Disordered Systems and Neural Networks · Cross-listed from quant-ph
A Gauge Sign Rule for Quantum Rotor Networks
Swagata Acharya
The sign problem is the non-positive path-integral weight that makes a
quantum system hard to simulate classically. It shows up in problems that look unrelated, from
fermion antisymmetry and
geometric frustration to real-time
evolution, topological angles, and finite density. We study it here for compact continuous variables, modeled as networks of
quantum rotors, $\hat H=\sum_i 4E_C(\hat n_i-n_{g,i})^2-\sum_{\langle ij\rangle} E_{ij}\cos(\hat\phi_i-\hat\phi_j-\theta_{ij})$. For these, a single gauge-invariant quantity controls the obstruction, the frustration flux through the independent loops of the interaction graph. We prove a sign rule, the rotor analogue of Marshall's. The charge-basis
Hamiltonian is sign-free if and only if every loop flux vanishes modulo $2\pi$. Exact diagonalization and density-
matrix renormalization then show that the sign cost is a gauge-invariant function of the flux. For a single loop it vanishes at zero flux, peaks at $\pi$, and is exponentially small in the loop's perimeter. Summed over many loops it is extensive, growing with system size. The same loop flux generates the sign of three problems usually treated apart, namely the Mott transition (through the slave-rotor mapping), compact $U(1)$
lattice gauge theory, and frustrated continuous optimization. A superconducting rotor array realizes both the model and its sign natively.
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Soft Condensed Matter
Static compliance and directional instability in indefinite conformation states
Yuan Yu
A conformation tensor is positive definite for every physically realizable
polymer microstructural state. Numerical discretization can move the conformation tensor outside the positive-definite domain. This raises a question: can the least
eigenvalue alone identify the first unstable direction? We answer it by linearizing Oldroyd-B,
equilibrium-normalized FENE-P and Giesekus models about uniform frozen states. All include solvent viscosity and stress
diffusion. We examine every non-zero planar
Fourier mode, assuming each model's uncoupled constitutive tangent is strictly stable. The margin $1+r\chi$ measures the balance between solvent damping and the zero-frequency
polymer response. The complete velocity–conformation system is stable if and only if this margin is positive. At zero margin, a simple stationary root appears; finite inertia changes growth rates but not the neutral boundary. At fixed wavenumber and other parameters, decreasing $\lambda_1$ identifies the first neutral direction. Oldroyd-B and
equilibrium-normalized FENE-P first become neutral along principal directions; Giesekus mobility can instead make an oblique direction neutral first. For the reference case, onset is $\lambda_{1,c}=-1.933$ at $\theta_c=23.94^\circ$, before the principal-axis prediction. Along this family, the all-direction threshold approaches $-2.319$ as the other principal stretch grows, whereas the formal principal-axis extrapolation tends to negative infinity. A rational-parameter counterexample,
matrix spectra and uniform forced-base calculations test the neutral boundary and both sides. These results concern one linear, uniform, planar
Fourier mode, not nonlinear or inhomogeneous-flow stability. Within this scope, onset depends not on indefiniteness alone but also on constitutive-tangent geometry and wavevector direction.
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Superconductivity · Cross-listed from nlin.PS
On the kinks in discrete systems
Eugene Kogan
We use perturbation theory to study kinks in nonlinear Klein–Gordon ($\phi^4$ and sine-Gordon) chains and in a discrete series-connected Josephson transmission line. The expansion parameter is the ratio of the
lattice period to the kink width. The next-to-leading-order approximation modifies the kink profiles obtained previously in the leading-order approximation.
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Materials Science
Two-Dimensional Hexagonal BX3 (X = P, As) Monolayers as High-Capacity, Fast-Charging Anode Platforms for Lithium- and Sodium-Ion Batteries
Jakkapat Seeyangnok, Joongjai Panpranot and Udomsilp Pinsook
The rapid advancement of alkali-metal ion batteries demands robust anode platforms combining high specific capacities with rapid charge-discharge kinetics. Using first-principles density functional theory (DFT), we systematically evaluate two-dimensional (2D) hexagonal BX3 (X = P, As) monolayers as high-performance dual-use anodes for lithium-ion (LIBs) and sodium-ion batteries (SIBs). Both metallic host architectures display strong thermodynamic affinities for Li+ and Na+ adsorption, favoring the hollow H3 site through synergistic ionic charge transfer and orbital hybridization. Climbing image nudged elastic band (CI-NEB) calculations reveal low direct H3 -> H3
diffusion barriers: 0.40 eV (BP3) and 0.26 eV (BAs3) for Li+, and 0.26 eV (BP3) and 0.19 eV (BAs3) for Na+, confirming exceptional high-rate kinetics. Thermodynamic convex hulls establish maximum stable lithiation at Li3BX3, yielding low average operating potentials of 0.39 V (BP3) and 0.35 V (BAs3) alongside theoretical specific capacities of 775 mAh/g and 341 mAh/g, respectively, with BP3 doubling commercial graphite (372 mAh/g). For SIBs, multi-layer sodiation expands storage up to Na15BP3 and Na12BAs3, delivering ultrahigh capacities of 3875 mAh/g (BP3) and 1365 mAh/g (BAs3) at low voltages of 0.18 V and 0.15 V. Crucially, projected density of states (PDOS) analyses confirm that both frameworks preserve intrinsic metallic conductivity throughout all charging stages. These combined properties establish 2D BX3 monolayers as outstanding, structurally resilient anode candidates for next-generation LIB and SIB energy storage technologies.
