Quantum Physics
A note on tomography of states with low stabilizer rank
Arkopal Dutt
In this note, we consider
tomography of $n$-
qubit quantum states $|\psi \rangle$ that are promised to have stabilizer rank $k$ i.e., admit a stabilizer decomposition of $|\psi\rangle = \sum_{i=1}^k c_i |\phi_i\rangle$ where each $|\phi_i\rangle$ is a stabilizer state. We give a
tomography protocol for such states up to trace distance $\varepsilon > 0$ running in $\textsf{poly}(n,2^k,1/\varepsilon)$ time and thus can handle $k=O(\log n)$ efficiently. This follows from first showing that the stabilizer extent $\xi(|\psi\rangle)$, which is the minimal $\ell_1$ norm over the coefficients $\{c_i\}$ of any stabilizer decomposition of $|\psi\rangle$, can be bounded as $\xi(|\psi\rangle) \leq 2^{O(k)}$ and improving upon the previous best bound of $k^{O(k)}$. The protocol is then obtained by utilizing a
tomography protocol for states with bounded stabilizer extent.
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Quantum Physics
Super-Exponential Advantage of Squeezed Light in Phase Estimation under Discrete Phase Randomisation
Lorcan O. Conlon, V Vijendran, Aritra Das et al. (+7 more)
A paradigmatic task in
quantum metrology is that of phase estimation. For this task it is commonly believed, under reasonable assumptions about prior information, that a quadratic advantage in sensitivity is the maximum possible advantage offered by the use of
quantum resources. In this work, we consider a channel that implements a phase shift by an angle $2\pi k/M$, where $k$ is a uniformly random unknown integer, in addition to a small unknown phase shift of interest. We show that, subject to a constraint on the mean
photon number per channel use, there is a super-exponential separation between the
quantum Fisher information (QFI) attainable using a squeezed
vacuum state and that attainable using coherent states. This advantage holds over any state obtained from a coherent state via phase covariant channels. Specifically, when the mean
photon number per channel use is 1, the ratio of their QFI grows as $\Omega[(M/\sqrt{2}e)^M]$. For a mean
photon number per channel use of $M/\log(M)$, the squeezed
vacuum QFI is $\Omega(M^{3/2}/\sqrt{\log(M)})$, whereas for a coherent state it is at most $\exp[-M\log\log(M)+O(M)]$. We complement this QFI analysis with non-asymptotic estimation results. For a mean
photon number per channel use of $M/\log M$, an explicit squeezed-
vacuum protocol estimates the phase to accuracy $O(1/M)$ using $O(\sqrt{M\log M})$ channel uses, whereas every coherent state protocol requires at least $\exp[M\log\log M-O(M)]$ channel uses. We consider the effects of noise and show that the ratio of their QFIs can still grow super-exponentially in $M$. Finally, under fixed optical loss and thermal noise, choosing $\bar n=M^2/(\log M)^{3/2}$ allows squeezed
vacuum with heterodyne detection to achieve accuracy $O(1/M)$ using sub-polynomially many channel uses, whereas every protocol in the specified classical family requires super-polynomially many.
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All authors Lorcan O. Conlon, V Vijendran, Aritra Das, Yu-Xin Wang, Erfan Abbasgholinejad, Anthony J. Brady, Jacob Bringewatt, Sean R. Muleady, Syed M. Assad, Alexey V. Gorshkov
Quantum Physics
Breaking the cubic barrier for the inverse-free Solovay-Kitaev algorithm
Adam Bouland, Victor Shyaka and Chenyi Zhang
The Solovay-Kitaev
algorithm states that it is possible to efficiently compile
unitaries to accuracy $\epsilon$ in $\text{polylog}(1/\epsilon)$ time using any universal gate set. While Solovay and Kitaev's initial work addressed inverse-closed gate sets, recently Bouland and Giurgicǎ-Tiron showed it is possible to efficiently compile arbitrary gate sets without inverses. However, the exponent of their compilation
algorithm is high. For example the inverse-free exponent for a
qubit is over $8.62$, while information theoretically it is known that an inverse-free exponent of $3$ is possible in any dimension by a result of Oszmaniec, Sawicki, and Horodecki. This leads to a natural question: can one improve the exponent in Bouland and Giurgicǎ-Tiron's
algorithm? And are there any cases where the inverse-free exponent is below 3, thus surpassing existing information-theoretic arguments? To answer this question, we first show that a special case of the inverse-free compiling problem – namely Pauli gates supplemented by an irrational rotation of a
qubit - admits a highly efficient compilation
algorithm with an exponent at most $\approx 2.138$. Our
algorithm fuses ideas from prior
algorithms of Kuperberg and Sardharwalla, Cubitt, Harrow and Linden to construct an efficient “Pauli golf” compilation routine. We then extend these ideas to the general inverse-free case for a
qubit, where we give a compiling
algorithm with exponent at most $2.988$. This result uses a novel form of approximate “aiming” of
unitary corrections to improve the compilation efficiency. Our results give two examples of
quantum compiling
algorithms surpassing information-theoretic arguments, and demonstrate that there are many efficiency gains possible for inverse-free compilation.
