Mesoscale and Nanoscale Physics
Topological Boundary States and the Edge Chain in Semi-Infinite Two-Dimensional Insulators
Ilya Iakoub, Nicolas Levasseur and Richard MacKenzie
We show that it is possible to compute the adiabatically protected edge and corner states of semi-infinite, two-dimensional, topological
insulators by considering the first layer of
lattice sites, what we call the "edge chain," independently from the bulk. We start by accepting this claim as an ansatz, then, using the Shemesh
theorem, we show that the edge states one finds using our procedure are adiabatically protected, provided we restrict ourselves to adiabatic evolutions that do not break chiral
symmetry. We show explicit examples of our method in a 2D extension of the SSH model, the SSH3 model, the Haldane model and the Breathing Kagome
Lattice.
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Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.str-el
Antiferromagnetism-altered plasmon dynamics
Yifan Su, Suheng Xu, Rocco A. Vitalone et al. (+17 more)
The interaction between plasmons and
magnons is a long-sought phenomenon with implications for fundamental physics and spintronics applications. In three-dimensional systems, this coupling is suppressed by the large mismatch in energy scales, but two-dimensional (2D) plasmons with gapless dispersion can overlap with
magnons over a broad spectral range. Despite numerous theoretical predictions, experimental observation of
magnon-plasmon interaction has remained elusive. In this work, we study a first-of-its-kind hybrid plasmon-
magnon platform based on 2D materials. By deploying scattering-type scanning near-field optical microscopy (s-SNOM) with terahertz radiation, we image propagating plasmon wavepackets at a
graphene/NiPS$_3$ interface and track their dynamics across the antiferromagnetic transition of NiPS$_3$. We observe a clear renormalization of the plasmon-polariton dispersion concurrent with the onset of antiferromagnetic order. With complementary Raman scattering and nano-terahertz spectroscopy, we unveil spectral weight redistribution and dielectric screening changes, potentially associated with the multi-
magnon continuum, as the underlying mechanism. These results provide solid evidence of coupling between plasmon and antiferromagnetic order, marking a cornerstone for a potential platform for hybrid
magnon-plasmon interactions in 2D materials, opening avenues for coherent
spin-plasmon devices and tunable terahertz spintronic components.
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All authors Yifan Su, Suheng Xu, Rocco A. Vitalone, Ziyu Liu, Emil Viñas Boström, Na Wu, Chun-Ying Huang, Zhuquan Zhang, Jaehoon Jung, Daniel G. Chica, Vinícius da Silveira Lan Avelar, Yiping Wang, Takashi Taniguchi, Kenji Watanabe, James C. Hone, Xiaoyang Zhu, Cory R. Dean, Xavier Roy, Angel Rubio, D. N. Basov
Mesoscale and Nanoscale Physics
Deterministic nanofabrication for engineering nanowire quantum dot devices
Tarun Patel, Matteo Pennacchietti, Greg Holloway et al. (+8 more)
Semiconductor quantum dots (QDs) are a leading platform for realising bright, wavelength-tunable sources of single and entangled
photon pairs for photonic
quantum technologies. Site-selected nanowire
quantum dots (NWQDs) are a promising platform for fabricating such photonic devices in a scalable manner. However, implementing additional structures around the photonic nanowire while maintaining its vertical growth geometry has remained a challenge. In this work, we develop a deterministic pick-and-place technique to conduct a vertical-to-vertical transfer of NWQDs from the growth substrate to arbitrary templates. Using this transfer technique, we enhance the
photon extraction efficiency to 75% by implementing a bottom gold mirror and tune the emission wavelength by 3.6 GHz via implementing electrostatic gates around the QD. Importantly, we measure low-multiphoton probability (g^(2)(0) = 0.002) and high indistinguishability (>80% for +/-100 ps) of the QD emission after the transfer process, yielding high-quality devices. These results demonstrate the repeatability and versatility of the developed transfer technique, which is an enabling step towards scalable single and entangled
photon sources.
