arXiv subjects

H. Chang

Publications and source records attributed to H. Chang.

7 recordsLinked to original sources

arXiv2023

Experimental evidences of a current-biased Josephson junction device can be worked as a macroscopic "Boson" or "Fermion" and the combination

According to the statistical distribution laws, all the elementary particles in the real 3+1-dimensional world must and only be chosen as either bosons or fermions, without exception and not both. Here, we experimentally verified that a quantized current-biased Josephson junction (CBJJ), as an artificial macroscopic "particle", can be served as either boson or fermion, depending on its biased dc-current. By using the high vacuum two-angle electron beam evaporations, we fabricated the CBJJ devices and calibrated their physical parameters by applying low-frequency signal drivings. The microwave transmission characteristics of the fabricated CBJJ devices are analyzed by using the input-output theory and measured at 50mK temperature environment under low power limit. The experimental results verify the theoretical predictions, i.e., when the bias current is significantly lower than the critical one of the junction, the device works in a well linear regime and thus works as a harmonic oscillator, i.e., a "boson"; while if the biased current is sufficiently large (especially approaches to its critical current), the device works manifestly in the nonlinear regime and thus can be served as a two-level artificial atom, i.e., a "fermion". Therefore, by adjusting the biased dc-current, the CBJJ device can be effectively switched from the boson-type macroscopic particle to the fermion-type one, and thus may open the new approach of the superconducting quantum device application.

quant-ph↗

arXiv2020

Computation harvesting in road traffic dynamics

Owing to recent advances in artificial intelligence and internet of things (IoT) technologies, collected big data facilitates high computational performance, while its computational resources and energy cost are large. Moreover, data are often collected but not used. To solve these problems, we propose a framework for a computational model that follows a natural computational system, such as the human brain, and does not rely heavily on electronic computers. In particular, we propose a methodology based on the concept of `computation harvesting', which uses IoT data collected from rich sensors and leaves most of the computational processes to real-world phenomena as collected data. This aspect assumes that large-scale computations can be fast and resilient. Herein, we perform prediction tasks using real-world road traffic data to show the feasibility of computation harvesting. First, we show that the substantial computation in traffic flow is resilient against sensor failure and real-time traffic changes due to several combinations of harvesting from spatiotemporal dynamics to synthesize specific patterns. Next, we show the practicality of this method as a real-time prediction because of its low computational cost. Finally, we show that, compared to conventional methods, our method requires lower resources while providing a comparable performance.

cs.LG↗

arXiv2015

Large Fermi Surface of Heavy Electrons at the Border of Mott Insulating State in NiS2

One of the early triumphs of quantum physics is the explanation why some materials are metallic whereas others are insulating. While a treatment based on single electron states correctly predicts the character of most materials this approach can fail spectacularly, when the electrostatic repulsion between electrons causes strong correlations. Not only can these favor new and subtle forms of order in metals, such as magnetism or superconductivity, they can even cause the electrons in a half-filled energy band to lock into position altogether, producing a correlated, or Mott insulator. Arguably the most extreme manifestation of electronic correlations in dense electronic matter, the transition into the Mott insulating state raises a number of fundamental questions. Foremost among these is the fate of the electronic Fermi surface and the associated charge carrier mass, as the Mott transition is approached at low temperature, which have been particularly controversial in the high temperature superconducting cuprates. We report the first direct observation of the Fermi surface on the metallic side of a Mott insulating transition by high pressure quantum oscillatory measurements in NiS2. Our results point at a large Fermi surface consistent with Luttinger's theorem and a strongly enhanced carrier effective mass, suggesting that electron localization occurs via a diverging effective mass and concomitant slowing down of charge carriers as predicted theoretically.

cond-mat.str-el↗

arXiv2015

Large spin-wave bullet in a ferrimagnetic insulator driven by spin Hall effect

Due to its transverse nature, spin Hall effects (SHE) provide the possibility to excite and detect spin currents and magnetization dynamics even in magnetic insulators. Magnetic insulators are outstanding materials for the investigation of nonlinear phenomena and for novel low power spintronics applications because of their extremely low Gilbert damping. Here, we report on the direct imaging of electrically driven spin-torque ferromagnetic resonance (ST-FMR) in the ferrimagnetic insulator Y$_3$Fe$_5$O$_{12}$ based on the excitation and detection by SHEs. The driven spin dynamics in Y$_3$Fe$_5$O$_{12}$ is directly imaged by spatially-resolved microfocused Brillouin light scattering (BLS) spectroscopy. Previously, ST-FMR experiments assumed a uniform precession across the sample, which is not valid in our measurements. A strong spin-wave localization in the center of the sample is observed indicating the formation of a nonlinear, self-localized spin-wave `bullet'.

cond-mat.mes-hall↗

arXiv2011

An Empirical Investigation on Important Subgraphs in Cooperation-Competition networks

Subgraphs are very important for understanding structure and function of complex networks. Dyad and triad are the elementary subgraphs. We focus on the distribution of their act degree defined as the number of activities, events or organizations they join, which indicates the importance of the subgraphs. The empirical studies show that, in a lot of real world systems, the dyad or triad act degree distributions follow "shifted power law" (SPL), where α and γ are constants. We defined a "heterogeneity index", H, to describe how it is uneven and analytically deduced the correlation between H and α and γ. This manuscript, which shows the details of the empirical studies, serves as an online supplement of a paper submitted to a journal.

physics.soc-ph↗

arXiv2008

Observation of atom pairs in spontaneous four wave mixing of two colliding Bose-Einstein Condensates

We study atom scattering from two colliding Bose-Einstein condensates using a position sensitive, time resolved, single atom detector. In analogy to quantum optics, the process can also be thought of as spontaneous, degenerate four wave mixing of de Broglie waves. We find a clear correlation between atoms with opposite momenta, demonstrating pair production in the scattering process. We also observe a Hanbury Brown and Twiss correlation for collinear momenta, which permits an independent measurement of the size of the pair production source and thus the size of the spatial mode. The back to back pairs occupy very nearly two oppositely directed spatial modes, a promising feature for future quantum optics experiments.

quant-ph↗

arXiv2008

One MEMS Design Tool with Maximal Six Design Flows

This paper presents one MEMS design tool with total six design flows, which makes it possible that the MEMS designers are able to choose the most suitable design flow for their specific devices. The design tool is divided into three levels and interconnected by six interfaces. The three levels are lumped-element model based system level, finite element analysis based device level and process level, which covers nearly all modeling and simulation functions for MEMS design. The six interfaces are proposed to automatically transmit the design data between every two levels, thus the maximal six design flows could be realized. The interfaces take the netlist, solid model and layout as the data inlet and outlet for the system, device and process level respectively. The realization of these interfaces are presented and verified by design examples, which also proves that the enough flexibility in the design flow can really increase the design efficiency.

cs.OH↗