Quantum Physics · Cross-listed from cond-mat.str-el
Remarks on non-invertible symmetries on a tensor product Hilbert space in 1+1 dimensions
Kansei Inamura
We propose an index of non-invertible
symmetry operators in 1+1 dimensions and discuss its relation to the realizability of non-invertible
symmetries on the tensor product of finite dimensional on-site
Hilbert spaces on the
lattice. Our index generalizes the Gross-Nesme-Vogts-Werner index of invertible
symmetry operators represented by
quantum cellular automata (QCAs). Assuming that all fusion channels of
symmetry operators have the same index, we show that the fusion rules of finitely many
symmetry operators on a tensor product
Hilbert space can agree, up to QCAs, only with those of weakly integral fusion categories. We also discuss an attempt to establish an index theory for non-invertible
symmetries within the framework of tensor networks. To this end, we first propose a general class of
matrix product operators (MPOs) that describe non-invertible
symmetries on a tensor product
Hilbert space. These MPOs, which we refer to as topological injective MPOs, include all invertible
symmetries, non-anomalous fusion category
symmetries, and the Kramers-Wannier
symmetries for finite abelian groups. For topological injective MPOs, we construct the defect
Hilbert spaces and the corresponding sequential
quantum circuit representations. We also show that all fusion channels of topological injective MPOs have the same index if there exist fusion and splitting tensors that satisfy appropriate conditions. The existence of such fusion and splitting tensors has not been proven in general, although we construct them explicitly for all examples of topological injective MPOs listed above.
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Quantum Physics
Scalable Preparation of Matrix Product States with Sequential and Brick Wall Quantum Circuits
Tomasz Szołdra, Rick Mukherjee and Peter Schmelcher
Preparing arbitrary
quantum states requires exponential resources.
Matrix Product States (MPS) admit more efficient constructions, particularly when accuracy is traded for
circuit complexity. Existing approaches to MPS preparation mostly rely on heuristic
circuits that are deterministic but quickly saturate in accuracy, or on variational optimization methods that reach high fidelities but scale poorly. This work introduces an end-to-end MPS preparation framework that combines the strengths of both strategies within a single pipeline. Heuristic staircase-like and brick wall disentangler
circuits provide warm-start initializations for variational optimization, enabling high-fidelity state preparation for large systems. Target MPSs are either specified as physical
quantum states or constructed from classical
datasets via amplitude encoding, using step-by-step singular value decompositions or tensor cross interpolation. The framework incorporates
entanglement-based
qubit reordering, reformulated as a quadratic assignment problem, and low-level optimizations that reduce depths by up to 50% and CNOT counts by 33%. We evaluate the full pipeline on
datasets of varying complexity across systems of 19-50
qubits and identify trade-offs between fidelity, gate count, and
circuit depth. Optimized brick wall
circuits typically achieve the lowest depths, while the optimized staircase-like
circuits minimize gate counts. Overall, our results provide principled and scalable protocols for preparing MPSs as
quantum circuits, supporting utility-scale applications on near-term
quantum devices.
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Quantum Physics
A New Angle on Quantum Subspace Diagonalization for Quantum Chemistry
Xeno De Vriendt, Jacob Bringewatt, Nik O. Gjonbalaj et al. (+5 more)
Quantum subspace diagonalization and
quantum Krylov
algorithms offer a feasible, pre- or early-fault tolerant alternative to
quantum phase estimation for using
quantum computers to estimate the low-lying spectra of
quantum systems. However, despite promising proof-of-principle results, such methods suffer from high sensitivity to noise (including intrinsic sources such as sampling noise), making their utility for realistic industry-relevant problems an open question. To improve the potential applicability of such methods, we introduce a new variant of thresholding for noisy generalized
eigenvalue problems that arise in
quantum subspace diagonalization that has the potential to better control sensitivity to noise. Our approach leverages eigenvector-preserving transformations (rotations) of the generalized
eigenvalue problem prior to thresholding. We study this effect in practical settings by applying this rotation thresholding scheme to an iterative
quantum Krylov
algorithm for several chemical systems, including the industry-relevant Fe(III)-NTA chelate complex. We develop a particular heuristic to select the rotation angle from noisy data and find for certain systems and noise regimes that the samples required to reach a target error for ground state estimation can be reduced by a factor of up to 100. Furthermore, with oracle access to the optimal transformation, more dramatic improvements are possible and we observe reductions in sample requirements by up to $10^4$, motivating the continued development of methods that can realize these improvements in practice. While we develop our approach in the context of
quantum subspace diagonalization, the improved thresholding scheme we develop could be advantageous in any context where one must solve noisy, ill-conditioned generalized
eigenvalue problems.
