Showing 1–50 of 148 results for author: Ma, R

Laterally Differentiated Polymorphs: a route to multifunctional nanostructures

Authors: Pete E. Lauer, Kensuke Hayashi, Yuichiro Kunai, Ondřej Wojewoda, Jan Klíma, Ekaterina Pribytova, Michal Urbánek, Aubrey Penn, Takayuki Kikuchi, Renzhi Ma, Takayoshi Sasaki, Takaaki Taniguchi, Caroline A. Ross

Abstract: Multifunctional materials can exhibit emergent behavior from the coupling of two or more different properties. For example, coupling between magnetic and ferroelectric order enables electrical control of the magnetic state, enabling for example magnetoelectric memory or logic devices that combine the nonvolatility of magnetic order with the energy efficiency of voltage control. Magnetic iron garne… ▽ More Multifunctional materials can exhibit emergent behavior from the coupling of two or more different properties. For example, coupling between magnetic and ferroelectric order enables electrical control of the magnetic state, enabling for example magnetoelectric memory or logic devices that combine the nonvolatility of magnetic order with the energy efficiency of voltage control. Magnetic iron garnets have outstanding magnonic and magnetooptical properties making them valuable in a range of technologies, but they have not been successfully incorporated into thin film two-phase magnetoelectric nanocomposites. Taking advantage of heterogeneously patterned substrates, this work demonstrates the engineering of garnet-perovskite composites in which both phases are polymorphs with the same composition but dramatically different structures and properties. Applying an electric field to the perovskite phase modulates the magnon dispersion and magnetooptical response of the garnet, opening a path to voltage-controlled garnet devices. △ Less

Submitted 8 April, 2026; originally announced April 2026.

Physics-informed neural operator for predictive parametric phase-field modelling

Authors: Nanxi Chen, Airong Chen, Rujin Ma

Abstract: Predicting the microstructural and morphological evolution of materials through phase-field modelling is computationally intensive, particularly for high-throughput parametric studies. While neural operators such as the Fourier neural operator (FNO) show promise in accelerating the solution of parametric partial differential equations (PDEs), the lack of explicit physical constraints, may limit ge… ▽ More Predicting the microstructural and morphological evolution of materials through phase-field modelling is computationally intensive, particularly for high-throughput parametric studies. While neural operators such as the Fourier neural operator (FNO) show promise in accelerating the solution of parametric partial differential equations (PDEs), the lack of explicit physical constraints, may limit generalisation and long-term accuracy for complex phase-field dynamics. Here, we develop a physics-informed neural operator framework to learn parametric phase-field PDEs, namely PF-PINO. By embedding the residuals of phase-field governing equations into the data-fidelity loss function, our framework effectively enforces physical constraints during training. We validate PF-PINO against benchmark phase-field problems, including electrochemical corrosion, dendritic crystal solidification, and spinodal decomposition. Our results demonstrate that PF-PINO significantly outperforms conventional FNO in accuracy, generalisation capability, and long-term stability. This work provides a robust and efficient computational tool for phase-field modelling and highlights the potential of physics-informed neural operators to advance scientific machine learning for complex interfacial evolution problems. △ Less

Submitted 10 March, 2026; originally announced March 2026.

Confinement-Induced Symmetry Breaking of Active Surfaces

Authors: Da Gao, Alexander Mietke, Rui Ma

Abstract: The actomyosin cortex, a thin layer of a cross-linked polymer network near the cell surface, generates active forces that are responsible for cell shape changes. Many developmental processes that involve such cell shape changes, most prominently embryonic cell division, are spatially confined by eggshells. To investigate the potential role of confinement in redirecting active stresses and enabling… ▽ More The actomyosin cortex, a thin layer of a cross-linked polymer network near the cell surface, generates active forces that are responsible for cell shape changes. Many developmental processes that involve such cell shape changes, most prominently embryonic cell division, are spatially confined by eggshells. To investigate the potential role of confinement in redirecting active stresses and enabling symmetry breaking phenomena during cell shape transformations, we study a hydrodynamic minimal model in which the cell cortex is represented as an active fluid surface that undergoes symmetric division in the absence of confinement. When enclosed by an ellipsoidal shell, a spontaneous symmetry-breaking transition emerges at a critical degree of confinement, where symmetrically dividing surfaces become unstable and polarized geometries appear. We show that this transition is controlled by the tightness of the confinement and analyze the solution space of stationary surfaces to identify the mechanisms underlying confinement-induced symmetry breaking. △ Less

Submitted 24 February, 2026; originally announced February 2026.

Comments: 20 pages,10 figures

Average Categorical Symmetries in One-Dimensional Disordered Systems

Authors: Yabo Li, Meng Cheng, Ruochen Ma

Abstract: We study one-dimensional disordered systems with average non-invertible symmetries, where quenched disorder may locally break part of the symmetry while preserving it upon disorder averaging. A canonical example is the random transverse-field Ising model, which at criticality exhibits an average Kramers-Wannier duality. We consider the general setting in which the full symmetry is described by a… ▽ More We study one-dimensional disordered systems with average non-invertible symmetries, where quenched disorder may locally break part of the symmetry while preserving it upon disorder averaging. A canonical example is the random transverse-field Ising model, which at criticality exhibits an average Kramers-Wannier duality. We consider the general setting in which the full symmetry is described by a $G$-graded fusion category $\mathcal{B}$, whose identity component $\mathcal{A}$ remains exact, while the components with nontrivial $G$-grading are realized either exactly or only on average. We develop a topological holographic framework that encodes the symmetry data of the 1D system in a 2D topological order $\mathcal{Z}[\mathcal{A}]$ (the Drinfeld center of $\mathcal{A}$), enriched by an exact or, respectively, average $G$ symmetry. Within this framework, we obtain a complete classification of anomalies and average symmetry-protected topological (SPT) phases: when the components with nontrivial $G$-grading are realized only on average, the symmetry is anomaly-free if and only if $\mathcal{Z}[\mathcal{A}]$ admits a magnetic Lagrangian algebra that is invariant under the permutation action of $G$ on anyons. When an anomaly is present, we show that the ground state of a single disorder realization is long-range entangled with probability one in the thermodynamic limit, and is expected to exhibit power-law Griffiths singularities in the low-energy spectrum. Finally, we present an explicit, exactly solvable lattice model based on a symmetry-enriched string-net construction. It yields trivial ground state ensemble in the anomaly-free case, and exhibits exotic low-energy behavior in the presence of an average anomaly. △ Less

Submitted 9 February, 2026; originally announced February 2026.

Comments: 29+5 pages, 7 figures

Quantum Entanglement and Teleportation of Magnons in Coupled Spin Chains

Authors: Zian Xia, Ruoban Ma, Chang Shu, Huaiyang Yuan, Jiang Xiao

Abstract: This study explores how entanglement and quantum teleportation of magnons can be achieved in coupled spin chain systems. By utilizing different magnetic configurations, we show that parallel spin chains function like magnonic beam splitters, whereas anti-parallel chains produce two-magnon squeezing and strong entanglement. Combining these components, we design magnonic circuits capable of continuo… ▽ More This study explores how entanglement and quantum teleportation of magnons can be achieved in coupled spin chain systems. By utilizing different magnetic configurations, we show that parallel spin chains function like magnonic beam splitters, whereas anti-parallel chains produce two-magnon squeezing and strong entanglement. Combining these components, we design magnonic circuits capable of continuous-variable quantum entanglement and teleportation, supported by quantum Langevin simulations. △ Less

Submitted 19 January, 2026; originally announced January 2026.

Comments: 9 pages, 4 figures

Unified Geometric Perspective for Spin-1 Systems: Bridging Nematic Director and Majorana Stars

Authors: Jiangnan Biguo, Rourou Ma

Abstract: We present a unified geometric approach for spin-1 systems that connects seemingly distinct geometric representations such as the nematic director, the Cartesian representation and the Majorana stellar representation. Starting from a product state of two distinguishable spin-1/2 particles, we provide a direct way to capture crucial geometric information. This perspective reveals the fundamental in… ▽ More We present a unified geometric approach for spin-1 systems that connects seemingly distinct geometric representations such as the nematic director, the Cartesian representation and the Majorana stellar representation. Starting from a product state of two distinguishable spin-1/2 particles, we provide a direct way to capture crucial geometric information. This perspective reveals the fundamental interplay between subspace projection and geometric constraints. This approach effectively maps magnetic solitons onto a kink model, allowing us to derive their equations of motion, a task not readily achieved with traditional methods. This simplified dynamical description reveals that the novel transition of these solitons in a harmonic trap corresponds to a fundamental transformation between kink and dip structures in the underlying geometry. △ Less

Submitted 11 January, 2026; originally announced January 2026.

Comments: 5 pages, 2 figures

Wigner polarons reveal Wigner crystal dynamics in a monolayer semiconductor

Authors: Lifu Zhang, Liuxin Gu, Haydn S. Adlong, Arthur Christianen, Eugen Dizer, Ruihao Ni, Rundong Ma, Suji Park, Houk Jang, Takashi Taniguchi, Kenji Watanabe, Ilya Esterlis, Richard Schmidt, Atac Imamoglu, You Zhou

Abstract: Wigner crystals, lattices made purely of electrons, are a quintessential paradigm of studying correlation-driven quantum phase transitions. Despite decades of research, the internal dynamics of Wigner crystals has remained extremely challenging to access, with most experiments probing only static order or collective motion. Here, we establish monolayer WSe2 as a new materials platform to host zero… ▽ More Wigner crystals, lattices made purely of electrons, are a quintessential paradigm of studying correlation-driven quantum phase transitions. Despite decades of research, the internal dynamics of Wigner crystals has remained extremely challenging to access, with most experiments probing only static order or collective motion. Here, we establish monolayer WSe2 as a new materials platform to host zero-field Wigner crystals and then demonstrate that exciton spectroscopy provides a direct means to probe both static and dynamic properties of these electron lattices. We uncover striking optical resonances that we identify as Wigner polarons, quasiparticles formed when the electron lattice is locally distorted by exciton-Wigner crystal coupling. We further achieve all-optical control of spins in the Wigner crystal, directly probing valley-dependent Wigner polaron scattering well above the magnetic ordering temperature and in the absence of any external magnetic field. Finally, we demonstrate optical melting of the Wigner crystal and observe intriguingly different responses of the umklapp (static) and Wigner polaron (dynamic) resonances to optical excitation. Our results open up exciting new avenues for elucidating electron dynamics and achieving ultrafast optical control of interaction-driven quantum phase transitions in strongly correlated electron systems. △ Less

Submitted 18 December, 2025; originally announced December 2025.