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All authors Tarun Patel, Matteo Pennacchietti, Greg Holloway, Stephen R. Harrigan, Sayan Gangopadhyay, Anthony Drouin, Megha Jain, Dan Dalacu, Philip J. Poole, Sasan Vosoogh-Grayli, Michael E. Reimer
Mesoscale and Nanoscale Physics
Flux noise without flux tunability in superconducting qubits
Daniel Kruti and Roman-Pascal Riwar
Flux noise is unanimously recognised as a leading dephasing mechanism for flux-tunable superconducting
qubits. However, our microscopic understanding remains incomplete, and basic effects like Faraday's law of induction have only very recently come into focus. Based on a
quantum geometric description of the Faraday effect, we provide an in-depth derivation of the coupling of generic
magnetic sources to thin film superconducting structures, under appropriate consideration of the device geometry. We apply the resulting framework to time-varying
magnetic dipoles, describing surface or substrate
spins, as well as current-carrying flux lines. We show that flux noise not only affects dephasing, but also provides a fundamental limit for the
qubit quality factor - notably, even when the
qubit contains no loops and is thus nominally not flux-tunable. Assuming surface
spins as the origin for universal flux noise, we expect that this quality factor limit might be reached in the near term. For flux lines, we formulate a minimal safety distance to conserve the
qubit performance, potentially constraining the scale-up of
quantum hardware. This distance is boosted in the presence of large capacitor wings typical for transmons, due to a
lensing of the electromotive field which is largely independent of Meissner screening.
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Mesoscale and Nanoscale Physics
Tuning Andreev reflection and conductance in proximitized nanowires through the spin-orbit field direction
Leonardo Musca and Fabrizio Dolcini
We investigate the Andreev reflection (AR) and the nonlinear conductance in a normal-
superconductor junction realized with a proximitized
semiconductor nanowire exposed to a
magnetic field along its axis. We show that, while at zero energy the AR coefficient is determined by the topological phase of the superconducting side of the junction, at finite energy the AR is strongly affected by the directions of the Rashba
spin-orbit field characterizing the normal and the proximitized sides. The tunability of the AR and the nonlinear conductance as a function of the
spin-orbit misalignment angle is particularly pronounced when the proximitized side is in the topologically trivial phase. The
spin-orbit field direction is revealed to be an efficient knob to control the electron transport through the hybrid junction, realizing an electrically widely tunable device. The implementation in realistic setups is discussed.
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Mesoscale and Nanoscale Physics
Relaxation effects on Hartree-Fock ground states in twisted bilayer graphene at even integer fillings
Tianyu Kong, Alexander B. Watson, Lin Lin et al. (+2 more)
A standard approach for studying magic angle twisted bilayer
graphene (MATBG)'s correlated electronic phase diagram is to project the Coulomb interaction down to effective models only involving electrons in single-particle flat bands and some nearby remote bands. We provide a novel systematic derivation of a single-particle continuum model of MATBG's single-particle properties which incorporates structural relaxation while remaining in the Lagrangian frame. We project the Coulomb interactions down to electrons occupying the flat bands of this model and compute the Hartree-Fock many-body ground states at fillings $\nu = \pm 2$. We find that incorporating relaxation effects drives the model into a semi-metallic phase at $- 2$ because of particle-hole asymmetry in the relaxed model's single-particle dispersion and because the flat band wavefunctions become more concentrated leading to an enhanced Hartree potential. Our results corroborate recent ab initio density functional theory studies which also found semi-metallic phases at $-2$. We discuss potential explanations for why such phases have not been seen in experiments.
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All authors Tianyu Kong, Alexander B. Watson, Lin Lin, Mitchell Luskin, Kevin D. Stubbs
Mesoscale and Nanoscale Physics
Emergence of the magnetic octupole Rashba-Edelstein effect from spin-orbit entanglement
Hojun Lee and Seungyun Han
Magnetic multipoles have attracted growing interest as order parameters and dynamical degrees of freedom in unconventional magnets, yet it remains unclear how broadly they can emerge as active electronic degrees of freedom. Here, we show that
spin-orbit-entangled multiorbital states can host
magnetic octupole (MO) degrees of freedom. In Rashba systems, this gives rise to an MO Rashba texture accompanying the J-Rashba texture. Remarkably,
spin-orbital
entanglement can realize a pure-MO limit in which the
spin and orbital-angular-momentum textures vanish while the MO texture remains finite. An applied electric field converts this texture into a nonequilibrium MO polarization through an MO Rashba-Edelstein effect. Around the pure-MO regime, the MO Edelstein response dominates over the conventional
spin response, showing that multipolar responses need not be small corrections to dipolar
spin physics. Our results establish an interface-based route for electrically generating nonequilibrium multipolar
magnetic polarization in
spin-orbit-coupled systems.