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All authors Xeno De Vriendt, Jacob Bringewatt, Nik O. Gjonbalaj, Stefan Ostermann, Davide Vodola, Johannes Borregaard, Michael Kühn, Susanne F. Yelin
Quantum Physics · Cross-listed from cond-mat.mes-hall
Rabi oscillations induced by nonresonant gyrating drive
Baksa Kolok and András Pályi
Coherent control of two-level
quantum systems is typically achieved using resonant driving fields, forming the basis for
qubit operations. Here, we report a mechanism for inducing complete Rabi oscillations in monochromatically driven two-level
quantum systems, when the drive frequency is much larger than the Larmor frequency of the
qubit. This effect$\unicode{x2015}$Rabi oscillations induced by nonresonant gyrating drive (RING)$\unicode{x2015}$requires a gyrating control field, i.e., an
elliptic drive trajectory that encloses a nonzero area per cycle. We illustrate the effect with numerical simulations, and provide an analytical understanding via a simple effective
Hamiltonian obtained from Floquet theory and perturbation theory. We show that RING enables coherent oscillations without relying on resonant energy exchange, allows for high-pass noise filtering, provides access to non-Abelian phases in finite
magnetic fields. We detail a realization in electrically driven
spin-orbit
qubits and argue that the RING mechanism enables amplification of the Rabi frequency using the same gate voltage amplitudes at higher drive frequencies. Our results broaden the landscape of
quantum control techniques, by highlighting a pathway to achieving coherent oscillations under off-resonant driving conditions.
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Quantum Physics
Millisecond-Scale Calibration and Benchmarking of Superconducting Qubits
Malthe A. Marciniak, Rune T. Birke, Johann B. Severin et al. (+13 more)
Superconducting
qubit parameters drift on sub-second timescales, motivating calibration and benchmarking techniques that can be executed on millisecond timescales. We demonstrate an on-FPGA workflow that co-locates pulse generation, data acquisition, analysis, and feed-forward, eliminating CPU round trips. Within this workflow, we introduce sparse-sampling and on-FPGA inference tools, including computationally efficient methods for estimation of exponential and sine-like response functions, as well as on-FPGA implementations of Nelder-Mead optimization and golden-section search. These methods enable low-latency primitives for readout calibration, spectroscopy, pulse-amplitude calibration, coherence estimation, and benchmarking. We deploy this toolset to estimate $T_1$ in 10 ms, optimize readout parameters in 100 ms, optimize pulse amplitudes in 1 ms, and perform Clifford randomized gate benchmarking in 107 ms on a flux-tunable superconducting transmon
qubit. Running a closed-loop on-FPGA recalibration protocol continuously for 6 hours enables more than 74,000 consecutive recalibrations and yields gate errors that consistently retain better performance than the baseline initial calibration. Correlation analysis shows that recalibration suppresses coupling of gate error to control-parameter drift while preserving a coherence-linked performance. Finally, we quantify uncertainty versus time-to-decision under our sparse sampling approaches and identify optimal parameter regimes for efficient estimation of
qubit and pulse parameters.
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All authors Malthe A. Marciniak, Rune T. Birke, Johann B. Severin, Fabrizio Berritta, Daniel Kjær, Filip Nilsson, Smitha N. Themadath, Sangeeth Kallatt, James L. Webb, Kristoffer Bentsen, Tonny Madsen, Zhenhai Sun, Svend Krøjer, Christopher W. Warren, Jacob Hastrup, Morten Kjaergaard
Quantum Physics
Benchmarking Classical and Quantum Optimization Approaches for Rider-Order Assignment
Tharrmashastha SAPV, Surya Prakash Palanivel, Jasjyot Singh Gulati et al. (+1 more)
The logistics industry is widely regarded as a promising application domain for emerging optimization paradigms, including
quantum computing. The Rider-Order Assignment problem is a practically motivated optimization problem arising in online food delivery and related logistics applications. While the problem is closely related to the classical matching problem, the inclusion of realistic operational constraints renders it computationally challenging. In this work, we formulate the Rider-Order Assignment problem as a constrained binary optimization problem and perform a comparative analysis of classical,
quantum-inspired, and gate-based
quantum solvers for this problem across multiple instance sizes. Solver performance is assessed using solution quality, computational runtime, and constraint satisfaction, with a consistent post-processing procedure applied to ensure feasibility.
