Quantum Physics · Cross-listed from physics.chem-ph
Ab initio study of highly charged ion-induced Coulomb explosion imaging
Misa Viveiros, Samuel S. Taylor, Cody Covington et al. (+1 more)
We present a theoretical investigation of ion-induced Coulomb explosion imaging (CEI) of pyridazine molecules driven by energetic C$^{5+}$ projectiles, using time-dependent density-functional theory (TDDFT) with Ehrenfest
nuclear dynamics. By systematically varying the projectile's impact point and orientation relative to the molecular plane, we compare orthogonal and in-plane trajectories and quantify their effects on fragment momenta, electron-density response, and atom-resolved ionization. Newton plots and time-resolved density snapshots show that trajectories avoiding direct atomic collisions yield the most faithful structural reconstructions, whereas direct impacts impart large, highly localized momenta that distort the recovered geometry. Planar trajectories generate substantially greater ionization and broader momentum distributions than orthogonal ones due to deeper traversal through the molecular electron cloud. Quantitative analysis of electron removal at 10~fs confirms that projectile proximity and orientation strongly modulate both local and global ionization. These findings clarify how impact geometry governs the fidelity of ion-induced CEI structural recovery and help explain the variability and noise observed in experimental CEI measurements. More broadly, the results highlight both the strengths and the intrinsic limitations of ion-induced CEI and identify key considerations for interpreting experiments.
Read the full abstract ▾
All authors Misa Viveiros, Samuel S. Taylor, Cody Covington, Kálmán Varga
Quantum Physics · Cross-listed from cond-mat.mtrl-sci
Moire-Engineered Ferroelectric Transistors for Nearly Trap-free, Low-Power and Non-Volatile 2D Electronics
Arup Singha, Shaili Sett, Kenji Watanabe et al. (+3 more)
Long-range moire patterns in twisted WSe2 enable a built-in, moire-length-scale ferroelectric polarization that can be directly harnessed in electronic devices. Such a built-in ferroic landscape offers a compelling means to enable ultralow-voltage and non-volatile electronic functionality in two-dimensional materials; however, achieving stable polarization control without charge trapping has remained a persistent challenge. Here, we demonstrate a moire-engineered ferroelectric field-effect transistor (FeFET) utilizing twisted WSe2
bilayers that leverages atomically clean van der Waals interfaces to achieve efficient polarization-channel coupling and trap-suppressed, ultralow-voltage operation (subthreshold swing of 64 mV per decade). The device exhibits a stable non-volatile
memory window of 0.10 V and high mobility, exceeding the performance of previously reported two-dimensional FeFET and matching that of advanced silicon-based devices. In addition, capacitance-voltage spectroscopy, corroborated by self-consistent Landau-Ginzburg-Devonshire modeling, indicates ultrafast ferroelectric switching (~0.5 microseconds). These results establish moire-engineered ferroelectricity as a practical and scalable route toward ultraclean, low-power, and non-volatile 2D electronics, bridging atomistic
lattice engineering with functional device architectures for next-generation
memory and logic technologies.
Read the full abstract ▾
All authors Arup Singha, Shaili Sett, Kenji Watanabe, Takashi Taniguchi, Arindam Ghosh, Rahul Debnath
Quantum Physics
Deterministic Equations for Feedback Control of Open Quantum Systems II: Properties of the memory function
Alberto J. B. Rosal, Patrick P. Potts and Gabriel T. Landi
Feedback uses past detection outcomes to dynamically modify a
quantum system and is central to
quantum control. These outcomes can be stored in a
memory, defined as a
stochastic function of past measurements. In this work, we investigate the main properties of a general
memory function subject to arbitrary feedback dynamics. We show that the
memory can be treated as a classical system coupled to the monitored
quantum system, and that their joint
evolution is described by a hybrid bipartite state. This framework allows us to introduce information-theoretic measures that quantify the correlations between the system and the
memory. Furthermore, we develop a general framework to characterize the statistics of the
memory – such as moments, cumulants, and correlation functions – which can be applied both to general feedback-control protocols and to monitored systems without feedback. As an application, we analyze feedback schemes based on detection events in a two-level system coupled to a thermal bath, focusing on protocols that stabilize either the excited-state population or Rabi oscillations against thermal dissipation.