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Mesoscale and Nanoscale Physics
QArray+: A physics-informed GPU-accelerated simulator for quantum dot arrays
Pranav Vaidhyanathan, Barnaby van Straaten, Alice Petrillo et al. (+6 more)
Semiconductor quantum-dot arrays are a compelling platform for scalable
quantum technologies, yet their practical operation is hindered by the complexity of tuning large-scale devices. Existing automation tools rely on simplified physical models—such as constant-capacitance approximations and
equilibrium Hubbard models—which assume instantaneous relaxation to a steady state. These frameworks fail in experimentally critical regimes where measurement rates exceed tunneling dynamics, necessitating more sophisticated non-
equilibrium control strategies. To bridge this gap, we introduce QArray+, an extension of the QArray framework that incorporates gate-dependent tunnel coupling and a
quantum open-system description of dissipative processes. This approach enables the unified simulation of coherent interdot charge-state hybridization and the non-
equilibrium latching dynamics essential for training robust machine-learning models for automated device operation. Implemented in JAX with GPU acceleration, QArray+ scales across GPUs and multi-node systems. For example, a charge stability diagram for a 100X100 grid of gate voltages over 64 dots can be computed in $\sim0.17\,\mathrm{s}$ on multiple GPUs. Since interdot interactions are short-ranged and the corresponding tuning corrections are local, simulations at these scales capture the physics relevant to even larger devices. These capabilities support high-throughput
dataset generation for automated device tuning.
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All authors Pranav Vaidhyanathan, Barnaby van Straaten, Alice Petrillo, Rahul Marchand, Edwin De Nicolo, Menno Veldhorst, Brucek Khailany, Taylor L. Patti, Natalia Ares
Mesoscale and Nanoscale Physics
Twist as a Mechanical Switch for Reconfigurable Stacking in h-BN
Gautham Vijayan, Zhaoheng Zhang, Kenji Watanabe et al. (+5 more)
Twistronics of layered materials has emerged as a highly active field due to its profound implications for
quantum electronics and materials engineering. However, the controllable manipulation of interlayer stacking remains a significant experimental challenge. Here, the homogeneous contact between hexagonal boron nitride layers is shown to be reproducibly switched between two distinct stable stacking configurations via an externally applied torque. Combining experiments and computational modelling, we identify the stacking order of these stable states as the commensurate AA and AB modes. These two states are associated with different rotational torque maxima, exhibiting an asymmetry ratio of 0.7, and distinct dynamics as a function of the twist angle. Moreover, the peak torque values scale linearly with contact area, highlighting the dominant role of edge elasticity in the twisting process. Given that the AA and AB stacking modes correspond to different out-of-plane electric polarization states, our findings offer a pathway for reconfigurable nano- and micro-electromechanical devices.
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All authors Gautham Vijayan, Zhaoheng Zhang, Kenji Watanabe, Takashi Taniguchi, Michael Urbakh, Oded Hod, Xiang Gao, Elad Koren
Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.mtrl-sci
From Goldene to Noblene: exhaustive enumeration of the ordered Au-Ag-Cu monolayer alloys
Marcelo Lopes Pereira Junior
Two-dimensional metals became a laboratory reality with the isolation of Goldene, a gold sheet one atom thick released by chemical exfoliation, which raises the question of what alloying can achieve on the same close-packed
lattice. Here we combine an exhaustive enumeration of derivative superstructures with density functional theory to map the ordered Au-Ag-Cu monolayer
alloys, relaxing every
symmetry-inequivalent arrangement up to four atoms per
cell and extending the set with larger
cells selected by a fitted model. We find that the arrangement of the atoms, and not their proportion, controls the mixing energy, since the spread among the orderings of a single composition is several times the step between neighboring compositions, one composition spans more than 50~meV/atom between two arrangements of the same three atoms, and at two compositions the arrangement decides the sign. The energetics is carried by a competition between Au-Cu contacts, which bind, and Ag-Cu contacts, which do not, and bulk enthalpies computed under the same protocol show that this chemistry is not uniformly rescaled in two dimensions, since Au-Cu orders more strongly in the monolayer than in the
crystal while the other two weaken. A pair model completed by an elastic size-mismatch term reproduces the computed energies to a few meV/atom and returns a composition landscape whose convex hull no balanced ternary composition reaches. One equimolar ordering, which we name Noblene, is the only structure in which every atom is surrounded exclusively by unlike species, and it is dynamically stable and metallic, and carries a Poisson's ratio above one half, higher than that of any of the three pure monolayers. Since Noblene sits on the
lattice that Goldene already realizes, the route that produced Goldene is a plausible starting point for its synthesis.
