum Physics
Many-Body Super- and Subradiance in Ordered Atomic Arrays
Alec Douglas, Lin Su, Michal Szurek et al. (+7 more)
When
quantum emitters couple indistinguishably to light, they can synchronize into a collective light matter system with radiative properties profoundly different from those of independent particles. To date, the resulting collective effects have largely been confined to point like or homogeneous ensembles. Here, we open access to a qualitatively new collective regime by realizing geometrically ordered, spatially extended atom arrays with subwavelength spacing. This establishes a fundamentally new platform in which collective emission is no longer confined to a single Dicke mode but instead emerges from an ordered network of
photon mediated interactions. We find that 2D atom arrays undergo strong super and subradiant emission. Despite subwavelength spacing, we achieve site resolved imaging and directly observe the buildup of spatial correlations, demonstrating the transformation of cooperative decay into a strongly correlated many-body process. We observe extensive scaling of superradiance, uncover superradiant revivals, and reveal the
ferromagnetic nature of superradiance and the
antiferromagnetic nature of subradiance. Our results realize a novel programmable platform for exploring and utilizing dissipative many-body
quantum physics, opening new possibilities for
photon capture, storage, and atom
photon entanglement.
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All authors Alec Douglas, Lin Su, Michal Szurek, Robin Groth, Sandra Brandstetter, Ognjen Marković, Oriol Rubies-Bigorda, Stefan Ostermann, Susanne F. Yelin, Markus Greiner
Quantum Physics
Measuring what matters: A scalable framework for application-level quantum benchmarking
Willie Aboumrad, Claudio Girotto, Joshua Goings et al. (+16 more)
As
quantum computing systems continue to mature, there is an increasing need for benchmarking methodologies that capture performance in terms of meaningful, application-level metrics. In this work, we present a scalable framework for application-level
quantum benchmarking that is designed to support internal system evaluation and cross-platform comparison across technology providers. Our framework is guided by a set of core principles, including measurability, simplicity, scalability, and extensibility. We present 13
benchmark families that reflect realistic workloads across multiple domains. This enables the systematic evaluation of the quality of solutions, the total execution time, total used energy, as well as Time-to-Solution. The
benchmarks are designed to be reproducible, interpretable across stakeholder groups, and adaptable to evolving system capabilities. The framework aims to bridge the gap between low-level performance metrics and real-world value, providing a unified approach to assessing
quantum systems. The resulting
benchmarks support development and validation and contribute to the foundation of industry-wide benchmarking standards.
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All authors Willie Aboumrad, Claudio Girotto, Joshua Goings, Luning Zhao, Miguel Angel Lopez-Ruiz, Daiwei Zhu, Ananth Kaushik, Sayonee Ray, Samwel Sekwao, Jason Iaconis, Andrew Arrasmith, Andrii Maksymov, Yvette de Sereville, Felix Tripier, Far McKon, Coleman Collins, Evgeny Epifanovsky, Masako Yamada, Martin Roetteler
Quantum Physics
Hybrid Quantum-Classical Optimization Workflows for the Shipment Selection Problem
Miguel Angel Lopez-Ruiz, Daiwei Zhu, Jonas Hatzenbuhler et al. (+8 more)
We present a
quantum optimization framework for the Shipment Selection Problem (SSP) in electric freight logistics, developed jointly by IonQ and Einride. Idle gaps arising from
stochastic shipment cancellations reduce fleet utilization and revenue; filling them optimally requires solving a combinatorial assignment problem with quadratic inter-gap dependencies. We formulate the SSP as a Mixed-Integer Quadratic Program, map it to an Ising cost
Hamiltonian, and solve it using Iterative-QAOA, a non-variational warm-start extension of the
Quantum Approximate Optimization
Algorithm (QAOA) with a fixed linear-ramp parameter schedule. An end-to-end hybrid workflow integrates Einride's vehicle routing problem (VRP) solver with IonQ's
quantum simulations, enabling evaluation on real, anonymized logistics data spanning up to 130
qubits. We assess solution quality through application-level performance metrics, including Shipments Delivered (SD), Schedule Compatibility Score (SCS), and Total Drive Distance (TDD). When the
quantum assignment is passed to the classical solver as a warm start, the resulting hybrid workflow achieves improvements of up to 12% in SD and a reduction of up to 6% in total drive distance per shipment for specific instances, while total operational cost remains effectively unchanged. For the subset of instances within reach of current devices (20-35
qubits), the workflow is additionally executed on IonQ trapped-ion
quantum hardware, where the hardware results closely reproduce the noiseless simulations. These results show that Iterative-QAOA can generate compatibility-aware assignments that become operationally valuable when embedded in a hybrid logistics optimization workflow.