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Statistical Mechanics · Cross-listed from physics.chem-ph
A Mesoscopic Ginzburg–Landau Model for Vibrational Strong Coupling Enhanced Rayleigh Scattering in Molecular Liquids
Wenxiang Ying and Abraham Nitzan
Recent experiments by Sandeep et al. [Angew. Chem. Int. Ed. 65, e16917 (2026)] suggest that vibrational strong coupling (VSC) in molecular
liquids can generate mesoscopic phenomena beyond single-molecule observables, including resonantly enhanced Rayleigh scattering, abrupt concentration thresholds, and thermal collapse. Motivated by these observations, we construct a mesoscopic Ginzburg–Landau model with two coupled fields: a cavity-controlled collective vibrational polarization $P$ and a secondary structural field $m$ whose long-wavelength susceptibility is renormalized by the collective vibrational polarization intensity $P^2$, assumed to govern long-wavelength density/dielectric fluctuations. With calibrated parameters, the model captures the observed Rayleigh enhancement, collective scaling relations, and threshold-like behavior, while explaining why polaritonic/IR signatures may persist when Rayleigh scattering disappears. The model further predicts enhanced long-wavelength density/dielectric correlations, enlarged mesoscopic correlation lengths, and slowed structural dynamics in the regime with strong Rayleigh enhancement, providing direct experimental tests through small-angle X-ray/
neutron scattering and dynamic light-scattering probes.
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Statistical Mechanics · Cross-listed from physics.flu-dyn
Circulation Statistics in Rayleigh-Bénard Convection
Giovanni Saisse, Roshan J. Samuel, Luca Moriconi et al. (+2 more)
Important statistical properties of velocity circulation in homogeneous isotropic
turbulence (HIT) have been unveiled in recent years, raising the question of whether they persist, or are modified, in other classes of turbulent flows. Motivated by the dominant role of small-scale structures in the circulation fluctuations of HIT, we investigate their relevance in direct numerical simulations of Rayleigh-Bénard convection at a Rayleigh number of $10^9$ and Prandtl number of $O(1)$. Within the thermal boundary layer (TBL), the distribution of elementary
vortices is found to be strongly correlated with the temperature field, while the statistics of their core aspect ratios is significantly altered. Additionally, the probability distribution functions of circulation, computed for planar contours which are parallel to the walls, display salient features closely akin to those observed in HIT, with the Area Rule (a connection between circulation statistics and minimal surfaces) remaining particularly well satisfied – except for a possible transitional region at a distance of a few TBL thicknesses. Away from the TBL, as expected, the overall statistical behavior of these structures likewise resembles that of HIT, where the intermittent spatial distribution of small
vortex tubes is instead determined by the energy dissipation field.
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All authors Giovanni Saisse, Roshan J. Samuel, Luca Moriconi, Jörg Schumacher, Katepalli R. Sreenivasan
Materials Science
exa-PD: A scalable high-performance workflow for multi-element phase diagram construction
Zhuo Ye, Feng Zhang, Maxim Moraru et al. (+4 more)
Exa-PD is a highly parallelizable workflow designed for the construction of multi-element phase diagrams (PDs). It uses standard sampling techniques, molecular dynamics (MD) and Monte Carlo (MC) as implemented in the LAMMPS package, to simultaneously sample multiple phases over a fine temperature-composition mesh for free-energy calculations. Parsl serves as the global workflow engine, coordinating large ensembles of MD and MC tasks to achieve massive parallelization with strong scalability. The resulting free energies of
liquid and solid phases are then fed to CALPHAD modeling via the PyCalphad package to construct multi-element PDs.