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Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.mtrl-sci
Spin Hall Magnetoresistance in Antiferromagnetic Insulators
Stephan Geprägs, Matthias Opel, Johanna Fischer et al. (+4 more)
Antiferromagnetic materials promise improved performance for spintronic applications, as they are robust against external
magnetic field perturbations and allow for faster magnetization dynamics compared to ferromagnets. The direct observation of the antiferromagnetic state, however, is challenging due to the absence of a macroscopic magnetization. We show that the
spin Hall magnetoresistance (SMR) is a versatile tool to probe the antiferromagnetic
spin structure via simple electrical transport experiments by investigating the easy-plane antiferromagnetic
insulators alpha-Fe2O3 (hematite) and NiO in bilayer
heterostructures with a Pt heavy-metal top electrode. While rotating an external
magnetic field in three orthogonal planes, we record the longitudinal and the transverse resistivities of Pt and observe characteristic resistivity modulations consistent with the SMR effect. We analyze both their amplitude and phase and compare the data to the results from a prototypical collinear ferrimagnetic Y3Fe5O12/Pt bilayer. The observed
magnetic field dependence is explained in a comprehensive model, based on two
magnetic sublattices and taking into account
magnetic field-induced modifications of the domain structure. Our results show that the SMR effect allows to readout the
spin configuration and to investigate magnetoelastic effects in antiferromagnetic multi-domain materials. We demonstrate that the SMR amplitude scales with the sum of the absolute sublattice magnetizations in ferrimagnetic and antiferromagnetic materials. In alpha-Fe2O3/Pt bilayers, we find an unexpectedly large SMR amplitude of 2.5E-3, twice as high as for prototype Y3Fe5O12/Pt bilayers, making the system particularly interesting for room-temperature antiferromagnetic spintronic applications.
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All authors Stephan Geprägs, Matthias Opel, Johanna Fischer, Philipp Schwenke, Matthias Althammer, Hans Huebl, Rudolf Gross
Mesoscale and Nanoscale Physics
Nonreciprocal Magnon Hanle Effect in Antiferromagnetic $\alpha$-Fe$_2$O$_3$
Janine Gückelhorn, Sebastián de-la-Peña, Monika Scheufele et al. (+8 more)
The precession of the
magnon pseudospin about the
equilibrium pseudofield, the latter capturing the nature of magnonic eigenexcitations in an antiferromagnet, gives rise to the
magnon Hanle effect. Its realization via electrically injected and detected
spin transport in an antiferromagnetic
insulator demonstrates its high potential for devices and as a convenient probe for
magnon eigenmodes and the underlying
spin interactions in the antiferromagnet. Here, we observe a non-reciprocity in the Hanle signal measured in alpha-Fe2O3 using two spatially separated Pt electrodes as
spin injector and detector. Interchanging their roles alters the detected
magnon spin signal. The recorded difference depends on the applied
magnetic field and reverses sign when the signal passes its nominal maximum at the so-called compensation field. Our findings unlock the high potential of antiferromagnetic magnonics towards the realization of electronics-inspired phenomena.
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All authors Janine Gückelhorn, Sebastián de-la-Peña, Monika Scheufele, Matthias Grammer, Matthias Opel, Stephan Geprägs, Juan Carlos Cuevas, Rudolf Gross, Hans Huebl, Akashdeep Kamra, Matthias Althammer
Mesoscale and Nanoscale Physics · Cross-listed from physics.optics
Exceptional Topological Signatures of Non-Hermitian Photonic Hopf-Link Braids
Samit Kumar Gupta
Non-Hermitian physics endows the non-Abelian systems with exceptional
topology characterized by non-commutative braid patterns. Interplay of distinct competing sources of non-Hermiticity may induce novel topological effects. Here, we provide a generalized Hatano-Nelson model with higher-order nonreciprocal hoppings, non-Abelian gauge fields, and staggered gain-loss processes showing the exceptional topological structure of the Hopf-link braids that undergoes a EP-mediated topological phase transition. We demonstrate that mixing multiple nonreciprocal channels drives the system into highly intricate, nested complex energy Hopf-link braids and expands the topological landscape up to higher-order braiding sectors. Furthermore, utilizing biorthogonal eigenvector tracking, we map the structural
evolution of the exceptional phase boundaries via the maximum Petermann factor in the phase angle parameter planes. We show that the gain-loss non-Hermiticity drives a topological crossover where the extended exceptional contours constrict into isolated regimes. The demonstration of EP-mediated topological phase transition of Hopf-link braids and the associated rich exceptional phase portraits may offer new physical insights with promising applications in robust, fault-tolerant communication channels and
quantum computing platforms.