Read the full abstract ▾
Quantum Physics
On Dirac-type correlations
James Fullwood and Boyu Yang
Quantum correlations often defy an explanation in terms of fundamental notions of classical physics, such as causality, locality, and realism. While the mathematical theory underpinning
quantum correlations between spacelike separated systems has been well-established since the 1930s, the mathematical theory for correlations between non-spacelike separated systems is much less developed. In this work, we develop the theory of what we refer to as "local-density operators", which we view as joint states for possibly non-spacelike separated
quantum systems. Local-density operators are unit trace operators whose marginals are genuine density operators, which we show not only subsumes the notion of density operator, but also several extensions of the notion of density operator into the spatiotemporal domain, such as pseudo-density operators and
quantum states over time. More importantly, we prove a result which establishes a one-to-one correspondence between local-density operators and what we refer to as "Dirac measures", which are complex-valued measures on the space of separable projectors associated with two
quantum systems. In the case that one of the systems is the trivial
quantum system with a one-dimensional
Hilbert space, our result recovers the fundamental result known as Gleason's
Theorem, which implies that the Born rule from
quantum theory is the only way in which one may assign probabilities to the outcomes of measurements performed on
quantum systems in a non-contextual manner. As such, our results establish a direct generalization of Gleason's
Theorem to measurements performed on possibly non-spacelike separated systems, thus extending the mathematical theory of
quantum correlations across space to
quantum correlations across space and time.
Read the full abstract ▾
Quantum Physics
Coherent and compact van der Waals transmon qubits
Jesse Balgley, Jinho Park, Xuanjing Chu et al. (+9 more)
State-of-the-art superconducting
qubits rely on a limited set of thin-film materials. Expanding their materials palette can improve performance, extend operating regimes, and introduce new functionalities, but conventional thin-film fabrication hinders systematic exploration of new material combinations. Van der Waals (vdW) materials offer a highly modular crystalline platform that facilitates such exploration while enabling gate-tunability, higher-temperature operation, and compact
qubit geometries. Yet it remains unknown whether a fully vdW superconducting
qubit can support
quantum coherence and what mechanisms dominate loss at both low and elevated temperatures in such a device. Here we demonstrate
quantum-coherent merged-element transmons made entirely from vdW Josephson junctions. These first-generation, fully crystalline
qubits achieve microsecond lifetimes in an ultra-compact footprint without external shunt capacitors. Energy relaxation measurements, together with microwave characterization of vdW capacitors, point to dielectric loss as the dominant relaxation channel up to hundreds of millikelvin. These results establish vdW materials as a viable platform for compact superconducting
quantum devices.
Read the full abstract ▾
All authors Jesse Balgley, Jinho Park, Xuanjing Chu, Jiru Liu, Madisen Holbrook, Kenji Watanabe, Takashi Taniguchi, Archana Kamal, Leonardo Ranzani, Martin V. Gustafsson, James Hone, Kin Chung Fong
Quantum Physics
Observation of a Topological Berry Phase with a Single Phonon in an Ion Microtrap Array
Justin F. Niedermeyer, Nathan K. Lysne, Katherine C. McCormick et al. (+11 more)
Controlled
quantum mechanical motion of trapped atomic ions can be used to simulate and explore collective
quantum phenomena and to process
quantum information. Groups of cold atomic ions in an externally applied trapping potential self-organize into "Coulomb
crystals" due to their mutual electrostatic repulsion. The motion of the ions in these
crystals is strongly coupled, and the eigenmodes of motion all involve multiple ions. While this enables studies of many-body physics, it limits the flexibility and tunability of the system as a
quantum platform. Here, we demonstrate an array of trapped ions in individual trapping sites whose motional modes can be controllably coupled and decoupled by tuning the local applied confining potential for each ion. We show that a single motional
quantum, or
phonon, can be coherently shared among two or three ions confined at the vertices of an equilateral triangle 30 $\mu$m on a side. We can adiabatically tune the ion participation in the motional modes around a closed contour in configuration space, observing that the single-
phonon wavefunction acquires a topological Berry phase if the contour encircles a conical intersection of motional
eigenvalue surfaces. We observe this phase by single-
phonon interference and study its breakdown as the motional mode tuning becomes non-adiabiatic. Our results show that precise, individual
quantum control of ion motion in a two-dimensional array can provide unique access to
quantum multi-body effects.