Comments: Main Text and Supplementary Information

Atomic Visualization of Bulk and Surface Superconductivity in Weyl Semimetal γ-PtBi2

Authors: Hao Zhang, Hui Chen, Zichen Huang, Zi-Ang Wang, Guangyuan Han, Ruisong Ma, Xiangde Zhu, Wei Ning, Chengmin Shen, Qing Huan, Hong-Jun Gao

Abstract: A bulk superconductor hosting intrinsic surface superconductivity provides a unique platform to study Majorana bound states. The superconductor, trigonal γ-PtBi2, is a promising candidate, as surface superconducting gaps and topological surface states have been observed. However, the simultaneous presence of bulk and surface superconductivity has not been resolved. Here, we directly visualize coex… ▽ More A bulk superconductor hosting intrinsic surface superconductivity provides a unique platform to study Majorana bound states. The superconductor, trigonal γ-PtBi2, is a promising candidate, as surface superconducting gaps and topological surface states have been observed. However, the simultaneous presence of bulk and surface superconductivity has not been resolved. Here, we directly visualize coexisting bulk and surface superconducting gaps in trigonal PtBi2 by using ultra-low-temperature scanning tunneling microscopy/spectroscopy. The bulk gap is Δ ~ 0.053 meV with a critical temperature (Tc) ~ 0.5 K and a critical field below 0.01 T, accompanied by a vortex lattice and bound states, yielding a coherence length of ~200 nm. Remarkably, certain surface regions show a much larger gap of Δ ~ 0.42 meV, persisting up to Tc ~ 3 K and surviving magnetic fields up to 2 T, yet lacking a static vortex lattice. This coexistence of robust surface and bulk superconductivity establishes γ-PtBi2 as a unique platform for investigating the interplay between bulk and surface Cooper pairings in superconducting topological materials. △ Less

Submitted 19 November, 2025; originally announced November 2025.

Journal ref: Chin. Phys. Lett. 42, 120708 (2025)

Charge stripe and superconductivity tuned by interlayer interaction in a sign-problem-free bilayer extended Hubbard model

Authors: Runyu Ma, Zenghui Fan, Hongxin Liu, Tianxing Ma, Hai-Qing Lin

Abstract: Competing orders represent a central challenge in understanding strongly correlated systems. In this work, we employ projector quantum Monte Carlo simulations to study a sign-problem-free bilayer extended Hubbard model. In this model, a charge stripe phase, characterized by a peak at momentum $k_x=2πδ$ is induced by highly anisotropic interlayer spin-exchange coupling $J_z$, and strongly suppresse… ▽ More Competing orders represent a central challenge in understanding strongly correlated systems. In this work, we employ projector quantum Monte Carlo simulations to study a sign-problem-free bilayer extended Hubbard model. In this model, a charge stripe phase, characterized by a peak at momentum $k_x=2πδ$ is induced by highly anisotropic interlayer spin-exchange coupling $J_z$, and strongly suppressed upon introducing the spin-flip term $J_\bot$; in contrast, \(J_\perp\) favors the emergence of interlayer pairing superconductivity. We further demonstrate that the anisotropy of the interlayer spin-exchange directly governs the competition between these two phases, while the on-site interaction \(U\) plays a complex role in tuning both the charge stripe and superconductivity. Our work identifies the key factors driving charge stripe formation, highlights the sensitivity of both the charge stripe and superconducting phases to interaction parameters, and thereby provides valuable insights into competing orders in strongly correlated systems. △ Less

Submitted 28 October, 2025; originally announced October 2025.

Comments: 6 pages and 6 figures

The Superconducting Transition due to the spontaneous Interlayer Loop Current fluctuations

Authors: Zenghui Fan, Runyu Ma, Stefano Chesi, Congjun Wu, Tianxing Ma

Abstract: Loop currents, as an orbital magnetism, have been proposed as a possible fluctuation mechanism for superconducting pairing, which always remains elusive. Here, we investigate the role of an interlayer loop current fluctuation in mediating superconductivity using an unbiased bilayer $t-J_{\perp}-V$ model via sign-problem-free projector quantum Monte Carlo simulations. The model spontaneously genera… ▽ More Loop currents, as an orbital magnetism, have been proposed as a possible fluctuation mechanism for superconducting pairing, which always remains elusive. Here, we investigate the role of an interlayer loop current fluctuation in mediating superconductivity using an unbiased bilayer $t-J_{\perp}-V$ model via sign-problem-free projector quantum Monte Carlo simulations. The model spontaneously generates the interlayer loop current by breaking time-reversal and translational symmetries, favored by interlayer Coulomb repusion. With hole doping, the loop current is rapidly suppressed, while its fluctuations give rise to an interlayer $s$-wave superconductivity. Our results establish a phase diagram to demonstrate a superconducting transition due to the interlayer loop current fluctuations. It also provides possible insights into some physics related to bilayer nickelates, with which it shares a similar structure and a large interlayer spin exchange. △ Less

Submitted 22 October, 2025; originally announced October 2025.

Comments: MAIN TEXT: 7 pages, 5 figures; SUPPLEMENTARY MATERIALS(attached in the end): 2 pages, 4 figures

Circuit-based characterization of finite-temperature quantum phases and self-correcting quantum memory

Authors: Ruochen Ma, Vedika Khemani, Shengqi Sang

Abstract: Quantum phases at zero temperature can be characterized as equivalence classes under local unitary transformations: two ground states within a gapped phase can be transformed into each other via a local unitary circuit. We generalize this circuit-based characterization of phases to systems at finite-temperature thermal equilibrium described by Gibbs states. We construct a channel circuit that appr… ▽ More Quantum phases at zero temperature can be characterized as equivalence classes under local unitary transformations: two ground states within a gapped phase can be transformed into each other via a local unitary circuit. We generalize this circuit-based characterization of phases to systems at finite-temperature thermal equilibrium described by Gibbs states. We construct a channel circuit that approximately transforms one Gibbs state into another provided the two are connected by a path in parameter space along which a certain correlation-decay condition holds. For finite-dimensional systems of linear size $L$ and approximation error $ε$, the locality of the circuit is ${\rm polylog}({\rm poly}(L)/ε)$. The correlation-decay condition, which we specify, is expected to be satisfied in the interior of many noncritical thermal phases, including those displaying discrete symmetry breaking and topological order. As an application, we show that any system in the same thermal phase as a zero-temperature topological code coherently preserves quantum information for a macroscopically long time, establishing self-correction as a universal property of thermal phases. As part of the proof, we provide explicit encoding and decoding channel circuits to encode information into, and decode it from, a system in thermal equilibrium. △ Less

Submitted 24 December, 2025; v1 submitted 18 September, 2025; originally announced September 2025.

Towards a hybrid 3D transmon qubit with topological insulator-based Josephson junctions

Authors: Sheng-Wen Huang, Ramya Suresh, Jian Liao, Botao Du, Zachary Miles, Leonid P. Rokhinson, Yong P. Chen, Ruichao Ma

Abstract: Superconducting quantum circuits provide a versatile platform for studying quantum materials by leveraging precise microwave control and utilizing the tools of circuit quantum electrodynamics (QED). Hybrid circuit devices incorporating novel quantum materials could also lead to new qubit functionalities, such as gate tunability and noise resilience. Here, we report experimental progress towards a… ▽ More Superconducting quantum circuits provide a versatile platform for studying quantum materials by leveraging precise microwave control and utilizing the tools of circuit quantum electrodynamics (QED). Hybrid circuit devices incorporating novel quantum materials could also lead to new qubit functionalities, such as gate tunability and noise resilience. Here, we report experimental progress towards a transmon-like qubit made with a superconductor-topological insulator-superconductor (S-TI-S) Josephson junction using exfoliated BiSbTeSe2. We present a design that enables us to systematically characterize the hybrid device, from DC transport of the S-TI-S junction, to RF spectroscopy, to full circuit QED control and measurement of the hybrid qubit. In addition, we utilize a high-quality-factor superconducting cavity to characterize material and fabrication-induced losses, thereby guiding our efforts to improve device quality. △ Less

Submitted 22 June, 2025; originally announced June 2025.

Graphene Nanoribbons as a Majorana Platform

Authors: Ruize Ma, Michele Pizzochero, Gaurav Chaudhary

Abstract: Graphene nanoribbons support a range of electronic phases that can be controlled via external stimuli. Zigzag-edged graphene nanoribbons (ZGNRs), in particular, exhibit an antiferromagnetic insulating ground state that transitions to a half-metallic phase under a transverse electric field or when embedded inside hexagonal Boron Nitride. Here, we consider a simple model of a heterostructure of a ZG… ▽ More Graphene nanoribbons support a range of electronic phases that can be controlled via external stimuli. Zigzag-edged graphene nanoribbons (ZGNRs), in particular, exhibit an antiferromagnetic insulating ground state that transitions to a half-metallic phase under a transverse electric field or when embedded inside hexagonal Boron Nitride. Here, we consider a simple model of a heterostructure of a ZGNR with an Ising superconductor and show that, the Ising superconductor with a parent s-wave spin-singlet pairing can induce spin-triplet odd-parity pairing in the half-metallic phase of the ZGNR. The resulting superconducting phase is topologically nontrivial, with gate-tunable transitions that enable the emergence of Majorana zero modes. △ Less

Submitted 14 July, 2025; v1 submitted 17 June, 2025; originally announced June 2025.

Breathing-Driven Metal-Insulator Transition in Correlated Kagome Systems

Authors: Qingzhuo Duan, Zixuan Jia, Zenghui Fan, Runyu Ma, Jingyao Meng, Bing Huang, Tianxing Ma

Abstract: Inspired by the recent discovery of breathing kagome materials \(\rm Nb_3Cl_8\) and \(\rm Nb_3TeCl_7\), we have explored the influence of the breathing effect on the Hubbard model of the kagome lattice. Utilizing the determinant quantum Monte Carlo method, we first investigated the average sign problem in the breathing kagome lattice, which is significantly affected by both the breathing strength… ▽ More Inspired by the recent discovery of breathing kagome materials \(\rm Nb_3Cl_8\) and \(\rm Nb_3TeCl_7\), we have explored the influence of the breathing effect on the Hubbard model of the kagome lattice. Utilizing the determinant quantum Monte Carlo method, we first investigated the average sign problem in the breathing kagome lattice, which is significantly affected by both the breathing strength and the interaction strength. Secondly, we calculated the electronic kinetic energy, the direct current conductivity, and the electronic density of states at the Fermi level to determine the critical interaction strength for the metal-insulator transition. Our results indicate that the breathing effect, in conjunction with the interaction strength, drives the kagome system from a metal to an insulator. Finally, we evaluated the magnetic properties and constructed a phase diagram incorporating both transport and magnetic properties. The phase diagram reveals that as the interaction strength increases, the system transitions from a paramagnetic metal to a Mott insulator. Our research provides a theoretical guidance for utilizing the breathing effect to control the band gaps, conductivity, and magnetic properties of kagome materials with electronic interactions. △ Less

Submitted 9 June, 2025; originally announced June 2025.

