Quantum Physics
Katherine Van Kirk and Craig Gidney
A major practical obstacle to Regev's factoring
algorithm is its large space usage. In particular, the
algorithm was believed to be incompatible with "
qubit recycling," which streams the control
qubits in phase estimation rather than storing them all simultaneously. We show how to fix this streaming problem. We build on the construction of Ragavan and Vaikuntanathan, which used Fibonacci accumulators to reduce the
qubit count from $O(n^{1.5})$ to $11.32n$. We make two key improvements. First, we use superposition masking to prevent unwanted information from entering the accumulators, removing the need for uncomputation. Second, we show how to perform phase estimation using Fibonacci powers of a
unitary operation rather than powers of two. This avoids various encoding conversions required by the construction of Ragavan and Vaikuntanathan. After these improvements, the phase-estimation
qubits are used only once in the
circuit, allowing them to be streamed. Our improvements reduce the space usage of Regev's factoring
algorithm to $n+M(n)+O(\sqrt{n})$, where $M(n)$ is the space required for an in-place multiplication. For example, using the in-place multiplier of Luo et al. (2026), Regev's
algorithm can factor an $n$-bit integer using $4n+O(\sqrt{n})$
qubits. Although our construction still falls short of the $n/2+\epsilon n$
qubits sufficient for leading implementations of Shor's
algorithm, it is the lowest-space instantiation of Regev's
algorithm to date and suggests that Regev's
algorithm is still far from fully optimized.
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Strongly Correlated Electrons
Strong metamagnetic switching and anisotropic magnetotransport in the distorted kagome magnet Tb6Ti4Al43
Lipika, Sneh, Shobha Singh et al. (+4 more)
We report a comprehensive investigation of the
magnetic, electrical, and thermodynamic properties of single crystalline Tb6Ti4Al43, in which Tb atoms form a distorted kagome
lattice embedded within a complex Ti-Al framework. Tb6Ti4Al43 exhibits pronounced
magnetic anisotropy and
antiferromagnetic ordering at approximately 19 K. For
magnetic field applied along the c-axis, a strong metamagnetic switching is observed, accompanied by a clear asymmetric hysteresis at low temperatures, while for field applied along the ab plane, a
spin-flop transition is observed. The effect of field induced
magnetic states is strongly reflected in magnetotransport measurements, giving rise to pronounced anomalies in magnetoresistance and an anomalous
Hall contribution. A significant intrinsic contribution to the anomalous
Hall conductivity is observed, highlighting the Berry
curvature effects arising from the system's momentum-space
topology. Our results highlight the interplay of
spin, charge, and
lattice degrees of freedom in Tb6Ti4Al43 and establish this distorted kagome antiferromagnet as a promising platform for field-tunable multifunctional behaviour, including electrically readable
magnetic switching,
spin manipulation, and magneto-mechanical functionalities.
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All authors Lipika, Sneh, Shobha Singh, Ralf Koban, Walter Schnelle, Rie Umetsu, Kaustuv Manna
Quantum Physics
Qubit CSS codes with Universal Transversal Gates
Arpit Dua, Adam Holmes, Michael J. Gullans et al. (+1 more)
The Eastin-Knill
theorem rules out a universal set of transversal logical gates on any code that detects single-
qubit errors. The
theorem constrains one partition of the
qubits at a time. We show that depth-one layers of few-
qubit gates, each respecting its own partition, can together generate a universal logical gate set on an error-correcting code. Each logical gate generator is then a single depth-one layer followed by error correction of the same stabilizer code, with no magic-state
distillation, code switching, gauge fixing,
lattice surgery, or other gadgets. We show that such codes can be found by applying an entangling
circuit to a lower-distance "seed" code admitting a depth-one non-Clifford gate and an appropriate "kernel" code. We construct 47 codes with depth-one generating sets that tolerate at least one faulty gate per layer, including a [[37,1,7]] and a [[59,1,9]] code, both of check weight at most eight.
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All authors Arpit Dua, Adam Holmes, Michael J. Gullans, Victor V. Albert
Quantum Physics
Random Order in Quantum Streaming: Replenishment and Robust Lower Bounds
Nadezhda Voronova
How can random order change the role of
quantum memory in streaming? Later classical input can restore the usefulness of a
quantum state consumed by earlier queries. We call this replenishment. We construct an artificial problem based on Hidden Matching, with repeated coordinate data and online matching requests. It admits a one-pass
quantum algorithm using polylogarithmic space in uniformly random order, but unconditionally requires
polynomial space both classically in random order and quantumly when all updates precede the requests. To prove the
quantum lower bound, we strengthen the consumability bounds of Gilboa, Jain, and McClean for Multiple Hidden Matching. Without prior
entanglement, any
quantum encoding supporting $r$ independent matching requests requires $\Omega(r)$
qubits for $r\le N^{1/2-\delta}$ and every fixed $\delta\in(0,1/2)$, even with simultaneous revelation and arbitrary joint decoding. For sequential requests, the linear bound extends through $r=\Theta(\sqrt N)$. We also adapt Kallaugher's triangle-counting
algorithm to uniformly random streams in which every edge is repeated equally often. Rebuilding the
quantum sketch and resampling the classical
estimator improve its expected-space bound in suitable parameter regimes. Finally, we extend the robust Noisy Gap Cycle framework of Assadi and Sundaresan to
quantum streaming. A
quantum communication lower bound for Block Hidden XOR yields an $\Omega(n)$ space lower bound in random edge order for large enough cycles, with consequences for several graph problems. Thus random order can enable replenishment of small
quantum representations, while substantial space requirements persist for other tasks.