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All authors Miguel Angel Lopez-Ruiz, Daiwei Zhu, Jonas Hatzenbuhler, Shudian Zhao, Claudio Girotto, Willie Aboumrad, Jonas Alm, Julia Kompalla, Mena Issler, Ananth Kaushik, Martin Roetteler
Quantum Physics · Cross-listed from math-ph
Trapped bosons in mean field QED, nonlinear resonance cascades and dynamical BEC formation
Thomas Chen and Ali Mezher
In this paper, we study a system of
bosons trapped in a confining potential, interacting with a quantized field of coherent
photons in the mean field description of non-relativistic
Quantum Electrodynamics (QED) obtained by [N. Leopold and P. Pickl , 2017]. We derive the effective nonlinear cascade equations governing the emission and absorption of coherent
photons by the
boson subsystem in a combined weak-coupling and macroscopic time limit. We demonstrate that solutions to this nonlinear cascade determine a monotone decreasing energy flow in the
boson subsystem, and thereby describe the dynamical formation of a Bose-Einstein condensate (BEC) with full ground state occupation, under conservation of the total
boson $L^2$ mass. We note that this process is crucially different from thermal relaxation to the ground state, and fundamentally depends on the nonlinear nature of the cascade dynamics.
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Quantum Physics
Sub-nanosecond control for spin-defect quantum memories with a low-cost, compact FPGA platform
Victor Marcenac, Tommy Nguyen, Julie Chen et al. (+8 more)
Dynamical decoupling techniques are widely used to characterize and control the environments of solid-state
quantum defects, enabling solid-state
quantum memories and nanoscale
quantum sensors. However, resolution is often limited by the timing granularity of control hardware, which can undersample narrow spectral features and distort extracted parameters. Here, we demonstrate sub-nanosecond timing control on an inexpensive FPGA-based platform by extending the open-source QICK (
Quantum Instrumentation Control Kit) framework using a waveform-offset method. This approach achieves an effective timing resolution of 200~ps on an RF system-on-chip device without modification to the underlying hardware. We apply this capability to dynamical decoupling spectroscopy of nitrogen-vacancy centers in diamond, enabling precise extraction of hyperfine couplings of individual $^{13}\mathrm{C}$
nuclear spins and resolving spectral features that are otherwise undersampled. These results demonstrate that high-resolution, device-level characterization of
spin-based
quantum memories can be achieved using flexible, inexpensive control hardware, providing a scalable alternative to commercial arbitrary waveform generators.
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All authors Victor Marcenac, Tommy Nguyen, Julie Chen, Weitao He, Enrique Garcia, Yuyang Han, Bethany E. Matthews, Tiamike Dudley, Andrew Mounce, Kai-Mei C. Fu, Maxwell F. Parsons
Quantum Physics
First-principles study of dispersive readout in circuit QED
Angela Riva, Prakritish Gogoi, Nicolas Gheeraert et al. (+4 more)
The speed and fidelity of dispersive readout of superconducting
qubits should improve by increasing the amplitude of the measurement drive. Experiments show, however, that beyond some drive amplitude there is always a saturation or drop in fidelity, often associated with a decrease in
qubit energy relaxation time $T_1$. A simple Lindblad master equation does not capture the latter effect. More involved approaches based on effective master equations rely on strong assumptions about the spectra of the system and the bath and only partially agree with observations. Here, we perform a first-principles simulation of the full
unitary dynamics of dispersive readout by considering the
circuit QED
Hamiltonian coupled to a microscopic model for the measurement transmission line, allowing for its arbitrary spectrum, including filters. Our access to the dynamics of the bath degrees of freedom allows us to investigate the emission spectrum of the system as a function of drive power. We show how the dependence of
qubit $T_1$ on readout drive amplitude is sensitive to the details of the bath spectrum. In particular, we find that $T_1$ drops with increasing drive amplitude when a Purcell notch filter is placed at the
qubit frequency, and that the Lindblad master equation shows general qualitative defects compared to the first-principles model.