Comments: 7 Pages and 7 Figures

Journal ref: Chin. Phys. Lett.42, 090712(2025)

Probing Quantum Anomalous Hall States in Twisted Bilayer WSe2 via Attractive Polaron Spectroscopy

Authors: Beini Gao, Mahdi Ghafariasl, Mahmoud Jalali Mehrabad, Tsung-Sheng Huang, Lifu Zhang, Deric Session, Pranshoo Upadhyay, Rundong Ma, Ghadah Alshalan, Daniel Gustavo Suárez Forero, Supratik Sarkar, Suji Park, Houk Jang, Kenji Watanabe, Takashi Taniguchi, Ming Xie, You Zhou, Mohammad Hafezi

Abstract: Moiré superlattices in semiconductors exhibit a rich variety of interaction-induced topological states, including quantum anomalous Hall (QAH) effects. A recent study hinted that twisted WSe2 homobilayer (tWSe2) could host a QAH state but lacked direct evidence of ferromagnetism, a key hallmark of this phase. Here, we report the first direct evidence of QAH states in tWSe2 with spontaneous ferroma… ▽ More Moiré superlattices in semiconductors exhibit a rich variety of interaction-induced topological states, including quantum anomalous Hall (QAH) effects. A recent study hinted that twisted WSe2 homobilayer (tWSe2) could host a QAH state but lacked direct evidence of ferromagnetism, a key hallmark of this phase. Here, we report the first direct evidence of QAH states in tWSe2 with spontaneous ferromagnetism. Specifically, we employ polarization-resolved attractive polaron spectroscopy on a dual-gated, 2 degree tWSe2 and observe direct signatures of spontaneous time-reversal symmetry breaking at hole filling ν= 1. Together with a Chern number measurement via Streda formula analysis, we identify this magnetized state as a topological state, characterized by C = 1. Furthermore, we demonstrate that these topological and magnetic properties are tunable via a finite displacement field, between a QAH ferromagnetic state and an antiferromagnetic state. Our findings position tWSe2 as a highly versatile, stable, and optically addressable platform for investigating topological order and strong correlations in two-dimensional landscapes. △ Less

Submitted 10 March, 2026; v1 submitted 15 April, 2025; originally announced April 2025.

Enhanced Superconductivity and Mixed-dimensional Behaviour in Infinite-layer Samarium Nickelate Thin Films

Authors: Mingwei Yang, Heng Wang, Jiayin Tang, Junping Luo, Xianfeng Wu, Wenjing Xu, Aile Wang, Yuetong Wu, Ruilin Mao, Ze Wang, Zhicheng Pei, Guangdi Zhou, Zhengang Dong, Bohan Feng, Lingchi Shi, Wenjie Meng, Chuanying Xi, Li Pi, Qingyou Lu, Jun Okamoto, Hsiao-Yu Huang, Di-Jing Huang, Haoliang Huang, Qisi Wang, Peng Gao , et al. (2 additional authors not shown)

Abstract: Rare-earth infinite-layer nickelates represent an emerging class of unconventional superconductors, with materials synthesis largely limited to early lanthanide compounds. Here, we report the synthesis and characterization of phase-pure superconducting samarium-based infinite-layer nickelate thin films, including the first demonstration of Sm$_{1-x}$Sr$_x$NiO$_2$, along with co-doped variants inco… ▽ More Rare-earth infinite-layer nickelates represent an emerging class of unconventional superconductors, with materials synthesis largely limited to early lanthanide compounds. Here, we report the synthesis and characterization of phase-pure superconducting samarium-based infinite-layer nickelate thin films, including the first demonstration of Sm$_{1-x}$Sr$_x$NiO$_2$, along with co-doped variants incorporating europium and calcium. These films, grown on LSAT (001) substrates, exhibit coherent lattice structures up to $\sim$ 9 nm thickness with minimal stacking faults. The co-doped compounds achieve a record-small $c$-axis parameter of 3.26 Å and display remarkable superconducting transition temperatures up to 32.5 K. These results establish a clear correlation between decreasing $c$-axis parameter and increasing critical temperature across different rare-earth systems. In addition, angle-dependent magnetoresistance investigations reveal the existence of a hybrid mixture of 2D and 3D superconductivity in this novel system with enhanced coupling between the rare-earth 5d and Ni 3d orbitals, confirmed by resonant inelastic X-ray scattering experiments. As the concentration of Eu increases, the system exhibits a clear tendency towards 3D superconductivity. Furthermore, we observe distinctive negative magnetoresistance in the europium-containing samples. These findings advocate clear materials design principles for higher transition temperatures and exotic physics in infinite-layer nickelate superconductors through structural engineering of the rare-earth site. △ Less

Submitted 20 August, 2025; v1 submitted 24 March, 2025; originally announced March 2025.

Comments: Main text: 20 pages, 4 figures. Supplementary: 11 pages, 9 figures

Anatomy of Spin Wave Polarization in Ferromagnets

Authors: Yutian Wang, Ruoban Ma, Jiang Xiao

Abstract: Spin waves in ferromagnetic materials are predominantly characterized by right-handed circular polarization due to symmetry breaking induced by net magnetization. However, magnetic interactions, including the external magnetic field, Heisenberg exchange, Dzyaloshinskii-Moriya interaction, and dipole-dipole interaction, can modify this behavior, leading to elliptical polarization. This study provid… ▽ More Spin waves in ferromagnetic materials are predominantly characterized by right-handed circular polarization due to symmetry breaking induced by net magnetization. However, magnetic interactions, including the external magnetic field, Heisenberg exchange, Dzyaloshinskii-Moriya interaction, and dipole-dipole interaction, can modify this behavior, leading to elliptical polarization. This study provides a systematic analysis of these interactions and their influence on spin wave polarization, establishing principles to predict traits such as polarization degree and orientation based on equilibrium magnetization textures. The framework is applied to diverse magnetic configurations, including spin spirals, domain walls, and Skyrmions, offering a comprehensive yet simple approach to understanding polarization dynamics in ferromagnetic systems. △ Less

Submitted 18 July, 2025; v1 submitted 19 February, 2025; originally announced February 2025.

Comments: 8 pages, 3 figures

Self-organized dynamics and emergent shape spaces of active isotropic fluid surfaces

Authors: Da Gao, Huayang Sun, Rui Ma, Alexander Mietke

Abstract: Theories of self-organized active fluid surfaces have emerged as an important class of minimal models for the shape dynamics of biological membranes, cells and tissues. However, due to their inherent geometric nonlinearities and the absence of general minimization principles in active systems, it remains a major challenge to systematically study the emergent shape spaces such theories give rise to… ▽ More Theories of self-organized active fluid surfaces have emerged as an important class of minimal models for the shape dynamics of biological membranes, cells and tissues. However, due to their inherent geometric nonlinearities and the absence of general minimization principles in active systems, it remains a major challenge to systematically study the emergent shape spaces such theories give rise to. Here, we introduce a novel variational approach that allows for a direct computation of stationary surface geometries and flows, which enables the classification of non-equilibrium phase transitions in shape spaces described by active surface theories. To achieve this, we construct a dissipation functional systematically from the entropy production in active surfaces and show how generic symmetries imposed by Onsager relations can be exploited to also account for reactive non-dissipative terms in constitutive laws. This functional is supplemented by Lagrange multipliers that relax nonlinear geometric constraints, which leads to a tractable variational problem suitable for implicit dynamic simulations and explicit calculations of non-trivial steady state geometries and flows. We apply this framework to study the dynamics of open fluid membranes and closed active fluid surfaces, and characterize the space of stationary solutions that corresponding surfaces and flows occupy. These analyses rationalize the interplay of first-order shape transitions of internally and externally forced fluid membranes, reveal degenerate regions in stationary shape spaces of mechanochemically active surfaces and identify a mechanism by which hydrodynamic screening controls the geometry of active surfaces undergoing cell division-like shape transformations. △ Less

Submitted 14 July, 2025; v1 submitted 29 January, 2025; originally announced January 2025.

Comments: 29 pages, 9 figures

Melting through Barrier-Crossing: The Role of Equilibrium Thermally Activated Particles

Authors: Rongchao Ma

Abstract: Melting is often understood in purely equilibrium terms, where crystalline order disappears once the free energy of the solid equals that of the liquid. Yet at the microscopic level, the initiating events for melting can often be traced to the formation of defects or local ``jumps'' over interatomic barriers. In this work, we offer a unified interpretation of melting by focusing on the equilibrium… ▽ More Melting is often understood in purely equilibrium terms, where crystalline order disappears once the free energy of the solid equals that of the liquid. Yet at the microscopic level, the initiating events for melting can often be traced to the formation of defects or local ``jumps'' over interatomic barriers. In this work, we offer a unified interpretation of melting by focusing on the equilibrium fraction of particles whose energy exceeds a characteristic barrier \(E_a\). We show that when this fraction surpasses a small but critical threshold \cite{Feder1958,Kraftmakher1998} (on the order of \(10^{-4}\)-\(10^{-3}\)), the crystal loses its rigidity, thus reconciling Born's mechanical-instability picture with the older Lindemann notion of large atomic displacements. We derive this threshold condition from standard Boltzmann (and Bose/Fermi) statistics, ensuring consistency with standard thermodynamics. Our approach naturally extends to vortex lattices in superconductors (where vortex activation energies play the role of \(E_a\)) and to quantum-lattice systems (Hubbard-type models). Crucially, while the interpretation emphasizes barrier crossing, the criterion itself is built on equilibrium statistical mechanics, offering a transparent link between defect formation rates and the macroscopic transition. △ Less

Submitted 28 January, 2025; v1 submitted 27 January, 2025; originally announced January 2025.