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Quantum Physics
Approximate cloning of structured pure states
Yaroslav Herasymenko, Junqiao Lin, Philip Verduyn Lunel et al. (+1 more)
The no-cloning
theorem is a cornerstone result in
quantum mechanics that forbids copying of general
quantum information. More quantitatively, even given $N$ copies of an unknown state, any channel producing an $(N+1)$-copy state incurs a nonzero trace-distance error on some inputs. Turning this around, one can ask about the sample complexity of approximate $N\rightarrow N+1$ cloning: for a desired small error $\epsilon$, what $N$ suffices? For arbitrary pure states on a
Hilbert space $H$, the answer is $N\simeq \dim H/\epsilon$ - astronomically large for most $H$ of interest. What if the input is promised to lie in a structured family? We examine a range of families fundamental to many-body physics and
quantum information: $n$-mode fermionic Gaussian and Slater states, $n$-mode bosonic Gaussian states, and qudit phase states. For
fermions, we construct optimal cloning channels, reducing the complexity from exponential to
polynomial in $n$. For bosonic Gaussian states, we construct an explicit cloner that certifies
polynomial complexity, without any constraint on the energy of the state; this channel, however, is not optimal in general. The fermionic and bosonic results follow from a single representation-theoretic framework, which generalizes previous work by Werner and by Chiribella and Yang; it also yields the cloners'
unitary implementation. Furthermore, we explain why for many families the cloning complexity is linear in the dimension of the family
manifold, via a controlled saddle-point evaluation of the frame potential at high $N$. The same calculation accounts for the analogous scaling of
tomography complexity. The above framework does not cover phase states; for these we give an independent construction of a channel with optimal cloning fidelity. Our work complements recent results on cloning stabilizer states.
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All authors Yaroslav Herasymenko, Junqiao Lin, Philip Verduyn Lunel, Dmitry Grinko
Quantum Physics
Certifying Measurement Incompatibility under Bounded Classical Communication
Oxana Shaya
Measurement incompatibility enables
quantum advantages in communication and state discrimination. It is also necessary for Bell nonlocality, which is used in device-independent protocols for
quantum key distribution and private randomness generation. Classical communication can influence the receiver's outcome and must therefore be accounted for when certifying measurement incompatibility. We introduce union maximal leakage, which quantifies the information needed for a common classical explanation of all observed probabilities and is computed from them by a linear program. If a message of at most $k$ bits precedes the receiver's independent measurement choice, compatible measurements for each message give union maximal leakage at most $k$. This bound holds with any input-independent nonsignalling shared resource. In
quantum theory, a violation also implies that the initially shared state is entangled. Conversely, union maximal leakage determines the minimum classical communication needed to reproduce the observations with compatible measurements and arbitrary nonsignalling assistance. For a fixed shared
quantum state and receiver measurements, a violation is possible exactly when, for some message value, the receiver's measurements are Bell-nonlocal against two-outcome sender measurements on that state. For binary receiver outcomes, we show that a violation also certifies randomness private from the sender, even when the receiver's measurement depends on the sender's message and the sender retains
quantum side information. We quantify this
privacy through an explicit conditional
entropy bound and establish composably secure randomness extraction in sequential protocols with device
memory.
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Quantum Physics
Tight Query Lower Bounds for Quantum Sampling, with an Application to Certified Randomness
Keshav Bhateja, Mehdi Esmaili and Atul Mantri
Random
circuit sampling experiments, the leading demonstrations of
quantum computational advantage, are tested with the linear cross-
entropy benchmark (XEB), which scores outcomes by their ideal probabilities. We study what a high XEB score certifies about an untrusted
quantum device. In the
quantum query model, we show that the honest sampler's ideal score acts as a Tsirelson bound for efficient devices and certified randomness. First, exceeding the ideal score by a constant requires $\Omega(N^{1/3})$ queries for the Haar and
Fourier oracle ensembles with $N$ outcomes, and this bound is tight; this proves an earlier
conjecture for Haar-random states and extends it to
Fourier sampling. Second, for
Fourier sampling and for Haar-random states accessed through the canonical state-preparation oracle, the $n$-bit output of a device that makes polynomially many queries and scores within $o(1)$ of the ideal score has $n-O(\log n)$ bits of smooth min-
entropy, even against an adversary who is entangled with the device and later learns the oracle; this is nearly optimal. As a corollary, sampling the collision distribution, which is proportional to the square of the ideal distribution, has query complexity $\Theta(N^{1/3})$, and a coherent version of the same
algorithm approximately prepares
quantum Hadamard products of states with uniform amplitude magnitudes. Both lower bounds rest on progress measures that bound the excess over the ideal score and increase only slightly with each query. For
Fourier sampling the measure is the norm of the coherent amplitudes for removing pairs in a purification of the random function, combining the
polynomial method with the compressed oracle technique; for Haar-random states it is the square root of the average level in an expansion in Dirichlet orthogonal
polynomials, controlled by an exact identity for the effect of one observation.