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All authors Zhuo Ye, Feng Zhang, Maxim Moraru, Weiyi Xia, Ying Wai Li, Yongxin Yao, Cai-Zhuang Wang
Strongly Correlated Electrons
Data-efficient reconstruction of critical quantum dynamics via blind fractional-envelope extrapolation
Hyunju Kim, Hyun-Yong Lee and Heung-Sik Kim
Simulating real-time dynamics of
quantum systems is often limited to short times by
entanglement growth. Finite-pole reconstructions such as linear prediction and related machineries extrapolate such data reliably when the spectrum is a finite set of excitations, but at criticality the low-energy spectrum is a power-law continuum $A(\omega)\sim|\omega|^{\alpha-1}$ – a branch cut whose real-time tail $G(t)\sim t^{-\alpha}$ finitely many poles cannot represent. Here we develop a fractional-calculus-motivated envelope extrapolation for such data. Its structure is motivated by a fractional form of Schwinger–Dyson (fSD) equation, in which the Laplace symbol $s^{\alpha}$ carries the branch cut analytically while the residual self-energy remains meromorphic. On real data we employ the corresponding operational alternative – the exponent $\alpha$ is selected blindly inside the fit window, the signal is detrended by $t^{\alpha}$, the residual is fitted by a stabilized finite-pole model, and the algebraic envelope is restored. On the critical XXZ chain this blind fractional-envelope method (fSD for short) extrapolates short-time data typically several-fold more accurately than finite-pole methods, with the exponent $\alpha$ identified blindly from the fit window alone and bracketing the closed-form Luttinger value at weak coupling. The same blind search finds the $z=2$ dilute-
magnon exponent $\alpha=1/2$ at the $\Delta=1$ saturation transition, and the advantage persists in the gapped free-
magnon phase with its sharp band edges. On noncritical dynamical mean-field spectra, whose low-frequency response is regular, fSD by contrast fails to select any stable fractional envelope and reduces to the standard pole result rather than manufacturing a spurious power law, making it an efficient and accurate route to
quantum critical dynamics when only short simulation times are accessible.
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Materials Science
Ab initio time-dependent GW approach for nonequilibrium exciton-phonon coupled dynamics across momentum space
Zhenfa Zheng, Benran Zhang, Jiawei Ruan et al. (+10 more)
The dynamics of optical excitations in materials generally involves intertwined electron-hole (e-h) and electron-
phonon (e-ph) interactions out of
equilibrium. However, a full theoretical description of such nonequilibrium dynamics requires a systematic treatment of the coherent excitonic excitations and
exciton-
phonon interactions across the entire
crystal momentum space in real time, which remains a major challenge and out of reach for first-principles approaches. Here, we present a new ab initio time-dependent adiabatic GW methodology that incorporates full finite-momentum e-h and e-ph couplings, enabling real-time simulations of the coherently coupled
exciton-
phonon dynamics. The excitonic excitations are naturally described by the equation of motion of the interacting single-particle density
matrix, whereas their couplings to
phonons are formulated within a linear-response framework, hence the simulations can be efficiently carried out within a primitive unit
cell. We demonstrate the capabilities of this new approach by investigating the direct-to-indirect
exciton transitions in monolayer WSe2 in a pump-probe setup of time-resolved and angle-resolved photoemission spectroscopy. Our results reveal that the
phonon-mediated ultrafast intervalley dynamics of
excitons of this system is within ~0.5 ps, manifested as in-gap photoemission intensity transfer from the K-valley to the Q-valley. This work establishes a comprehensive and practical nonequilibrium Green's function framework for accurately simulating nonequilibrium and coherent excitations involving coupled
excitons and
phonons from first principles.
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All authors Zhenfa Zheng, Benran Zhang, Jiawei Ruan, Chih-En Hsu, Zien Zhu, Supavit Pokawanvit, Felipe H. da Jornada, Hung-Chung Hsueh, Ting Cao, Mauro Del Ben, Yang-Hao Chan, Steven G. Louie, Zhenglu Li
Materials Science
Phase-Field Simulation of Dendrite Evolution in All-Solid-State Sodium Batteries during Cycling
Chengyin Wu, Wolfgang Windl, Jung-Hyun Kim et al. (+1 more)
Dendrite growth during cycling remains a critical challenge for all-solid-state batteries (SSBs), limiting the full realization of their inherent safety and high energy density. In particular, the mechanisms of continuous dendrite penetration during charge-discharge cycling remain poorly understood and are difficult to characterize experimentally. This study applies a phase-field model, informed by density functional theory calculations, to rationalize and visualize the dendrite penetration behaviors during cycling in sodium (Na) SSBs with pure Na or Na-Sb
alloy anodes and polycrystalline Na$_3$SbS$_4$ electrolyte. We show that dendrite stripping is intrinsically asymmetric with respect to plating due to grain boundary geometry, leading to the formation of isolated Na metal that persists between cycles. This residual Na metal becomes kinetically stabilized at grain-boundary junctions and is readily reactivated during subsequent plating, thereby accelerating and amplifying dendrite penetration. We further investigate the effects of applied voltage, solid-electrolyte microstructure, and anode chemistry on this phenomenon. These findings establish isolated Na metal as a key contributor for continued dendrite propagation in Na SSBs and provide design principles for stabilizing anode/electrolyte interfaces in Na SSBs.