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All authors Tharrmashastha SAPV, Surya Prakash Palanivel, Jasjyot Singh Gulati, M Maruthu Pandi
Quantum Physics
Resource-Efficient Teleportation of High-Dimensional Quantum Coherence via Initial Phase Engineering
Long Huang, Cai-Hong Liao, Yan-Ling Li et al. (+1 more)
High-dimensional
quantum systems leverage an expanded
Hilbert space to enhance resilience against decoherence and noise. However, standard
quantum teleportation is fundamentally limited by the quadratic growth of measurement complexity and high classical communication overhead, requiring the resolution of $d^2$ Bell states and $2\log_2 d$ classical bits. In this study, we propose a resource-efficient high-dimensional coherence teleportation (REHDCT) protocol. By designing $d$ sets of specialized positive operator-valued measure (POVM) bases, our protocol achieves a 50% reduction in classical communication by utilizing one of the $d$ designed POVM sets, which effectively scales the measurement complexity from $O(d^2)$ to $O(d)$. Furthermore, we demonstrate that by utilizing initial phase engineering to align the target qudit with the measurement basis, theoretically perfect teleportation of
quantum coherence can be achieved for arbitrary qudit states. A quantitative robustness analysis reveals that the protocol remains highly resilient to operational errors, maintaining an efficiency above 99.6% even under a 0.1 rad phase deviation for $d=16$. Our analysis under various noise models (amplitude damping, phase flip, depolarizing, and dit-flip) confirms that high-dimensional systems exhibit an expanding
quantum advantage window as dimensionality increases. Notably, under dit-flip noise, perfect coherence teleportation can be restored through the optimal selection of the POVM basis. These findings establish REHDCT as a practical, hardware-friendly framework for resource-efficient
quantum communication in future high-dimensional networks.
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All authors Long Huang, Cai-Hong Liao, Yan-Ling Li, Xing Xiao
Quantum Physics
Universal Sequential Changepoint Detection of Quantum Observables via Classical Shadows
Matteo Zecchin, Osvaldo Simeone and Aaditya Ramdas
We study sequential
quantum changepoint detection in settings where the pre- and post-change regimes are specified through constraints on the expectation values of a finite set of observables. We consider an architecture with separate measurement and detection modules, and assume that the observables relevant to the detector are unknown to the measurement device. For this scenario, we introduce shadow-based sequential changepoint e-detection (eSCD), a novel protocol that combines a universal measurement strategy based on classical shadows with a nonparametric sequential test built on e-detectors. Classical shadows provide universality with respect to the detector's choice of observables, while the e-detector framework enables explicit control of the average run length (ARL) to false alarm. Under an ARL constraint, we establish finite-sample guarantees on the worst-case expected detection delay of eSCD. Numerical experiments validate the theory and demonstrate that eSCD achieves performance competitive with observable-specific measurement strategies, while retaining full measurement universality.
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Quantum Physics · Cross-listed from cond-mat.str-el
Parity-dependent double degeneracy and spectral statistics in the projected dice lattice
Koushik Swaminathan, Anouar Moustaj, Jose L. Lado et al. (+1 more)
We investigate the spectral statistics of an interacting fermionic system derived by projecting the Hubbard interaction onto the two lowest-energy, degenerate flat bands of the dice
lattice subjected to a $\pi$-flux. Surprisingly, the distributions of level spacings and gap ratios correspond to distinct Gaussian ensembles, depending on the parity of the particle number. For an even number of particles, the spectra conform to the Gaussian Orthogonal Ensemble, as expected for a time-reversal-symmetric
Hamiltonian. In stark contrast, the odd-parity sector exhibits exact double degeneracy of all eigenstates even after resolving all known
symmetries, and the Gaussian
Unitary Ensemble accurately describes the spacing distribution between these doublets. The simultaneous emergence of two different random-
matrix ensembles within a single physical system constitutes an unprecedented finding, opening new avenues for both random
matrix theory and flat-band physics.