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All authors Angela Riva, Prakritish Gogoi, Nicolas Gheeraert, Serge Florens, Alex W. Chin, Alain Sarlette, Alexandru Petrescu
Quantum Physics
Frustration-Induced Expressibility Limitations in Variational Quantum Algorithms
Sandip Maiti
Geometric frustration, arising from competing interactions that prevent simultaneous energy minimization, presents a fundamental challenge for variational
quantum algorithms applied to
quantum many-body systems. We investigate the transverse-field Ising model on a square
lattice with frustrated diagonal coupling and show that
geometric frustration leads to strongly inhomogeneous correlations that are difficult to capture using standard
Hamiltonian-inspired ansätze with global parameters. As a result, the required
circuit depth increases significantly in the intermediate-field regime. We demonstrate that this limitation is not caused by optimization difficulties such as barren plateaus, but instead arises from insufficient expressibility of the ansatz. By introducing bond-resolved variational parameters, we recover accurate results at reduced
circuit depth. We also study low-energy excitations and find that near-degenerate spectra in the frustrated regime further challenge variational methods. Our results provide a clear physical explanation for the limitations of variational
quantum algorithms in frustrated systems and suggest improved ansatz design strategies for
quantum simulation.
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Quantum Physics
A Comparative Study of Hybrid Quantum and Classical Genetic Algorithms in Portfolio Optimization
Romeu Rossi Junior, José Augusto Miranda Nacif, Leonardo Antônio Mendes Souza et al. (+1 more)
This work investigates the performance of a Hybrid
Quantum Genetic
Algorithm (HQGA) compared to a classical Genetic
Algorithm (GA) for solving the portfolio optimization problem. Our results indicate that the HQGA converges faster to the optimal solution than its classical counterpart, while also maintaining a higher level of population diversity throughout the optimization process. In addition, the HQGA requires significantly fewer evaluations-to-solution than a brute-force approach to reach the global optimum.
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All authors Romeu Rossi Junior, José Augusto Miranda Nacif, Leonardo Antônio Mendes Souza, Marcus Henrique Soares Mendes
Quantum Physics
NV-ensemble enabled microwave/NV parametric amplifier with optimal driving
Roman Ovsiannikov, Kurt Jacobs, Andrii G. Sotnikov et al. (+2 more)
In our recent study [arXiv:2601.03407] we showed that a hybrid non-degenerate parametric amplifier could be realized for a microwave mode and an ensemble of NV-centers (or other
spins) by parametrically driving the
spin ensemble. The parametric driving was sinusoidal at the sum of the
spin and cavities frequencies. Here we consider whether the performance of the amplifier can be improved by using a more complex drive. Employing numerical optimization, we find that the optimal driving is primarily a sum of harmonics of the sum frequency. The optimal drive, which is essentially a square wave, ramps up the amplification rate by about 40 %, while limiting the drive to four harmonics improves the amplification by about 22 %.
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All authors Roman Ovsiannikov, Kurt Jacobs, Andrii G. Sotnikov, Matthew E. Trusheim, Denys I. Bondar
Quantum Physics
Robust quantum metrology using disordered probes
Vishnupriya K., Harikrishnan K. J. and Amit Kumar Pal
Disorder is ubiquitous in
quantum devices including
quantum probes designed and fabricated for
quantum parameter estimation and sensing. We investigate the robustness of a
quantum probe against the presence of glassy disorder. We define a disorder marker quantifying the effect of the disorder by expanding the
quantum Fisher information in terms of different orders of the standardized central moments of the disorder-distributions. We classify the
quantum probes in terms of the possible values of the disorder marker, and analytically show, for a disorder-sensitive probe with identical and weak disorder on all or a subset of the parameters of the probe-
Hamiltonian, that the absolute value of the disorder marker exhibits a quadratic dependence on the disorder strength. We derive a robustness scale intrinsic to the probe that competes with the disorder, and provide a prescription for estimating the maximum disorder strength that the probe can withstand from the disorder-free probe-
Hamiltonian for a given initial state of the probe, which can be computed without the disorder averaging. We demonstrate our results in the case of a single-
qubit probe under disordered
magnetic field, and a multi-
qubit probe described by a disordered one-dimensional Kitaev model with nearest-neighbor interactions.