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Quantum Physics
A Basis-Aware Approach to Quantum Sampling of the Fermi-Hubbard Ladder
Adam Leicester, Zixu Wang, Jack Mandell et al. (+4 more)
Sample-based
quantum diagonalization can reduce the classical cost of many-body calculations by restricting diagonalization to configurations identified through
quantum sampling, but its efficiency depends on how compactly the target state is represented in the sampled basis. We investigate this dependence for sample-based Krylov
quantum diagonalization of the half-filled
Fermi-Hubbard ladder using physically motivated one-body orbital rotations. Across position, momentum, bonding/antibonding, and leg-mode representations, the most compressible basis varies systematically with interaction strength and hopping anisotropy, with momentum sampling favored in the weakly interacting regime and geometry- or interaction-adapted representations becoming advantageous as the dominant energy scale changes. Near intermediate interaction and isotropic hopping, however, even the most favorable representation remains poorly compressible. Statevector SKQD calculations further show that basis choice strongly affects sampling efficiency. Hardware calculations on systems containing up to 120
qubits retain qualitative signatures of this basis dependence while revealing increasing particle-number leakage and reconstruction sensitivity with system size. These results show that scalable sample-based diagonalization requires co-design of the sampled representation,
quantum circuit, and classical reconstruction procedure.
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All authors Adam Leicester, Zixu Wang, Jack Mandell, Yangyang Xu, Osama Muhammad Raisuddin, Haimeng Zhang, Jian Shi
Quantum Physics
Reaching the Limits of Ground-State Metrology with Many-Body Probes
Erik L. André, Víctor Izquierdo, Ricard Puig et al. (+2 more)
We investigate the physical requirements to reach the ultimate limits of ground-state metrology – i.e., the estimation of an unknown parameter $\theta$ of an $N$-body
Hamiltonian via measurements on its ground state – using many-body probes featuring either short-range or long-range interactions. We characterize the conditions to saturate two fundamental limits of the
quantum Fisher information $F_\theta$: the static ground-state bound $F_\theta \lesssim N^2/\Delta^2$, where $\Delta$ is the spectral gap, and the dynamical Heisenberg limit $F_\theta \lesssim N^2 \tau^2$, where $\tau$ is the total protocol duration. To saturate the static limit, we argue that short-range interacting systems require a spectral gap that closes with $N$. At second-order
quantum critical points this leads to a universal condition on the critical exponents, $\nu(d+z)=1$, which can be approached arbitrarily closely, as we show for the XXZ chain; cat-like ground states at first-order transitions provide an alternative route to static optimality. In contrast, we find that all-to-all interacting models can achieve optimality even in gapped regimes. Furthermore, reaching the dynamical bound is tightly related to the ground-state preparation time; we demonstrate that its optimal, inverse-gap profile can be obtained via local adiabatic protocols. By analyzing paradigmatic systems – the transverse-field Ising chain, the XXZ chain, a squeezing
Hamiltonian, and the two-mode Bose-Hubbard model – we identify specific many-body probes capable of approaching both limits. Overall, our results provide a theoretical basis for the design of (local) many-body ground-state sensors operating at the ultimate limits of
quantum precision.
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All authors Erik L. André, Víctor Izquierdo, Ricard Puig, John Calsamiglia, Martí Perarnau-Llobet
High Energy Physics (Theory)
Quantum Gravity from Gluing Consistency: AdS/CFT to Spin-Foams
Chethan Krishnan
We argue that BF theory with $SO(d+1,1)$ gauge group provides a SymTFT ”skeleton” for building AdS$_{d+1}$/CFT$_d$ pairs via gluing consistency as the bootstrap principle, loosely analogous to how compact Chern-Simons theory is a TQFT skeleton for rational CFTs. This is a non-perturbative $bulk$ framework for
quantum gravity. The bootstrap is formulated as presentation independence of physical amplitudes within a universal, defect-closed BF sewing calculus, which includes Wilson lines, codimension-two monodromy defects, and their junctions. The flat BF connection encodes the conformal geometry of the boundary, while Wilson-line path integrals construct candidate
quantum-
gravity microstates and charge sectors. When the bootstrapped spectrum has a stress tensor, Ward identities naturally connect it to the $B$-field, a relation we call generalized simplicity. In large-$N$, large-gap regimes admitting a gravitational EFT, this motivates the introduction of an effective notion of the $B$-field. In the Einstein limit, this becomes the ”simplicity” relation used in
spin-foam models. Conventional
spin-foam models try to obtain
gravity by constraining BF theory. We suggest instead that BF theory is the Platonic sewing skeleton, from which theories are to be bootstrapped. Despite the topological nature of the skeleton, perturbative local bulk fields can emerge via Wilson-towers of multi-trace primaries, reproducing their one-loop determinants. We note that the BF
Fourier kernel is a suggestive higher-dimensional analogue of the modular-$S$ structure. Because the bulk gluing principle in itself does not require a boundary description, the framework is conceptually broader than AdS/CFT. We sketch how de Sitter space may fit into this picture, with a natural role for observers. Our approach elevates gluing consistency to a universal bulk principle underlying theories of
quantum gravity.
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Quantum Physics
Exponential quantum space advantage in random data streams
Adam Bouland, Matthew Ding and Siddhartha Jain
We show two unconditional
quantum space advantages in the random-order streaming model. First, we show the Yamakawa–Zhandry Code Intersection problem admits exponential
quantum advantage in the streaming model when its inputs are streamed in random order. This means
quantum computers exhibit exponential space advantage even when simply receiving $(x,f(x))$ pairs for a uniformly random function $f$ in a uniformly random order. Our lower bound is shown using density-restoring partitions as in the work of Göös, Gur, Jain, and Li (STOC 2025) combined with a convex potential, similar to the work of Raz (J.ACM 2018) on parity learning and its generalization by Garg, Raz, and Tal (STOC 2018). Second, we use our framework to show
quantum space advantage for the Optimal
Polynomial Intersection (OPI) problem in certain regimes via a streaming version of the Decoded
Quantum Interferometry
algorithm (Nature 2025; arXiv:2510.10967). In particular, we show that for degree $d$ and $n$ evaluation points, attaining $1/2 + \Omega(\sqrt{d/n})$ fraction of satisfied OPI constraints via streaming requires $\Omega(n)$ classical bits of
memory but only $O(d\log n)$
qubits. This yields provable
quantum advantage in a "low-rate" regime when the number of evaluation points is much larger than the degree, with a space advantage that can be as large as exponential in certain parameter settings.