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All authors Koushik Swaminathan, Anouar Moustaj, Jose L. Lado, Sebastiano Peotta
Quantum Physics
Single-shot GHZ characterization with connectivity-aware fanout constructions
Giancarlo Gatti
We propose a practical recipe to transform any depth-$L$ block of CNOTs that prepares $n$-
qubit GHZ states into an $n$-
qubit fanout gate (multitarget-CNOT) of depth $2L-1$, without the need for ancilla
qubits. Considering known logarithmic-depth
circuits to prepare GHZ-states, this allows us to construct an $n$-
qubit fanout gate with depth $2\log_2(n)-1$, reproducing previous ancillaless constructions. We employ our recipe to construct $n$-
qubit fanout gates under heavy-hex connectivity restrictions, obtaining a depth of $O(n^{1/2})$, again reproducing previous complexity theory constructions. Using this recipe on the ibm\_fez architecture yields a $156$-
qubit fanout construction with depth $33$. Additionally, we show how to employ these $n$-
qubit fanout constructions to measure complete sets of commuting observables from the $n$-body Pauli group with the same depth, allowing for efficient single-shot characterization of any GHZ-like state in a given known basis, e.g. fully characterizing a single copy of a $156$-
qubit GHZ state using
circuit depth $33$ in $\textit{ibm\_fez}$ (its preparation requires an additional depth of $17$).
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Quantum Physics
Operational performance of finite-key entanglement-based satellite quantum key distribution
Jasminder S. Sidhu, Sarah E. McCarthy, Cameron Paterson et al. (+3 more)
Establishing information-theoretically secure communication between arbitrary locations on Earth is a central goal of
quantum networking, for which space-based distribution of
quantum entanglement is a leading approach. Modelling and analysis of the performance of satellite
entanglement pair distribution is therefore important for the architecture and design of future constellations and space systems. However,
entanglement-based
quantum key distribution in the absence of
quantum repeaters, is especially prone to finite-key effects due to low coincident count rates compared to trusted-node single-path links. Quantifying these effects under realistic orbital conditions is therefore essential for the design of practical satellite
quantum communication systems. Here, we develop a high-fidelity model of pair distribution from a low-Earth-orbit satellite that captures orbital dynamics, elevation-dependent loss, background noise, and extraneous detector effects. Integrating this with a finite-key security framework for the BBM92 protocol, we optimise the secret key length across different overpass geometries, orbital altitudes, and optical ground station (OGS) separations. We show that secure key generation remains feasible in early clear daytime conditions using baseline parameters representative of current technologies, while showing that modest system improvements could further extend daytime operation. Finally, we evaluate the annual secret key performance for representative intercity-scale OGS pairings. Our results provide quantitative performance bounds and practical design guidelines for near-term
entanglement-based satellite QKD, enabling informed trade-offs between satellite payload complexity, ground infrastructure, and achievable secure key throughput.
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All authors Jasminder S. Sidhu, Sarah E. McCarthy, Cameron Paterson, Nathan Walk, Jens Eisert, Daniel K. L. Oi
Quantum Physics
Learning functions of quantum states with distributed architectures
Marta Gili, Eliana Fiorelli, Ane Blázquez-García et al. (+2 more)
Distributed architectures are gaining prominence in
quantum machine learning as a means to overcome hardware limitations and enable scalable
quantum information processing. In this context, we analyze the design and performance of distributed
Quantum Extreme Learning Machine (QELM) architectures for learning functions of
quantum states directly from data, restricting measurements to easily implementable projective measurements in the computational basis. The aim is to determine which schemes can effectively recover specific properties of input
quantum states, including both linear and nonlinear features, while also quantifying the resource requirements in terms of measurements and reservoir dimensionality. We compare standard three-layer QELM with a spatially multiplexed architecture composed of multiple independent three-layer units for linear (
quantum) tasks, showing a linear reduction in resource requirements per unit. For nonlinear properties, the study examines the multiple-injection architecture and introduces a novel distributed design that incorporates
entanglement between subsystems within a spatially multiplexed framework, evaluating its performance through the reconstruction of complex nonlinear quantities such as
polynomial targets, Rényi
entropy, and
entanglement measures. Our results demonstrate that the distributed design enables the reconstruction of higher-order nonlinearities by increasing the number of interacting subsystems with reduced resources, rather than increasing the size of an individual reservoir, providing a scalable and hardware-efficient route to
quantum property learning.
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All authors Marta Gili, Eliana Fiorelli, Ane Blázquez-García, Gian Luca Giorgi, Roberta Zambrini
Quantum Physics · Cross-listed from physics.app-ph
Experimental setup for the combined study of spin ensembles and superconducting quantum circuits
Lukas Vogl, Gerhard B. P. Huber, Ana Strinić et al. (+5 more)
A hybrid
quantum computing architecture combining
quantum processors and
quantum memory units allows for exploiting each component's unique properties to enhance the overall performance of the total system. However, superconducting
qubits are highly sensitive to
magnetic fields, while
spin ensembles require finite fields for control, creating a major integration challenge. In this work, we demonstrate the first experimental setup that satisfies these constraints and provides verified
qubit stability. Our cryogenic setup comprises two spatially and magnetically decoupled sample volumes inside a single dilution refrigerator: one hosting flux-tunable superconducting
qubits and the other a
spin ensemble equipped with a superconducting solenoid generating fields up to 50 mT. We show that several layers of Cryophy shielding and an additional superconducting aluminum shield suppress
magnetic crosstalk by more than eight orders of magnitude, ensuring stability of the
qubit's performance. Moreover, the operation of the solenoid adds minimal thermal load on the relevant stages of the dilution refrigerator. Our results enable scalable hybrid
quantum architectures with low-loss integration, marking a key step toward scalable hybrid
quantum computing platforms.