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All authors Chengyin Wu, Wolfgang Windl, Jung-Hyun Kim, Yanzhou Ji
Mesoscale and Nanoscale Physics
Dynamical unmasking of $p$-wave magnetism by ac spin and dc orbital polarizations
Yantao Li, Jacob Linder and Pavlo Sukhachov
Odd-parity magnets have strong
spin polarization in momentum space but no net magnetization, making their
spin texture hidden from conventional magnetometry. We show that a monochromatic electric field dynamically lifts this cancellation in a $p$-wave magnet. Within each drive cycle, the field produces a net ac
spin polarization linear in the driving field whose interband component is resonantly enhanced at the nonrelativistic exchange gap. Because this polarization oscillates at the drive frequency, it vanishes upon period averaging. The orbital channel follows a different hierarchy: its linear response cancels in momentum space, whereas interband coherence produces a rectified dc orbital polarization at second order when the field has components parallel and transverse to the $p$-wave
spin-splitting direction. Together, the ac
spin and dc orbital responses dynamically unmask $p$-wave magnetism without requiring any
spin-orbit coupling.
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Statistical Mechanics
Fragmented ETH and Ensemble Inequivalence
C. L. Sriram, Soumya Kanti Pal and Lea F. Santos
We investigate thermalization in finite
quantum systems with strong long-range interactions. Nearly conserved quantities inherited from the fully connected limit organize the
Hilbert space into weakly coupled sectors and split the many-body spectrum into energy bands. Despite the resulting breakdown of global ergodicity,
quantum chaos develops within individual energy bands, enabling the definition of microcanonical ensembles within the bands. This supports a band-resolved formulation of thermalization, which we term fragmented eigenstate thermalization hypothesis (fETH). Unlike conventional ETH, finite-size scaling in fETH obeys a
symmetry-imposed selection rule that restricts which system sizes can be compared. This band-resolved description has consequences for
equilibrium statistical mechanics. While microcanonical ensembles remain confined to a single band, canonical ensembles mix different bands. This mismatch explains ensemble inequivalence without invoking
equilibrium phase transitions. Our results apply broadly to
Hamiltonians near a fully permutation-symmetric limit.
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Strongly Correlated Electrons
Field-induced first order transitions and phase coexistence in the Kitaev quantum spin liquid candidate BaCo2(AsO4)2
Tanner J. Legvold, Bin Gao, Rong-Zhu Lin et al. (+9 more)
BaCo2(AsO4)2 (BCAO) is an insulating Kitaev
quantum spin liquid candidate with a rich low-temperature phase diagram. Below 5 K, it exhibits double-zigzag
magnetic order. Upon application of an in-plane
magnetic field, the
magnetic structure first transforms into an up-up-down (UUD) state near 0.12 T and then enters a fully
spin-polarized
ferromagnetic (FM) state near 0.5 T. In the narrow field regime close to the polarized phase, a finite residual thermal conductivity has been reported, suggesting a possible field-induced
quantum spin liquid phase. Using
neutron scattering, we show that the field-induced double-zigzag-to-UUD transition near 0.15 T is accompanied by the emergence of a cluster of localized UUD
spin excitations that coexist with conventional
spin waves. Upon further increasing field, BCAO undergoes a first-order UUD-to-FM transition with coexistence of UUD and FM phases, accompanied by a sharp response in the
spin Seebeck coefficient. These results do not support a
quantum spin liquid scenario near the UUD-to-FM critical field. Instead, modeling indicates that the broad excitations arise from bound
spin-flip pairs, while a low-lying dispersive branch near the FM phase boundary carries the same sign of magnetization as the FM order. These excitations naturally account for the observed sign of the
spin Seebeck response and are likely relevant to the thermal conductivity near the critical field.
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All authors Tanner J. Legvold, Bin Gao, Rong-Zhu Lin, Violet Williams, Tong Chen, Dehong Yu, Chien-Lung Huang, Gage Eichman, Renjie Lui, Benedetta Flebus, Pengcheng Dai, Douglas Natelson
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Zi-Bo Jin and Yi Zhang
Non-Hermitian systems offer new opportunities for
quantum optimization and computation. Here, we show that non-Hermitian
quantum adiabatic
algorithms require not only a real, gapped spectrum, but also a stable pseudospectrum. We propose a novel framework by mapping non-
unitary quantum circuits to local
Hamiltonian paths, thereby preserving their optimization advantages and shallow depth. While a direct non-Hermitian extension of the Feynman-Kitaev construction suffers severe pseudospectral instability, our history-decoupled construction yields both a controlled pseudospectrum and a real, gapped spectrum. Using the CK
benchmark family of maximum independent set problems, we demonstrate
polynomial-
evolution-time non-Hermitian adiabatic computation that remains robust against perturbations. We further discuss a feasible optical implementation using coupled waveguides with an auxiliary lossy channel. Our work establishes pseudospectral stability, alongside real, gapped spectra, as key principles and a practical route for non-Hermitian
quantum adiabatic computation.