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Statistical Mechanics · Cross-listed from q-bio.NC
Interplay between Excitability and Noise in Analog Spiking Neurons
Léopold Van Brandt, Alon Ascoli, Michele Bonnin et al. (+3 more)
A spiking
neuron is a dynamical system exhibiting a limit cycle (a spike) when subject to sufficiently excitatory input. Famous neuroscience experiments by Bryant and Segundo as well as Mainen and Sejnowski revealed that the spike times of some biological
neurons are more reliable when subject to time-varying stimuli compared to constant ones. Provided with an industrial physics-based transient noise SPICE simulation framework compatible with foundry transistor compact models, we have demonstrated similar behaviours for a CMOS analog spiking
neuron designed for neuromorphic computing hardware platforms. Under constant excitation current, the
neuron operates in oscillatory regime and the empirical periods (interspike intervals) suffer from accumulated phase noise (jitter) during successive cycles, mainly due to the thermal noise of transistors. A time-varying input is reported to be capable of triggering output spikes according to a controlled statetransition mechanism, thereby significantly reducing the spike time jitter in the excitability regime. The physical limitation of the oscillatory or rate-coding regime in terms of reliabilitydissipation tradeoff is further evidenced by a
stochastic thermodynamic uncertainty relation, a
theorem that applies to general overdamped dissipative
stochastic dynamical systems.
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All authors Léopold Van Brandt, Alon Ascoli, Michele Bonnin, Grégoire Brandsteert, Denis Flandre, Jean-Charles Delvenne
Optics
Novel functionalities enabled by asymmetric reconfiguration in VO2-dielectric metasurfaces
P. Hostalet-Vicent, L.M. Máñez-Espina, K. Schouteden et al. (+5 more)
Bianisotropic metasurfaces provide electromagnetic functionalities that cannot be achieved through electric and
magnetic responses alone, enabling asymmetric scattering, directional absorption, and advanced wavefront control. At optical frequencies, however, most demonstrations rely on static nanostructures whose magnetoelectric response is fixed after fabrication. Here, we investigate the opportunities enabled by dynamic reconfiguration of electromagnetic bianisotropy using a thermally tunable silicon–VO$_2$ metasurface operating in the near-infrared. By combining a collective-polarizability framework with numerical simulations and experimental characterization, we show that the
insulator-to-metal transition of VO$_2$ modifies not only the electric and
magnetic responses of the metasurface, but also its magnetoelectric coupling, providing access to distinct bianisotropic states within a single platform. Temperature-dependent experimental characterization confirms the thermally driven
evolution of the absorption asymmetry. Based on this framework, we identify different operational regimes and demonstrate how bianisotropy reconfiguration enables transmissive and reflective directional functionalities, including transmission power-limiting, power-dependent asymmetric reflection, and power-dependent absorptivity/emissivity. These results establish dynamic control of magnetoelectric coupling as a powerful degree of freedom for multifunctional and adaptive photonic metasurfaces for optical and thermal applications.
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All authors P. Hostalet-Vicent, L.M. Máñez-Espina, K. Schouteden, J. P. Locquet, M. Seo, T. Mengual-Chulia, P. Sanchis, A. Díaz-Rubio
Cosmology and Nongalactic Astrophysics
AI-assisted super-resolution cosmological simulations V: Cosmology-aware super-resolution
Xiaowen Zhang, Patrick Lachance, Rupert A.C. Croft et al. (+2 more)
We present a cosmology-aware generative model for super-resolution (SR) of cosmological $N$-body simulations in particle phase space. The model jointly generates displacements and velocities, conditioning a generative
adversarial network (GAN) based generator and discriminator on evolved low-resolution (LR) fields and five $\Lambda$CDM parameters $(\Omega_m,\Omega_b,h,n_s,\sigma_8)$. We train a single model on 100 matched low-high resolution pairs from the Quijote Latin-hypercube suite at $z = 0$, mapping $512^3$ to $1024^3$ particles in $1\,h^{-1}\,\mathrm{Gpc}$ boxes. On ten cosmologies excluded from SR training, the model reproduces the broad matter distribution and the cosmological variation of clustering and
halo abundances. Over $0.1<k<3\,h\,\mathrm{Mpc}^{-1}$, the mean of the per-cosmology maximum absolute power-spectrum errors is $3.6\%$, while FoF
halo abundances agree with HR to within $15\%$ in the analyzed mass bins below $10^{14.8}\,h^{-1}M_\odot$. Satellite abundances and occupations retain larger, mass-dependent discrepancies. Corrections measured at one near-fiducial cosmology reduce a shared component of these systematic errors when applied to the other nine test cosmologies. A power spectrum based inference test also shows that calibration reduces the mean shifts in all parameters. These results extend our SR model across cosmologies and provide 6D phase space realizations for subsequent studies of non-linear structure and field-level cosmological inference.
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All authors Xiaowen Zhang, Patrick Lachance, Rupert A.C. Croft, Tiziana Di Matteo, Francisco Villaescusa-Navarro
Quantum Physics
Out-of-control Hamiltonian Learning
Weiyuan Gong, Muzhou Ma, Sitan Chen et al. (+2 more)
Learning the
Hamiltonian of a many-body system from its dynamics is a central task in
quantum science, yet the
algorithms with the strongest provable guarantees assume some level of
quantum control–fast, arbitrary single-
qubit gates interleaved with time
evolution, and measurements in arbitrary bases–that is beyond the capabilities of near-term analog
quantum simulators. Motivated by analog atom- and ion-based platforms, we study
Hamiltonian learning under minimal access models. Uniform state preparation and measurements: We first consider the setting where in every experiment, one can rotate each
qubit to the same state, perform short-time
evolution, and measure every
qubit in the same basis. Surprisingly, we show that for generic 2-local
Hamiltonians on any interaction graph, all of the parameters can be reconstructed from such experiments. Computational basis state preparation and measurements: We then consider a similarly constrained setting, but where state preparation and measurement are restricted to the computational basis. For nearest-neighbor
Hamiltonians with only Pauli $X/Z$ interactions, a class which captures contemporary Rydberg atom platforms, we show that over 1D and 2D rectangular
lattices, all of the parameters can be reconstructed from such experiments up to unavoidable gauges. Our protocols introduce new techniques for solving structured
polynomial systems over an extensive number of parameters. Taken together, our results suggest that one can learn a great deal from the dynamics of
quantum many-body systems even under the most stringent experimental constraints.