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All authors Lukas Vogl, Gerhard B. P. Huber, Ana Strinić, Achim Marx, Stefan Filipp, Kirill G. Fedorov, Rudolf Gross, Nadezhda P. Kukharchyk
Quantum Physics
Experimental challenges and prospects for quantum-enhanced energy conversion: Stationary Fano coherence in V-type qutrits interacting with polarized incoherent radiation
Ludovica Donati, Francesco Saverio Cataliotti and Stefano Gherardini
Quantum coherence offers potential for energy conversion technologies. It influences light absorption and emission, affecting energy conversion limits and efficiency. As a result,
quantum coherence is being harnessed to boost performance in
quantum heat engines, photocells, and photosynthetic-inspired platforms. Of particular interest in this context is the generation of Fano coherences, i.e., the formation of
quantum coherences due to the interaction with the continuum of modes characterizing an incoherent process. We aim to formalize mathematically the possibility of achieving steady-state Fano coherence in a V-type three-level
quantum system using polarized incoherent radiation, without requiring the energy difference between the excited levels to tend to zero. We perform this analysis by deriving the Bloch-Redfield equation from first-principles by quantizing the incoherent radiation. The resulting reduced dynamics of the system are analysed, so as to determine the lifetime of Fano coherence and identify the conditions under which it becomes stationary. We characterise distinct dynamical regimes, ranging from weak to strong pumping, in which steady-state Fano coherence emerges, and we quantitatively determine its magnitude. For each regime, we analyse the generation of Fano coherence as a function of both the intensity of the incoherent pumping and the energy splitting between the excited levels. We also assess how obtaining Fano coherence is modified by symmetric or asymmetric decay rates. These findings indicate that a three-level
quantum system driven by polarized incoherent light can act as a robust resource for coherence-assisted energy conversion and storage. Finally, we discuss the experimental challenges associated with the implementation of the proposed model using an ensemble of Rubidium atoms.
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Quantum Physics · Cross-listed from cond-mat.quant-gas
First-order phase transition in atom-molecule quantum degenerate mixtures with coherent three-body recombination
G. A. Bougas, A. Vardi, H. R. Sadeghpour et al. (+2 more)
We map the phase diagram of a two-mode atom-molecule Bose-Einstein condensate with Fano-Feshbach and coherent three-body recombination (cTBR) terms. The standard second order phase transition observed as the molecular energy is tuned through the Feshbach resonance, is replaced by a first order transition when cTBR becomes prominent, due to a double-well structure in the free energy landscape. This transition is associated with atom-molecule
entanglement, bistability, and molecular metastability. Our results establish cTBR as a powerful knob for
quantum state engineering and control of reaction dynamics in ultracold chemistry.
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All authors G. A. Bougas, A. Vardi, H. R. Sadeghpour, C. Chin, S. I. Mistakidis
Quantum Physics · Cross-listed from hep-th
On the near-horizon interpretation of Krylov dynamics
Hyun-Sik Jeong
The Lanczos recursion maps operator growth onto the motion of a wave function on a semi-infinite chain, and for linearly growing Lanczos coefficients the deep region of the chain behaves like the near-horizon region of a black hole. We develop this correspondence in the time domain and determine how far it extends. Writing the Krylov equation as an exactly skew-adjoint difference operator, we derive a
unitary continuum limit whose corrections are suppressed by $n^{-2}$ once the origin of the chain is fixed by the offset of the Lanczos coefficients. For $b_n\simeq\alpha n$ the Krylov
evolution is
chiral transport in $\ln n$, which coincides with infalling waves near the horizon of an AdS$_2$ black hole when the Krylov depth is identified with the blueshift of an infalling particle; this fixes $\alpha=\pi T$, while staggered configurations of the chain carry the outgoing chirality. For $b_n=\alpha\sqrt{n(n+2h-1)}$ the correspondence is exact: the Krylov basis is the discrete series of $\mathrm{SL}(2,\mathbb{R})$ carried by a bulk scalar of mass $m^2L^2=h(h-1)$, the Liouvillian is the boost generator of the black hole at temperature $T=\alpha/\pi$, and positivity of $b_n^2$ reproduces the Breitenlohner–Freedman bound, saturated by strictly linear coefficients. Beyond leading order we prove that, for every Lanczos sequence with a smooth large-$n$ expansion, the ingoing solutions of the Krylov equation have coefficients
polynomial in frequency to all orders in $1/n$, whereas a massive bulk field has a pole at the first special point $\omega=-2\pi iT$ with residue proportional to $m^2$. Smooth subleading Lanczos data therefore cannot encode the bulk mass locally. The obstruction persists for the BTZ black hole, for which we obtain the Lanczos coefficients in closed form.
