arXiv subjects

H. Mukai

Publications and source records attributed to H. Mukai.

6 recordsLinked to original sources

arXiv2025

Efficient spectrum analysis for multi-junction superconducting circuit

The extraction of transition frequencies from a spectrum has conventionally relied on empirical methods, and particularly in complex systems, it is a time-consuming and cumbersome process. To address this challenge, we establish a semi-automated efficient and precise spectrum analysis method. It first employs image processing methods to extract transition frequencies, subsequently estimating the Hamiltonians of a superconducting quantum circuit containing multiple Josephson junctions. In addition, we determine the suitable range of approximations in simulation methods, evaluating the physical reliability of the analysis.

quant-ph↗

arXiv2019

Pseudo-2D superconducting quantum computing circuit for the surface code: the proposal and preliminary tests

Of the many potential hardware platforms, superconducting quantum circuits have become the leading contender for constructing a scalable quantum computing system. All current architecture designs necessitate a 2D arrangement of superconducting qubits with nearest neighbour interactions, compatible with powerful quantum error correction using the surface code. A major hurdle for scalability in superconducting systems is the so called wiring problem, where qubits internal to a chip-set become inaccessible for external control/readout lines. Current approaches resort to intricate and exotic 3D wiring and packaging technology which is a significant engineering challenge to realize, while maintaining qubit fidelity. Here we solve this problem and present a modified superconducting scalable micro-architecture that does not require any 3D external line technology and reverts back to a completely planar design. This is enabled by a new pseudo-2D resonator network that provides inter-qubit connections via airbridges. We carried out experiments to examine the feasibility of the newly introduced airbridge component. The measured quality factor of these new inter-qubit resonators is sufficient for high fidelity gates, below the threshold for the surface code, with negligible measured cross-talk. The resulting physical separation of the external wirings and the inter-qubit connections on-chip should reduce cross-talk and decoherence as the chip-set increases in size. This result demonstrates that a large-scale, fully error corrected quantum computer can be constructed by monolithic integration technologies without additional overhead and without special packaging know-hows.

quant-ph↗

arXiv2013

Antipersistent behavior of defects in a lyotropic liquid crystal during annihilation

We report on the dynamical behavior of defects of strength s = +/- 1/2 in a lyotropic liquid crystal during the annihilation process. By following their positions using time resolved polarizing microscopy technique, we present statistically significant evidence that the relative velocity between defect pairs is Gaussian distributed, anti-persistent and long-range correlated. We further show that simulations of the Lebwohl-Lasher model reproduce quite well our experimental findings.

cond-mat.soft↗

arXiv2013

Spin blocker made of semiconductor double quantum well using the Rashba effect

We propose a lateral spin-blockade device that uses an InGaAs/InAlAs double quantum well (DQW), where the values of the Rashba spin-orbit parameter $α_{\rm R}$ are opposite in sign but equal in magnitude between the constituent quantum wells (QW). By tuning the channel length of DQW and the magnitude of the externally applied in-plane magnetic field, one can block the transmission of one spin (e.g., spin-down) component, leading to a spin-polarized current. Such a spin-blocking effect, brought about by wave vector matching of the spin-split Fermi surfaces between the two QWs, paves the way for a new scheme of spin-polarized electric current generation for future spintronics applications based on semiconductor band engineering.

cond-mat.mes-hall↗

arXiv2013

Annihilation dynamics of stringlike topological defects in a nematic lyotropic liquid crystal

Topological defects can appear whenever there is some type of ordering. Its ubiquity in nature has been the subject of several studies, from early Universe to condensed matter. In this work, we investigated the annihilation dynamics of defects and antidefects in a lyotropic nematic liquid crystal (ternary mixture of potassium laurate, decanol and deionized-destilated water) using the polarized optical light microscopy technique. We analyzed Schlieren textures with topological defects produced due to a symmetry breaking in the transition of the isotropic to nematic calamitic phase after a temperature quench. As result, we obtained for the distance D between two annihilating defects (defect-antidefect pair), as a function of time t remaining for the annihilation, the scaling law D ~ t^α, with α= 0.390 and standard deviation σ= 0.085. Our findings go in the direction to extend experimental results related to dynamics of defects in liquid crystals since only thermotropic and polymerics ones had been investigated. In addition, our results are in good quantitative agreement with previous investigations on the subject.

cond-mat.soft↗

arXiv2002

Nonminimal coupling, equivalence principle and exact Foldy-Wouthuysen transformation

It is shown that the exact Foldy-Wouthuysen transformation for spin-0 particles on spacetimes described by the metrics $ds^2 = V^2 dt^2 - W^2 d {\bf{x}}^2$, where $V=V({\bf{x}})$ and $W=W({\bf{x}})$, only exists if the scalar field is nonminimally coupled to the Ricci scalar field with a coupling constant equal to 1/6. The nonminimal coupling term, in turn, does not violate the equivalence principle. As an application we obtain the nonrelativistic Foldy-Wouthuysen Hamiltonian concerning the general solution to the linearized field equations of higher-derivative gravity for a static pointlike source in the Teyssandier gauge.

gr-qc↗