Read the full abstract ▾
All authors Justin F. Niedermeyer, Nathan K. Lysne, Katherine C. McCormick, Jonas Keller, Craig W. Hogle, Matthew G. Blain, Edwin J. Heller, Roman Schmied, Robert Jördens, Susanna L. Todaro, David J. Wineland, Andrew C. Wilson, Daniel H. Slichter, Dietrich Leibfried
Quantum Physics
F2: Offline Reinforcement Learning for Hamiltonian Simulation via Free-Fermionic Subroutine Compilation
Ethan Decker, Christopher Watson, Junyu Zhou et al. (+5 more)
Compiling shallow and accurate
quantum circuits for
Hamiltonian simulation remains challenging due to hardware constraints and the combinatorial complexity of minimizing gate count and
circuit depth. Existing optimization method pipelines rely on hand-engineered classical heuristics, which cannot learn input-dependent structure and therefore miss substantial opportunities for
circuit reduction. We introduce F2, an offline reinforcement learning framework that exploits free-fermionic structure to efficiently compile Trotter-based
Hamiltonian simulation
circuits. F2 provides (i) a reinforcement-learning environment over classically simulatable free-fermionic subroutines, (ii) architectural and objective-level inductive biases that stabilize long-horizon value learning, and (iii) a reversible synthetic-trajectory generation mechanism that consistently yields abundant, guaranteed-successful offline data. Across
benchmarks spanning
lattice models,
protein fragments, and crystalline materials (12-222
qubits), F2 reduces gate count by 47% and depth by 38% on average relative to strong baselines (Qiskit, Cirq/OpenFermion) while maintaining average errors of 10^(-7). These results show that aligning deep reinforcement learning with the algebraic structure of
quantum dynamics enables substantial improvements in
circuit synthesis, suggesting a promising direction for scalable, learning-based
quantum compilation
Read the full abstract ▾
All authors Ethan Decker, Christopher Watson, Junyu Zhou, Yuhao Liu, Chenxu Liu, Ang Li, Gushu Li, Samuel Stein
Quantum Physics
Classical and quantum dynamics of a particle confined in a paraboloidal cavity
Ángel E. Reyna-Cruz and Julio C. Gutiérrez-Vega
We present a classical and
quantum analysis of a particle confined in a three-dimensional paraboloidal cavity formed by two confocal paraboloids. Classically, the system is integrable and presents three independent constants of motion, namely, the energy, the $z$-component of the angular momentum, and a third dynamical constant associated with the paraboloidal geometry, which can be derived from the separability of the Hamilton–Jacobi equation. We derive closed-form analytical expressions for the actions, which allow us to determine the two conditions to get periodic closed trajectories. We classify these trajectories through the indices $(s,t,\ell)$. The caustic paraboloids that bound the motion provide a complete
geometric characterization of admissible trajectories.
Quantum mechanically, separability of the Schrödinger equation in
parabolic coordinates yields eigenmodes described by Whittaker functions. We determine the energy spectrum and identify degeneracies arising not only from azimuthal
symmetry but also from specific cavity deformations. A direct correspondence between classical trajectories and
quantum eigenstates reveals that probability densities concentrate in the classically allowed region with controlled penetration into forbidden zones.
Read the full abstract ▾
Quantum Physics
Information-Theoretic Analysis of Weak Measurements and Their Reversal
Luis D. Zambrano Palma, Yusef Maleki and M. Suhail Zubairy
We study trade-off relations in information extraction from
quantum systems subject to null-result weak measurements, where the absence of a detected
photon continuously updates the system state. We present a detailed analysis of
qubit and qutrit systems and investigate a general framework for a multilevel
quantum system. We develop a dynamical characterization of null-result weak measurements that quantifies the information extracted over time, revealing the amount of the obtained information and also the rate of the information accumulation. The characterizations are obtained by examining the time-dependent
evolution of the information theoretic quantities. More specifically, we consider Shannon
entropy, mutual information, fidelity, and relative
entropy to characterize the weak measurement dynamics. Our results provide an information theoretic analysis of the weak measurement process and highlight the dynamical nature of information extraction and reversibility in the weak measurement processes.
Read the full abstract ▾
Quantum Physics · Cross-listed from hep-th
Entanglement Through Topological Defects: Reconciling Theory with Numerics
Christian Northe and Paolo Rossi
Present theoretical predictions for the
entanglement entropy through topological defects are violated by numerical simulations. In order to resolve this, we introduce a paradigm shift in the preparation of reduced density
matrices in the presence of topological defects, and emphasize the role of defect networks with which they can be dressed. We consider the cases of grouplike and duality defects in detail for the Ising model, and find agreement with all numerically found
entanglement entropies. Since our construction functions at the level of reduced density
matrices, it accounts for topological defects beyond the
entanglement entropy to other
entanglement measures.
Read the full abstract ▾
Quantum Physics
Measurement-and Feedback-Driven Non-Equilibrium Phase Transitions on a Quantum Processor
Zhiyi Wu, Xuandong Sun, Songlei Wang et al. (+8 more)
Mid-
circuit measurements and feedback operations conditioned on the measurement outcomes are essential for implementing
quantum error-correction on
quantum hardware. When integrated in
quantum many-body dynamics, they can give rise to novel non-
equilibrium phase transitions both at the level of each individual
quantum trajectory and the averaged
quantum channel. Experimentally resolving both transitions on realistic devices has been challenging due to limitations on the fidelity and the significant latency for performing mid-
circuit measurements and feedback operations in real time. Here, we develop a superconducting
quantum processor that enables global mid-
circuit measurement with an average
quantum non-demolition (QND) fidelity of 98.7% and fast conditional feedback with a 200 ns real-time decision latency. Using this platform, we demonstrate the coexistence of an absorbing-state transition in the
quantum channel and a measurement-induced
entanglement transition at the level of individual
quantum trajectories. For the absorbing-state transition, we experimentally extract a set of critical exponents at the transition point, which is in excellent agreement with the directed percolation universality class. Crucially, the two transitions occur at distinct values of the tuning parameter. Our results demonstrate that adaptive
quantum circuits provide a powerful platform for exploring non-
equilibrium quantum many-body dynamics.