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Quantum Physics
The Power of Two Bases: Robust and copy-optimal certification of nearly all quantum states with few-qubit measurements
Andrea Coladangelo, Jerry Li, Joseph Slote et al. (+1 more)
A central task in
quantum information science is state certification: testing whether an unknown state is $\epsilon_1$-close to a fixed target state, or $\epsilon_2$-far. Recent work has shown that surprisingly simple measurement protocols–comprising only single-
qubit measurements–suffice to certify arbitrary $n$-
qubit states [Huang, Preskill, Soleimanifar '25; Gupta, He, O'Donnell '25]. However, these certification protocols are not robust: rather than allowing constant $\epsilon_1$, they can only positively certify states within $\epsilon_1=O(1/n)$ trace distance of the target. In many experimental settings, the appropriate error tolerance is constant as the system size grows, so this lack of robustness renders existing tests inapplicable at scale, no matter how many times the test is repeated. Here we present robust certification protocols based on few-
qubit measurements that apply to all but a $O(2^{-n})$-fraction of pure target states. Our first protocol achieves constant robustness, i.e. $\epsilon_1=\Theta(1)$, using a single $O(\log n)$-
qubit measurement along with single-
qubit measurements in the $Z$ or $X$ basis on the other
qubits. As a corollary of its robustness, this protocol also achieves constant (in $n$) copy complexity, which is optimal. Our second protocol uses exclusively single-
qubit measurements and is nearly robust: $\epsilon_1=\Omega(1/\log n)$. Our tests are based on a new uncertainty principle for conditional fidelities, which may be of independent interest.
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All authors Andrea Coladangelo, Jerry Li, Joseph Slote, Ellen Wu
Quantum Physics · Cross-listed from cond-mat.mes-hall
Quantization Mapping on Dirac Dynamics via Voltage-Driven Charge Density in Monolayer Graphene: A Klein Paradox and Entropy-Ruled Wavevector Mechanics Study
Karuppuchamy Navamani
Thermodynamics coupled
quantum features on electron and hole dynamics in Dirac materials is quite interesting and crucial for real device applications such as electronic, thermoelectric, energy devices, and
quantum circuits. The correlation between the formation of electron-hole puddles near the charge neutrality point (CNP) and the role of disorder in terms of differential
entropy is fundamentally important for the Dirac transport mechanism in
graphene systems, but not yet well-established. With this motivation, we map the energy quantization for Dirac materials through the empirical relation of voltage-driven charge density in monolayer
graphene, using the differential
entropy (h)-ruled wavevector (k) mechanics. For this work, we propose the four postulates which are the key observable descriptions of earlier research reports, to study the precise electronic transport via an
entropy-guided wavevector propagation approach, along with the Klein paradox, which pertains to the ultrafast dynamics in the Dirac or quasi-Dirac systems. The introduced h-ruled k and h-ruled N relations generalize the electron dynamics in both the unbounded and potentially bounded Dirac systems. Through the quantization mapping procedure under different voltage-driven potential (U=eV) boundary conditions, the observed energy shift from lower to excited
quantum state obeys the relation of N(k)=N(U)^3; here, N(U) is the voltage-driven potential energy contribution factor for the
quantum state existence. In such a way, the mapped electron density,
diffusion coefficient, and mobility for bounded Dirac materials are increased by orders of N^3, N^2, and N, respectively. This study reveals information about the interaction potential-DOS relationship in the Dirac materials.