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Mesoscale and Nanoscale Physics
Direct Observation of the Zigzag Edge States of a Supramolecular Diatomic Kagome Lattice
Ryohei Nemoto, Xiangzhi Meng, Behzad Mortezapour et al. (+11 more)
Lattice geometry plays a fundamental role in the behavior of Bloch electrons in a
crystal. The diatomic Kagome
lattice, an extension of the honeycomb and Kagome
lattices, is predicted to give rise to emergent and topological phenomena, but its experimental investigation has been limited thus far. Here, we fabricate a diatomic Kagome
lattice through self-assembly of a triptycene derivative with phenazine moieties (Trip-Phz)—a $\mathrm{C_3}$-symmetric, non-planar $\pi$-conjugated molecule. Our scanning tunneling microscopy (STM) observations show that Trip-Phz forms a highly ordered diatomic Kagome
lattice terminated by zigzag-type edges on the Pb(111) surface. Combined STM measurements and tight-binding calculations provide direct evidence for the existence of the edge states that correspond to those of
graphene. These states are topological edge states dictated by the quantization of the Zak phase and the bulk-edge correspondence.This work reveals an ideal platform for exploring
quantum materials with unique
lattice geometries using supramolecular technology.
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All authors Ryohei Nemoto, Xiangzhi Meng, Behzad Mortezapour, Alexander Weismann, Saya Nakano, Masahisa Tsuchiizu, Ryuichi Arafune, Noriaki Takagi, Sho Nakamura, Katsunori Wakabayashi, Rie Suizu, Richard Berndt, Takashi Uchihashi, Kunio Awaga
Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.mtrl-sci
'pySNOW': a Python Suite for the NanO-World
Sofia Zinzani, Gilberto Nardi, Giacomo Becatti et al. (+4 more)
In computational materials science, numerical simulations are indispensable tools for revealing atomic-scale processes. For building blocks of the nanoworld, such as nanoparticles and nanoalloys, atomistic simulations provide detailed insight into their behaviour under diverse conditions. These simulations enable the study of formation and growth mechanisms, transport phenomena, chemophysical stability, and chemical reactions, including catalytic processes. To unravel the complex structure–property relationships that characterise nanoobjects, it is crucial to develop robust and insightful representations of their atomistic structure at global and local scales. Such descriptions enhance our understanding of nanoparticle behaviour and play a key role in guiding their rational design in silico for targeted applications.
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All authors Sofia Zinzani, Gilberto Nardi, Giacomo Becatti, Davide Alimonti, Letícia F. Basso, Kevin Rossi, Francesca Baletto
Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.mtrl-sci
Chemical pressure and vacancies in crystals under nonhydrostatic stress
Michiel Sprik
Inhomogeneous stress is a driving force for
diffusion of vacancies in
crystals. The other way around a non-uniform distribution of vacancies induces stress. The accepted theory of composition-stress coupling in
crystals is Larché-Cahn (LC) theory. Composition is defined in terms of the population of
lattice sites with a limit of one-particle per site. Coupling is modelled by adding a compositional strain term to the elastic strain in the constitutive relation for stress. An alternative mechanism, proposed here, is letting the site binding energy vary with spatial (deformed) density. This generates a chemical pressure adding to the elastic stress. The governing equations for this model are derived using non-
equilibrium continuum thermodynamic methods. The gradient of the chemical pressure has a dual function acting both as the drift force for migration and as an effective internal one body force in the Cauchy equation for the elastic stress. The practical evaluation presented in the paper is restricted to
equilibrium properties. We examine the effect of externally applied non-hydrostatic stress, either in the form of surface tractions or a one-body force density (gravitation). The model system is a one component
crystal with a fixed number of
lattice sites. The number of particles can be variable but is always smaller than the number of
lattice sites. The linear elastic response is modelled by the standard Lamé stress tensor. The results for systems deformed by surface tractions are in qualitative agreement with LC theory allowing for differences in the expression for the elastic moduli. Deviations are more serious for the
crystal deformed by gravitation.