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All authors Weiyuan Gong, Muzhou Ma, Sitan Chen, Jordan Cotler, Hsin-Yuan Huang
Computational Physics
Mechanism-resolved phase-field fracture of composite shells with a certified admissible constitutive operator
Altaf Ahmad Lone, R. T. Durai Prabhakaran, Timon Rabczuk et al. (+1 more)
Phase-field models of fracture in fibre-reinforced shells are usually formulated against a single closed-form stored energy, so that the stress, consistent tangent and plane-stress condensation are derived and verified for that expression alone. Here the constitutive law enters instead as a replaceable operator. The Green-Lagrange strain of a geometrically exact Reissner-Mindlin shell is pulled back through the Cholesky factor of the reference metric and resolved on four mutually orthogonal invariants with an exact closure identity, making the separation into fibre, inter-fibre and interaction channels a change of basis rather than a modelling assumption. On a curved midsurface, the metric, Cholesky factor and fibre direction vary through the thickness through the shifter I -
zeta b, and the invariants inherit that dependence. The tension-compression split, channel degradation, plane-stress condensation, consistent tangent and finite-element assembly are all expressed in the channel potentials and their derivatives, allowing either closed-form or learned operators. The fibre-transverse interaction energy is stored once and degraded by the product of the fields whose mechanisms it couples. Six conditions define admissible operators; the two linear invariants are proved convex in the deformation gradient, the
geometric tangent is shown independent of the material tangent, and the plane-stress condensation is regular wherever the residual stiffness is positive. A three-tier protocol certifies the
algebra, solver state and admission of a state as training data. Numerical studies on notched IM7/8552 shells verify the discretisation in thin and curved regimes and show that fibre orientation governs the damage envelope and load capacity, while
curvature drives a through-thickness fracture asymmetry that a single midsurface field cannot represent.
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All authors Altaf Ahmad Lone, R. T. Durai Prabhakaran, Timon Rabczuk, Xiaoying Zhuang
Quantum Physics
Shyam Dhamapurkar, Mohit Garg, Manaswi Paraashar et al. (+1 more)
We consider the following data compression problem. Given a string $x \in \{0,1\}^m$ of Hamming weight at most $n$, compress it into a shorter string $y \in \{0,1\}^s$ so that any bit $x_i$ of $x$ can be retrieved without any error using at most $t$
quantum queries to the standard oracle encoding of $y$. If queries are allowed to be adaptive we show how optimal compression up to a logarithmic factor can be achieved. If the queries are required to be made non-adaptively, we show schemes whose space is optimal in its dependence on $m$ except for a logarithmic factor, and is at most quadratically worse when compared to the optimum in its dependence on $n$.
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All authors Shyam Dhamapurkar, Mohit Garg, Manaswi Paraashar, Jaikumar Radhakrishnan
Disordered Systems and Neural Networks · Cross-listed from stat.ML
A Solvable Model of Adaptive Learning Rate Rescaling: Acceleration, Stability & Scaling
Itay Lavie, Clarissa Lauditi and Cengiz Pehlevan
A recurring design principle in modern optimizers is to decouple update magnitude from the raw gradient norm, yet its consequences for learning-curve and resource scaling remain unclear. We isolate this mechanism by studying normalized SGD in a random-feature model with power-law teacher and data covariance. Fixed-norm updates induce an effective learning rate that grows as gradients shrink. We derive a dynamical mean-field theory (DMFT) describing the joint dependence of the loss on training time, model width and batch size. Normalization initially accelerates SGD, mapping the power-law exponent $r_{\rm SGD}<1$ to $2r_{\rm SGD}/(1-r_{\rm SGD})$, with exponential convergence at $r_{\rm SGD}=1$ and formal finite-time convergence for $r_{\rm SGD}>1$. At finite step size, however, the same feedback ultimately breaks the acceleration and leads to marginal stability. The late-time theory yields width-limited, edge-of-
stochastic-stability (EoSS), and deterministic edge-of-stability (EoS) regimes. These phases determine when larger batches or wider models reduce serial training time at comparable compute. We quantify in which of these phases increased batch size or width can compensate the excess compute use per step by fewer optimization steps to target loss. Linearized ResNet experiments on CIFAR-5M support the predicted acceleration, breakdown, and resource-scaling trends. Together, these results connect normalization-induced acceleration, EoS effects, and width–batch allocation within a solvable theory.