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Quantum Physics
Dissipative continuation for ground-state preparation at chemical transition states
Thomas W. Watts, Soumya Sarkar, Daniel Collins et al. (+4 more)
Simulating chemical reactions exhibits a pronounced unevenness in computational difficulty: while
equilibrium reactant and product geometries are often tractable, transition-state (TS) geometries frequently display strong multi-reference character that challenges both classical solvers and coherent
quantum state-preparation methods. We introduce a dissipative continuation protocol for preparing electronic ground states near TS geometries within a hybrid classical–
quantum workflow. In the intended setting, classical electronic-structure methods supply an approximate TS geometry, a computationally motivated continuation path, and a locally compatible active-space representation along that path. Starting from a warm start at a tractable geometry on the same aligned path, the
quantum routine transports the state toward the TS using orbital-gauge-aligned
Hamiltonians and engineered dissipative cooling primitives that repeatedly contract population into the instantaneous low-energy sector. We prove that, for continuation paths satisfying a Lipschitz smoothness condition and a localized Eigenstate Thermalization Hypothesis (ETH)-motivated downward-drift condition within the relevant energy window, the ground state at the target geometry can be prepared to total energy error $\epsilon_E$ with total ideal cooling-step complexity $\widetilde{O}(C_{\mathrm{DK}}^2 N_o^2 / \epsilon_E)$. Here $C_{\mathrm{DK}}$ quantifies ground-state rotation along the aligned path. The corresponding logical gate count is obtained by multiplying this primitive count by the cost of implementing one dissipative step, which is
polynomial in the block-encoding size of the Lindbladian under standard Lindblad-simulation
algorithms. This identifies a structured regime in which dissipative continuation provides a conditional route to ground-state preparation at strongly correlated TS geometries.
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All authors Thomas W. Watts, Soumya Sarkar, Daniel Collins, Nam Nguyen, Luke Quezada, Michael J. Bremner, Samuel J. Elman
Quantum Physics
Scalable and Highly Fault-Tolerant Circular Quantum Byzantine Agreement
Chen-Xun Weng, Ming-Yang Li, Shi-Gen Li et al. (+4 more)
Quantum Byzantine agreement (QBA), a cornerstone of
quantum blockchain, offers inherent advantages in security and fault tolerance over classical protocols, guaranteed by the laws of
quantum mechanics. However, existing multiparty QBA protocols face challenges for large-scale deployment due to exponential communication complexity or reliance on complex multi-particle
entanglement. To address this, we propose a multiparty circular QBA protocol that adopts a semi-decentralized architecture, leveraging circular message gathering and
quantum digital signatures to achieve quadratic communication complexity and enhanced fault tolerance. Our protocol is experimentally feasible, requiring only weak coherent states, and is compatible with existing
star-shaped
quantum networks. Simulations conducted on a global satellite-to-ground network demonstrate that the protocol sustains high consensus rates among multiple users, even when employing different key generation protocols under realistic conditions. This work presents a scalable framework for large-scale QBA networks, establishing the foundation for a practical
quantum blockchain that enables secure and fault-tolerant decentralized services.
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All authors Chen-Xun Weng, Ming-Yang Li, Shi-Gen Li, Mengya Zhu, Xiao-Ran Sun, Hua-Lei Yin, Zeng-Bing Chen
Quantum Physics · Cross-listed from gr-qc
Complete freezing of initially maximal entanglement in Schwarzschild black hole
Si-Han Li, Hui-Chen Yang, Rui-Yang Xu et al. (+1 more)
Gravitational effects associated with black holes are widely believed to universally degrade
quantum entanglement, with the loss of maximal
entanglement being particularly severe and even irreversible for bosonic fields. In this work, we investigate the
entanglement properties of the four-
qubit cluster state ($CL_4$) for fermionic fields in the curved spacetime of a Schwarzschild black hole. Remarkably, we uncover a counterintuitive phenomenon: as the Hawking temperature increases,
quantum entanglement ($1$-$3$ tangle) of the $CL_4$ state remains strictly constant, indicating a “complete freezing of initially maximal
entanglement". This constitutes the first explicit example in which maximal
entanglement remains perfectly preserved in a black hole environment, defying the conventional expectation that gravitational effects can only suppress maximal
quantum correlations. Moreover, our results indicate that, within a relativistic framework, the $CL_4$ state constitutes a high-quality
quantum resource with potential applications in relativistic
quantum information processing, and may significantly improve the performance of such protocols.