Read the full abstract ▾
All authors Zhiyi Wu, Xuandong Sun, Songlei Wang, Jiawei Zhang, Xiaohan Yang, Ji Chu, Jingjing Niu, Youpeng Zhong, Xiao Chen, Zhi-Cheng Yang, Dapeng Yu
Quantum Physics
Coherence-limited digital control of a superconducting qubit using a Josephson pulse generator at 3 K
M. A. Castellanos-Beltran, A. J. Sirois, L. Howe et al. (+4 more)
Compared to traditional
semiconductor control electronics (TSCE) located at room temperature, cryogenic single flux
quantum (SFQ) electronics can provide
qubit measurement and control alternatives that address critical issues related to scalability of cryogenic
quantum processors. Single-
qubit control and readout have been demonstrated recently using SFQ
circuits coupled to superconducting
qubits. Experiments where the SFQ electronics are co-located with the
qubit have suffered from excess decoherence and loss due to quasiparticle poisoning of the
qubit. A previous experiment by our group showed that moving the control electronics to the 3 K stage of the dilution refrigerator avoided this source of decoherence in a high-coherence 3D transmon geometry. In this paper, we also generate the pulses at the 3 K stage but have optimized the
qubit design and control lines for scalable 2D transmon devices. We directly compare the
qubit lifetime $T_1$, coherence time $T_2^*$ and gate fidelity when the
qubit is controlled by the Josephson pulse generator (JPG)
circuit versus the TSCE setup. We find agreement to within the daily fluctuations for $T_1$ and $T_2^*$, and agreement to within 10% for randomized benchmarking. We also performed interleaved randomized benchmarking on individual JPG gates demonstrating an average error per gate of $0.46$% showing good agreement with what is expected based on the
qubit coherence and higher-state leakage. These results are an order of magnitude improvement in gate fidelity over our previous work and demonstrate that a Josephson microwave source operated at 3 K is a promising component for scalable
qubit control.
Read the full abstract ▾
All authors M. A. Castellanos-Beltran, A. J. Sirois, L. Howe, D. I. Olaya, J. Biesecker, S. P. Benz, P. F. Hopkins
Quantum Physics · Cross-listed from hep-th
Strong-field regime within effective field theory
Sebastián Franchino-Viñas, Jérémie Quevillon and Diego Saviot
Building upon the Covariant Derivative Expansion, we develop a method to compute effective actions that is able to capture non-perturbative effects induced by strong background fields. We demonstrate the method in scalar QED, by deriving the full second-derivative corrections to the scalar Heisenberg–Euler effective action. The corresponding result is interpreted as an effective field theory with three characteristic scales, two of which are large (mass and field strength) in comparison with the remaining one (derivatives of the field). As an application, we show that, at this order, the transseries structure of the Schwinger pair production rate is preserved, even if the involved coefficients are modified. Our analysis also helps clarify recent disagreements concerning the coefficients of this effective action.
Read the full abstract ▾
Quantum Physics
Exchange Symmetry in Multiphoton Quantum Interference
Shreya Kumar, Alex E Jones, Daniel Bhatti et al. (+1 more)
Photons are
bosons, and yet, when prepared in specific entangled states, they can exhibit non-bosonic behaviour. While this phenomenon has so far been studied in two-
photon systems, exchange
symmetries and interference effects in multi-
photon scenarios remain largely unexplored. In this work, we show that multi-
photon states uncover a rich landscape of exchange
symmetries. With three
photons already, multiple pairwise combinations are possible, where each pair of
photons can exhibit either bosonic, fermionic, or anyonic exchange
symmetry. This gives rise to mixed
symmetry systems that are not possible to achieve with two
photon alone. We experimentally investigate how these
symmetry configurations manifest themselves in the observed interference of three
photons. We show that multi-
photon interference can be effectively turned on and off by tuning the
symmetry of the constituent pairs. The possibility of accessing and tuning new
quantum statistics in a scalable photonic platform not only deepens our understanding of
quantum systems, but is also highly relevant for
quantum technologies that rely on
quantum interference.