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Quantum Physics
Clarifications on the Experimental Status of Real Quantum Theory
Timothée Hoffreumon and Mischa P. Woods
In our previous paper on the matter, we proved that real
quantum theory (RQT) cannot be experimentally falsified without the experiment falsifying
quantum theory (QT) as well. Our result is in direct contradiction to the central claim of an article by Renou et al., published in Nature [600, 625–629 (2021)], reporting a bilocal network experiment that could falsify real
quantum theory without falsifying
quantum theory. The purpose of this note is to address several seemingly natural attempts to recover the experimental conclusion of Renou et al. We first explain how these results, although based on nonlocality experiments, are far from a Bell-like level of proof. Then we explain why the proposed experiment requires an experimentally untestable premise about independent preparations necessarily being represented as product states. Finally, we discuss some concerns that lie outside the scope of both results.
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Quantum Physics
Martino Bernasconi and Giulio Malavolta
We study a multilinear optimization problem for tensors with bounded Frobenius norm, where each of the $k$ local factors of dimension $d$ is chosen from a convex set. We give a deterministic
algorithm running in time $d^{O(k)}$ for constant additive approximations. As applications, we obtain the first
polynomial-time
algorithms at constant accuracy for weak membership in the
nuclear-norm unit ball of high-order tensors and for multipartite
quantum separability in Frobenius norm. Our approach views tensor optimization as a cooperative multiprover game and combines this perspective with a recursive spectral compression procedure. We then show that related ideas admit a
quantum implementation when the input state is given through copies, rather than an explicit classical description. In these settings we obtain an
algorithm to solve Frobenius-norm separability testing using $\text{poly}(k)$ copies and $\text{poly}(k\log d)$ time.
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Earth and Planetary Astrophysics
Temporal Variability of Titan's Middle-Atmospheric Zonal Winds from Southern Fall to Late Winter (2016-2023)
Martin A. Cordiner, Yuan Lian, Juan M. Lora et al. (+10 more)
Previous ALMA observations have revealed unexpectedly strong and rapid variations in Titan's high-altitude equatorial zonal winds, which present a challenge to our understanding of this moon's atmospheric dynamics. Here we report further measurements of Titan's zonal wind field at middle atmospheric altitudes $\approx200$-490 km, based on ALMA observations of spatially and spectrally resolved CH$_3$CN emission between 2016-2023 (corresponding to a
solar longitude $L_s=81.6^{\circ}$-$156.4^{\circ}$, spanning Titan's late southern autumn to late winter). These observations indicate substantial, ongoing, rapid temporal variability of Titan's zonal winds, on timescales as short as $\approx1$ Earth month ($0.9^{\circ}$ in $L_s$). The strongest variability is at (near-)equatorial latitudes where the zonal winds are fastest (up to $240\pm26$ ms$^{-1}$), with repeated $\sim40$ ms$^{-1}$ fluctuations occurring between $L_s=146.0^{\circ}$-$156.4^{\circ}$. The observed longer-term trends are qualitatively well-reproduced by two independent, state-of-the-art general circulation models (GCMs), which match the observed decrease in zonal wind speeds over a broad range of latitudes between $L_s=81.6^{\circ}$-$146.0^{\circ}$, followed by a more moderate increase between $L_s=146.0^{\circ}$-$156.4^{\circ}$. The wind speeds at mid-to-high latitudes ($\sim-45^{\circ}$ south) are also typically reasonably well reproduced by the GCMs (differing by $\lesssim30$%). However, the equatorial wind speeds are up to a factor of $\sim2$ faster than model predictions (with the greatest discrepancy around solstice; $L_s\approx90^{\circ}$). Rapid temporal variability of the retrieved zonal winds indicates the presence of strong atmospheric instabilities that are not well reproduced by models, suggesting a need for future GCM improvements.
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All authors Martin A. Cordiner, Yuan Lian, Juan M. Lora, Nicholas A. Lombardo, Lucy Wright, Jonathon Nosowitz, Richard Cosentino, Nicholas A. Teanby, Conor A. Nixon, Alexander E. Thelen, Claire E. Newman, Steven B. Charnley, Eliot F. Young
Instrumentation and Detectors · Cross-listed from cs.AI
NeutronGym: Physics-Graded Neutron Instrument Design for LLM Agents
Lijie Ding and Changwoo Do
Designing a scientific instrument tests whether
language-model
agents can do physics rather than recall it, provided the grading cannot be argued with. We introduce NeutronGym, to our knowledge the first executable environment for
neutron instrument design:
agents build instruments through validating tools, McStas ray-traces what they build, and a level-resolved ladder grades syntax, runtime, structure and science with no LLM judge. Procedural families supply unlimited instances of a fixed layout whose design parameters the
agent must set, with held-out parameter regimes; a curated slice, McStasBench, adds 16 tasks from published instruments behind memorization probes and a sandbox. Seven models reproduce at most 7 of the 16, none retrieves a reference, and none meets an improvement target. The environment also trains. Reinforcement learning on its reward takes Qwen3-8B from 11% to 77% of held-out instances of a family whose targets come from a hidden design (69% at a second seed), past an untrained Qwen3-32B, and the recipe holds, at one seed each, on three further gated families. The analysis says what that gain is. Without the ladder's partial credit it collapses by 60 points. From reward alone the trained model reaches what a classical optimizer reaches, at the
agent's simulation budget, only when handed the closed-form physics (77% against 81%, a gap that does not separate at this size), while frontier models still solve 98-99%. Getting a trustworthy result meant failing four task designs that no-model baselines could solve, and we release the probes that found them.