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Mesoscale and Nanoscale Physics
Nanoscale stray fields from micromagnets for optimal spin qubit architecture
Sandrine Lopes, Quentin Schaeverbeke, Matthieu M. Desjardins et al. (+3 more)
On-chip micromagnets generate local
magnetic-field asymmetries, enabling electrical control of
spin qubits via electric dipole
spin resonance and their integration into
circuit quantum electrodynamics (QED) architectures. Accurate prediction of
spin-
qubit performance requires modeling micromagnet stray fields beyond the saturated-magnet approximation, accounting for nonuniform magnetization. Here, we combine thin-film characterization of Co, Co/Ta multilayers, and CoFe films with nanoscale stray-field measurements using NV-center magnetometry in the unsaturated regime to establish a reliable micromagnetic simulation framework. We show that CoFe micromagnets generate antisymmetric fields in double
quantum-dot geometries exceeding +/- 100mT, owing to their high saturation magnetization and favorable magnetocrystalline anisotropy. For
spin qubits coupled to microwave resonators, the predicted
spin-
photon coupling reaches $\left| g_s/g_c \right| \approx 0.5$, where $g_c$ denotes the charge-
photon coupling strength of the underlying charge
qubit, highlighting the potential for high-fidelity operations in
circuit QED architectures.
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All authors Sandrine Lopes, Quentin Schaeverbeke, Matthieu M. Desjardins, Daniel Lacour, Michel Hehn, François Montaigne
Materials Science
Spontaneous Nanopatterning and Strain Relaxation in SiGe Layers Grown by Oxidative Solid Phase Epitaxy
Sophie E. Bierer, Trevor R. Smith, Arezoo Mafi et al. (+5 more)
The wafer-scale monolithic integration of III-V materials on Si would lead to revolutionary optoelectronic hardware for data, computing and other applications. However, heteroepitaxy of III-Vs on Si requires overcoming the large
lattice and thermal mismatches between the materials and reducing threading dislocations densities. In this work, we explore the oxidative solid phase epitaxy (SPE) of Ge+ implanted Si(111) to form ultra-thin strain-relieving SiGe metamorphic buffer layers for heteroepitaxy on Si. The SPE process is shown to result in a nanopatterning of the Ge concentration variation across the sample surface, visible by scanning and transmission electron microscopy (SEM and TEM). The concentration patterning is the result of a hexagonal network of Shockley partial dislocations at the SiGe/Si interface. Analyzing the pattern spacing observed by SEM is demonstrated as an easy, non-destructive method for obtaining the local strain state of SiGe layers. This work is important for engineering ultra-thin SiGe metamorphic buffer layers for III-V optoelectronics heteroepitaxy on the silicon platform.
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All authors Sophie E. Bierer, Trevor R. Smith, Arezoo Mafi, Sunzhuoran Wang, Chengqian Liao, Vatsalkumar Patel, Andrew P. Knights, Ryan B. Lewis
Disordered Systems and Neural Networks · Cross-listed from quant-ph
Locality of deep thermalisation through the lens of entanglement teleportation
Saptarshi Mandal, Alan Sherry and Sthitadhi Roy
Deep thermalisation characterises the emergence of universal
quantum state ensembles on subsystems due to projective measurements on their complement. We study the notion of locality, or lack thereof, in this phenomenon by considering a subsystem partitioned into two disjoint subregions which remain causally disconnected at all times under
unitary dynamics. We show that the onset of deep thermalisation in this geometry is fundamentally bounded by measurement-induced
entanglement teleportation between the subregions. While measurements on the environment generate
entanglement across the disconnected partitions – suggesting an apparent non-locality – we demonstrate that generic locally interacting systems exhibit an emergent locality. Specifically, the timescales for both deep thermalisation and
entanglement teleportation scale logarithmically with the distance separating the subregions. Exceptions to this include special
circuits where the randomness of the measurement outcomes is perfectly transmitted to the ensemble of states of the subsystem, conditioned on the outcomes; in such cases the timescale for deep thermalisation is finite leading to genuine non-locality.
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Strongly Correlated Electrons
Single-component twisted $\mathbb{Z}_3$ orthogonal metal in an $e/3$-anyon fluid
Zhaoyu Han, Ashvin Vishwanath and Eslam Khalaf
We propose an unconventional metallic phase emerging upon doping the $1/3$ Laughlin Fractional Chern
insulator, which can serve as a parent state to anyon superconductivity with arbitrary
chiral central charge. It is a twisted $\mathbb{Z}_3$ orthogonal metal: a state with vanishing electron quasiparticle weight but a single well-defined
Fermi surface of emergent charge-$e/3$
fermions coupled to a Dijkgraaf-Witten twisted $\mathbb{Z}_3$ gauge field. It is manifestly symmetric under the projective action of translations on the three low-energy valleys and is fully gapped in the valley sector. Pairing this fractionalized
Fermi surface then removes the topological order and produces a family of
superconductors whose
chiral central charge is directly set by the BdG band
topology of the paired $e/3$
fermions, while the angular momentum of the physical order parameter is constrained to be a multiple of three. This scenario provides a route to superconducting states beyond anyon-superconductivity constructions based on $2e/3$ anyons. The metallic phase itself carries distinctive “fractional Fermiology” signatures: $e/3$ shot noise, anomalous
quantum oscillations, and a $6\pi$ ac Josephson effect when it mediates the Josephson coupling between
superconductors. We construct explicit wavefunction ansatz realizing the phase, and discuss energetics considerations that might favor this state over competing metallic states. We show that the construction extends to higher Laughlin states but not to Jain states.