Read the full abstract ▾
All authors Shreya Kumar, Alex E Jones, Daniel Bhatti, Stefanie Barz
Quantum Physics · Cross-listed from cond-mat.quant-gas
Vortex leapfrogging and superfluid dissipation mechanisms in a fluid of light
Myrann Baker-Rasooli, Nathan du Toit, Nicolas Pavloff et al. (+1 more)
We report the experimental observation of
vortex leapfrogging in a two-dimensional fluid of light. By imprinting two
vortex-antivortex pairs and tracking their real-time
evolution through phase-resolved imaging, we observe a dynamics that is accurately described by a point-
vortex model with an outward background flow. By precisely controlling the initial
vortex separation, we identify configurations in which leapfrogging breaks down and determine the corresponding dissipation mechanisms. The first originates from phase-slip events occurring at large injected velocities. The second arises when the injection of multi-charged
vortices leads to the formation of a dispersive shock wave which acts as a continuous source of phase slippage. These mechanisms advance our understanding of
vortex dynamics and dissipation in superfluids.
Read the full abstract ▾
All authors Myrann Baker-Rasooli, Nathan du Toit, Nicolas Pavloff, Quentin Glorieux
Quantum Physics
Quantum algorithms for viscosity solutions to nonlinear Hamilton-Jacobi equations based on an entropy penalisation method
Shi Jin and Nana Liu
We present a framework for efficient extraction of the viscosity solutions of nonlinear Hamilton-Jacobi equations with convex
Hamiltonians. These viscosity solutions play a central role in areas such as front propagation, mean-field games, optimal control, machine learning, and a direct application to the forced Burgers' equation. Our method is based on an
entropy penalisation method proposed by Gomes and Valdinoci, which generalises the Cole-
Hopf transform from quadratic to general convex
Hamiltonians, allowing a reformulation of viscous Hamilton-Jacobi dynamics by a discrete-time linear dynamics which approximates a linear heat-like
parabolic equation, and can also extend to continuous-time dynamics. This makes the method suitable for
quantum simulation. The validity of these results hold for arbitrary nonlinearity that correspond to convex
Hamiltonians, and for arbitrarily long times, thus obviating a chief obstacle in most
quantum algorithms for nonlinear partial differential equations. We provide
quantum algorithms, both analog and digital, for extracting pointwise values, gradients, minima, and function evaluations at the minimiser of the viscosity solution, without requiring nonlinear updates or full state reconstruction.
Read the full abstract ▾
Quantum Physics
Quantum computing of nonlinear reacting flows via the probability density function method
Jizhi Zhang, Ziang Yang, Zhaoyuan Meng et al. (+2 more)
Quantum computing offers the promise of speedups for scientific computations, but its application to reacting flows is hindered by nonlinear source terms, the challenges of time-dependent simulations, and the difficulty of extracting meaningful physical quantities from
quantum states. We employ a probability density function (PDF) formulation to transform the nonlinear reacting-flow governing equations into high-dimensional linear ones. The entire temporal
evolution is then solved as a single large linear system using the history state method, which avoids the measurement bottleneck of conventional time-marching schemes and fully leverages the advantages of
quantum linear system
algorithms. To extract the quantity of interest from the resulting
quantum state, we develop an efficient
algorithm to measure the statistical moments of the PDF, bypassing the need for costly full-state
tomography. A computational complexity analysis shows that the measurement
algorithm achieves a complexity
polynomial in the logarithm of the system size using low-order
polynomial approximations, compared to the exponential cost of the exact operator, thereby retaining the
quantum advantage gained from solving the linear system. We validate the framework in two stages: an a priori test confirms the accuracy of the measurement
algorithm on beta distributions with known analytical moments, and a perfectly stirred reactor simulation demonstrates the capability to capture the PDF
evolution and statistics of a nonlinear reactive system. This work establishes a pathway for applying
quantum computing to nonlinear reacting flows.
Read the full abstract ▾
All authors Jizhi Zhang, Ziang Yang, Zhaoyuan Meng, Zhen Lu, Yue Yang
Quantum Physics
Fair Benchmarking of Optimisation Applications
Frank Phillipson
Quantum optimisation is emerging as a promising approach alongside classical heuristics and specialised hardware, yet its performance is often difficult to assess fairly. Traditional benchmarking methods, rooted in digital complexity theory, do not directly capture the continuous dynamics, probabilistic outcomes, and workflow overheads of
quantum and hybrid systems. This paper proposes principles and protocols for fair benchmarking of
quantum optimisation, emphasising end-to-end workflows, transparency in tuning and reporting, problem diversity, and avoidance of speculative claims. By extending lessons from classical benchmarking and incorporating application-driven and energy-aware metrics, we outline a framework that enables practitioners to evaluate
quantum methods responsibly, ensuring reproducibility, comparability, and trust in reported results.