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Mesoscale and Nanoscale Physics
Rank-Selective Optical Tomography of Higher-Wave Altermagnetism
Meysam Bagheri Tagani, Carmine Autieri and Sahar Izadi Vishkayi
Identifying the spatial rank of higher-wave altermagnetic order optically is challenging because local electric-dipole response does not uniquely resolve distinct continuum harmonics. We show that finite
photon momentum turns one-
photon spin-resolved absorption into a rank-selective
tomography. For the planar $|m|=\ell$ sector of an even-parity $\ell$-wave component, a joint
Fourier projection in polarization and momentum angle isolates $\mathcal T_\ell\propto\eta_\ell q^{\ell-2}$, yielding the hierarchy $d:q^0$, $g:q^2$, and $i:q^4$; phase changes track rotations of the selected
magnetic harmonic. A Ward-consistent finite-$q$ microscopic calculation reproduces these powers without imposing them. Although discrete
crystal symmetry can generate lower-order local aliases, they are orthogonal to the selected momentum harmonic and cannot contaminate it below $q^{\ell-2}$. In MnTe, whose nonrelativistic parent order is three-dimensional $g$ wave while
spin–orbit coupling lowers the exact relativistic
spin-momentum-locking
symmetry, first-principles calculations show that more than $99.9\%$ of the
Fourier power of the Néel-projected $A$-region
spin-energy contrast remains in the parent $g$-wave-derived $m=3$ harmonic. Structured near fields place the required momentum window within experimental reach.
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Mesoscale and Nanoscale Physics
Direct observation of flat bands in near-magic-angle twisted bilayer CVD graphene
Gianluigi Baiardi, Alex Boschi, Giulia Piccinini et al. (+13 more)
Advances in chemical vapor deposition (CVD) growth have driven
graphene crystal quality to unprecedented levels, yet it is still unknown whether this route can realize the fragile flat-band and correlated states of the magic-angle (MA) twisted bilayer
graphene (TBG). Here, we report on the experimental observation by room-temperature nano-angle-resolved photoemission spectroscopy (nano-ARPES) of flat bands in a TBG sample close to the MA, assembled via a grow-and-stack protocol based on low-pressure CVD of
graphene on copper. Our study indicates electronic bands fully comparable to those measured in exfoliation-based samples and determines the size of the largest near-MA domain to be compatible with electronic transport experiments, motivating further experiments on flat band physics in CVD-
graphene.
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All authors Gianluigi Baiardi, Alex Boschi, Giulia Piccinini, Vaidotas Mišeikis, Lorenzo Cavicchi, Aaron Bostwick, Chris Jozwiak, Eli Rotenberg, Kenji Watanabe, Takashi Taniguchi, Marco Polini, Fabio Beltram, Antonio Rossi, Stiven Forti, Sergio Pezzini, Camilla Coletti
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Implementation of quantum gates by Floquet analysis of kicked quantum system
Andrea De Luca, Carola Ciaramelletti and Simone Paganelli
Precise control of multi-
qubit architectures remains a critical bottleneck in superconducting
quantum processors. In this work, we investigate the synthesis of high-fidelity
quantum operations and state transfer protocols within an extended superconducting linear chain, scaling from three to seven sites. Using Floquet theory, we model the periodic drive as a train of delta-like pulses, mapping the
quantum control problem onto quasi-energy resonance conditions. Combining the Baker-Campbell-Hausdorff expansion with Floquet spectral decomposition, we analytically identify optimal driving parameters, refined via the Covariance
Matrix Adaptation
Evolution Strategy (CMA-ES). In the three-
qubit architecture, this enables high-fidelity synthesis of the iSWAP gate. Extending to a seven-site chain, we implement periodic trains of finite-width Gaussian pulses to activate distinct double-excitation transport channels with ultra-short gate durations t_gate (~170 ns). This achieves a clear scale separation from energy-relaxation times (T1) typical of fixed-frequency transmon devices with tunable couplers, such as IBM
Quantum hardware. Finally, we
benchmark stability under realistic imperfections, revealing a heightened sensitivity to static parameter disorder at the sub-percent level (eta ~ 10^-3) driven by spectral crowding, and discuss how closed-loop
topologies could mitigate this constraint. This framework bridges time-periodic control theory and practical
quantum gate engineering.