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Quantum Physics
Random-Oracle Unitary Synthesis is Impossible
Andrew Huang, Akshar Ramkumar and John Wright
A major open problem in
quantum complexity is the question of
unitary synthesis—namely, is it possible to efficiently implement any
unitary, given the ability to evaluate any classical function in superposition? Inspired by a recent work by Brakerski and Yuen (CRYPTO 2026), we propose an “average-case”
unitary synthesis problem, which asks whether it is possible to efficiently implement a Haar random
unitary given access to a random Boolean function. We then demonstrate a superpolynomial query lower bound, establishing that
unitary synthesis in this model is impossible. Along with our main result, we settle in the negative a question Brakerski and Yuen pose, of whether scalable pseudorandom
unitaries (PRUs) can be implemented in the ROM-PRU model. In particular, we show that in the ROM-PRU model, no $\Omega(N^{1+\gamma})$
unitary design on $n$
qubits, where $N=2^n$, can be efficiently achieved for any $\gamma > 0$. On the other hand, we construct an $O(N)$-design in $\text{poly}(n)$ queries in the same model, surpassing the previously best known results which constructed $O(\sqrt{N})$-designs.
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Mathematical Physics
A Cohomological Characterization of the Clifford Hierarchy
Junaid Aftab
The Clifford hierarchy plays a central role in fault-tolerant
quantum computation, but its higher levels remain only partially understood. Recent work on
quantum higher order
Fourier analysis characterizes membership in the Clifford hierarchy using
quantum derivatives, but does not provide an explicit description of the individual levels. In this work, we address this problem by showing that the collection of
quantum derivatives of a
unitary operator forms a non-abelian \(1\)-cocycle, and conversely that every such \(1\)-cocycle arises from a
unitary operator. This yields a recursive cohomological characterization of the Clifford hierarchy. We then specialize this framework to the third level and decompose the cocycle data into
symplectic, affine, and phase components, each admitting a cohomological interpretation. As applications, we give a new proof that every two-qudit gate in the third level of the Clifford hierarchy is semi-Clifford, and prove for the first time that every three-qudit gate in the third level is semi-Clifford.
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High Energy Physics (Phenomenology)
Polarised cross sections for loop-induced processes with SHERPA+RECOLA
Mareen Hoppe, Marek Schönherr and Frank Siegert
Studying vector
boson polarisation has become an integral part of the LHC physics programme in recent years, as it provides an independent test of the electroweak
symmetry-breaking mechanism and the gauge sector of the electroweak Standard Model. These measurements require polarised templates from parton-shower Monte Carlo simulations. Their accuracy does not yet meet the precision requirements of upcoming measurements, leading to significant modelling uncertainties in experimental analyses that will constrain the LHC's polarisation sensitivity at latest in the HL-LHC phase. Polarised loop-induced processes have so far not been included in most parton-shower event generators, despite contributing significantly to processes of interest. In this work, we present the extension of the polarisation framework in the Monte Carlo event generator SHERPA to polarised loop-induced processes at fixed LO and LO matched to parton shower. In addition to a description of the methodology based on polarised amplitudes from the RECOLA
matrix element generator, we discuss polarisation effects in relevant inclusive, loop-induced processes and their jet-associated counterparts, several of them for the first time. Both the influence of different polarisation definitions and of QCD and QED resummation effects are investigated.
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Quantum Physics
Measurement-free Preparation of Surface-Code States with Digital-Analog Counterdiabatic Drivings
Shubham Kumar, Balaganchi A. Bhargava, Paolo A. Erdman et al. (+5 more)
Preparing stabilizer-code states with shallow
circuits is an important primitive for near-term
quantum error correction in superconducting
circuits, where logical-state initialization requires four-body stabilizer correlations from native one- and two-body controls. We introduce a digital-analog method for the preparation of surface-code ground-state
manifolds. The method exploits a structural property of the adiabatic gauge potential, mapping stabilizer-local counterdiabatic terms to digital-analog blocks on the superconducting layout using fixed-angle two-
qubit XY gates, single-
qubit rotations, and analog exchange-interaction evolutions. The dressed blocks generate higher-order operators used as the variational ansatz to determine the counterdiabatic terms within the Sels-Polkovnikov adiabatic-gauge-potential framework. We
benchmark checkerboard plaquette-stabilizer grids up to 4 x 4; the square-grid instances correspond to rotated surface codes, while the rectangular cases probe the scaling of the method. For all grids, the proposed method generates the dominant four-body counterdiabatic basis and, at short
evolution times, substantially improves ground-state preparation compared with bare adiabatic
evolution. We further generalize the construction to n x m stabilizer
lattices and show that digital-analog synthesis can reduce the entangling depth by an order of magnitude. Together, these results establish a direct connection between stabilizer geometry, the structure of the counterdiabatic gauge potential, and digital-analog control for measurement-free preparation of stabilizer-code states on near-term superconducting architectures.
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All authors Shubham Kumar, Balaganchi A. Bhargava, Paolo A. Erdman, Anne-Maria Visuri, Jose D. Mart{\i}n-Guerrero, Yolanda Vives-Gilabert, Enrique Solano, Narendra N. Hegade
Materials Science
Strain tunability of electron and hole g-factors in CsPb$X_3$: bulk and nanocrystals
Aleksander Cząstkiewicz, Paweł Scharoch and Krzysztof Gawarecki
In this paper, we theoretically study the electron and hole $g$-factors in inorganic lead-halide perovskites for the reference cubic phase. We employ an 18-band $k \cdot p$ model and determine its parameters using target band structures obtained from DFT calculations. We use the linear response theory to calculate the $g$-factors and investigate their dependence on external strain. We then perform real-space calculations of the electron and hole $g$-factors in perovskite nanocrystals. We show that the bulk $g$-factors can be tuned over a wide range by external strain. In some cases, strain can be used to tune the $g$-factor through zero. By contrast, the carrier $g$-factors in CsPb$X_3$ nanocrystals are considerably less sensitive to strain due to
quantum confinement.