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Soft Condensed Matter
Mass-induced Mpemba effect in a polymer-bead system
Hosung Kwak, Yongjoo Baek and Hawoong Jeong
We propose a physically motivated model in which the Mpemba effect is induced by the system's inertia. The model describes a
polymer undergoing a denaturation transition whose force-extension curve contains a weak-force plateau that slows relaxation. In the presence of inertia, a farther initial state can reach and cross the plateau sooner, producing the Mpemba effect. Increasing the bead mass broadens the range of initial conditions over which this mechanism operates. A similar mechanism also generates the inverse Mpemba effect.
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Mesoscale and Nanoscale Physics
Long-range and steady-state entanglement of nitrogen vacancy centers using microwaves as a drive and synthetic antiferromagnet as a dissipator
Federico Garcia-Gaitan and Branislav K. Nikolic
The search for optimal schemes and dissipative environments that can mediate long-range
entanglement between two distant nitrogen-vacancy centers (NVCs) in diamond has been the subject of vigorous efforts over the past decade due to potential applications of such microscopic solid-state
qubits in
quantum sensing and
quantum computing. However, stabilizing
entanglement of NVCs into a steady state poses a significant challenge, typically requiring tuning the environment out of
equilibrium. Here we microscopically and rigorously derive a Lindblad
quantum master equation (QME) for a system of two driven-dissipative NVCs, where the drive is microwave radiation and dissipation is provided by a single
magnetic bath that is kept in
equilibrium. The jump operators within the Lindblad QME are expressed in terms of Keldysh Green's functions defined as correlators of dipolar field operators of the bath. This QME makes it possible to predict precise conditions for long-range and steady-state
entanglement of two NVCs, while suggesting that a synthetic antiferromagnet could be an optimal choice for a dissipative environment. By using realistic parameters from available experiments, we estimate steady-state concurrence reaching $\mathcal{C}\simeq 0.28$ for two NVCs separated by $\sim 100 \: \mathrm{nm}$.
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Materials Science · Cross-listed from quant-ph
Coulomb blockade in microscopic material defects as a source of decoherence and noise in solid-state quantum circuits
R. Banerjee, L. P. Lindoy, M. Hegedus et al. (+9 more)
A critical limitation of solid-state
quantum devices arises from the materials from which they are fabricated: uncontrolled surfaces, interfaces, and structural imperfections introduce numerous sources of loss and decoherence. Despite extensive efforts, linking these decoherence mechanisms to their microscopic material origins – essential for developing effective mitigation strategies – remains an outstanding challenge that has slowed coherence improvements. Here, using scanning gate microscopy on live superconducting
circuits we identify a previously unrecognised decoherence mechanism originating from Coulomb blockade and microwave-driven charge tunnelling in metallic grains. Such grains are ubiquitous in thin-film devices fabricated by standard lithography processes. By characterising multiple defects across different devices, we find such defects to be as common and as debilitating to device performance as two-level system (TLS) defects, while originating from a fundamentally different physical mechanism. Importantly, conventional characterisation techniques would misattribute this loss to other, microwave power-independent processes. Our observations thus reveal a widespread source of decoherence in superconducting
circuits, challenging the prevailing paradigm that coherence lifetimes are primarily limited by TLS defects. Eliminating metallic grains during fabrication provides a clear and practical route to suppress this mechanism, offering a pathway towards improved coherence and reduced noise in microwave-based solid-state
quantum devices.
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All authors R. Banerjee, L. P. Lindoy, M. Hegedus, A. Hutcheson, T. Hawkins, E. Daghigh-Ahmadi, S. Samaddar, T. Barker, J. P. Goff, A. Ya. Tzalenchuk, I. Rungger, S. E. de Graaf
Superconductivity
Altermagnetic spin textures coupled to superconductors: Domain wall spin-triplet superconductivity and supercurrent-induced torques
Yasir Dar, Mathias S. Scheurer and Constantin Schrade
Motivated by the absence of sizable stray fields and the recently discovered highly non-trivial impact of altermagnetic textures on itinerant electrons, we here study the form of Cooper pairs in spatially varying altermagnets coupled to conventional $s$-wave
superconductors. As a consequence of the detrimental impact of altermagnetism on
spin-singlet pairing and the local
symmetry reduction caused by textures in the
magnetic order parameter, we show that superconductivity predominantly impacts the regions between altermagnetic domains. Focusing on a planar radial domain wall for concreteness, we show that emergent Zeeman and
spin-orbit fields create spatially separated triplet hotspots and transitions between nodal and fully gapped superconducting regions, whose structure is set by both the domain wall and the altermagnetic order parameter. We also identify a reciprocal effect, where a supercurrent generates a quasiparticle-mediated quadrupolar torque that inherits the
symmetry of the altermagnetic order. Our results show that accounting for spatial inhomogeneities in the altermagnetic order parameter is essential for an understanding of the superconducting proximity effect and suggest that hybrid systems of altermagnetic textures and
superconductors offer unique opportunities for local engineering of Cooper pairs and for detecting altermagnetic order.