Comments: 3 figures

The Connection between Spin Wave Polarization and Dissipation

Authors: Yutian Wang, Jiongjie Wang, Ruoban Ma, Jiang Xiao

Abstract: This study establishes a fundamental connection between the dissipation and polarization of spin waves, which are often treated as independent phenomena. Through theoretical analysis and numerical validation, we demonstrate that within the linearized spin wave regime, a spin wave mode's dissipation rate, defined as the ratio of linewidth to the resonance frequency, exceeds Gilbert damping by a fac… ▽ More This study establishes a fundamental connection between the dissipation and polarization of spin waves, which are often treated as independent phenomena. Through theoretical analysis and numerical validation, we demonstrate that within the linearized spin wave regime, a spin wave mode's dissipation rate, defined as the ratio of linewidth to the resonance frequency, exceeds Gilbert damping by a factor given by its spatially averaged polarization. This average is governed by a non-positive definite weight, whose magnitude depends on the magnon density of the local excitation, while its sign is dictated by the local polarization handedness. Remarkably, this universal connection applies across diverse magnetic interactions and textures, offering crucial insights into spin wave dynamics and dissipation. △ Less

Submitted 26 January, 2025; originally announced January 2025.

Comments: 9 pages, 2 figures

Quantum confining excitons with electrostatic moiré superlattice

Authors: Liuxin Gu, Lifu Zhang, Sam Felsenfeld, Rundong Ma, Suji Park, Houk Jang, Takashi Taniguchi, Kenji Watanabe, You Zhou

Abstract: Quantum confining excitons has been a persistent challenge in the pursuit of strong exciton interactions and quantum light generation. Unlike electrons, which can be readily controlled via electric fields, imposing strong nanoscale potentials on excitons to enable quantum confinement has proven challenging. In this study, we utilize piezoresponse force microscopy to image the domain structures of… ▽ More Quantum confining excitons has been a persistent challenge in the pursuit of strong exciton interactions and quantum light generation. Unlike electrons, which can be readily controlled via electric fields, imposing strong nanoscale potentials on excitons to enable quantum confinement has proven challenging. In this study, we utilize piezoresponse force microscopy to image the domain structures of twisted hexagonal boron nitride (hBN), revealing evidence of strong in-plane electric fields at the domain boundaries. By placing a monolayer MoSe2 only one to two nanometers away from the twisted hBN interface, we observe energy splitting of neutral excitons and Fermi polarons by several millielectronvolts at the moiré domain boundaries. By directly correlating local structural and optical properties, we attribute such observations to excitons confined in a nanoscale one-dimensional electrostatic potential created by the strong in-plane electric fields at the moiré domain boundaries. Intriguingly, this 1D quantum confinement results in pronounced polarization anisotropy in the excitons' reflection and emission, persistent to temperatures as high as ~80 Kelvins. These findings open new avenues for exploring and controlling strongly interacting excitons for classical and quantum optoelectronics. △ Less

Submitted 20 January, 2025; originally announced January 2025.

Comments: 23 pages, 11 figures

Nonreciprocal ballistic transport in multi-layer Weyl semimetal films with surface engineering

Authors: M. H. Zou, R. Ma, S. J. Xu, W. Chen, H. Geng, L. Sheng, D. Y. Xing

Abstract: Weyl semimetal (WSM) thin films exhibit distinct electronic properties compared to their bulk counterparts. In this study, we theoretically investigate the nonreciprocal ballistic transport phenomena arising in WSM thin films due to surface modifications. Our analysis demonstrates that the nonreciprocity is sub-band-resolved, where the surface states provide the dominant contribution to the nonrec… ▽ More Weyl semimetal (WSM) thin films exhibit distinct electronic properties compared to their bulk counterparts. In this study, we theoretically investigate the nonreciprocal ballistic transport phenomena arising in WSM thin films due to surface modifications. Our analysis demonstrates that the nonreciprocity is sub-band-resolved, where the surface states provide the dominant contribution to the nonreciprocity, whereas the bulk states introduce a negative correction. Calculations further reveal a quantum size effect: overall, the nonreciprocal signal decreases with increasing film thickness, but it undergoes discontinuities as the Fermi energy approaches the bottom of a sub-band. Moreover, we observe that the density of states (DOS) in such multi-layer systems exhibits a thickness-independent pattern, which can be effectively explained by a single-variable theory. △ Less

Submitted 15 April, 2025; v1 submitted 7 January, 2025; originally announced January 2025.

Comments: 10 pages, 5 figures

Pairing correlation of the Kagome-lattice Hubbard model with the nearest-neighbor interaction

Authors: Chen Yang, Chao Chen, Runyu Ma, Ying Liang, Tianxing Ma

Abstract: A recently discovered family of Kagome lattice materials, $\emph{A}\mathrm{V}_{3}\mathrm{Sb}_{5}$($\emph{A}$= $\mathrm{K,Rb,Cs}$), has attracted great interest, especially in the debate over its dominant superconducting pairing symmetry. To explore this issue, we study the superconducting pairing behavior within the Kagome-Hubbard model through the constrained path Monte Carlo method. It is found… ▽ More A recently discovered family of Kagome lattice materials, $\emph{A}\mathrm{V}_{3}\mathrm{Sb}_{5}$($\emph{A}$= $\mathrm{K,Rb,Cs}$), has attracted great interest, especially in the debate over its dominant superconducting pairing symmetry. To explore this issue, we study the superconducting pairing behavior within the Kagome-Hubbard model through the constrained path Monte Carlo method. It is found that doping around the Dirac point generates a dominant next-nearest-neighbour-$d$ pairing symmetry driven by on-site Coulomb interaction $U$. However, when considering the nearest-neighbor interaction $V$, it may induce nearest-neighbor-$p$ pairing to become the preferred pairing symmetry. Our results provide useful information to identify the dominant superconducting pairing symmetry in $\emph{A}\mathrm{V}_{3}\mathrm{Sb}_{5}$ family. △ Less

Submitted 30 December, 2024; originally announced January 2025.

Journal ref: Chinese Phys. B 33, 107404(2024)

Electrically-tunable ultra-flat bands and $π$-electron magnetism in graphene nanoribbons

Authors: Ruize Ma, Nikita V. Tepliakov, Arash A. Mostofi, Michele Pizzochero

Abstract: Atomically thin crystals hosting flat electronic bands have been recently identified as a rich playground for exploring and engineering strongly correlated phases. Yet, their variety remains limited, primarily to two-dimensional moiré superlattices. Here, we predict the formation of reversible, electrically-induced ultra-flat bands and $π$-electron magnetism in one-dimensional chevron graphene nan… ▽ More Atomically thin crystals hosting flat electronic bands have been recently identified as a rich playground for exploring and engineering strongly correlated phases. Yet, their variety remains limited, primarily to two-dimensional moiré superlattices. Here, we predict the formation of reversible, electrically-induced ultra-flat bands and $π$-electron magnetism in one-dimensional chevron graphene nanoribbons. Our $ab$ $initio$ calculations show that the application of a transverse electric field to these nanoribbons generates a pair of isolated, nearly perfectly flat bands with widths of approximately 1 meV around the Fermi level. Upon charge doping, these flat bands undergo a Stoner-like electronic instability, resulting in the spontaneous emergence of local magnetic moments at the edges of the otherwise non-magnetic nanoribbon, akin to a one-dimensional spin-$\frac{1}{2}$ chain. Our findings expand the class of carbon-based nanostructures exhibiting flat bands and establish a novel route for inducing correlated electronic phases in chevron graphene nanoribbons. △ Less

Submitted 20 December, 2024; originally announced December 2024.

Extending the atomic decomposition and many-body representation, a chemistry-motivated monomer-centered approach for machine learning potentials

Authors: Qi Yu, Ruitao Ma, Chen Qu, Riccardo Conte, Apurba Nandi, Priyanka Pandey, Paul L. Houston, Dong H. Zhang, Joel M. Bowman

Abstract: Most widely used machine learned (ML) potentials for condensed phase applications rely on many-body permutationally invariant polynomial (PIP) or atom-centered neural networks (NN). However, these approaches often lack chemical interpretability in atomistic energy decomposition and the computational efficiency of traditional force fields has not been fully achieved. Here, we present a novel method… ▽ More Most widely used machine learned (ML) potentials for condensed phase applications rely on many-body permutationally invariant polynomial (PIP) or atom-centered neural networks (NN). However, these approaches often lack chemical interpretability in atomistic energy decomposition and the computational efficiency of traditional force fields has not been fully achieved. Here, we present a novel method that combines aspects of both approaches, and achieves state-of-the-art balance of accuracy and force field-level speed. This method utilizes a monomer-centered representation, where the potential energy is decomposed into the sum of chemically meaningful monomeric energies. Without sophisticated neural network design, the structural descriptors of monomers are described by 1-body and 2-body effective interactions, enforced by appropriate sets of PIPs as inputs to the feed forward NN. We demonstrate the performance of this method through systematic assessments of models for gas-phase water trimer, liquid water, and also liquid CO2. The high accuracy, fast speed, and flexibility of this method provide a new route for constructing accurate ML potentials and enabling large-scale quantum and classical simulations for complex molecular systems. △ Less

Submitted 30 November, 2024; originally announced December 2024.

Quantum Cellular Automata on Symmetric Subalgebras

Authors: Ruochen Ma, Yabo Li, Meng Cheng

Abstract: We investigate quantum cellular automata (QCA) on one-dimensional spin systems defined over a subalgebra of the full local operator algebra - the symmetric subalgebra under a finite Abelian group symmetry $G$. For systems where each site carries a regular representation of $G$, we establish a complete classification of such subalgebra QCAs based on two topological invariants: (1) a surjective homo… ▽ More We investigate quantum cellular automata (QCA) on one-dimensional spin systems defined over a subalgebra of the full local operator algebra - the symmetric subalgebra under a finite Abelian group symmetry $G$. For systems where each site carries a regular representation of $G$, we establish a complete classification of such subalgebra QCAs based on two topological invariants: (1) a surjective homomorphism from the group of subalgebra QCAs to the group of anyon permutation symmetries in a $(2+1)d$ $G$ gauge theory; and (2) a generalization of the Gross-Nesme-Vogts-Werner (GNVW) index that characterizes the flow of the symmetric subalgebra. Specifically, two subalgebra QCAs correspond to the same anyon permutation and share the same index if and only if they differ by a finite-depth unitary circuit composed of $G$-symmetric local gates. We also identify a set of operations that generate all subalgebra QCAs through finite compositions. As an example, we examine the Kramers-Wannier duality on a $\mathbb{Z}_2$ symmetric subalgebra, demonstrating that it maps to the $e$-$m$ permutation in the two-dimensional toric code and has an irrational index of $\sqrt{2}$. Therefore, it cannot be extended to a QCA over the full local operator algebra and mixes nontrivially with lattice translations. △ Less

Submitted 28 November, 2024; originally announced November 2024.