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Quantum Physics
Entanglement of purification for Werner states: canonical purification and nonadditivity
Zahra Baghali Khanian and Amir-Reza Negari
We prove that the von Neumann
entanglement of purification is nonadditive. For two-
qubit Werner states $W(f)$ with singlet weight $1/64\le f\le1/4$, we show that canonical purification is globally optimal: its
entanglement, also known as reflected
entropy, gives the exact
entanglement of purification. In contrast, the regularized
entanglement of purification lies strictly below the reflected
entropy for $0<f<f_\ast$, where $f_\ast\approx0.017$. Together, these results establish nonadditivity throughout $1/64\le f<f_\ast$. Our canonical-optimality proof generalizes the proof in [1], which established Rényi nonadditivity for $0\le\alpha<1$ using classical two-
qubit states. We thus resolve the additivity question at $\alpha=1$. Remarkably, nonadditivity is again witnessed by separable states and no
entanglement in the underlying states is required.
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Quantum Physics
Discriminating Lindbladian Dynamics
Robert Salzmann, Ludovico Lami, Martin B. Plenio et al. (+1 more)
The fundamental task of
quantum hypothesis testing, which consists in discriminating
quantum objects, has been extensively studied for
quantum states and channels. Here, we investigate the fundamental limits of discriminating an arbitrary pair of
quantum Markovian dynamics generated by Lindbladians, focusing on the roles of total exposure time and temporal resolution. We allow adaptive choices of
evolution durations and arbitrary instantaneous controls between them. We characterise the optimal type-II error exponent (Stein exponent) as the largest instantaneous increase of
quantum relative
entropy, and give an algebraic criterion for its finiteness in terms of the Lindbladians. Remarkably, an infinite exponent is equivalent to a vanishing type-II error probability at sufficiently large finite total time, for every positive type-I tolerance. While some dynamics admit a finite protocol with zero type-II error, others require increasingly fine temporal control. For the latter, the error vanishes as the minimum allowed
evolution duration, or resolution time, tends to zero at fixed sufficiently large total time, but remains bounded away from zero at every fixed positive resolution time. We achieve this using
quantum Zeno protocols, establishing temporal resolution as a resource for discrimination. When the null hypothesis is the identity
semigroup, an infinite asymptotic error exponent has a stronger consequence: at a fixed finite total exposure time, the type-II error can be made arbitrarily small while keeping the type-I error exactly zero. This is impossible in the corresponding classical setting. Discriminating the identity
semigroup from generalised amplitude damping on a
qubit provides examples of all three regimes: a finite asymptotic error exponent, zero type-II error attainable at positive resolution time, and vanishing type-II error requiring the resolution time to tend to zero.
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All authors Robert Salzmann, Ludovico Lami, Martin B. Plenio, Susana F. Huelga
Biological Physics
Cost convexity controls the architecture of resistance-optimal networks
Hugo Tovar, Genaro Vázquez-Victorio, Enrique Hernández-Lemus et al. (+2 more)
A conducting network improves access to its interior only by spending material, so architectures compare only at equal budget. We redistribute conductance under a power-law resource law $\C_{\alpha}=\sum_e a_e w_e^{\alpha}$ and measure access by the reciprocal of the mean pairwise effective resistance. When the cost is strictly convex the allocation is unique and every admissible edge keeps positive conductance; at $\alpha=1$ uniqueness survives but an edge can be priced out. The marginal worth of an edge is then its squared biharmonic distance, a Murray-type balance whose balanced quantity is global rather than junction-local. The same optimum scores any weighted network at its own budget, separating an allocation factor from a topological one. Under concave cost the marginal price of an incipient channel diverges, the feasible set is nonconvex, and conductance condenses onto sparse backbones. The uniform
star and the uniform complete graph cross at $\alpha_c(n)=\log(n/2)/\log(n-1)$, near which intermediate states beat both. Up to $n=64$ the best states found grow approximately linearly in $n$, so channels per node change much less than the active fraction does. Loops are governed instead by a collapse exponent $\alpha^{*}(n)$, resolved to $0.005$ at every size: it rises from $0.555$ at $n=8$ to $0.675$ at $n=64$, and the collapse across it is abrupt, the support at $n=64$ falling from $133$ active edges to the $63$ of a spanning tree. A fixed exponent therefore changes character with size by crossing this boundary. One prescribed source and sink instead gives a loopless optimum.