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Strongly Correlated Electrons
Fermiology of the kagome compound LuNb6Sn6 probed by de Haas-van Alphen oscillations
Tucker Beekmann, Caue Kaufmann Ribeiro, Kyryl Shtefiienko et al. (+4 more)
We report a detailed de Haas-van Alphen (dHvA) study of the recently discovered kagome metal LuNb6Sn6 using torque magnetometry, magnetization, and heat-capacity measurements. Temperature-dependent torque and heat-capacity data reveal a charge density wave (CDW) transition at T_CDW = 85 K. The thermal hysteresis observed in both measurements establishes the first-order nature of the transition.
Quantum oscillation measurements identify two major dHvA frequencies: F_alpha ~ 20 T and F_beta ~ 200 T, and their angular dependence is consistent with ellipsoidal
Fermi surface (FS) pockets. Landau fan diagram analysis reveals evidence for a nontrivial Berry phase associated with the F_alpha pocket, indicating possible nontrivial electronic
topology in LuNb6Sn6. Analysis of the temperature and
magnetic field dependence of the oscillations using the Lifshitz-Kosevich formula yields electronic parameters that indicate anisotropic
quantum transport properties. First-principles calculations provide further insight into the electronic structure, revealing Dirac-like band crossings, a flat band, and multiple van Hove singularities near the
Fermi level. Our calculations based on the pristine phase cannot fully reproduce the experimentally observed
quantum oscillation frequencies, suggesting that CDW-induced FS reconstruction plays a crucial role in the ground-state electronic structure of LuNb6Sn6. These results provide new insight into the FS
topology and electronic structure of LuNb6Sn6, enriching our understanding of the electronic properties of kagome materials.
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All authors Tucker Beekmann, Caue Kaufmann Ribeiro, Kyryl Shtefiienko, Jiaqiang Yan, Brenden R. Ortiz, Christopher A. Mizzi, Keshav Shrestha
Strongly Correlated Electrons · Cross-listed from hep-th
Analytical Structure and Spectroscopic Signatures of Quartic Nonlinear Electrodynamics in Holographic Fermion Systems
Vitor Neves da Silva and Luiz Antonio Barreiro
We investigate the effects of the leading string-inspired quartic correction $\alpha'^2F^4$ on
holographic fermions and charge transport in a bottom-up AdS$_4$/CFT$_3$ model. Working in the probe limit, we derive the nonlinear electrostatic background, obtain an exact first integral of the gauge equation, establish the associated constitutive relation, and identify the endpoint of the globally regular electrostatic branch. A nonlinear response function naturally emerges from the gauge sector and provides a unified description of the background, gauge-field fluctuations, and transport coefficients. Using these analytical backgrounds, we compute the fermionic retarded Green's function and spectral function. The quartic interaction shifts the
Fermi momentum, enhances the spectral weight, increases the renormalized
Fermi velocity, and reduces both momentum and energy linewidths, providing spectroscopic signatures consistent with enhanced quasiparticle coherence while preserving the
holographic Fermi surface. We further investigate optical and DC conductivities, showing that the nonlinear interaction redistributes the optical response from the infrared toward intermediate frequencies, whereas the DC conductivity is obtained analytically as $\sigma_{\mathrm{DC}}=\mathcal K(1)=\rho/E(1)$ and decreases monotonically with increasing nonlinear coupling. These results establish a direct connection between nonlinear bulk electrodynamics, momentum-resolved spectroscopic observables, and transport properties in the dual strongly coupled theory.
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Soft Condensed Matter
Catalytic Crosstalk: Cooperative Enzyme Dynamics in Artificial Crowded Environments
Rik Chakraborty, Manisha Jhajhria, Arnab Maiti et al. (+4 more)
In cellular environments, enzymes operate under densely crowded conditions that often hinder catalytic efficiency by limiting substrate
diffusion and essential conformational dynamics. While reports suggest that crowding can often lead to inhibition of enzyme's catalytic activity, persistent efficiency of cellular biochemistry hints at underlying cooperative mechanisms among these molecules. Here, we experimentally demonstrate catalytic crosstalk between two enzymes - catalase and urease - in artificially crowded environments. Our results reveal that when co-localized in dense media, these enzymes mutually enhance each other's catalytic activity and dynamic behavior. This cooperative interaction leads to a net increase in reaction rates and mobility, suggesting an emergent many-body effect in enzyme assemblies. Modeling enzymes as dimeric active particles, we propose a minimal simulation framework that qualitatively captures the observed synergy. Our findings show that inter-enzyme cooperation can counteract the detrimental effects of crowding, offering insights into how enzymatic efficiency is sustained in complex biological milieu.