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Quantum Physics
Quantum state transfer on a scalable network under unital and non-unital noise
Monika Rani, Subhashish Banerjee, Nikhil Swami et al. (+1 more)
We investigate
quantum state transfer on a class of bipartite graphs, namely the butterfly graphs, within the framework of discrete-time
quantum walks. These graphs facilitate the construction of scalable
quantum networks that enable communication between a sender and a receiver via perfect state transfer. Our analysis demonstrates that state transfer occurs across different butterfly graphs, thereby extending the known families of networks that support high-fidelity
quantum state transfer. In addition to the ideal noiseless dynamics, we further investigate the robustness of
quantum state transfer in the presence of non-Markovian environmental noise, specifically, random telegraph noise, modified Ornstein-Uhlenbeck noise, which are examples of unital noise and non-Markovian amplitude damping noise, non-unital noise. These noise models capture different types of system-environment interactions and
memory effects that influence the coherence of the
quantum walk. These findings contribute to the theoretical understanding of how butterfly graph constructions influence
quantum transport phenomena.
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All authors Monika Rani, Subhashish Banerjee, Nikhil Swami, Supriyo Dutta
Quantum Physics · Cross-listed from hep-ph
Quantum simulating multi-particle processes in high energy nuclear physics: dijet production and color (de)coherence
João Barata, Meijian Li, Wenyang Qian et al. (+2 more)
Hard scattering events in high-energy collisions produce highly virtual partons that subsequently fragment into collimated hadronic cascades. When such partonic showers evolve in a QCD medium, as in deep-inelastic scattering or heavy-ion collisions, the resulting multi-particle distributions encode information about the surrounding matter. Decades of theoretical developments have led to a consistent and order-by-order improvable perturbative description of the shower. This description needs, however, the non-perturbative input that encodes the structure of the hadronic matter. The determination of such input remains challenging within conventional computational approaches, thereby limiting the applicability of the approach. In this work, we develop a framework that employs
quantum simulation techniques to compute multi-particle processes in such environments by mapping partonic cross-sections to
quantum circuits. As
benchmarks, we analyze dipole formation and the QCD
antenna radiation pattern at leading order in the strong coupling constant, comparing the results with analytic estimates in simplified limits. The
quantum circuit formulation here introduced naturally extends to higher perturbative orders and enables amplitude-level computations in complex matter backgrounds. This provides a systematic foundation for applying
quantum information science methods to study multi-particle dynamics in QCD media.
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All authors João Barata, Meijian Li, Wenyang Qian, Carlos A. Salgado, João M. Silva
Quantum Physics
Spectrum analysis with quantum dynamical systems. II. Finite-time analysis
Xinyi Sui and Mankei Tsang
The prequel to this work [Ng et al., Phys. Rev. A 93, 042121 (2016)] proposes the method of spectral
photon counting to enhance noise spectroscopy with an optical interferometer. While the predicted enhancement over homodyne detection is promising, the results there are derived by taking an asymptotic limit of infinite observation time; their validity for a finite time remains unclear. To validate the theory, here we perform a numerical study of a finite-time model. Assuming that the signal is an Ornstein–Uhlenbeck process with an unknown variance parameter, we evaluate the Fisher information for homodyne detection, a lower bound on the Fisher information for spectral
photon counting, and a
quantum upper bound, all without taking the infinite-time limit. To confirm that the Fisher-information quantities are satisfactory precision measures, we also compute the errors of the maximum-likelihood
estimator by Monte-Carlo simulations. The results demonstrate that the Fisher-information quantities and the estimation errors all smoothly approach their asymptotic limits, and the advantage of spectral
photon counting over homodyne detection can remain substantial for finite times.
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Quantum Physics · Cross-listed from math-ph
Feynman's linear divergence problem
Alexander Sakhnovich and Lev Sakhnovich
First, we consider generalized wave and scattering operators and derive modifications of commutation relations (between scattering operators and unperturbed operators) when the corresponding deviation factors behave as $\exp\{i t {\mathcal C}_{\pm}\}$ for $t\to \pm \infty$. Then, we construct so called secondary generalized scattering operators for the related case of linear divergence in QED, which gives a positive answer (in that case) to the well-known problem of J. R. Oppenheimer regarding scattering operators in QED: "Can the procedure be freed of the expansion in $\varepsilon$ and carried out rigorously?"