Comments: 46+9 pages, 13 figures

Tunneling Spectroscopy in Superconducting Circuit Lattices

Authors: Botao Du, Qihao Guo, Santiago López, Ruichao Ma

Abstract: We demonstrate tunneling spectroscopy of synthetic quantum matter in superconducting circuit lattices. We measure site-resolved excitation spectra by coupling the lattice to engineered driven-dissipative particle baths that serve as local tunneling probes. Using incoherent particle source and drain, we independently extract quasi-particle and quasi-hole spectra and reconstruct the spatial structur… ▽ More We demonstrate tunneling spectroscopy of synthetic quantum matter in superconducting circuit lattices. We measure site-resolved excitation spectra by coupling the lattice to engineered driven-dissipative particle baths that serve as local tunneling probes. Using incoherent particle source and drain, we independently extract quasi-particle and quasi-hole spectra and reconstruct the spatial structure of collective excitations. We perform spectroscopy of a strongly interacting Bose-Hubbard lattice at different densities, observing changes in energy gaps across the superfluid to Mott-insulator transition and the effects of three-body interactions. Our results provide a new toolset for characterizing many-body states in analog quantum simulators. △ Less

Submitted 9 May, 2025; v1 submitted 12 November, 2024; originally announced November 2024.

Comments: Main text (9 pages, 4 figures) and Supplemental Material (4 pages, 1 table, 2 figures). Published version

Journal ref: Phys. Rev. Research 7, L022038 (2025)

High proton conductivity through angstrom-porous titania

Authors: Y. Ji, G. -P. Hao, Y. -T. Tan, W. Q. Xiong, Y. Liu, W. Z. Zhou, D. -M. Tang, R. Z. Ma, S. J. Yuan, T. Sasaki, M. Lozada-Hidalgo, A. K. Geim, Pengzhan Sun

Abstract: Two dimensional (2D) crystals have attracted strong interest as a new class of proton conducting materials that can block atoms, molecules and ions while allowing proton transport through the atomically thin basal planes. Although 2D materials exhibit this perfect selectivity, the reported proton conductivities have been relatively low. Here we show that vacancy-rich titania monolayers are highly… ▽ More Two dimensional (2D) crystals have attracted strong interest as a new class of proton conducting materials that can block atoms, molecules and ions while allowing proton transport through the atomically thin basal planes. Although 2D materials exhibit this perfect selectivity, the reported proton conductivities have been relatively low. Here we show that vacancy-rich titania monolayers are highly permeable to protons while remaining impermeable to helium with proton conductivity exceeding 100 S cm-2 at 200 C and surpassing targets set by industry roadmaps. The fast and selective proton transport is attributed to an extremely high density of titanium-atom vacancies (one per square nm), which effectively turns titania monolayers into angstrom-scale sieves. Our findings highlight the potential of 2D oxides as membrane materials for hydrogen-based technologies. △ Less

Submitted 8 October, 2024; originally announced October 2024.

Journal ref: Nature Communications 15, 10546 (2024)

Competition between $d$-wave and $d$+$is$-wave superconductivity in the Hubbard model on a checkerboard lattice

Authors: Yue Pan, Runyu Ma, Chao Chen, Zixuan Jia, Tianxing Ma

Abstract: By employing determinant quantum Monte Carlo simulations, we investigate a checkerboard lattice with next-nearest-neighbor hopping $t'$ as the frustration-control parameter, which exhibits an energetically partial flat-band in the system. Our numerical simulation identifies the dominant pairing symmetry of the checkerboard lattice Hubbard model, and we reveal the competition between the $d$-wave a… ▽ More By employing determinant quantum Monte Carlo simulations, we investigate a checkerboard lattice with next-nearest-neighbor hopping $t'$ as the frustration-control parameter, which exhibits an energetically partial flat-band in the system. Our numerical simulation identifies the dominant pairing symmetry of the checkerboard lattice Hubbard model, and we reveal the competition between the $d$-wave and $d+is$ wave in the parameter space of electron filling $\avg{n}$ and frustration control parameter $t^{\prime}/t$. To ensure the reliability and accuracy of our results, we evaluate the sign problem. We also find that the spin susceptibility, the effective pairing interactions of different pairing symmetries and the superconducting instability are enhanced as the on-site Coulomb interaction increases, demonstrating that superconductivity is driven by strong electron--electron correlation. Our work provides a further understanding of pairing symmetry in the Hubbard model and improves prospects for exploring rich correlated behaviors in frustrated systems. △ Less

Submitted 24 September, 2024; originally announced September 2024.

Comments: 9 pages and 13 figures

Journal ref: Phys. Rev. B 110,144509(2024)

Precise structure and polarization determination of Hf0.5Zr0.5O2 with electron ptychography

Authors: Xiaoyue Gao1, Zhuohui Liu, Bo Han, Xiaowen Zhang, Ruilin Mao, Ruochen Shi, Ruixue Zhu, Jiangbo Lu, Tao Wang, Chen Ge, Peng Gao

Abstract: Hf0.5Zr0.5O2 (HZO) is a promising candidate for next generation ferroelectric memories and transistors. However, its ferroelectricity origin is still under debate due to the complex of its phase and microstructure in practical samples. In this study, we investigate the atomic structure of substrate-free HZO freestanding film with multislice electron ptychography, for which the ultra-high space res… ▽ More Hf0.5Zr0.5O2 (HZO) is a promising candidate for next generation ferroelectric memories and transistors. However, its ferroelectricity origin is still under debate due to the complex of its phase and microstructure in practical samples. In this study, we investigate the atomic structure of substrate-free HZO freestanding film with multislice electron ptychography, for which the ultra-high space resolution (up to ~25 pm) and capability to simultaneously image the cation and oxygen allow us to precisely determine the intrinsic atomic structures of different phases and reveal subtle changes among them. We clarify that the orthorhombic phase is ferroelectric with spontaneous polarization ~34{\pm}4 μC/cm2 (corresponding to 56{\pm}6 pm in displacement) that is accurately measured through statistical analysis. Significant polarization suppression is observed near the grain boundary, while no distinguishable structural changes are detected near the 180° ferroelectric domain walls. Through the direct oxygen imaging of orthorhombic phase from the [111] zone axis, we quantify a substantial number of oxygen vacancies with a preferential distribution, which influences the polarization direction and strength. These findings provide fundamentals for HZO research, and thus lay a foundation for the design of high-performance ferroelectric devices. △ Less

Submitted 18 September, 2024; originally announced September 2024.

Drone based superconducting single photon detection system with detection efficiency more than 90%

Authors: Ruoyan Ma, Zhimin Guo, Dai Chen, Xiaojun Dai, You Xiao, ChengJun Zhang, Jiamin Xiong, Jia Huang, Xingyu Zhang, Xiaoyu Liu, Liangliang Rong, Hao Li, Xiaofu Zhang, Lixing You

Abstract: Bounded by the size, weight, and power consumption (SWaP) of conventional superconducting single photon detectors (SSPD), applications of SSPDs were commonly confined in the laboratory. However, booming demands for high efficiency single photon detector incorporated with avionic platforms arise with the development of remote imaging and sensing or long-haul quantum communication without topographi… ▽ More Bounded by the size, weight, and power consumption (SWaP) of conventional superconducting single photon detectors (SSPD), applications of SSPDs were commonly confined in the laboratory. However, booming demands for high efficiency single photon detector incorporated with avionic platforms arise with the development of remote imaging and sensing or long-haul quantum communication without topographical constraints. We herein designed and manufactured the first drone based SSPD system with a SDE as high as 91.8%. This drone based SSPD system is established with high performance NbTiN SSPDs, self-developed miniature liquid helium dewar, and homemade integrated electric setups, which is able to be launched in complex topographical conditions. Such a drone based SSPD system may open the use of SSPDs for applications that demand high-SDE in complex environments. △ Less

Submitted 11 August, 2024; originally announced August 2024.

Parameters dependent superconducting transition temperature in high temperature superconductors

Authors: Runyu Ma, Tianxing Ma, Congjun Wu

Abstract: Understanding the evolution of the superconducting transition temperature in relation to doping and interaction strengths is one of the most challenging problems in high temperature superconductivity. By refining determinant quantum Monte Carlo algorithm, we characterize the parameter dependence of the superconducting transition temperature within a bilayer Hubbard model, which is sign-problem-fre… ▽ More Understanding the evolution of the superconducting transition temperature in relation to doping and interaction strengths is one of the most challenging problems in high temperature superconductivity. By refining determinant quantum Monte Carlo algorithm, we characterize the parameter dependence of the superconducting transition temperature within a bilayer Hubbard model, which is sign-problem-free at arbitrary filling. A striking feature of this model is its similarities to the bilayer nickelate-based superconductor $\mathrm{La}_{3}\mathrm{Ni}_{2}\mathrm{O}_{7}$, where superconductivity emerge from the bilayer $\mathrm{Ni}\mathrm{O}_{2}$ planes. We find that interlayer spin-exchange $J$ is critical to interlayer pairing, ant that on-site interaction $U$ contributes negatively to superconductivity at low doping levels but positively to it at high doping levels. Our findings identify the key parameter dependent superconducting transition temperature in nickelate-based superconductors and provide a new understanding of the high temperature superconductivity. △ Less

Submitted 4 August, 2024; originally announced August 2024.

Comments: 6 pages and 6 figures

Journal ref: Chin. Phys. Lett. 42, 110705 (2025)

Exploring Loss Landscapes through the Lens of Spin Glass Theory

Authors: Hao Liao, Wei Zhang, Zhanyi Huang, Zexiao Long, Mingyang Zhou, Xiaoqun Wu, Rui Mao, Chi Ho Yeung

Abstract: In the past decade, significant strides in deep learning have led to numerous groundbreaking applications. Despite these advancements, the understanding of the high generalizability of deep learning, especially in such an over-parametrized space, remains limited. For instance, in deep neural networks (DNNs), their internal representations, decision-making mechanism, absence of overfitting in an ov… ▽ More In the past decade, significant strides in deep learning have led to numerous groundbreaking applications. Despite these advancements, the understanding of the high generalizability of deep learning, especially in such an over-parametrized space, remains limited. For instance, in deep neural networks (DNNs), their internal representations, decision-making mechanism, absence of overfitting in an over-parametrized space, superior generalizability, etc., remain less understood. Successful applications are often considered as empirical rather than scientific achievement. This paper delves into the loss landscape of DNNs through the lens of spin glass in statistical physics, a system characterized by a complex energy landscape with numerous metastable states, as a novel perspective in understanding how DNNs work. We investigated the loss landscape of single hidden layer neural networks activated by Rectified Linear Unit (ReLU) function, and introduced several protocols to examine the analogy between DNNs and spin glass. Specifically, we used (1) random walk in the parameter space of DNNs to unravel the structures in their loss landscape; (2) a permutation-interpolation protocol to study the connection between copies of identical regions in the loss landscape due to the permutation symmetry in the hidden layers; (3) hierarchical clustering to reveal the hierarchy among trained solutions of DNNs, reminiscent of the so-called Replica Symmetry Breaking (RSB) phenomenon (i.e. the Parisi solution) in spin glass; (4) finally, we examine the relationship between the ruggedness of DNN's loss landscape and its generalizability, showing an improvement of flattened minima. △ Less

Submitted 16 September, 2024; v1 submitted 30 July, 2024; originally announced July 2024.

