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Analysis of Critical Points in a Permutation Model on Hierarchical Lattices by Real-Space Renormalization Group
Authors:
Ryuki Ito,
Taisei Matsuo,
Masayuki Ohzeki
Abstract:
The permutation model is a classical spin system where elements of the symmetric group interact with one another. The partition function of this model is directly related to the entanglement structure of random quantum circuits and random tensor networks. In these contexts, the entanglement entropy undergoes a transition between area-law and volume-law scaling, depending on the model parameters. T…
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The permutation model is a classical spin system where elements of the symmetric group interact with one another. The partition function of this model is directly related to the entanglement structure of random quantum circuits and random tensor networks. In these contexts, the entanglement entropy undergoes a transition between area-law and volume-law scaling, depending on the model parameters. This transition point has attracted considerable attention. In the present work, we investigate the ferromagnetic-paramagnetic phase transition of the permutation model, which corresponds to the entanglement entropy transition. Using exact real-space renormalization group calculations on self-dual hierarchical lattices, we numerically determine finite-replica critical points for (q=mn=2,...,6). We compare the results with the duality prediction based on the Fourier transform of the symmetric group and then extrapolate the b=3 data toward the replica limit $mn\to0$, where the effective dimension is two. The comparison supports the duality-based estimate while also clarifying the systematic uncertainty associated with the extrapolation formula.
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Submitted 25 May, 2026;
originally announced May 2026.
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Spin Hall effect and Berry curvature of gravitons from quantum field theory
Authors:
Ritsuki Ito,
Kazuya Mameda,
Naoki Yamamoto
Abstract:
Based on quantum field theory of linearized gravity, we formulate the Wigner function for right- and left-handed gravitons. By applying the Wigner transformation to the second-order metric perturbations in the graviton energy-momentum tensor obtained from the Einstein-Hilbert action, we demonstrate the emergence of the spin Hall effect of gravitons in curved spacetime. This effect originates from…
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Based on quantum field theory of linearized gravity, we formulate the Wigner function for right- and left-handed gravitons. By applying the Wigner transformation to the second-order metric perturbations in the graviton energy-momentum tensor obtained from the Einstein-Hilbert action, we demonstrate the emergence of the spin Hall effect of gravitons in curved spacetime. This effect originates from the Berry curvature of gravitons, which has opposite signs for right- and left-handed helicities, and leads to a helicity-dependent splitting of the graviton energy Hall current. The magnitude of this splitting is found to be exactly twice that of the corresponding spin Hall current for photons.
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Submitted 19 May, 2026;
originally announced May 2026.
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High-temperature helical edge states in BiSbTeSe$_2$/graphene van der Waals heterostructure
Authors:
Yoichi Tanabe,
Ngoc Han Tu,
Ming-Chun Jiang,
Yi Ling Chiew,
Mitsutaka Haruta,
Kiyohiro Adachi,
David Pomaranski,
Ryo Ito,
Yuya Shimazaki,
Daisuke Hashizume,
Xiuzhen Yu,
Guang-Yu Guo,
Ryotaro Arita,
Michihisa Yamamoto
Abstract:
Van der Waals heterostructures have been used to tailor atomic layers into various artificial materials through interactions at heterointerfaces. The interplay between the band gap created by the band folding of the interfacial potential and the band inversion driven by enhanced spin-orbit interaction (SOI) through band hybridization enables us to realize a two-dimensional topological insulator (2…
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Van der Waals heterostructures have been used to tailor atomic layers into various artificial materials through interactions at heterointerfaces. The interplay between the band gap created by the band folding of the interfacial potential and the band inversion driven by enhanced spin-orbit interaction (SOI) through band hybridization enables us to realize a two-dimensional topological insulator (2D-TI). Here we report the realization of graphene 2D-TIs by epitaxial growth of three-dimensional topological insulator (3D-TI) BiSbTeSe$_2$ ultrathin films on graphene. By increasing the BiSbTeSe$_2$ thickness from 2 nm to 9 nm to enhance SOI on graphene, the electronic state is altered from the trivial Kekul${é}$ insulator to the 2D-TI. The nonlocal transport reveals the helical edge conduction which survives up to 200 K at maximum. Our graphene 2D-TI is stable, easy to make electrical contacts, and of high quality. It offers various applications including spin-current conversion and platforms for Majorana fermions in junctions to superconductors.
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Submitted 25 June, 2025;
originally announced June 2025.