Read the full abstract ▾
Quantum Physics
Symmetry-Based Quantum Codes Beyond the Pauli Group
Zachary P. Bradshaw, Margarite L. LaBorde and Dillon Montero
Typical stabilizer codes aim to solve the general problem of fault-tolerance without regard for the structure of a specific system. By incorporating a broader representation-theoretic perspective, we provide a generalized framework that allows the code designer to take this structure into account. For any representation of a finite group, we produce a
quantum code with a code space invariant under the group action, providing passive error mitigation against errors belonging to the image of the representation. Furthermore, errors outside this scope are detected and diagnosed by performing a projective measurement onto the isotypic components corresponding to irreducible representations of the chosen group, effectively generalizing syndrome extraction to
symmetry-resolved
quantum measurements. We show that all stabilizer codes are a special case of this construction, including qudit stabilizer codes, and show that there is a natural one logical
qubit code associated to the dihedral group. Thus we provide a unifying framework for existing codes while simultaneously facilitating
symmetry-aware codes tailored to specific systems.
Read the full abstract ▾
Quantum Physics
On the relevance of Hermitian-preserving trace-preserving linear maps in asymptotic information retrieval in quantum communication
Arindam Mitra and Jatin Ghai
In
quantum technologies,
quantum channels are essential for transmitting
quantum states.
Quantum channels usually introduce noise, thereby reducing the information in a state. These are mathematically described by completely positive trace-preserving linear maps that represent the generic
evolution of
quantum systems and are also special cases of Hermitian-preserving trace-preserving (HPTP) linear maps. Concatenating a
quantum channel with another
quantum channel makes it noisier and degrades its information and resource preservability. In this work, we demonstrate a physically meaningful way to compare a pair of
quantum channels using Hermitian-preserving trace-preserving linear maps. Precisely, given a pair of
quantum channels $\Lambda_1, \Lambda_2$ and an arbitrary unknown input state, we show that the output state of the
quantum channel $\Lambda_2$ from the pair can be uniquely identified from the output statistics of the other channel $\Lambda_1$ from the pair, using some POVM, iff $\Lambda_2$ can be obtained from $\Lambda_1$ by concatenating it with a Hermitian-preserving trace-preserving linear map that is not necessarily positive. In such cases, $\Lambda_2$ may not always be obtained from $\Lambda_1$ through post-processing. The relation between these channels is a preorder, and we study its characterization in this work. In other words, we provide an operational interpretation of this preorder induced by HPTP linear maps in a communication scenario. Furthermore, we characterize the difficulty of implementing $\Lambda_2$ given that $\Lambda_1$ has already been implemented via a quantifier, namely, physical implementability. We also illustrate the implications of our results for the incompatibility of
quantum devices through an example. In short, we provide valuable insights about the relevance of Hermitian-preserving trace-preserving linear maps in physically motivated settings.
Read the full abstract ▾
Quantum Physics
Fast-feedback protocols for calibration and drift control in quantum computers
Alicia B. Magann, Nathan E. Miller, Robin Blume-Kohout et al. (+2 more)
We introduce two classes of lightweight, adaptive calibration protocols for
quantum computers that leverage fast feedback. The first enables shot-by-shot updates to device parameters using measurement outcomes from simple, indefinite-outcome
quantum circuits. This low-latency approach supports rapid tuning of one or more parameters in real time to mitigate drift. The second protocol updates parameters after collecting measurements from definite-outcome
circuits (e.g.~syndrome extraction
circuits for
quantum error correction), balancing efficiency with classical control overheads. We use numerical simulations to demonstrate that both methods can calibrate 1- and 2-
qubit gates rapidly and accurately even in the presence of decoherence, state preparation and measurement (SPAM) errors, and parameter drift. We propose and demonstrate effective adaptive strategies for tuning the hyperparameters of both protocols. Finally, we demonstrate the feasibility of real-time in-situ calibration of
qubits performing
quantum error correction, using only syndrome data, via numerical simulations of syndrome extraction in the [[5,1,3]] code.
Read the full abstract ▾
All authors Alicia B. Magann, Nathan E. Miller, Robin Blume-Kohout, Peter Maunz, Kevin C. Young
Quantum Physics · Cross-listed from hep-th
Nonlinear Quantum Mechanics and Artificial Intelligence
Jonathan Oppenheim
We examine a criterion for relativistic covariance of nonlinear
quantum field theory recently proposed by GPT-5 and published in Physics Letters B. We show that this criterion inadvertently tests a different property – locality of the
Hamiltonian – and is insensitive to whether the theory is nonlinear. We recall the correct criterion, identified by Gisin and Polchinski thirty-five years ago, and reformulate their result in field-theoretic
language.