Comments: 24 pages, 11 figures

Comparison of superconducting pairing in doped cuprates and nickelates within an extended Hubbard model

Authors: Yicheng Xiong, Hang Ma, Hongxing Liu, Runyu Ma, Tianxing Ma

Abstract: Within a Hubbard model, we investigate the superconducting pairing behavior of infinite-layer nickelate $\mathrm{NdNiO_2}$ and cuprate superconductors by using the determinant quantum Monte Carlo method. Our focus is on comparing their dominant pairing symmetries. The results indicate that the $d_{x^2-y^2}$ pairing interaction is significantly enhanced at low temperatures in both doped nickelates… ▽ More Within a Hubbard model, we investigate the superconducting pairing behavior of infinite-layer nickelate $\mathrm{NdNiO_2}$ and cuprate superconductors by using the determinant quantum Monte Carlo method. Our focus is on comparing their dominant pairing symmetries. The results indicate that the $d_{x^2-y^2}$ pairing interaction is significantly enhanced at low temperatures in both doped nickelates and cuprates, whereas other typical pairing symmetries are effectively suppressed, highlighting the dominance of the $d_{x^2-y^2}$ pairing form. Additionally, we find that the effective pairing interaction for $d_{x^2-y^2}$ pairing in doped nickelates is slightly lower than that in doped cuprates, which may be attributed to the different degrees of Fermi surface warping caused by the third-nearest hopping $t''$. Further studies show that the hole doping and interaction strength have significant effects on the $d_{x^2-y^2}$ pairing interaction within the selected parameter range. The $d_{x^2-y^2}$ pairing interaction is notably weakened when the hole doping increases, whereas it is significantly enhanced with increasing Coulomb interaction strength $U$. This comparative analysis reveals the similarities and differences in the pairing behaviors of doped nickelates and cuprates, which may provide further insights into understanding the superconducting properties of these two classes of materials. △ Less

Submitted 27 January, 2025; v1 submitted 12 June, 2024; originally announced June 2024.

Comments: 8 pages and 12 figures. Published version

Journal ref: Phys. Rev. B 111, 045151 (2025)

Velocity Scanning Tomography for Room-Temperature Quantum Simulation

Authors: Jiefei Wang, Ruosong Mao, Xingqi Xu, Yunzhou Lu, Jianhao Dai, Xiao Liu, Gang-Qin Liu, Dawei Lu, Huizhu Hu, Shi-Yao Zhu, Han Cai, Da-Wei Wang

Abstract: Quantum simulation offers an analog approach for exploring exotic quantum phenomena using controllable platforms, typically necessitating ultracold temperatures to maintain the quantum coherence. Superradiance lattices (SLs) have been harnessed to simulate coherent topological physics at room temperature, but the thermal motion of atoms remains a notable challenge in accurately measuring the physi… ▽ More Quantum simulation offers an analog approach for exploring exotic quantum phenomena using controllable platforms, typically necessitating ultracold temperatures to maintain the quantum coherence. Superradiance lattices (SLs) have been harnessed to simulate coherent topological physics at room temperature, but the thermal motion of atoms remains a notable challenge in accurately measuring the physical quantities. To overcome this obstacle, we invent and validate a velocity scanning tomography technique to discern the responses of atoms with different velocities, allowing cold-atom spectroscopic resolution within room-temperature SLs. By comparing absorption spectra with and without atoms moving at specific velocities, we can derive the Wannier-Stark ladders of the SL across various effective static electric fields, their strengths being proportional to the atomic velocities. We extract the Zak phase of the SL by monitoring the ladder frequency shift as a function of the atomic velocity, effectively demonstrating the topological winding of the energy bands. Our research signifies the feasibility of room-temperature quantum simulation and facilitates their applications in quantum information processing. △ Less

Submitted 4 June, 2024; originally announced June 2024.

Comments: 6 pages, 4 figures

Lieb-Schultz-Mattis Theorem with Long-Range Interactions

Authors: Ruochen Ma

Abstract: We prove the Lieb-Schultz-Mattis theorem in $d$-dimensional spin systems exhibiting $SO(3)$ spin rotation and lattice translation symmetries in the presence of $k-$local interactions decaying as $\sim 1/r^α$ with distance $r$. Two types of Hamiltonians are considered: Type I comprises long-range spin-spin couplings, while Type II features long-range couplings between $SO(3)$ symmetric local operat… ▽ More We prove the Lieb-Schultz-Mattis theorem in $d$-dimensional spin systems exhibiting $SO(3)$ spin rotation and lattice translation symmetries in the presence of $k-$local interactions decaying as $\sim 1/r^α$ with distance $r$. Two types of Hamiltonians are considered: Type I comprises long-range spin-spin couplings, while Type II features long-range couplings between $SO(3)$ symmetric local operators. For spin-$\frac{1}{2}$ systems, it is shown that Type I cannot have a unique symmetric ground state with a nonzero excitation gap when the interaction decays sufficiently fast, \ie when $α>\max(3d,4d-2)$. For Type II, the condition becomes $α>\max(3d-1,4d-3)$. In $1d$, this ingappability condition is improved to $α>2$ for Type I and $α>0$ for Type II by examining the energy of a state with a uniform $2π$ twist. Notably, in $2d$, a Type II Hamiltonian with van der Waals interaction is subject to the constraint of the theorem. △ Less

Submitted 8 September, 2024; v1 submitted 23 May, 2024; originally announced May 2024.

Comments: 12 pages, 2 figures, published version

Journal ref: Phys. Rev. B 110, 104412, 2024

Strong-to-Weak Spontaneous Symmetry Breaking in Mixed Quantum States

Authors: Leonardo A. Lessa, Ruochen Ma, Jian-Hao Zhang, Zhen Bi, Meng Cheng, Chong Wang

Abstract: Symmetry in mixed quantum states can manifest in two distinct forms: strong symmetry, where each individual pure state in the quantum ensemble is symmetric with the same charge, and weak symmetry, which applies only to the entire ensemble. This paper explores a novel type of spontaneous symmetry breaking (SSB) where a strong symmetry is broken to a weak one. While the SSB of a weak symmetry is mea… ▽ More Symmetry in mixed quantum states can manifest in two distinct forms: strong symmetry, where each individual pure state in the quantum ensemble is symmetric with the same charge, and weak symmetry, which applies only to the entire ensemble. This paper explores a novel type of spontaneous symmetry breaking (SSB) where a strong symmetry is broken to a weak one. While the SSB of a weak symmetry is measured by the long-ranged two-point correlation function, the strong-to-weak SSB (SW-SSB) is measured by the fidelity correlator. We prove that SW-SSB is a universal property of mixed-state quantum phases, in the sense that the phenomenon of SW-SSB is robust against symmetric low-depth local quantum channels. We also show that the symmetry breaking is "spontaneous" in the sense that the effect of a local symmetry-breaking measurement cannot be recovered locally. We argue that a thermal state at a nonzero temperature in the canonical ensemble (with fixed symmetry charge) should have spontaneously broken strong symmetry. Additionally, we study non-thermal scenarios where decoherence induces SW-SSB, leading to phase transitions described by classical statistical models with bond randomness. In particular, the SW-SSB transition of a decohered Ising model can be viewed as the "ungauged" version of the celebrated toric code decodability transition. We confirm that, in the decohered Ising model, the SW-SSB transition defined by the fidelity correlator is the only physical transition in terms of channel recoverability. We also comment on other (inequivalent) definitions of SW-SSB, through correlation functions with higher Renyi indices. △ Less

Submitted 17 November, 2024; v1 submitted 6 May, 2024; originally announced May 2024.

Comments: 17+6 pages, 4 figures

Journal ref: PRX Quantum 6, 010344 (2025)

A diverse set of two-qubit gates for spin qubits in semiconductor quantum dots

Authors: Ming Ni, Rong-Long Ma, Zhen-Zhen Kong, Ning Chu, Sheng-Kai Zhu, Chu Wang, Ao-Ran Li, Wei-Zhu Liao, Gang Cao, Gui-Lei Wang, Guang-Can Guo, Xuedong Hu, Hai-Ou Li, Guo-Ping Guo

Abstract: To realize large-scale quantum information processes, an ideal scheme for two-qubit operations should enable diverse operations with given hardware and physical interaction. However, for spin qubits in semiconductor quantum dots, the common two-qubit operations, including CPhase gates, SWAP gates, and CROT gates, are realized with distinct parameter regions and control waveforms, posing challenges… ▽ More To realize large-scale quantum information processes, an ideal scheme for two-qubit operations should enable diverse operations with given hardware and physical interaction. However, for spin qubits in semiconductor quantum dots, the common two-qubit operations, including CPhase gates, SWAP gates, and CROT gates, are realized with distinct parameter regions and control waveforms, posing challenges for their simultaneous implementation. Here, taking advantage of the inherent Heisenberg interaction between spin qubits, we propose and verify a fast composite two-qubit gate scheme to extend the available two-qubit gate types as well as reduce the requirements for device properties. Apart from the formerly proposed CPhase (controlled-phase) gates and SWAP gates, theoretical results indicate that the iSWAP-family gate and Fermionic simulation (fSim) gate set are additionally available for spin qubits. Meanwhile, our gate scheme limits the parameter requirements of all essential two-qubit gates to a common J~ΔE_Z region, facilitate the simultaneous realization of them. Furthermore, we present the preliminary experimental demonstration of the composite gate scheme, observing excellent match between the measured and simulated results. With this versatile composite gate scheme, broad-spectrum two-qubit operations allow us to efficiently utilize the hardware and the underlying physics resources, helping accelerate and broaden the scope of the upcoming noise intermediate-scale quantum (NISQ) computing. △ Less

Submitted 29 April, 2024; originally announced April 2024.