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All authors Hugo Tovar, Genaro Vázquez-Victorio, Enrique Hernández-Lemus, Alejandra Cervera, Daniel Pérez-Calixto
Quantum Physics
Maryam Mudassar, Zhi-Yuan Wei, Alexander Schuckert et al. (+3 more)
Fault-tolerant
quantum simulation requires compiling
symmetry-preserving time evolutions into discrete gate sets. Standard Clifford+T synthesis can break continuous
symmetries even when the target
evolution preserves them, causing compiled simulations to lose essential features of the original system. We develop a fault-tolerant compilation framework that preserves SU(2)
symmetry exactly. We characterize the number-theoretic obstruction preventing
symmetry-preserving
unitary Clifford+T
circuits from approximating arbitrary SU(2)-symmetric evolutions and circumvent it using measurement and feed-forward. The resulting synthesis confines compilation errors to the
symmetry-preserving operator
algebra rather than introducing
symmetry-breaking perturbations. We demonstrate the
algorithm by simulating transport in the one-dimensional Heisenberg model. At a lower matched T-count, for instance, 54 T gates per two-site Trotter step, standard synthesis yields an incorrect transport exponent, whereas our
symmetry-preserving compilation reproduces the expected exponent for the same expected T-count. If instead each approach is allocated whatever resources are necessary to estimate this exponent to the same accuracy, our construction reduces the T-count by approximately a factor of five. We further extend the framework to gauge
symmetries in
lattice gauge theories and to particle-number and
spin symmetries in fermionic models relevant to
quantum chemistry and the
Fermi-Hubbard model. These results show that
symmetry-preserving fault-tolerant compilation can qualitatively change the effects of synthesis error while substantially reducing the resources required for
quantum simulation.
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All authors Maryam Mudassar, Zhi-Yuan Wei, Alexander Schuckert, Michael J. Lawler, Michael J. Gullans, Daniel Gottesman
Soft Condensed Matter
Surface Charge–Potential Relation for Spherical Particles in Electrolyte Solutions
Olga I. Vinogradova and Elena F. Silkina
Predicting the relationship between surface charge density and electrostatic potential for spherical particles remains a fundamental challenge in colloid science. Because the governing non-linear Poisson–Boltzmann equation lacks a general exact analytical solution, researchers typically rely on numerical calculations or various semi-empirical approximations. In this paper, we overcome these limitations by developing a dual-asymptotic framework that provides explicit, closed-form expressions for this surface charge–potential relationship across the entire spectrum of particle
curvature. For weakly curved systems, where the Debye length $\lambda_D$ is much smaller than the particle radius $R$ ($\lambda_D/R \ll 1$), a formal mathematical derivation rigorously establishes the Ohshima–Healy–White formula as an exact regular perturbation expansion. Conversely, for highly curved spheres ($R/\lambda_D \ll 1$), we employ singular perturbation analysis using the scaled particle radius as the small parameter. This approach provides a first-principles mathematical justification for the spherical Debye–Hückel theory, proving that its leading-order expansion remains asymptotically exact within the full non-linear Poisson–Boltzmann framework due to the
geometric deactivation of non-linearity. Crucially, we map the exact limits of this
geometric regulation, demonstrating how non-linear screening re-emerges as the particle radius increases, with the breakdown threshold governed by the interplay between
curvature and surface charge density.
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Strongly Correlated Electrons
Decohering Kitaev's Sixteenfold Way: A Holographic Approach
Shuyu Zhang, Linhao Li, Zhen Bi et al. (+2 more)
We study anyon decoherence in 2D topological order, with the
fermion decoherence in Kitaev's sixteenfold way as explicit examples. The sixteenfold way includes
chiral topological phases, which are believed to admit no commuting projector
Hamiltonian, making it challenging to study their decoherence directly. We further
conjecture the density
matrix produced by this decoherence induced phase transition can be obtained by a three-step procedure: first lift the topological order to its Walker-Wang model, followed by a transition to another Walker-Wang model, and finally trace over the bulk degrees of freedom. This establishes a connection between the decoherence of a topological order and a pure state phase transition in its 3D counterpart. Many examples are given. In particular, we show that decohering the
fermion in each of the sixteen states always yields an intrinsically mixed-state topological order, a consequence of the fact the corresponding 3D bulk always transits into the 3D fermionic toric code (fTC). Our result suggests a systematic method for studying anyon decoherence in
chiral topological orders at the level of commuting projector
Hamiltonians.
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All authors Shuyu Zhang, Linhao Li, Zhen Bi, Tzu-Chieh Wei, Zijian Song
Quantum Physics
The QICK Box: A Modular RF Front-End System for Quantum Control and Readout
L. Arnaldi, D. Martin, S. Sussman et al. (+11 more)
The QICK (
Quantum Instrumentation Control Kit), first introduced in 2022, is a standalone open source control system for
quantum information science. Since then, QICK has been migrated to new hardware platforms, expanded its functionality for applications with different types of
qubits (superconducting, atomic, ion-trapped, and
spin defects), as well as
quantum sensors, and
quantum networks. QICK is a highly optimized control kit, with a library of functions that can be used for more than one application. In particular, the software and firmware are customized to minimize latency and maximize control performance and throughput. In this white paper, we describe hardware details and performance of the QICK Box. The QICK Box features up to 16 outputs, up to 8 inputs, and 8 20-bit DC biases. Modular output and input daughtercards give the choice of signal chains optimized for fast DC-coupled signals or RF signals up to 10 GHz. Power levels, step attenuation, and bandpass filtering are controlled by software. We demonstrate the system's performance through single-shot readout measurements of a six-transmon device at the
Quantum Underground Instrumentation Experimental Testbed (QUIET) at Fermilab, achieving (91.7 +/- 0.4)% readout fidelity limited by T1 decay during the readout. The single shot readout signal-to-noise ratio (SNR) is 4.4 +/- 0.1 without a
quantum amplifier, confirming that the QICK Box is suitable for high-fidelity
quantum control and measurement applications. Advances in firmware and software will be described in a separate paper.