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All authors Si-Han Li, Hui-Chen Yang, Rui-Yang Xu, Shu-Min Wu
Quantum Physics
Control the qubit-qubit coupling with double superconducting resonators
Hui Wang, Rui Wang, Daichi Sugiyama et al. (+5 more)
We experimentally studied the switching off processes in the double-resonator coupler superconducting
quantum circuit. In both frequency and time-domain, we observed the variation of
qubit-
qubit effective coupling by tuning the frequency differences between
qubits and the double-resonator coupler. According to the measurement results, by just shifting about 50 MHz of
qubits' frequencies, we can tune the effective
qubit-
qubit coupling strength from switching off point to two
qubit gate point (effective coupling larger than 5 MHz) in double-resonator superconducting
quantum circuit.The double-resonator (coupler) superconducting
quantum circuit has the advantage of simple fabrications, introducing less flux noises, reducing occupancy of dilution refrigerator cables,which might supply a promising platform for future large-scale superconducting
quantum processors.
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All authors Hui Wang, Rui Wang, Daichi Sugiyama, Chih-Yao Shih, Ching-Yeh Chen, Hiroto Mukai, Hang Xue, J.S. Tsai
Quantum Physics · Cross-listed from gr-qc
Generalized entropic uncertainty relation and non-classicality in Schwarzschild black hole
Rui-Jie Yao and Dong Wang
The uncertainty principle constitutes a fundamental pillar of
quantum theory, representing one of the most distinctive features that differentiates
quantum mechanics from classical physics. In this study, we firstly propose a novel generalized entropic uncertainty relation (EUR) for arbitrary multi-measurement in the many-body systems, and rigorously derive a significantly tighter bound compared to existing formulations. Specifically, we discuss the proposed EUR in the context of Schwarzschild black hole, where we demonstrate the superior tightness of our derived bound. The study further elucidates the dynamical
evolution of multipartite
quantum coherence and
entanglement in the curved spacetime. A particularly noteworthy finding reveals the exact equivalence between
entanglement and $l_1$-norm coherence for arbitrary $N$-partite Greenberger-Horne-Zeilinger-type (GHZ-type) states. Moreover, we find that
quantum coherence is significantly diminished and the measurement uncertainty increases to a stable maximum with increasing Hawking temperature. Thus, the findings of this study contribute to a deeper understanding of non-classicality and
quantum resources in black holes.
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Quantum Physics
Structural control of two-level defect density revealed by high-throughput correlative measurements of Josephson junctions
Oliver F. Wolff, Harshvardhan Mantry, Rahim Raja et al. (+8 more)
Materials defects in Josephson junctions (JJs), often referred to as two-level systems (TLS), couple to superconducting
qubits and are a critical bottleneck for scalable
quantum processors. Despite their importance, understanding the microscopic sources of TLS and how to mitigate them has remained a major challenge. Here, we demonstrate a high-throughput, correlated approach to trace the microstructural origins of strongly-coupled TLS in Josephson
circuits. We assembled a massive
dataset of TLS across 6,000 Al/AlOx/Al JJs and more than 600 atomic resolution transmission electron microscopy images. We statistically link fabrication, microstructure, and TLS occurrence, revealing a strong correlation between Al electrode thickness, Al grain size, and TLS density. Correspondingly, we find a two-thirds reduction in TLS prompted by a change in electrode fabrication parameters. These results demonstrate a robust, data-driven methodology to understand and control defects in
quantum circuits and pave the way for significantly reducing TLS density.
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All authors Oliver F. Wolff, Harshvardhan Mantry, Rahim Raja, Wei-Hsiang Peng, Kaushik Singirikonda, Seungkyun Lee, Shishir Sudhaman, Rafael Goncalves, Pinshane Y. Huang, Angela Kou, Wolfgang Pfaff
Quantum Physics
The Pinnacle Architecture: Reducing the cost of breaking RSA-2048 to 100 000 physical qubits using quantum LDPC codes
Paul Webster, Lucas Berent, Omprakash Chandra et al. (+5 more)
The realisation of utility-scale
quantum computing inextricably depends on the design of practical, low-overhead fault-tolerant architectures. We introduce the Pinnacle Architecture, which uses
quantum low-density parity check (QLDPC) codes to allow for universal, fault-tolerant
quantum computation with a spacetime overhead significantly smaller than that of any competing architecture. With this architecture, we show that 2048-bit RSA integers can be factored with fewer than one hundred thousand physical
qubits, given a physical error rate of $10^{-3}$, code cycle time of $1$ microsecond and a reaction time of $10$ microseconds. We thereby demonstrate the feasibility of utility-scale
quantum computing with an order of magnitude fewer physical
qubits than has previously been believed necessary.
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All authors Paul Webster, Lucas Berent, Omprakash Chandra, Evan T. Hockings, Nouédyn Baspin, Felix Thomsen, Samuel C. Smith, Lawrence Z. Cohen