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All authors Rik Chakraborty, Manisha Jhajhria, Arnab Maiti, Nividha, Priyanka, Snigdha Thakur, Krishna Kanti Dey
Superconductivity
High-Q superconducting microwave resonators using MBE titanium nitride
Anand Ithepalli, Haoran Lu, Eegene Clara Chung et al. (+9 more)
Using molecular beam epitaxy, we have realized thin films of titanium nitride (TiN) on c-plane sapphire that exhibit the lowest observed full-width at half maximum X-ray rocking curve width of 18 arcsec. Though the (111) oriented TiN exhibits an abrupt and crystalline interface with sapphire, for the first time we observe sub-surface defects in the sapphire substrate, which nucleate structural defects in the epitaxial TiN layer. Using quarter-wavelength coplanar waveguide (CPW) resonators in a 3 \textmu m/6 \textmu m/3 \textmu m gap/strip/gap lines in a hanger geometry, we find the internal quality factor of the TiN resonators to be $>10^{6}$ in the single-
photon $\langle n \rangle \sim 1$ limit at 5.8 GHz and 10 mK, rising to $>20 \times 10^{6}$ at $\langle n \rangle \sim 10^{6}$. The results are of high interest for applications of superconducting TiN in several areas, and provide a path towards epitaxial Josephson junctions with crystalline barriers in the future for high coherence
qubits.
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All authors Anand Ithepalli, Haoran Lu, Eegene Clara Chung, Xiangqin Wang, Amit Rohan Rajapurohita, Keun-Yeol Park, Celesta S. Chang, Peter McMahon, Huili Grace Xing, David Muller, Valla Fatemi, Debdeep Jena
Superconductivity
Magnetic Order in bilayer Ruddlesden-Popper Nickelates
Yiming Wang, Guijing Duan, Zhiguang Liao et al. (+3 more)
The recent discovery of high-temperature superconductivity in the
bilayer nickelate La$_3$Ni$_2$O$_7$ has led to extensive interest in the correlation physics of its normal state. Given that the superconducitivity develops near a density wave order in the phase diagram, it is important to elucidate the nature of this order. Based on the accumulated experimental evidence for a bad metal state in proximity to an orbital-selective Mott phase, here we describe
magnetic correlations of the system in a conceptually new way – in terms of effective local moments experiencing a combination of RKKY and superexchange interactions. This gives rise to a
magnetic order with a wavevector that is close to $\mathbf{Q}=(\pi/2,\pi/2)$ and, at the same time, yields a clear understanding of the associated
spin dynamics. Our results are consistent with the rapidly emerging experiments about the
magnetic correlations in the density wave order of the
bilayer nickelate. Implications for unconventional superconductivity in this and related multiorbital systems are discussed.
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All authors Yiming Wang, Guijing Duan, Zhiguang Liao, Kuan-Sen Lin, Rong Yu, Qimiao Si
Materials Science
Hyperfine driven spin relaxation of charge carriers in metal-halide perovskites
Guillaume Lague, Frédérick Bernardot, Mauricio Calvo et al. (+6 more)
Spin relaxation of localized charge carriers in
semiconductors is primarily governed by hyperfine interaction with the surrounding
nuclear spin bath. While this mechanism is well-established in III-V bulk materials and
quantum dots, its critical role in metal halide perovskites (MHPs) has only recently emerged. Their inverted band structure induces an unusual hierarchy of hyperfine couplings, with hole interactions dominating electron interactions, particurlaly in Pb-based perovskites. Here, we adapt a
spin relaxation model - originally developed for
muon spin spectroscopy - to provide an exact description of longitudinal
spin relaxation for localized carriers across arbitrary hyperfine correlation times. This approach is motivated by recent experimental evidence in MAPbI3, which places carrier
spins in an intermediate correlation regime, where conventional mono-exponential approximations fail. Our analysis reveals distinct hyperfine relaxation channels: electrons couple primarily to halogen
nuclei, whereas holes are governed by metal
nuclei. This leads to a key prediction - perovskites with lighter halogens and metal cations exhibit significantly extended
spin lifetimes. Applied to time-resolved Faraday rotation data obtained from two perovskite samples, our model extracts key microscopic parameters - including the carrier localization volume and hyperfine correlation time - demonstrating the necessity of the exact dynamical solution over a single-exponential approximation. These findings provide microscopic insight into hyperfine-driven
spin relaxation in MHPs and establish a robust framework for characterizing carrier localization and
spin dynamics.
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All authors Guillaume Lague, Frédérick Bernardot, Mauricio Calvo, Olfa Selmi, Sofia Masi, Christophe Testelin, Hernan Miguez, Ivan Mora-Sero, Maria Chamarro