Comments: 23 pages, 6 figures,

Journal ref: Physical Review APPLIED 23, 024065 (2025)

Symmetry Protected Topological Phases of Mixed States in the Doubled Space

Authors: Ruochen Ma, Alex Turzillo

Abstract: The interplay of symmetry and topology in quantum many-body mixed states has recently garnered significant interest. In a phenomenon not seen in pure states, mixed states can exhibit average symmetries -- symmetries that act on component states while leaving the ensemble invariant. In this work, we systematically characterize symmetry protected topological (SPT) phases of short-range entangled (SR… ▽ More The interplay of symmetry and topology in quantum many-body mixed states has recently garnered significant interest. In a phenomenon not seen in pure states, mixed states can exhibit average symmetries -- symmetries that act on component states while leaving the ensemble invariant. In this work, we systematically characterize symmetry protected topological (SPT) phases of short-range entangled (SRE) mixed states of spin systems -- protected by both average and exact symmetries -- by studying their pure Choi states in a doubled Hilbert space, where the familiar notions and tools for SRE and SPT pure states apply. This advantage of the doubled space comes with a price: extra symmetries as well as subtleties around how hermiticity and positivity of the original density matrix constrain the possible SPT invariants. Nevertheless, the doubled space perspective allows us to obtain a systematic classification of mixed-state SPT (MSPT) phases. We also investigate the robustness of MSPT invariants under symmetric finite-depth quantum channels, the bulk-boundary correspondence for MSPT phases, and the consequences of the MSPT invariants for the separability of mixed states and the symmetry-protected sign problem. In addition to MSPT phases, we study the patterns of spontaneous symmetry breaking (SSB) of mixed states, including the phenomenon of exact-to-average SSB, and the order parameters that detect them. Mixed state SSB is related to an ingappability constraint on symmetric Lindbladian dynamics. △ Less

Submitted 2 June, 2024; v1 submitted 19 March, 2024; originally announced March 2024.

Comments: 31 pages, 10 figures, Theorems proven in more general cases, more references included

Probing Site-Resolved Current in Strongly Interacting Superconducting Circuit Lattices

Authors: Botao Du, Ramya Suresh, Santiago López, Jeremy Cadiente, Ruichao Ma

Abstract: Transport measurements are fundamental for understanding condensed matter phenomena, from superconductivity to the fractional quantum Hall effect. Analogously, they can be powerful tools for probing synthetic quantum matter in quantum simulators. Here we demonstrate the measurement of in-situ particle current in a superconducting circuit lattice and apply it to study transport in both coherent and… ▽ More Transport measurements are fundamental for understanding condensed matter phenomena, from superconductivity to the fractional quantum Hall effect. Analogously, they can be powerful tools for probing synthetic quantum matter in quantum simulators. Here we demonstrate the measurement of in-situ particle current in a superconducting circuit lattice and apply it to study transport in both coherent and bath-coupled lattices. Our method utilizes controlled tunneling in a double-well potential to map current to on-site density, revealing site-resolved current and current statistics. We prepare a strongly interacting Bose-Hubbard lattice at different lattice fillings, and observe the change in current statistics as the many-body states transition from superfluid to Mott insulator. Furthermore, we explore non-equilibrium current dynamics by coupling the lattice to engineered driven-dissipative baths that serve as tunable particle source and drain. We observe steady-state current in discrete conduction channels and interaction-assisted transport. These results establish a versatile platform to investigate microscopic quantum transport in superconducting circuits. △ Less

Submitted 8 July, 2024; v1 submitted 18 March, 2024; originally announced March 2024.

Comments: Revised version to be published in Phys. Rev. Lett

Journal ref: Phys. Rev. Lett. 133, 060601 (2024)

Nonreciprocal Ballistic Transport in Asymmetric Bands

Authors: Minhao Zou, Hao Geng, Rong Ma, Wei Chen, Li Sheng, Dingyu Xing

Abstract: Nonreciprocal transport in uniform systems has attracted great research interest recently and the existing theories mainly focus on the diffusive regime. In this study, we uncover a novel scenario for nonreciprocal charge transport in the ballistic regime enabled by asymmetric band structures of the system. The asymmetry of the bands induces unequal Coulomb potentials within the system as the bias… ▽ More Nonreciprocal transport in uniform systems has attracted great research interest recently and the existing theories mainly focus on the diffusive regime. In this study, we uncover a novel scenario for nonreciprocal charge transport in the ballistic regime enabled by asymmetric band structures of the system. The asymmetry of the bands induces unequal Coulomb potentials within the system as the bias voltage imposed by the electrodes inverts its sign. As a result, the bands undergo different energy shifts as the current flows in opposite directions, giving rise to the nonreciprocity. Utilizing the gauge-invariant nonlinear transport theory, we show that the nonreciprocal transport predominantly originates from the second-order conductance, which violates the Onsager reciprocal relation but fulfills a generalized reciprocal relation similar to that of unidirectional magnetoresistance. The ballistic nonreciprocal transport phenomena differ from the diffusive ones by considering the internal asymmetric Coulomb potential, a factor not accounted for in diffusive cases but undeniably crucial in ballistic scenarios. Our work opens a avenue for implementing nonreciprocal transport in the ballistic regime and provides an alternative perspective for further experimental explorations for nonreciprocal transport. △ Less

Submitted 20 December, 2023; originally announced December 2023.

Comments: 7 pages, 4 figures

Flat bands and superconductivity induced by periodic strain in monolayer graphene

Authors: Jingyao Meng, Runyu Ma, Tianxing Ma, Hai-Qing Lin

Abstract: Superconductivity in single-layer graphene has attracted considerable interest. Here, using the determinant quantum Monte Carlo method, we study transitions of superconductivity and magnetism in a monolayer graphene with a special periodic strain. Consistent with experiments, the deformation accumulates a series of flat bands, whose robustness under interaction is verified through electron localiz… ▽ More Superconductivity in single-layer graphene has attracted considerable interest. Here, using the determinant quantum Monte Carlo method, we study transitions of superconductivity and magnetism in a monolayer graphene with a special periodic strain. Consistent with experiments, the deformation accumulates a series of flat bands, whose robustness under interaction is verified through electron localization in real space. During the reconstruction of the band structure, the superconductivity appears in flat band range with next-nearest neighbor $d+id$ pairing symmetry dominating other modes and is accompanied by ferromagnetism caused by symmetry breaking. We also demonstrate that the strain-induced symmetry breaking would accumulate an energy-gap antiferromagnetic insulating phase at half filling even under the limitation of not strong enough interaction, which shows its potential as a platform that exhibits strongly correlated phenomena. △ Less

Submitted 29 December, 2024; v1 submitted 5 November, 2023; originally announced November 2023.

Comments: 9 pages, 12 figures. Published version

Journal ref: Phys. Rev. B 110, 235128(2024)

A SWAP Gate for Spin Qubits in Silicon

Authors: Ming Ni, Rong-Long Ma, Zhen-Zhen Kong, Xiao Xue, Sheng-Kai Zhu, Chu Wang, Ao-Ran Li, Ning Chu, Wei-Zhu Liao, Gang Cao, Gui-Lei Wang, Guang-Can Guo, Xuedong Hu, Hong-Wen Jiang, Hai-Ou Li, Guo-Ping Guo

Abstract: With one- and two-qubit gate fidelities approaching the fault-tolerance threshold for spin qubits in silicon, how to scale up the architecture and make large arrays of spin qubits become the more pressing challenges. In a scaled-up structure, qubit-to-qubit connectivity has crucial impact on gate counts of quantum error correction and general quantum algorithms. In our toolbox of quantum gates for… ▽ More With one- and two-qubit gate fidelities approaching the fault-tolerance threshold for spin qubits in silicon, how to scale up the architecture and make large arrays of spin qubits become the more pressing challenges. In a scaled-up structure, qubit-to-qubit connectivity has crucial impact on gate counts of quantum error correction and general quantum algorithms. In our toolbox of quantum gates for spin qubits, SWAP gate is quite versatile: it can help solve the connectivity problem by realizing both short- and long-range spin state transfer, and act as a basic two-qubit gate, which can reduce quantum circuit depth when combined with other two-qubit gates. However, for spin qubits in silicon quantum dots, high fidelity SWAP gates have not been demonstrated due to the requirements of large circuit bandwidth and a highly adjustable ratio between the strength of the exchange coupling J and the Zeeman energy difference Delta E_z. Here we demonstrate a fast SWAP gate with a duration of ~25 ns based on quantum dots in isotopically enriched silicon, with a highly adjustable ratio between J and Delta E_z, for over two orders of magnitude in our device. We are also able to calibrate the single-qubit local phases during the SWAP gate by incorporating single-qubit gates in our circuit. By independently reading out the qubits, we probe the anti-correlations between the two spins, estimate the operation fidelity and analyze the dominant error sources for our SWAP gate. These results pave the way for high fidelity SWAP gates, and processes based on them, such as quantum communication on chip and quantum simulation by engineering the Heisenberg Hamiltonian in silicon. △ Less

Submitted 10 October, 2023; originally announced October 2023.

Comments: 25 pages, 5 figures,

Journal ref: Nano Letters 25, 3766-3772 (2025)

Single spin qubit geometric gate in a silicon quantum dot

Authors: Rong-Long Ma, Ao-Ran Li, Chu Wang, Zhen-Zhen Kong, Wei-Zhu Liao, Ming Ni, Sheng-Kai Zhu, Ning Chu, Cheng-Xian Zhang, Di Liu, Gang Cao, Gui-Lei Wang, Hai-Ou Li, Guo-Ping Guo

Abstract: Preserving qubit coherence and maintaining high-fidelity qubit control under complex noise environment is an enduring challenge for scalable quantum computing. Here we demonstrate an addressable fault-tolerant single spin qubit with an average control fidelity of 99.12% via randomized benchmarking on a silicon quantum dot device with an integrated micromagnet. Its dephasing time T2* is 1.025 us an… ▽ More Preserving qubit coherence and maintaining high-fidelity qubit control under complex noise environment is an enduring challenge for scalable quantum computing. Here we demonstrate an addressable fault-tolerant single spin qubit with an average control fidelity of 99.12% via randomized benchmarking on a silicon quantum dot device with an integrated micromagnet. Its dephasing time T2* is 1.025 us and can be enlarged to 264 us by using the Hahn echo technique, reflecting strong low-frequency noise in our system. To break through the noise limitation, we introduce geometric quantum computing to obtain high control fidelity by exploiting its noise-resilient feature. However, the control fidelities of the geometric quantum gates are lower than 99%. According to our simulation, the noise-resilient feature of geometric quantum gates is masked by the heating effect. With further optimization to alleviate the heating effect, geometric quantum computing can be a potential approach to reproducibly achieving high-fidelity qubit control in a complex noise environment. △ Less

Submitted 10 October, 2023; originally announced October 2023.