Read the full abstract ▾
Quantum Physics
LUNA: LUT-Based Neural Architecture for Fast and Low-Cost Qubit Readout
M. A. Farooq, G. Di Guglielmo, A. Rajagopala et al. (+3 more)
Qubit readout is a critical operation in
quantum computing systems, which maps the analog response of
qubits into discrete classical states. Deep neural networks (DNNs) have recently emerged as a promising solution to improve readout accuracy . Prior hardware implementations of DNN-based readout are resource-intensive and suffer from high inference latency, limiting their practical use in low-latency decoding and
quantum error correction (QEC) loops. This paper proposes LUNA, a fast and efficient superconducting
qubit readout accelerator that combines low-cost integrator-based preprocessing with Look-Up Table (LUT) based neural networks for classification. The architecture uses simple integrators for dimensionality reduction with minimal hardware overhead, and employs LogicNets (DNNs synthesized into LUT logic) to drastically reduce resource usage while enabling ultra-low-latency inference. We integrate this with a differential
evolution based exploration and optimization framework to identify high-quality design points. Our results show up to a 10.95x reduction in area and 30% lower latency with little to no loss in fidelity compared to the state-of-the-art. LUNA enables scalable, low-footprint, and high-speed
qubit readout, supporting the development of larger and more reliable
quantum computing systems.
Read the full abstract ▾
All authors M. A. Farooq, G. Di Guglielmo, A. Rajagopala, N. Tran, V. A. Chhabria, A. Arora
Quantum Physics · Cross-listed from nucl-th
Trapped Fermions Through Kolmogorov-Arnold Wavefunctions
Paulo F. Bedaque, Jacob Cigliano, Hersh Kumar et al. (+2 more)
We investigate a variational Monte Carlo framework for trapped one-dimensional mixture of
spin-$\frac{1}{2}$
fermions using Kolmogorov-Arnold networks (KANs) to construct universal neural-network wavefunction ansätze. The method can, in principle, achieve arbitrary accuracy, limited only by the Monte Carlo sampling and was checked against exact results at sub-percent precision. For attractive interactions, it captures pairing effects, and in the
impurity case it agrees with known results. We present a method of systematic transfer learning in the number of network parameters, allowing for efficient training for a target precision. We vastly increase the efficiency of the method by incorporating the short-distance behavior of the wavefunction into the ansätz without biasing the method.
Read the full abstract ▾
All authors Paulo F. Bedaque, Jacob Cigliano, Hersh Kumar, Srijit Paul, Suryansh Rajawat
Quantum Physics
Strongly driven cavity quantum electrodynamical-optomechanical hybrid system
Xuxin Wang, Jiahe Pan, Tobias J. Kippenberg et al. (+1 more)
Hybrid
quantum systems harness the distinct advantages of different physical platforms, yet their integration is not always trivial due to potential incompatibilities in operational principles. Here, we theoretically propose and demonstrate a scheme for generating non-Gaussian mechanical states using a strongly driven hybrid system that combines cavity
quantum electrodynamics (QED) and cavity optomechanics. Our protocol prepares a non-Gaussian cavity state in the dispersive regime of cavity QED and subsequently transfers it to a mechanical oscillator using the optomechanical interaction enhanced by a coherent cavity drive. While non-Gaussian cavity state control in cavity QED is well established in the dispersive regime, its behavior under strong cavity drive, essential for cavity optomechanics, remains largely unexplored. To bridge this gap, we develop an efficient simulation framework to model cavity QED dynamics in the high-
photon-number regime. We show that a strong cavity drive can coherently displace the cavity state with minimal perturbations, effectively decoupling it from the
qubit. The resulting large coherent cavity field enhances the optomechanical coupling strength, enabling high-fidelity transfer of non-Gaussian cavity states to the mechanical mode. These results reveal new dynamical features of driven cavity QED and open a pathway toward realizing non-Gaussian mechanical
quantum memories and sensors.
Read the full abstract ▾
All authors Xuxin Wang, Jiahe Pan, Tobias J. Kippenberg, Shingo Kono
Quantum Physics
Statistical properties of quantum jumps between macroscopic states of light: reading an operational coherence record
Th. K. Mavrogordatos
We propose an experimental apparatus to reveal the
quantum coherence manifested in downward
quantum jumps of amplitude bistability. The underlying coherent superposition of macroscopic
quantum states is translated into the statistical properties of the integrated charge deposited in the detector
circuit of a mode-matched heterodyne/homodyne detection scheme. At first, the dynamical
evolution of a signal transmitted from an auxiliary cavity is employed to pinpoint a macroscopic switching event in a bistable main cavity subject to direct photodetection. Once the decision is made on the occurrence of a downward switch, the main cavity mode is let to freely decay to the
vacuum, monitored to the production of an integrated charge. In the long-time limit, the charge distribution over an identical collection of pure states generated during the jumps converges to the Q function (heterodyne detection) or marginals of the Wigner function (homodyne detection) dictated by the phase of the local oscillator. When fluctuations over the ensemble step in, we connect the statistical properties of several switching events and the ensuing production of current records, to the cavity field correlations associated with the breakdown of
photon blockade.