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All authors L. Arnaldi, D. Martin, S. Sussman, S. Uemura, K. Treptow, N. Wilcer, A. Colón Cesaní, O. Seidel, K. Anyang, G. Bratrud, F. Abouzahr, J. Christiansen-Salameh, D. Baxter, G. Cancelo
High Energy Physics (Theory)
Non-Renormalizability Properties of Quarter-BPS Correlators in $\mathcal{N}$=4 SYM
Agnese Bissi, Giulia Fardelli and Hector Puerta-Ramisa
We study extremal and next-to-extremal four-point correlators involving general quarter-BPS operators in $\mathcal{N}$=4 Super Yang-Mills. Using a combination of $R$-
symmetry considerations, operator product expansion content, and analytic superspace techniques, we show that such correlators get contributions only from operators belonging to short and semi-short multiplets. This result together with the non-renormalizability of the relevant three-point functions guarantees that all such four-point correlators are protected from
quantum corrections.
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Quantum Physics
Efficient fidelity simulation of high-rate magic distillation circuits
Xiao Xiao, Dominik Hangleiter, J. Pablo Bonilla Ataides et al. (+4 more)
Non-Clifford gates are essential for avoiding classical simulability under the Gottesman-Knill
theorem. An error-corrected
circuit with non-Clifford gates will therefore be an important element for realizing useful fault-tolerant
quantum algorithms. However, accurately understanding the fault-tolerant performance of such
circuits faces challenges due to the classical hardness of simulating these
circuits. We avoid simulating logical measurements and develop exact and efficient classical methods for benchmarking
circuits composed of X, CNOT, and diagonal gates in the Clifford hierarchy, including state and gate teleportation gadgets with feedforward. For
circuits with third-level diagonal gates, our benchmarking
algorithm efficiently samples syndrome statistics and estimates the output logical fidelity and expectation values of certain Clifford observables, including all Pauli observables. The evaluation of syndrome expectation values also extends to
circuits with fourth-level diagonal gates. Our
algorithm scales polynomially in the number of physical
qubits n and
circuit depth T, independent of the number of logical
qubits. The benchmarking applications include IQP sampling and magic state preparation/cultivation. We demonstrate the practical utility of our simulation
algorithms by using them to optimize high-rate magic state
distillation factories based on three copies of a [[27,3,3]] tricycle code.
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All authors Xiao Xiao, Dominik Hangleiter, J. Pablo Bonilla Ataides, Rohan Mehta, Varun Menon, Mikhail D. Lukin, Michael J. Gullans
High Energy Physics (Phenomenology)
Electroweak Transitions of Hyperons and Charmed Baryons: Opportunities and Prospects
Patrik Adlarson, Constantia Alexandrou, Simone Bacchio et al. (+9 more)
We present a phenomenology-driven overview of opportunities and outstanding challenges in
baryon electroweak transitions, focusing on hyperon and charmed-
baryon processes for which
lattice-QCD results are available, including semileptonic decays and selected radiative, dileptonic, and
neutrino-induced channels. We identify semileptonic decays of strange and charmed
baryons as a particularly promising domain for synergy between phenomenology, experiment, and
lattice QCD. Particular emphasis is placed on the determination of vector and axial form factors, the precision and model-independent extraction of $|V_{us}|$ from hyperon semileptonic decays including radiative corrections, and on searches for non-standard interactions through
lepton-
flavor- and CP-violating observables. We examine the momentum dependence of form factors in ground-state transitions, highlight the emerging $\Xi_c \to \Xi$ semileptonic puzzle stemming from tensions between
lattice-QCD predictions and experimental measurements, discuss inclusive decay rates, and outline strategies for extending these studies to transitions involving excited
baryon states. For completeness, we review also results involving beauty-
baryon decays.
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All authors Patrik Adlarson, Constantia Alexandrou, Simone Bacchio, Varvara Batozskaya, Johan Bijnens, Alexandre Brea Rodriguez, Gernot Eichmann, Andreas Konstantinou Andrzej Kupsc, Stefan Leupold, Piotr Salabura, Christoph Schwanda, Marcin Zieliński
Superconductivity
Layer-Asymmetry-Induced Topological Superconductivity in High-T$_c$ Bilayer Nickelates
Zhongyi Zhang, Congcong Le, Hoi Chun Po et al. (+3 more)
The recent discovery of high-T$_c$ superconductivity in
bilayer nickelates has highlighted the crucial role of interlayer coupling and motivated proposals for dominant interlayer pairing. Whether such pairing can support topological superconductivity, however, remains unexplored. Here, we demonstrate that substrate-supported
bilayer nickelate thin films can host an intrinsic time-reversal-invariant topological superconducting phase protected by diagonal mirror
symmetry. Using a two-orbital model derived from first-principles calculations, we show that a modest layer-asymmetric potential and layer-staggered Rashba
spin-orbit coupling drive the system into this topological phase over a broad parameter range with a dominant interlayer pairing. The nontrivial
topology arises from a reversal of the pairing sign on one of the
spin-split bonding
Fermi surfaces and is characterized by a nonzero mirror winding number along the diagonal direction, as well as a Majorana Kramers pair at the [11] edge. The phase also features bulk gap nodes located slightly away from the diagonal directions, featuring
chiral charge and zero-energy flat bands. We discuss experimental routes for realizing and tuning this phase. Our results establish high-T$_c$
bilayer nickelates as a promising platform for topological superconductivity, where tunable topological transitions and Majorana boundary modes can provide probes of unconventional pairing.