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Quantum Physics
Climbing the Fusion Tree: Center Ordering and Decoding Hierarchy in Non-Abelian Mixed States
Pablo Sala, Vlad Temkin, Cenke Xu et al. (+2 more)
We develop an operational approach to strong-to-weak spontaneous
symmetry breaking (sw-SSB) of a non-Abelian
symmetry group G. We formulate it as the decoding task of distinguishing two strongly symmetric states that differ by a pair of inserted irreps, after both are corrupted by strongly symmetric decoherence. For finite G, this task is dual to distinguishing logical states of the
quantum double D(G) under pure-charge noise. We derive a hierarchy of statistical mechanics models describing optimal decoding from the fusion outcomes measured on successively larger nested regions. As for maximum-likelihood decoders of Abelian codes the measured irreps act as quenched disorder obeying a Nishimori-like condition. Strikingly, because local irreps do not determine how they fuse globally, the strong $G\times G$
symmetry is realized only nonlocally, and irreps trivially charged under Z(G) (the center of G) can hide inside noise-generated ones. As a result, the strong
symmetry spontaneously breaks down to Z(G), times the weak
symmetry. The only transition at nonzero error rate is then an ordering of the center, whose threshold cannot decrease as the hierarchy is ascended. This conclusion holds at any finite level of the hierarchy for non-nilpotent groups. We confirm these predictions with tensor-network calculations for $S_3$ and SU(2). At the first level, the $S_3$ model, whose center is trivial, shows no transition, and the fidelity correlations of all irreps provably decay to non-zero values. The SU(2) model exhibits a $Z_2$ transition consistent with the Nishimori-Ising universality class, where the fidelity correlations of
spin-$1/2$ irreps become long-range. The threshold rises from the first to the second level of the hierarchy by $16\%$. Our results provide a systematic framework for studying non-Abelian sw-SSB and for constructing decoders for non Abelian topological codes.
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All authors Pablo Sala, Vlad Temkin, Cenke Xu, Daniel Podolsky, Ehud Altman
Strongly Correlated Electrons
Interacting quantum criticality with U(1) symmetry breaking in 1+1 dimensions
Mutsumi Shimomura and Kohei Kawabata
The Hohenberg-Mermin-Wagner
theorem motivates the expectation that continuous
symmetry remains unbroken in one-dimensional
quantum ground states. Here, contrary to this expectation, we demonstrate the spontaneous breaking of U(1)
spin-rotation
symmetry and the emergence of an interacting
quantum critical point in
lattice spin-$1/2$ and
spin-$1$ chains. Using subsystem Binder scaling, we locate the critical point and determine the correlation-length critical exponent as $\nu = 0.60 \pm 0.02$, distinct from the Gaussian value $1/2$ but consistent with the perturbative renormalization-group value. We further estimate the dynamical critical exponent to be $z = 1.986 \pm 0.005$ from the lowest neutral excitation gap and $z = 1.955 \pm 0.021$ from the longitudinal
spin correlations. The results $z < 2$ are incompatible with microscopic realizations of this critical theory by frustration-free models, implying a mechanism for continuous
symmetry breaking in one-dimensional
quantum ground states distinct from frustration freeness.
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Astrophysics of Galaxies
Unveiling the Origins of the Molecular Gas Reservoirs in Recently Quenched Massive Galaxies
E. Savitch, D. Narayanan, D. J. Setton et al. (+13 more)
Observations of quenched
galaxies across
cosmic time have revealed systems containing substantial molecular gas reservoirs, challenging the traditional picture of gas-poor, red and dead
galaxies. Using the Simba cosmological simulation, we investigate three possible hypotheses for the origin of molecular gas-rich quenched systems: (i) quiescence is temporary and the
galaxy will rejuvenate, (ii) molecular gas masses are overestimated due to an underestimated CO-to-H$_2$ conversion factor, or (iii)
star formation is ongoing but heavily obscured by
dust. Across $M_*>3\times10^9M_\odot$
galaxies from $z=0-2$, we find that all three mechanisms are plausible. Many seemingly quiescent, molecular gas-rich
galaxies host
dust-obscured
star formation, with visual optical depths increasing on average from $\tau_V\sim0.5-2.3$ from $z=0-2$. Assuming a Milky Way-like CO-to-H$_2$ conversion factor can overestimate molecular gas masses by a factor of $\sim\!5$ in non-
star-forming
galaxies, compared to $\sim\!1.45$ in
star-forming
galaxies. Temporary quiescence can also occur in gas-rich transitioning
galaxies on timescales ranging from $100\,\text{Myr}-2\,\text{Gyr}$, although this is most prominent at high
redshift and is relatively rare overall. Further work is needed to disentangle the relative contributions of these mechanisms across
cosmic time.