Read the full abstract ▾
Quantum Physics
Real-time collisions of fractional charges in a trapped-ion Jackiw-Rebbi field theory
Alan Kahan, Pablo Viñas, Torsten V. Zache et al. (+1 more)
We propose and analyze a trapped-ion
quantum simulator of the Jackiw-Rebbi model, a paradigmatic
quantum field theory in (1+1) dimensions where solitonic excitations of a scalar field can bind fermionic zero modes leading to fractionally-charged excitations. In our approach, the scalar field is a coarse-grained description of the planar zigzag ion displacements in the vicinity of a structural phase transition. The internal electronic states of the ions encode
spins with interactions mediated by the transverse
phonons and in-plane
spin-
phonon couplings with a zigzag pattern, which together correspond to a Yukawa-coupled Dirac field. Instead of assuming a fixed
soliton background, we study the effect of back-reaction and
quantum fluctuations on the coupled dynamics of the full
fermion-
boson system. We start by applying a Born-Oppenheimer approximation to obtain an effective Peierls-Nabarro potential for the topological kink, unveiling how the fermionic back-reaction can lead to localization of the kink. Beyond this limit, a truncated Wigner approximation combined with fermionic Gaussian states captures the
quantum spreading and localization of a kink and kink-antikink scattering. Our results reveal how back-reaction and
quantum fluctuations modify the stability and real-time
evolution of fractionalized
fermions, predicting experimentally accessible signatures in current trapped-ion architectures.
Read the full abstract ▾
All authors Alan Kahan, Pablo Viñas, Torsten V. Zache, Alejandro Bermudez
Quantum Physics · Cross-listed from cond-mat.stat-mech
Strong zero modes in integrable spin-S chains
Fabian H.L. Essler, Paul Fendley and Eric Vernier
We derive exact strong zero mode (ESZM) operators for integrable
spin-S chains with open boundary conditions and a boundary field. Their locality properties are generally weaker than in the previously known cases, but they still imply infinite coherence times in the vicinity of the edges. We explain how such integrable chains possess multiple ground states describing a first-order
quantum phase transition, and that the odd number of such states for integer S makes the weaker locality properties necessary. We make contact with more traditional approaches by showing how the ESZM for S=1/2 acts on energy eigenstates given by solutions of the Bethe equations.
Read the full abstract ▾
Quantum Physics
A scalable and real-time neural decoder for topological quantum codes
Andrew W. Senior, Thomas Edlich, Francisco J.H. Heras et al. (+21 more)
Fault-tolerant
quantum computing will require error rates far below those achievable with physical
qubits.
Quantum error correction (QEC) bridges this gap, but depends on decoders being simultaneously fast, accurate, and scalable. This combination of requirements remains unmet by a machine-learning decoder, nor by any decoder for promising resource-efficient codes such as the color code. Here we introduce AlphaQubit 2, a neural-network decoder that achieves near-optimal logical error rates for both surface and color codes at scale under realistic noise. For the color code, it is orders of magnitude faster than other high-accuracy decoders. We demonstrate real-time decoding faster than 1{\mu}s per cycle on commercial accelerators: for the surface code to distance 11, with better accuracy than leading real-time decoders; and the first real-time decoding of the color code to distance 9. These results support the practical application of a wider class of promising QEC codes, and establish a credible path towards high-accuracy, real-time neural decoding at the scales required for fault-tolerant
quantum computation.
Read the full abstract ▾
All authors Andrew W. Senior, Thomas Edlich, Francisco J.H. Heras, Lei M. Zhang, Oscar Higgott, James S. Spencer, Taylor Applebaum, Sam Blackwell, Justin Ledford, Akvilė Žemgulytė, Augustin Žídek, Noah Shutty, Andrew Cowie, Yin Li, George Holland, Peter Brooks, Charlie Beattie, Michael Newman, Alex Davies, Cody Jones, Sergio Boixo, Hartmut Neven, Pushmeet Kohli, Johannes Bausch
Quantum Physics · Cross-listed from hep-th
Grand Canonical vs Canonical Krylov Complexity in Double-Scaled Complex SYK Model
Stefan Forste, Yannic Kruse and Saurabh Natu
We consider the complex SYK model in the double-scaling limit. We obtain the transfer
matrix for the grand canonical ensemble and symmetrize it. In the (n,Q)- basis of chord states, the grand canonical transfer
matrix is block diagonal, where each block is the canonical transfer
matrix for the respective charge sector. We therefore conclude that the Krylov complexity for the grand canonical ensemble is given by the sum of the complexities in the charge sectors weighted by a probability function that depends on the chemical potential. Finally, we compute the Krylov complexity analytically in the limit of early and late time in the charge sector and numerically for both canonical and grand canonical ensemble.
Read the full abstract ▾