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All authors Zhongyi Zhang, Congcong Le, Hoi Chun Po, Jiangping Hu, Xianxin Wu, Shengshan Qin
Fluid Dynamics
Flow regime determines whether larval settlement hydrodynamics are governed by swimming speed or shape
Daniel Gysbers, Mark A. Levenstein and Gabriel Juarez
Larval dispersal and settlement govern the replenishment of sessile marine populations and the assembly of benthic communities, yet how larval traits interact with near-surface flow structures to direct settlement remains unclear. We used coupled hydrodynamic and larval-scale simulations to resolve how swimming speed and body shape, from circular to elongated, influence settlement in oscillatory flow over ridged substrates. Settlement success differed by up to an order of magnitude across trait combinations. Near-surface flow acted as a trait filter by differentially regulating transport to, retention near, and encounters with the substrate. The trait that mattered most depended on the local flow structure. Where rapid flow restricted access to settlement surfaces, swimming speed was most important. Where flow recirculated between substrate ridges, shape-dependent
alignment controlled transport and retention. These results link larval traits to flow-mediated settlement mechanisms and provide a physical framework for understanding how recruitment varies across complex benthic habitats.
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Quantum Physics
The exact LCU sampling overhead of collective diagonal unitaries: resonances and a continued-fraction dichotomy
Zhihui Wang, Sujit Roy, Manil Maskey et al. (+1 more)
The minimal sampling overhead of the quadratic collective phase $e^{-i\gamma K^2}$ over one layer of single-
qubit rotations is decided by the continued fraction of $\gamma/\pi$. Here $K$ is a collective observable with spectrum $\{0,\dots,n\}$, such as the permutation-symmetric Hamming weight. This gate is the cardinality-penalty layer of constrained optimization, the one-axis-twisting gate of
spin squeezing and the Kerr phase of a bosonic mode. Instead of compiling it to two-
qubit gates, we sample it as an LCU over such layers at overhead $\Gamma$. Our results give an optimality theory for this overhead. Ancilla-free sampling reproduces the target's outcome probabilities up to the minimal $\Gamma$, and no smaller factor works for every input; for permutation-symmetric $K$, independent per-
qubit angles or one layer of arbitrary single-
qubit gates give no further reduction. Rational angles $\pi p/q$ in lowest terms cost exactly $q$ once $n\ge2q-2$, attained uniquely by a uniform $q$-point sampler; the cost is $\Theta(n)$ if and only if $\gamma/\pi$ is badly approximable, and bounded in $n$ if and only if it is rational. A second result shows what the
symmetry buys: without it, the squaring phase of
Fourier arithmetic on $m$
qubits costs at least $2^{0.557m-O(1)}$ over single-
qubit gates, beyond the $2^{m/2}$ of every cut bound, by a new certificate-lifting argument. For constructions known only through upper bounds, it gives the optimum: the
Fourier-based LCU of Carrera Vazquez, Egger and Woerner is, at fixed $n$, optimal up to a constant at typical angles and beaten by $(n+1)/q$ at rational ones with an $n$-independent sampler; the Kerr decomposition of Upreti, Quesada and Chabaud is the unique optimum over phase shifters at rational parameters without
photon-number cutoff; and it identifies the rational couplings where one-axis twisting admits optimal cat decompositions.
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All authors Zhihui Wang, Sujit Roy, Manil Maskey, Rahul Ramachandran
Quantum Physics
Fault-tolerant and fully addressable unitary logical gates via round-robin sparsification
Kaavya Sahay and Cody Jones
For
quantum low-density parity check (qLDPC) codes, the ability to manipulate individual logical units of information, i.e. the use of addressable gates, enables maximal utility of their efficient encoding. We introduce explicit low-depth
unitary circuits that realize fully addressable and fault-tolerant two-
qubit Clifford gates for a subset of two-dimensional translationally invariant qLDPC codes. Our transversal
unitaries are created by applying a geometrically structured sparsification procedure to round-robin
circuits. We verify the general applicability of our protocol by proposing and numerically simulating a range of addressable CZs between toric, cyclic hypergraph-product, color, gross, and directional codes, demonstrating fault-tolerant
memory-like logical error rate scaling.
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Quantum Physics
Quantum Fire with Delegated Cloning
Rohit Chatterjee, Ananta Mukherjee, Vir Pathak et al. (+1 more)
Quantum fire is a recently introduced cryptographic primitive consisting of efficiently preparable
quantum states, called flames, that admit efficient cloning but resist efficient telegraphing, namely reconstruction via classical communication without preshared
entanglement. In all prior constructions of
quantum fire, cloning is a public operation that requires no separate key and every holder of a flame state can clone it. For applications to access control, however, an issuer may wish to delegate cloning to designated
quantum servers while withholding this capability from other flame holders. To address this, we introduce delegatable
quantum fire, in which cloning requires a separate key. We give two constructions in the classical-oracle model. Our first construction uses a classical secret key which enables cloning, and any user with the entire key may clone successfully. Our second construction, which we call torch-fire, uses
quantum cloning keys, called torches, which enable cloning while remaining unaffected in the process but cannot otherwise be split or delegated to enable additional cloning. An efficient adversary given $m$ torches cannot, except with negligible probability, enable more than $m$ noncommunicating parties to each clone a fresh, independently issued challenge flame. The adversary may jointly process its resources before separating the parties and distribute arbitrarily entangled registers among them. Both constructions are in the oracle model, relying on public classical oracles that allow queries in
quantum superposition.