Comments: 10 pages, 8 figures,

Journal ref: Phys. Rev. Applied 21, 014044 (2024)

Singlet-triplet-state readout in silicon-metal-oxide-semiconductor double quantum dots

Authors: Rong-Long Ma, Sheng-Kai Zhu, Zhen-Zhen Kong, Tai-Ping Sun, Ming Ni, Yu-Chen Zhou, Yuan Zhou, Gang Luo, Gang Cao, Gui-Lei Wang, Hai-Ou Li, Guo-Ping Guo

Abstract: High-fidelity singlet-triplet state readout is essential for large-scale quantum computing. However, the widely used threshold method of comparing a mean value with the fixed threshold will limit the judgment accuracy, especially for the relaxed triplet state, under the restriction of relaxation time and signal-to-noise ratio. Here, we achieve an enhanced latching readout based on Pauli spin block… ▽ More High-fidelity singlet-triplet state readout is essential for large-scale quantum computing. However, the widely used threshold method of comparing a mean value with the fixed threshold will limit the judgment accuracy, especially for the relaxed triplet state, under the restriction of relaxation time and signal-to-noise ratio. Here, we achieve an enhanced latching readout based on Pauli spin blockade in a Si-MOS double quantum dot device and demonstrate an average singlet-triplet state readout fidelity of 97.59% by the threshold method. We reveal the inherent deficiency of the threshold method for the relaxed triplet state classification and introduce machine learning as a relaxation-independent readout method to reduce the misjudgment. The readout fidelity for classifying the simulated single-shot traces can be improved to 99.67% by machine learning method, better than the threshold method of 97.54% which is consistent with the experimental result. This work indicates that machine learning method can be a strong potential candidate for alleviating the restrictions of stably achieving high-fidelity and high-accuracy singlet-triplet state readout in large-scale quantum computing. △ Less

Submitted 18 September, 2023; originally announced September 2023.

Comments: 11 pages,11 figures,

Journal ref: Phys. Rev. Applied 21, 034022 (2024)

Correcting on-chip distortion of control pulses with silicon spin qubits

Authors: Ming Ni, Rong-Long Ma, Zhen-Zhen Kong, Ning Chu, Wei-Zhu Liao, Sheng-Kai Zhu, Chu Wang, Gang Luo, Di Liu, Gang Cao, Gui-Lei Wang, Hai-Ou Li, Guo-Ping Guo

Abstract: Pulse distortion, as one of the coherent error sources, hinders the characterization and control of qubits. In the semiconductor quantum dot system, the distortions on measurement pulses and control pulses disturb the experimental results, while no effective calibration procedure has yet been reported. Here, we demonstrate two different calibration methods to calibrate and correct the distortion u… ▽ More Pulse distortion, as one of the coherent error sources, hinders the characterization and control of qubits. In the semiconductor quantum dot system, the distortions on measurement pulses and control pulses disturb the experimental results, while no effective calibration procedure has yet been reported. Here, we demonstrate two different calibration methods to calibrate and correct the distortion using the two-qubit system as a detector. The two calibration methods have different correction accuracy and complexity. One is the coarse predistortion (CPD) method, with which the distortion is partly relieved. The other method is the all predistortion (APD) method, with which we measure the transfer function and significantly improve the exchange oscillation homogeneity. The two methods use the exchange oscillation homogeneity as the metric and are appropriate for any qubit that oscillates with a diabatic pulse. With the APD procedure, an arbitrary control waveform can be accurately delivered to the device, which is essential for characterizing qubits and improving gate fidelity. △ Less

Submitted 18 September, 2023; originally announced September 2023.

Comments: 19 pages, 5 figures,

Journal ref: Chin. Phys. B 34, 010308 (2025)

Superconducting nanowire diode

Authors: Xiaofu Zhang, Qingchang Huan, Ruoyan Ma, Xingyu Zhang, Jia Huang, Xiaoyu Liu, Wei Peng, Hao Li, Zhen Wang, Xiaoming Xie, Lixing You

Abstract: Semiconducting diode with nonreciprocal transport effect underlies the cornerstone of contemporary integrated circuits (ICs) technology. Due to isotropic superconducting properties and the lack of breaking of inversion symmetry for conventional s-wave superconductors, such a superconducting peer is absent. Recently, a series of superconducting structures, including superconducting superlattice and… ▽ More Semiconducting diode with nonreciprocal transport effect underlies the cornerstone of contemporary integrated circuits (ICs) technology. Due to isotropic superconducting properties and the lack of breaking of inversion symmetry for conventional s-wave superconductors, such a superconducting peer is absent. Recently, a series of superconducting structures, including superconducting superlattice and quantum-material-based superconducting Josephson junction, have exhibited a superconducting diode effect in terms of polarity-dependent critical current. However, due to complex structures, these composite systems are not able to construct large-scale integrated superconducting circuits. Here, we demonstrated the minimal superconducting electric component-superconducting nanowire-based diode with a nonreciprocal transport effect under a perpendicular magnetic field, in which the superconducting to normal metallic phase transition relies on the polarity and amplitude of the bias current. Our nanowire diodes can be reliably operated nearly at all temperatures below the critical temperature, and the rectification efficiency at 2 K can be more than 24%. Moreover, the superconducting nanowire diode is able to rectify both square wave and sine wave signals without any distortion. Combining the superconducting nanowire-based diodes and transistors, superconducting nanowires hold the possibility to construct novel low-dissipation superconducting ICs. △ Less

Submitted 20 June, 2023; originally announced June 2023.

Effect of anisotropic impurity scattering in d-wave superconductors

Authors: Ze-Long Wang, Rui-Ying Mao, Da Wang, Qiang-Hua Wang

Abstract: In d$_{x^2-y^2}$-wave superconductors, the effect of s-wave point disorder has been extensively studied in the literature. In this work, we study the anisotropic disorder with a the form of $V_{kk'}^{\rm imp}=V_if_kf_{k'}$ with $f_k=\cos(2θ)$ (with $θ$ the azimuthal angle of $k$), as proposed to be caused by apical oxygen vacancies in overdoped La-based cuprate films, under the Born approximation.… ▽ More In d$_{x^2-y^2}$-wave superconductors, the effect of s-wave point disorder has been extensively studied in the literature. In this work, we study the anisotropic disorder with a the form of $V_{kk'}^{\rm imp}=V_if_kf_{k'}$ with $f_k=\cos(2θ)$ (with $θ$ the azimuthal angle of $k$), as proposed to be caused by apical oxygen vacancies in overdoped La-based cuprate films, under the Born approximation. The disorder self-energy and d-wave pairing affect each other and have to be solved simultaneously self-consistently. We find the self-energy is reduced at low frequencies and thus weakens the pair-breaking effect. This frequency-dependence vanishes in the dirty limit for which the disorder is well described by a scattering rate $Γ_k=Γ_if_k^2$. One consequence of the disorder effect is the gap-to-$T_c$ ratio $2Δ(0)/T_c$ is greatly enhanced by the d-wave disorder, much larger than the s-wave disorder and the clean BCS value $4.28$. At last, we generalize the d-wave scattering rate to a general form $Γ_θ=Γ_α|θ-θ_0|^α$ around each nodal direction $θ_0$. We find the density of states $ρ(ω)-ρ(0)\propto|ω|$ ($ω^2$) for all $α\ge1$ ($α<1$) in the limit of $ω\to0$. As a result, the superfluid density $ρ_s$ exhibits two and only two possible scaling behaviors: $ρ_s(0)-ρ_s(T)\propto T$ ($T^2$) for $α\ge1$ ($α<1$) in the low temperature limit. △ Less

Submitted 15 June, 2023; originally announced June 2023.

Comments: 5 pages, 6 figures

Journal ref: Chin. Phys. Lett. 40, 057402 (2023)

Strong ferromagnetic fluctuations in a doped checkerboard lattice

Authors: Yue Pan, Runyu Ma, Tianxing Ma

Abstract: Using the determinant quantum Monte Carlo method, we study the magnetic susceptibility in the parameter space of the on-site interaction $U$, temperature $T$, electron filling $\avg{n}$, and the frustration control parameter $t^{\prime}$ within the Hubbard model on a two-dimensional checkerboard lattice. It is shown that the system exhibits stable and strong ferromagnetic fluctuations about the el… ▽ More Using the determinant quantum Monte Carlo method, we study the magnetic susceptibility in the parameter space of the on-site interaction $U$, temperature $T$, electron filling $\avg{n}$, and the frustration control parameter $t^{\prime}$ within the Hubbard model on a two-dimensional checkerboard lattice. It is shown that the system exhibits stable and strong ferromagnetic fluctuations about the electron filling $\avg{n}\ge1.2$ for different $t^{\prime}$, and the ferromagnetic susceptibility is strongly enhanced by the increasing interaction and decreasing tempeture. We also discuss the sign problem to clarify which parameter region is accessible and reliable. Our findings not only demonstrate important implications for modulating magnetism in the checkerboard lattice, but will also provide a theoretical platform for a flat-band model that demonstrates a variety of physical properties. △ Less

Submitted 11 June, 2023; originally announced June 2023.

Comments: 6 pages, 6 figures

Journal ref: Phys. Rev. B 107, 245126 (2023)

Evolution of magnetic correlation in an inhomogeneous square lattice

Authors: Xiao Zhang, Runyu Ma, Zenghui Fan, Zixuan Jia, Lufeng Zhang, Tianxing Ma

Abstract: We explore the magnetic properties of a two-dimensional Hubbard model on an inhomogeneous square lattice, which provides a platform for tuning the bandwidth of the flat band. In its limit, this inhomogeneous square lattice turns into a Lieb lattice, and it exhibits abundant properties due to the flat band structure at the Fermi level. By using the determinant quantum Monte Carlo simulation, we cal… ▽ More We explore the magnetic properties of a two-dimensional Hubbard model on an inhomogeneous square lattice, which provides a platform for tuning the bandwidth of the flat band. In its limit, this inhomogeneous square lattice turns into a Lieb lattice, and it exhibits abundant properties due to the flat band structure at the Fermi level. By using the determinant quantum Monte Carlo simulation, we calculate the spin susceptibility, double occupancy, magnetization, spin structure factor, and effective pairing interaction of the system. It is found that the antiferromagnetic correlation is suppressed by the inhomogeneous strength and that the ferromagnetic correlation is enhanced. Both the antiferromagnetic correlation and ferromagnetic correlation are enhanced as the interaction increases. It is also found that the effective $d$-wave pairing interaction is suppressed by the increasing inhomogeneity. In addition, we also study the thermodynamic properties of the inhomogeneous square lattice, and the calculation of specific heat provide good support for our point. Our intensive numerical results provide a rich magnetic phase diagram over both the inhomogeneity and interaction. △ Less

Submitted 6 June, 2023; originally announced June 2023.

Journal ref: Phys. Rev. B 107, 235128 (2023)