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Mesoscale and Nanoscale Physics
Room-temperature local strain control of moiré excitons in MoS$_2$/WSe$_2$ heterobilayers
T. O. Oskolkova, Y. Koo, A. A. Shubnic et al. (+8 more)
Moiré superlattices in heterobilayers of atomically thin transition metal dichalcogenides provide a versatile platform for exploring
quantum many-body physics as they can trap
excitons, leading to the formation of quantized moiré
exciton states. However, such moiré
excitons have been predominantly studied at cryogenic temperatures, which severely limits their practical applications. Here, we demonstrate room-temperature activation and control of moiré
excitons in MoS$_2$/WSe$_2$ heterobilayers using local strain engineering. Applying mechanical strain with a modified atomic force microscopy tip, we observe a series of resonances attributed to interlayer
exciton states confined in the moiré potential. Power-dependent photoluminescence measurements elucidate the population dynamics of the moiré
exciton states, while controlled local strain enables continuous tuning of their emission wavelength to the center of the second telecom window. We provide a theoretical model that captures all experimentally observed features, including the unconventional spectral shape of the moiré
exciton emission. Our findings establish local tip-induced strain as a powerful tool for the on-demand manipulation of moiré
excitons, paving the way for room-temperature
quantum excitonic devices.
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All authors T. O. Oskolkova, Y. Koo, A. A. Shubnic, I. Yu. Chestnov, I. Choi, C. Cheng, D. Huang, T. Jiang, K.-D. Park, I. V. Iorsh, V. Kravtsov
Mesoscale and Nanoscale Physics
In silico design of magnonic lasing in constricted waveguides
Jean F. Oliveira da Silva, Rai M. Menezes and Milorad V. Milosevic
Analogue black-hole systems have been proposed in various physical platforms, including
magnetic materials, offering rich physics and promising applications such as wave lasing. However, their practical realization and characterization remain largely unexplored. Here, we present an in silico study of magnonic black-hole phenomena in constricted ferromagnetic waveguides driven by
spin-polarized currents. Using micromagnetic simulations with a two-dimensional Poisson solver to obtain realistic current-density profiles, we demonstrate the formation of a double-hole cavity bounded by analogue event horizons, enabling resonant
spin-wave amplification. We characterize the resonances as a function of
magnetic and
geometric parameters and identify the corresponding
spin-wave modes. We further show that gradual tapers enhance transmission by suppressing
spin-wave reflections, while interfacial Dzyaloshinskii-Moriya interaction can mimic the current-induced Doppler shift, substantially reducing the critical current density required for applications and, consequently, Joule heating. Finally, we demonstrate a
spin-wave
laser in which thermally excited
spin waves undergo selective amplification and coherent emission at well-defined resonance frequencies. These results provide design principles for magnonic analogues of gravitational systems and point toward their potential for advanced spintronic applications.
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Mesoscale and Nanoscale Physics · Cross-listed from math-ph
Heat transfer problem of a dense gas described by the Enskog equation with a modification of the Enskog factor
Shigeru Takata, Soma Sakata and Masanari Hattori
Heat transfer in a dense gas between two parallel plates is studied for assessing the quantitative difference of two variants of the Enskog equation, i.e., the original Enskog equation and the Enskog equation with a modified Enskog factor recently proposed in Phys. Rev. E 111, 065108 (2025). The main advantage of the latter is that the H
theorem, which the former lacks, has been established. The influence of the modification is assessed by comparing the macroscopic quantities in detail. It is found that the impact of this modification is quite limited and the two variants reasonably agree as a whole.
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Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.supr-con
Vortex-core Majorana coupling to a chiral edge in a $p_x+ip_y$ superconductor: Nonmonotonic spectral reorganization and coherent fermion-parity dynamics
Peiyao Liu and Yi Zhou
We study how
vortex–edge coupling reorganizes the low-energy sector of a finite two-dimensional \(p_x+ip_y\) superconducting disk as a function of the
vortex–boundary separation \(d\) and examine what this reorganization implies for the parity
memory associated with a prescribed
vortex-core Majorana wave packet, a resource relevant to Majorana-based
quantum operations. Bogoliubov–de Gennes calculations reveal nonmonotonic core–edge reorganization of the lowest positive-energy finite-disk eigenstate, with particularly rapid variation near \(d\simeq7\xi\), where \(\xi\) is the coherence length. To separate this eigenstate reorganization from the spectral representation of a prescribed state, we rigidly translate a centered-
vortex core-reference packet to each fixed
vortex position, restrict it to the target disk, and project it, without intermediate normalization, onto the particle-hole-complete low-energy subspace. For \(\Delta_0/E_F=0.36\) and disk radius \(R=30\xi\), the resulting retained norm exceeds \(0.98\) at all six sampled separations, \(4.25\leq d/\xi\leq8.25\), while, depending on \(d\), the spectral measure is concentrated near zero energy, fragmented over several low-energy levels, or dominated by finite-energy weight. Correspondingly, the signed parity correlator displays slow temporal variation, rapid coherent dephasing, or sign-changing oscillations, with possible finite-size recurrences at later times. Thus a large retained norm does not by itself imply spectral concentration or persistent parity
memory.