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Quantum Physics
Efficient Transpilation of OpenQASM 3.0 Dynamic Circuits to CUDA-Q: Performance and Expressiveness Advantages
Vinooth Kulkarni, Jaehyun Lee, Adam Hutchings et al. (+4 more)
Dynamic
quantum circuits with mid-
circuit measurement and classical feedforward are essential for near-term
algorithms such as error mitigation, adaptive phase estimation, and Variational
Quantum Eigensolvers (VQE), yet transpiling these programs across frameworks remains challenging due to inconsistent support for control flow and measurement semantics. We present a transpilation pipeline that converts OpenQASM 3.0 programs with classical control structures (conditionals and bounded loops) into optimized CUDA-Q C++ kernels, leveraging CUDA-Q's native mid-
circuit measurement and host-
language control flow to translate dynamic patterns without static
circuit expansion. Our open-source framework is validated on comprehensive test suites derived from IBM
Quantum's classical feedforward guide, including conditional reset, if-else branching, multi-bit predicates, and sequential feedforward, and on VQE-style parameterized
circuits with runtime parameter optimization. Experiments show that the resulting CUDA-Q kernels reduce
circuit depth by avoiding branch duplication, improve execution efficiency via low-latency classical feedback, and enhance code readability by directly mapping OpenQASM 3.0 control structures to C++ control flow, thereby bridging OpenQASM 3.0's portable
circuit specification with CUDA-Q's performance-oriented execution model for NISQ-era applications requiring dynamic
circuit capabilities.
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All authors Vinooth Kulkarni, Jaehyun Lee, Adam Hutchings, Anas Albahri, Jai Nana, Shuai Xu, Vipin Chaudhary
Quantum Physics · Cross-listed from cond-mat.mes-hall
Loop-dependent entangling holonomies in localized topological quartets
Kazuki Ikeda and Yaron Oz
A spectrally isolated quartet can admit a local two-
qubit description at each point in parameter space and still acquire a loop holonomy outside the local subgroup $\mathrm{U}(2)\otimes\mathrm{U}(2)$. We study this question in three localized topological settings, a BHZ ribbon, a spinful SSH chain, and a BBH corner quartet. On a fixed quartet, changing only the loop can move the holonomy from almost local to entangling. In BHZ, co-rotating and counter-rotating edge-field loops have nearly the same eigenphase data, but only the counter-rotating loop yields an Ising-like entangler. SSH gives a controlled-rotation example in a numerically stable edge quartet. BBH shows the same issue in a higher-order corner quartet. Standard Berry data, including Berry phases, Chern numbers, determinant phases, and eigenphase spectra, do not separate these cases. The main diagnostic is the distance from the loop holonomy to the extracted local subgroup. Canonical two-
qubit coordinates are used only after reduction failure has been identified. The quartet is the smallest setting in which this question can be tested explicitly. The same subgroup-reduction problem extends to any isolated multiplet with pointwise product type $D=\prod_{\alpha}d_\alpha$, where the relevant local subgroup is the embedded product group $G_{\mathbf d}=\mathrm{Im}[\prod_{\alpha}U(d_\alpha)\to U(D)]$. In the terminology of Ref.[arXiv:2601.13764], these examples realize loop-dependent entangling gluing.
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Quantum Physics
Minimizing classical resources in variational measurement-based quantum computation for generative modeling
Arunava Majumder, Hendrik Poulsen Nautrup and Hans J. Briegel
Measurement-based
quantum computation (MBQC) is a framework for
quantum information processing in which a computational task is carried out through one-
qubit measurements on a highly entangled resource state. Due to the indeterminacy of the outcomes of a
quantum measurement, the random outcomes of these operations, if not corrected, yield a variational
quantum channel family. Traditionally, this randomness is corrected through classical processing in order to ensure deterministic
unitary computations. Recently, variational measurement-based
quantum computation (VMBQC) has been introduced to exploit this measurement-induced randomness to gain an advantage in generative modeling. A limitation of this approach is that the corresponding channel model has twice as many parameters compared to the
unitary model, scaling as $N \times D$, where $N$ is the number of logical
qubits (width) and $D$ is the depth of the VMBQC model. This can often make optimization more difficult and may lead to poorly trainable models. In this paper, we present a restricted VMBQC model that extends the
unitary setting to a channel-based one using only a single additional trainable parameter. We show, both numerically and algebraically, that this minimal extension is sufficient to generate probability distributions that cannot be learned by the corresponding
unitary model.