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All authors E. Savitch, D. Narayanan, D. J. Setton, K. E. Whitaker, R. Bezanson, E. Cenci, R. Davé, V. R. D'Onofrio, R. Feldmann, J. E. Greene, M. Kriek, M. Parente, J. S. Spilker, K. A. Suess, D. Valentín-Martínez, D. Zimmerman
High Energy Physics (Experiment)
Design optimization of the inter-electrode structures in DC-RSD
N. Cartiglia, R. Arcidiacono, G. Bardelli et al. (+20 more)
DC-coupled Resistive Silicon Detectors (RSD) share charge among electrodes through a resistive n$^+$ surface layer, and the choice of inter-electrode structure — a trench, a resistive strip, or no structure at all — directly determines the achievable position resolution and its uniformity. This paper addresses the question of which structure best optimises the spatial resolution. To answer it quantitatively, DCRSD_SurfaceSimulator was developed, a ROOT-based tool that models the resistive surface as a two-dimensional Kirchhoff resistive network and solves for charge sharing as a function of hit position, surface resistivity, and inter-electrode structure. The simulator is validated against test-beam data from FBK DC-RSD sensors with 300, 500, and 1000~$\mu$m pixel pitch, reproducing the position resolution, its spatial uniformity, and the signal-sharing templates correctly. Using the validated simulator, trenches, resistive strips, and no containment are then compared on position resolution and its spatial uniformity, inter-electrode resistance, and signal leakage to outer pixels. Resistive strips are found to outperform trenches in resolution by approximately 25% for all tested strip resistances (500–2000~$\Omega$) and input impedances (0–100~$\Omega$), at a surface resistivity of 1000~$\Omega/\square$, and trace the origin of this difference to the spatial gradient of the charge-sharing fraction: trenches produce a markedly weaker and less uniform gradient, particularly away from the pixel centre, than either a resistive strip or a bare resistive surface.
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All authors N. Cartiglia, R. Arcidiacono, G. Bardelli, M. Boscardin, A. Cassese, M. Centis Vignali, T. Croci, M. Durando, M. Ferrero, A. Fondacci, S. Gaiero, O. Hammad Ali, L. Lanteri, A. Losana, L. Menzio, A. Morozzi, F. Moscatelli, D. Passeri, G. Paternoster, G. Sguazzoni, F. Siviero, V. Sola, L. Viliani
Quantum Physics
Quantum Gibbs State Preparation via Relative Decoding: From Fast-Mixing Sources to Broader Target Classes
Zhong-Xia Shang, Yufei Wang and Daniel Stilck França
Provable guarantees for preparing
quantum Gibbs states, such as rapid mixing or gapped coherent preparation paths, are known only for restricted
Hamiltonian families and usually must be re-derived for each new family. Building on homomorphic
polynomial transduction, a generalization of decoded
quantum interferometry (DQI) and
Hamiltonian DQI (HDQI), we show how relative decoding transfers such a guarantee from a source
Hamiltonian $H_A$ to a target $H_B$. Writing each
Hamiltonian as a sum of $m$ Pauli terms, the subsets of terms whose product is proportional to the identity, its relations, form a binary linear code, $K_A$ for the source and $K_B$ for the target, with the Pauli-label
matrix as parity-check
matrix as in DQI. Starting from the canonical thermofield double (TFD) of $H_A$, a Bell transform, a reversible label map, and a coherent decoder for the quotient code $K_B/K_A$ prepare an approximate TFD of $H_B$, and hence its Gibbs state. Because this decoder only resolves target relations absent from the source, the reachable inverse temperature is set by the relative distance $d_{\rm rel}$, the fewest terms in any such relation. It can far exceed the ordinary distance $d_{\rm ord}$, the fewest terms in any target relation, which bounds the uniform exact decoding radius of DQI and HDQI. We show that linear $d_{\rm rel}$ with efficient decoding at linear radius certifies a constant inverse temperature. As an example, starting from a nearest-neighbor
spin chain whose TFD is known to be preparable at every finite temperature, a sparse classical parity-check
matrix yields bounded-degree, geometrically nonlocal, noncommuting targets with $d_{\rm ord}=3$ and $d_{\rm rel}=\Theta(m)$. To our knowledge, this gives a new class of efficiently preparable TFDs.
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Astrophysics of Galaxies
Forming Molecular Hydrogen in a Galaxy Halo Through Star Formation Wind Interactions
Brad Koplitz, Sanchayeeta Borthakur, Timothy Heckman et al. (+5 more)
Molecular hydrogen (H$_2$) is the key ingredient for
star formation in
galaxies. However, how H$_2$ is distributed in and around
galaxies is an open question in astronomy. We report the detection of H$_2$ (covering excitation levels $J = 0$ to 3) in a unique environment at a distance of 139 kpc from a starbursting luminous infrared
galaxy. This is the furthest from a
galaxy that H$_2$ has been directly detected to date. This H$_2$ system is unlike any seen before, with a high molecular-to-atomic hydrogen ratio (2%) and an accompanying low neutral hydrogen column density (log$_{10}[N($H I$)/\mathrm{cm}^{-2}] = 18.52^{+0.13}_{-3.58}$). Our measurements reveal that the H$_2$ bearing cloud is traveling at $\sim$100 km s$^{-1}$ relative to the host
galaxy, has a super-
solar metallicity, and excites at a single, cold temperature ($245^{+25}_{-21}$ K) indicating a lack of the ”typical” core-envelope structure seen in other H$_2$ clouds. Furthermore, our analysis points to the H$_2$ likely being formed through interactions between
galactic winds and the gaseous
halo surrounding the
galaxy. The properties of this cloud suggest that the H$_2$ is short-lived, yet it presents crucial information on the microphysics of the wind-CGM interactions.
