A GHz-frequency multistrip acoustic beam splitter for quantum applications

Fri, 19 Jul 2024 08:40:40 GMT

题名: A GHz-frequency multistrip acoustic beam splitter for quantum applications 作者: Dumur, E.; Satzinger, K. J.; Peairs, G. A.; Chou, M. H.; Bienfait, A.; Chang, H. -S.; Conner, C. R.; Grebel, J.; Povey, R. G.; Zhong, Y. P.; Cleland, A. N. 摘要: We demonstrate a microwave-frequency, two-track acoustic beam splitter, based on a multistrip coupler design matched to four unidirectional transducers, two on each of the two acoustic tracks that make up the device. We explain the device design and its experimental implementation, showing good agreement between our model and the measured device scattering spectra. The beam splitter regime, dividing an input signal at port 1 into closely equal outputs at ports 2 and 3, is reached over a 94.7 MHz bandwidth centered at 4.79 GHz, with an output power division ratio |S-21/S-31|2=1.1 +/- 0.2. The measured bandwidth of the device is limited by the bandwidth of the transducers, rather than that of the multistrip coupler.

String condensations in 3+1D and Lagrangian algebras

Fri, 19 Jul 2024 08:36:01 GMT

题名: String condensations in 3+1D and Lagrangian algebras 作者: Zhao, Jiaheng; Lou, Jia-Qi; Zhang, Zhi-Hao; Hung, Ling-Yan; Kong, Liang; Tian, Yin 摘要: We present three Lagrangian algebras in the modular 2-category associated to the 3+1D Z(2) topological order and discuss their physical interpretations, connecting algebras with gapped boundary conditions, and interestingly, maps (braided autoequivalences) exchanging algebras with bulk domain walls. A Lagrangian algebra, together with its modules and local modules, encapsulates detailed physical data of strings condensing at a gapped boundary. In particular, the condensed strings can terminate at boundaries in non-trivial ways. This phenomenon has no lower dimensional analogue and corresponds to novel mathematical structures associated to higher algebras. We provide a layered construction and also explicit lattice realizations of these boundaries and illustrate the correspondence between physics and mathematics of these boundary conditions. This is a first detailed study of the mathematics of Lagrangian algebras in modular 2-categories and their corresponding physics, that brings together rich phenomena of string condensations, gapped boundaries and domain walls in 3+1D topological orders.

Differentially Private Federated Learning via Alternating Direction Method of Multipliers

Fri, 19 Jul 2024 06:38:34 GMT

题名: Differentially Private Federated Learning via Alternating Direction Method of Multipliers 作者: Luyan Yang 摘要: Federated Learning (FL) has emerged as a promising approach for collaborative machine learning across decentralized data sources. However, FL faces substantial challenges when confronted with heterogeneous data distributions and privacy concerns. In this paper, we introduce a novel method called DP-FedADMM, which aims to address these challenges by leveraging differential privacy (DP) and the alternating direction method of multipliers (ADMM). We find that introducing dual variables can effectively mitigates the impact of data heterogeneity. Furthermore, the incorporation of artificial noise into the update messages ensures client-level differential privacy during the federated learning process. Additionally, our research uncovers an interesting insight: the well-known DP-FedAvg can be viewed as a specific instance of DP-FedADMM. Our experiments demonstrate that DP-FedADMM exhibits superior convergence and a better trade-off between utility and privacy on heterogeneous data compared to DP-FedAvg.

Epitaxial Growth of Large-Scale 2D CrTe₂ Films on Amorphous Silicon Wafers With Low Thermal Budget