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All authors Rohit Chatterjee, Ananta Mukherjee, Vir Pathak, Supartha Podder
Quantum Physics · Cross-listed from cs.CR
Constant-Rate Certified Deletion
Kai-Min Chung, Tzu-Hsiang Huang, Wei-Hsiang Hung et al. (+1 more)
We present a unified framework for upgrading a broad class of cryptographic primitives to support constant-rate certified deletion. Previous constructions require a linear number of
qubits per encrypted bit of certified-deletable plaintext. In contrast, we obtain the first constant-rate constructions in the plain model that achieve certified deletion while preserving everlasting security. Our approach applies to a wide range of "all-or-nothing"-type primitives based on BB84-style encodings, including commitment schemes, public-key encryption, attribute-based encryption, and fully homomorphic encryption. Beyond this class, we also obtain constant-rate certified deletion for primitives built from subspace coset states, such as blind delegation, secure software leasing, functional encryption, and differing-inputs iO, and CCA-PKE. Importantly, our framework does not introduce any additional assumptions beyond those required by the underlying certified deletion primitives. Finally, under the hardness of SIS, we show that public verifiability can be incorporated into BB84- and coset-based certified deletion. In combination with our constant-rate constructions, this yields publicly verifiable certified deletion schemes with constant rate.
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All authors Kai-Min Chung, Tzu-Hsiang Huang, Wei-Hsiang Hung, Shota Yamada
Quantum Physics
Lifting Multiplicity in Randomized Benchmarking
Yale Fan and J. P. Marceaux
Randomized benchmarking comprises a suite of standard techniques for assessing the operational fidelity of
quantum processors. These techniques can be reliably applied to groups with process
matrix representations that are free of multiplicity. However, many groups that are naturally formed from native gates do have multiplicity, and it is difficult to draw robust conclusions from the resulting data. In this work, we present a new and intrinsic solution to the problem of multiplicity that completely eliminates the need to fit multi-exponential decays while still remaining robust to errors in state preparation and measurement. Our procedure, which we call lifted randomized benchmarking, generalizes key elements of both character and synthetic randomized benchmarking to
benchmark a target group of
quantum gates with respect to an enlarged group. We illustrate in numerical examples that our method can efficiently and reliably estimate the fidelity of two-
qubit gates relevant to experimental trapped-ion systems. These techniques may find applications beyond randomized benchmarking to
quantum tomography and learning, as well as the characterization of error-correcting codes.
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Quantum Physics
A Complete Proof of $\mathsf{QMA}_1$-Hardness for Weighted Gapped Clique Homology
Tal Barak
The computational complexity of simplicial homology has been studied since the question was raised by Kaibel and Pfetsch, and clique homology was later shown to be $\mathsf{QMA}_1$-hard by Crichigno and Kohler. King and Kohler subsequently introduced the weighted, spectrally gapped version considered here and developed a reduction intended to establish the same hardness result in this setting. We give a complete proof of the hard direction. The earlier King-Kohler argument contains a gap in the analysis of the nontrivially folded local gadgets, so the required topological and spectral properties have to be re-established on the clique complexes actually produced by the reduction. This is not a local repair of the published proof: the argument requires a new analysis of the local
topology, the filtered cochain complexes, and the interaction of many overlapping gadgets. Our proof uses exact finite certificates for the local combinatorial data and relative homology to determine the effect of each gadget on the encoded
qubit space. We then prove the finite-dimensional filtered-Hodge statement needed to recover the corresponding rank-one low-energy penalty and derive a quantitative global estimate that transfers the source-
Hamiltonian promise gap to the final weighted Hodge
Laplacian. Consequently, for fixed efficiently computable $k(n)$ and inverse-
polynomial $\gamma(n)$, weighted gapped clique homology is $\mathsf{QMA}_1(\mathcal G)$-hard. The previously known $\mathsf{QMA}$-containment argument is logically independent of the gap and remains unaffected.
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Chemical Physics
CIS(2): a state-specific, size-intensive perturbative correction to configuration interaction singles
Takashi Tsuchimochi
We present a state-specific second-order perturbation theory based on a configuration interaction singles (CIS) reference and its generalized Fock operator. Starting from a fully internally contracted construction, we retain the complete doubles space and internally contracted triples in the first-order wave function. We consider two partitions, Canonical and Block-diagonal, with reference excitation energies given by the Fock excitation gap $\omega^{(0)}$ and the CIS excitation energy $\omega_{\rm CIS}$, respectively. Our analysis establishes that strict size-intensivity is preserved when the contracted-triples denominators use bare Fock gaps and the occupied–virtual Fock block is projected to remove residual spectator coupling. Based on this observation, combining Canonical triples with Block-diagonal doubles yields a size-intensive Hybrid partition. These properties are verified for water with non-interacting helium atoms. Our formulation enables $O(o^3v^2)$ cost per
matrix–vector product in a semicanonical basis. On the QUEST\#1
benchmark, Canonical and Block-diagonal show opposite systematic biases, whereas Hybrid gives the best overall accuracy among the three partitions. Its mean absolute errors for singlets and triplets are 0.24 and 0.15~eV, compared with 0.28 and 0.22~eV for CIS(D). The improvement is largest for Rydberg excitations, although CIS(D) remains more accurate for valence singlets.
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