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All authors Brad Koplitz, Sanchayeeta Borthakur, Timothy Heckman, Frances H. Cashman, Evan Scannapieco, Jason Tumlinson, Hsiao-Wen Chen, Molly Peeples
Quantum Physics
Kramers' Theorem Leaves a Topological Footprint in Classical Records
Chon-Fai Kam and Kai-Wen Wong
Time reversal $\Theta$ squares to $-1$ on a half-integer
spin, so every state is orthogonal to its time reverse. This sign has been read only from
quantum objects. The
equilibrium state loses it, but the classical record keeps it. For a detector that resolves handedness, the probabilities that one stretch of record is followed by the time reverse of another measure the
cohomology class of time reversal, $\Theta^2=\pm1$. Their
matrix carries this sign in its signature, a topological integer that survives equal emission and absorption losses. A programmed emitter on
quantum processors reads it in about $10^3$ shots.
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Astrophysics of Galaxies
Disentangling the assembly of the central and diffuse stellar components in galaxy clusters through dynamical friction and tidal stripping
Frazer R. Pearce, Steven P. Bamford, Garreth Martin et al. (+7 more)
In
galaxy clusters, it is common to conceptually distinguish the central, brightest cluster
galaxy (BCG) from the more diffuse intracluster light (ICL). So far, however, this distinction has lacked a clear physical basis, confusing both theoretical and observational studies. We address this by presenting a dynamically motivated definition of the two
stellar components, evaluated using cluster zoom simulations from the Three Hundred project. We start with a motivational hindcasting approach, robustly tracing
stars from the centres of 107 present-day clusters back through the merger hierarchy. We find that the majority of the final BCG
stellar mass is typically contributed by the central
galaxies of only 3 to 5 progenitor
haloes. Most accreted
galaxies contribute no
stars to the BCG, instead surviving as satellites or depositing
stellar material throughout the cluster. This naturally leads to a definition of the BCG
stellar population as originating from the central
galaxies of the most massive infalling systems. These are delivered to the cluster centre via efficient dynamical friction and subsequently undergo violent relaxation. The ICL arises from the complementary population of
stars tidally stripped from the outskirts of all infalling systems. We therefore develop a
forecasting method, identifying
stars in the BCG and ICL via the dynamical fates of their originating
stellar systems. Applying this to 261 clusters, we find the resulting components remain spatially interleaved, but occupy distinct regions of phase space. Our physically defined BCG matches conventional aperture-based selections with high completeness, while providing a direct interpretation in terms of hierarchical assembly.
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All authors Frazer R. Pearce, Steven P. Bamford, Garreth Martin, Yannick M. Bahé, Harley J. Brown, Madeline Butler, Ana Contreras-Santos, Weiguang Cui, Nina Hatch, Alexander Knebe
Mathematical Physics · Cross-listed from math.AP
The $L^1$-realization of an elliptic operator with unbounded coefficients
Sallah Eddine Boutiah
We establish an $L^1$-theory for a class of
elliptic operators with unbounded coefficients, extending our earlier
semigroup generation results and those of Canale–Rhandi–Tacelli to the endpoint $p=1$. The $L^1$-realization generates a positive analytic $C_0$-
semigroup that is compact for every positive time. We characterize the generator domain through weighted estimates and prove consistency with the corresponding $L^p$-
semigroups for $1<p<\infty$.
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Materials Science
Structural, electronic, and magnetic properties of HoCo$_2$ thin films grown by pulsed laser deposition
Ajay Kumar, Christopher Burgio, Anis Biswas et al. (+1 more)
We report the growth and physical properties of HoCo$_2$ thin films on Si substrate by pulsed
laser deposition. Well-defined Kiessig fringes in the x-ray reflectivity data yield a film thickness of $35 \pm 1$~nm and demonstrate smooth film surface and interface profiles. Atomic force microscopy confirms the high morphological quality of the films, revealing subnanometer surface roughness of $\sim$170~pm. Two independently prepared films exhibit a reproducible ferrimagnetic transition at $T_{\mathrm{C}}=77\pm3$~K, demonstrating retention of the characteristic
magnetic ordering of bulk HoCo$_2$. However, the absence of resolvable thermal hysteresis indicates a predominantly continuous, second-order like transition in the films, in contrast to the first-order transition of bulk HoCo$_2$. At 5~K, the films exhibit clear
magnetic hysteresis with a coercive field of $\sim$600~Oe, substantially larger than the negligible coercivity of bulk HoCo$_2$. X-ray photoelectron spectroscopy reveals comparable Ho $4d$ and Co $2p$ core-level line shapes and broadly similar valence-band spectra for the bulk and film, indicating preservation of the essential local electronic environment and occupied electronic structure.
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All authors Ajay Kumar, Christopher Burgio, Anis Biswas, Yaroslav Mudryk
Fluid Dynamics
Accurate contact discontinuity resolving Boltzmann schemes based on peculiar velocity
Balwinder Singh and S. V. Raghurama Rao
Starting from the robust foundation of the peculiar velocity based upwind (PVU) Boltzmann scheme, which fails to recognize contact discontinuities, this paper introduces new variants for the numerical solutions of equations of gas dynamics. A modified partial differential equation (MPDE) analysis of the original scheme reveals that the numerical
diffusion coefficient corresponding to the peculiar velocity part does not vanish as the Mach number goes to zero. The numerical discretization of the peculiar velocity term is redesigned so that the numerical
diffusion depends only on the bulk fluid velocity across the stationary contact discontinuities, enabling its exact capture in 1D and exact capture of slip surfaces in 2D. The resulting variants achieve low numerical
diffusion while preserving the robustness of the original scheme, as demonstrated through several 1D and 2D
benchmark compressible flow test cases.
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