Fri, 19 Jul 2024 04:41:27 GMT

题名: Epitaxial Growth of Large-Scale 2D CrTe₂ Films on Amorphous Silicon Wafers With Low Thermal Budget 作者: Zhang, Xiaoqian; Li, Yue; Lu, Qiangsheng; Xiang, Xueqiang; Sun, Xiaozhen; Tang, Chunli; Mahdi, Muntasir; Conner, Clayton; Cook, Jacob; Xiong, Yuzan; Inman, Jerad; Jin, Wencan; Liu, Chang; Cai, PeiYu; Santos, Elton J. G.; Phatak, Charudatta; Zhang, Wei; Gao, Nan; Niu, Wei; Bian, Guang; Li, Peng; Yu, Dapeng; Long, Shibing 摘要: 2D van der Waals (vdW) magnets open landmark horizons in the development of innovative spintronic device architectures. However, their fabrication with large scale poses challenges due to high synthesis temperatures (>500 degrees C) and difficulties in integrating them with standard complementary metal-oxide semiconductor (CMOS) technology on amorphous substrates such as silicon oxide (SiO2) and silicon nitride (SiNx). Here, a seeded growth technique for crystallizing CrTe2 films on amorphous SiNx/Si and SiO2/Si substrates with a low thermal budget is presented. This fabrication process optimizes large-scale, granular atomic layers on amorphous substrates, yielding a substantial coercivity of 11.5 kilo-oersted, attributed to weak intergranular exchange coupling. Field-driven Neel-type stripe domain dynamics explain the amplified coercivity. Moreover, the granular CrTe2 devices on Si wafers display significantly enhanced magnetoresistance, more than doubling that of single-crystalline counterparts. Current-assisted magnetization switching, enabled by a substantial spin-orbit torque with a large spin Hall angle (85) and spin Hall conductivity (1.02 x 10(7) h/2e Omega(1) m(1)), is also demonstrated. These observations underscore the proficiency in manipulating crystallinity within integrated 2D magnetic films on Si wafers, paving the way for large-scale batch manufacturing of practical magnetoelectronic and spintronic devices, heralding a new era of technological innovation.

Experimental observation of multiple topological nodal structure in LaSb₂

Fri, 19 Jul 2024 04:38:10 GMT

题名: Experimental observation of multiple topological nodal structure in LaSb₂ 作者: Qiao, Yuxi; Wang, Fuyi; Wang, Huaiqiang; Tao, Zicheng; Jiang, Zhicheng; Liu, Zhengtai; Cho, Soohyun; Zhang, Fayuan; Meng, Qingkai; Xia, Wei; Yang, Yichen; Huang, Zhe; Liu, Jishan; Liu, Zhonghao; Zhu, Zengwei; Qiao, Shan; Guo, Yanfeng; Zhang, Haijun; Shen, Dawei 摘要: Unconventional fermions in the immensely studied topological semimetals are the source for rich exotic topological properties. Here, using symmetry analysis and first-principles calculations, we propose the coexistence of multiple topological nodal structure in LaSb2, including topological nodal surfaces, nodal lines and in particular eightfold degenerate nodal points, which have been scarcely observed in a single material. Further, utilizing angle-resolved photoemission spectroscopy, we confirm the existence of nodal surfaces and eightfold degenerate nodal points in LaSb2. The intriguing multiple topological nodal structure might play a crucial role in giving rise to the large linear magnetoresistance. Our work renews the insights into the exotic topological phenomena in LaSb2.

Critical behavior of the quantum Stirling heat engine

Fri, 19 Jul 2024 04:37:40 GMT

题名: Critical behavior of the quantum Stirling heat engine 作者: Wang, Yuan-Sheng; Yung, Man-Hong; Xu, Dazhi; Liu, Maoxin; Chen, Xiaosong 摘要: We investigate the performance of a Stirling cycle with a working substance (WS) modeled as the quantum Rabi model (QRM), exploring the impact of criticality on its efficiency. Our findings indicate that the criticality of the QRM has a positive effect on improving the efficiency of the Stirling cycle when the WS parameters are in the normal phase. Furthermore, we observe that the Carnot efficiency is asymptotically achievable as the WS parameter approaches the critical point, even when both temperatures of the cold and hot reservoirs are finite. Additionally, we derive the critical behavior for the efficiency of the Stirling cycle, demonstrating how the efficiency asymptotically approaches the Carnot efficiency as the WS parameter approaches the critical point. Our work deepens the understanding of the impact of criticality on the performance of a Stirling heat engine.