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Mesoscale and Nanoscale Physics
Persistence and emergence of quantum defects through pressure-induced phase changes
Alexander J Healey, Alan Salek, Christopher T-K Lew et al. (+15 more)
Extreme pressures can transform materials and their properties, but probing these in-situ is made challenging by the small sample volumes and access requirements demanded by diamond anvil
cells.
Quantum defects offer a route to local measurements under such conditions, yet their sensing performance can be dictated by pressure-induced changes in their own host material. On the other hand, pressure may also be harnessed as a tool to engineer and stabilize new
quantum defects with emergent functionalities. Here, we demonstrate both aspects within a unified platform based on optically active
spin-pair defects in hexagonal boron nitride (hBN). As robust
quantum sensors under pressure, these
spin-1/2 systems retain pressure-independent
spin resonances up to 20 GPa while maintaining or even enhancing their optical emission, in stark contrast to the
spin-1 boron-vacancy centre in the same material. Simultaneously, we show that compression acts as a means of
quantum defect engineering: the starting hBN undergoes an irreversible transformation into wurtzite boron nitride (wBN), during which the defect landscape is reconfigured.
Spin-pair sensors are seen to persist across this structural transition, however, depending on the starting material we also observe new, highly fluorescent defects in the wBN phase. These results establish
spin-pair defects in boron nitride as pressure-resilient
quantum sensors while highlighting high pressure itself as a versatile pathway for creating and tuning
quantum emitters.
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All authors Alexander J Healey, Alan Salek, Christopher T-K Lew, Zsolt Benedek, Brett C Johnson, Josiah E Hsi, Islay O Robertson, Kaijian Xing, Hiroshi Abe, Takeshi Ohshima, Kenji Watanabe, Takashi Taniguchi, Mehran Kianinina, Viktor Ivady, Igor Aharonovich, Dougal McCulloch, Jean-Philippe Tetienne, David A Broadway
Mesoscale and Nanoscale Physics
Complete Topological Classification with P and T Symmetries: Revealing a Topological Invariant Invisible to K-Theory
Chen Zhang and Y. X. Zhao
The K-theoretic framework provides a complete topological classification of the tenfold
symmetry classes and has been generalized to incorporate crystalline
symmetries. Here, we show that this classification is incomplete even in the elementary case of spinless systems possessing both P and T
symmetries. We obtain the complete classification through a first-principles analysis of the topological classes of P- and T-symmetric bands, namely, by classifying the corresponding symmetric clutching data. We identify a topological invariant that is invisible from the K-theoretic perspective when the occupied states at each inversion-invariant momentum have uniformly positive or uniformly negative parity. In special cases, such as when all inversion-invariant momenta have uniformly positive parity, this invariant can be interpreted as the second Stiefel–Whitney class or the Euler number defined over an inversion fundamental domain, namely, half of the Brillouin zone. Our work not only reveals a new topological invariant that cannot be determined from the parity spectra at inversion-invariant momenta under P and T
symmetries, but also demonstrates the existence of crystalline topological phases that are absent from the K-theoretic classification.
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Mesoscale and Nanoscale Physics · Cross-listed from cond-mat.mtrl-sci
Symmetry-enforced third-order nonlinear thermal Hall effects in altermagnets
Yun-Mei Li, Jiacheng Yao, Hua Wang et al. (+1 more)
Thermal Hall effect (THE) is a powerful probe of material properties, even in
insulators. Here we investigate the thermal response of altermagnets by developing a theory on Berry
curvature driven nonlinear THE from both electrons and
magnons. We identify
symmetry conditions under which the third-order THE dominates while linear and second-order contributions vanish. Notably, d-wave and i-wave altermagnets with out-of-plane Neel order satisfy these conditions, whereas in-plane order yields a dominant linear THE. Using KV2Se2O (a d-wave altermagnetic metal) and MnF2 (an altermagnetic
insulator) as concrete examples, we show nonzero third-order nonlinear THE from electrons and
magnons, respectively, both exhibiting a pi-periodic dependence on the direction of temperature gradient. These
symmetry-guaranteed Berry
curvature phenomena provide a diagnostic for altermagnetism in candidate materials and enable determination of the Neel vector orientation.
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All authors Yun-Mei Li, Jiacheng Yao, Hua Wang, Kai Chang