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Quantum Physics
A Systematic Study of Noise Effects in Hybrid Quantum-Classical Machine Learning
Bhavna Bose and Muhammad Faryad
Near-term
quantum machine learning (QML) models operate in environments wherein noise is unavoidable, arising from both imperfect classical data acquisition and the limitations of noisy intermediate-scale
quantum (NISQ) hardware. Although most existing studies have focused primarily on
quantum circuit noise in isolation, the combined influence of corrupted classical inputs and
quantum hardware noise has received comparatively little
attention. In this work, we present a systematic experimental study of the robustness of a variational
quantum classifier under realistic multi-level noise conditions. Using the Titanic
dataset as a
benchmark, a range of
dataset-level noise models-including speckle noise, impulse noise, quantization noise, and feature dropout are applied to classical features prior to
quantum encoding using a ZZ feature map. In parallel, hardware-inspired
quantum noise channels such as depolarizing noise, amplitude damping, phase damping, Pauli errors, and readout errors are incorporated at the
circuit level using the Qiskit Aer simulator. The experimental results indicate that noise in classical input data can significantly intensify the effects of
quantum decoherence, resulting in less stable training and noticeably lower classification accuracy. Together, these observations emphasize the importance of designing and evaluating
quantum machine learning pipelines with noise in mind, and highlight the need to consider classical and
quantum noise simultaneously when assessing QML performance in the NISQ era
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Quantum Physics
Quantum circuit optimization for arbitrary high-dimensional bipartite quantum computation
Gui-Long Jiang and Hai-Rui Wei
Implementation of high-dimensional (HD)
quantum gates shows very promising perspectives for HD
quantum computation. A bipartite
quantum system with arbitrary dimensions $n$ and $m$ is termed a quNit-quMit. Here we propose a synthesis scheme to construct the
quantum circuit for general quNit-quMit gates with controlled increment (CINC) gates and local gates. This shows that CINC gates combined with local gates form a universal gate set for HD
quantum computation. An upper bound of $O(n^2)$ CINC gates is achieved for arbitrary quNit-quMit gate implementation in the proposed scheme, which is the best known result. Especially for the controlled quNit-quMit gates, our scheme requires only 2 CINC gates, whereas the previous scheme required $2n$.
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Quantum Physics
Tackling instabilities of quantum Krylov subspace methods: an analysis of the numerical and statistical errors
Maria Gabriela Jordão Oliveira, Karl Michael Ziems and Nina Glaser
Krylov subspace methods are among the most extensively studied early fault-tolerant
quantum algorithms for estimating ground-state energies of
quantum systems. However, the rapid onset of ill-conditioning might make accurate energies difficult or even impossible to retrieve. In this communication, we analyse the numerical stability and statistical problems of these methods using numerical simulations both in the presence and absence of sampling noise. While in ideal numerical simulations the generalized
eigenvalue problem indeed becomes unstable with increased Krylov subspace size, we find that, in realistic noisy settings, these methods do not primarily suffer from ill-conditioning. Instead, statistical fluctuations dominate and can prevent reliable solution extraction unless appropriate regularization or filtering techniques are employed. We consequently introduce two new metrics, the imaginary and
unitary filters, that successfully assess the reliability of the obtained solutions without any knowledge of the true eigenspectrum.
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Quantum Physics · Cross-listed from cond-mat.mes-hall
Semiclassical theory of frequency dependent linear magneto-optical transport in Weyl semimetals
Azaz Ahmad, Pankaj Bhalla, Snehasish Nandy et al. (+1 more)
We develop a semiclassical Boltzmann theory for frequency-dependent magneto-optical transport in Weyl semimetals (WSMs), incorporating momentum-dependent relaxation via a scattering
matrix approach. The interplay of orbital
magnetic moment, Weyl cone tilt, intervalley scattering, and electromagnetic driving is analyzed to obtain the full conductivity tensor in the presence of a static
magnetic field. For untilted WSMs with orbital
magnetic moment, strong intervalley scattering in the weak ac regime induces a sign reversal of the longitudinal magneto-optical conductivity (LMOC), thereby suppressing the
chiral anomaly. In contrast, in the strong ac regime, intervalley scattering fails to neutralize the
chiral imbalance within a driving cycle, and no sign reversal is observed. Orbital
magnetic moment induces linear
magnetic-field contributions, while
chiral anomaly yields quadratic response accompanied by expected angular profiles. Tilt direction and orientation strongly affect LMOC such as, transverse tilt gives symmetric non-monotonic behavior, whereas parallel tilt leads to asymmetric, nearly monotonic response. Notably, negative LMOC arises intrinsically for parallel tilt, but requires orbital
magnetic moment for transverse tilt. These results highlight frequency-dependent conductivity as a sensitive probe of
chiral relaxation in MHz-THz magneto-optical experiments.
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All authors Azaz Ahmad, Pankaj Bhalla, Snehasish Nandy, Tanay Nag