Time-Dependent Ultrafast Quadratic Nonlinearity in an Epsilon-Near-Zero Platform

Fri, 19 Jul 2024 04:34:31 GMT

题名: Time-Dependent Ultrafast Quadratic Nonlinearity in an Epsilon-Near-Zero Platform 作者: Bykov, Anton Yu.; Deng, Junhong; Li, Guixin; Zayats, Anatoly V. 摘要: Ultrafast nonlinearity, which results in modulation of the linear optical response, is a basis for the development of time-varying media, in particular those operating in the epsilon-near-zero (ENZ) regime. Here, we demonstrate that the intraband excitation of hot electrons in the ENZ film results in a second-harmonic resonance shift of similar to 10 THz (40 nm) and second-harmonic generation (SHG) intensity changes of >100% with only minor (<1%) changes in linear transmission. The modulation is 10-fold enhanced by a plasmonic metasurface coupled to a film, allowing for ultrafast modulation of circularly polarized SHG. The effect is described by the plasma frequency renormalization in the ENZ material and the modification of the electron damping, with a possible influence of the hot-electron dynamics on the quadratic susceptibility. The results elucidate the nature of the second-order nonlinearity in ENZ materials and pave the way to the rational engineering of active nonlinear metamaterials and metasurfaces for time-varying applications.

Unification of spatiotemporal quantum formalisms: mapping between process and pseudo-density matrices via multiple-time states

Fri, 19 Jul 2024 04:17:44 GMT

题名: Unification of spatiotemporal quantum formalisms: mapping between process and pseudo-density matrices via multiple-time states 作者: Liu, Xiangjing; Jia, Zhian; Qiu, Yixian; Li, Fei; Dahlsten, Oscar 摘要: We consider the relation between three different approaches to defining quantum states across several times and locations: the pseudo-density matrix (PDM), the process matrix, and the multiple-time state approaches. Previous studies have shown that bipartite two-time states can reproduce the statistics of bipartite process matrices. Here, we show that the operational scenarios underlying two-time states can be represented as PDMs, and thereby construct a mapping from process matrices with measurements to PDMs. The existence of this mapping implies that PDMs can, like the process matrix, model processes with indefinite causal orders. The results contribute to the unification of quantum models of spatiotemporal states.

The structural, electronic, optical, and mechanical properties of carbon-based halides: An ab initio DFT approach

Fri, 19 Jul 2024 04:11:01 GMT

题名: The structural, electronic, optical, and mechanical properties of carbon-based halides: An ab initio DFT approach 作者: Tse, Geoffrey 摘要: In the present work, we choose the carbon-based halides CX4 (X = Br, Cl) to conduct a study on the ground-state properties using first-principles calculations based on density functional theory. We provide a comparative study for bromide and chloride materials using standard generalized gradient approximation functionals. A total of 80 atoms have been simulated on a single unit cell. A direct bandgap energy of 3.28 (4.64) eV for X = Br (X = Cl) with Z-Z transition is found on the studied materials. According to our partial density of states plot, a hybridization of s orbitals on C and X atoms is observed. Metallic properties have also been identified. A low reflectivity of 6% (12%) has been measured, which presents excellent material absorption. Such a material is also determined to be brittle, based on the calculated Pugh's ratio. The reflectivity (ductility) tends to increase as the X element increases down the Period Table. The negative Poisson's ratio found also suggests that the materials could be used as an electrode for metal-ion (e.g., Li, K, and Na) batteries.

Magnetized strangelets with anomalous magnetic moment and Coulomb interactions

Fri, 19 Jul 2024 04:05:24 GMT

题名: Magnetized strangelets with anomalous magnetic moment and Coulomb interactions 作者: Chen, Huai-Min; Li, Xiao-Wei; Xia, Cheng-Jun; Wang, Jing-Tao; Peng, Guang-Xiong 摘要: We study the magnetized strangelets in the baryon density -dependent quark mass model, including the effects of both confinement and lead -order perturbation interactions. The properties of magnetized strangelets are investigated under the field strength 2 x 1017 G, where the anisotropy caused by the strong magnetic field is insignificant and can be treated approximately as an isotropic system. The consideration of anomalous magnetic moments in the energy spectrum naturally solves the difficulty of infrared divergence encountered in integrating the density of states. The Coulomb interaction is accounted for using a self -consistent treatment. The energy per baryon, mechanically stable radius, strangeness, and electric charge of magnetized strangelets are presented, where their dependence on the field strength and parameter of confinement and perturbation are investigated.