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Dynamic scaling of vorticity in phase-separating superfluid mixtures
Authors:
Ryuta Ito,
Hiromitsu Takeuchi
Abstract:
Recently, it has been experimentally confirmed that non-equilibrium dynamics of phase separation in strongly ferromagnetic Bose-Einstein condensates of $^7$Li atoms obey the dynamic scaling law belonging to the binary-fluid universality class in the inertial hydrodynamic stage. The current work theoretically and numerically studies the dynamic scaling law of structure factor of vorticity in a phas…
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Recently, it has been experimentally confirmed that non-equilibrium dynamics of phase separation in strongly ferromagnetic Bose-Einstein condensates of $^7$Li atoms obey the dynamic scaling law belonging to the binary-fluid universality class in the inertial hydrodynamic stage. The current work theoretically and numerically studies the dynamic scaling law of structure factor of vorticity in a phase-separating binary superfluid mixture, equivalent to the $^7$Li condensates in a strong limit of quadratic Zeeman shift. We found a dynamic scaling law for the structure factor based on our numerical observation that the peak of the energy spectrum from turbulence theory does not vary in time in the stage. Similarly to freely decaying turbulence, a power-law hierarchy exists in the energy spectrum in our system, and we proposed a decay law of the energy based on the dynamic scaling law by introducing the microscopic, high-wavenumber cutoff.
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Submitted 18 June, 2025; v1 submitted 6 May, 2025;
originally announced May 2025.
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Semiconductor Circuits for Quantum Computing with Electronic Wave Packets
Authors:
David Pomaranski,
Ryo Ito,
Ngoc Han Tu,
Arne Ludwig,
Andreas D. Wieck,
Shintaro Takada,
Nobu-Hisa Kaneko,
Seddik Ouacel,
Christopher Bauerle,
Michihisa Yamamoto
Abstract:
Standard approaches to quantum computing require significant overhead to correct for errors. The hardware size for conventional quantum processors in solids often increases linearly with the number of physical qubits, such as for transmon qubits in superconducting circuits or electron spin qubits in quantum dot arrays. While photonic circuits based on flying qubits do not suffer from decoherence o…
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Standard approaches to quantum computing require significant overhead to correct for errors. The hardware size for conventional quantum processors in solids often increases linearly with the number of physical qubits, such as for transmon qubits in superconducting circuits or electron spin qubits in quantum dot arrays. While photonic circuits based on flying qubits do not suffer from decoherence or lack of potential scalability, they have encountered significant challenges to overcome photon loss in long delay circuits. Here, we propose an alternative approach that utilizes flying electronic wave packets propagating in solid-state quantum semiconductor circuits. Using a novel time-bin architecture for the electronic wave packets, hardware requirements are drastically reduced because qubits can be created on-demand and manipulated with a common hardware element, unlike the localized approach of wiring each qubit individually. The electronic Coulomb interaction enables reliable coupling and readout of qubits. Improving upon previous devices, we realize electronic interference at the level of a single quantized mode that can be used for manipulation of electronic wavepackets. This important landmark lays the foundation for fault-tolerant quantum computing with a compact and scalable architecture based on electron interferometry in semiconductors.
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Submitted 21 October, 2024;
originally announced October 2024.
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Electrical control of a Kondo spin screening cloud
Authors:
Ngoc Han Tu,
Donghoon Kim,
Minsoo L. Kim,
Jeongmin Shim,
Ryo Ito,
David Pomaranski,
Ivan V. Borzenets,
Arne Ludwig,
Andreas D. Wieck,
Heung-Sun Sim,
Michihisa Yamamoto
Abstract:
Quantitative analysis of quantum many-body systems, consisting of numerous itinerant electrons that interact with localized spins or electrons, is a long-standing issue. The Kondo cloud, a quantum many-body object of conduction electrons that screens a single localized spin, is the building block of such strongly correlated electronic systems. While quantitative analysis of the Kondo cloud associa…
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Quantitative analysis of quantum many-body systems, consisting of numerous itinerant electrons that interact with localized spins or electrons, is a long-standing issue. The Kondo cloud, a quantum many-body object of conduction electrons that screens a single localized spin, is the building block of such strongly correlated electronic systems. While quantitative analysis of the Kondo cloud associated with a single magnetic impurity is well established for uniform conduction electrons, the fundamental properties of a deformed Kondo cloud influenced by conduction electrons with a modulated density of states remain unsolved. Here we report engineering of the Kondo cloud deformation by confining a part of the cloud into a quantum box called the Kondo box that mimics realistic material systems. We demonstrate quantitative control of the Kondo cloud by developing a way of tuning quantum interference in the box and monitoring the Kondo entanglement. The temperature dependence of the entanglement reveals counterintuitively that the cloud shape is altered mainly outside the box although the quantum interference in the box is tuned. Our work provides a way to simulate various strongly correlated systems by integrating the Kondo cloud, which is not possible in the current theoretical framework.
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Submitted 25 March, 2025; v1 submitted 18 April, 2024;
originally announced April 2024.
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Coherent beam splitting of flying electrons driven by a surface acoustic wave
Authors:
R. Ito,
S. Takada,
A. Ludwig,
A. D. Wieck,
S. Tarucha,
M. Yamamoto
Abstract:
We develop a coherent beam splitter for single electrons driven through two tunnel-coupled quantum wires by surface acoustic waves (SAWs). The output current through each wire oscillates with gate voltages to tune the tunnel-coupling and potential difference between the wires. This oscillation is assigned to coherent electron tunneling motion that can be used to encode a flying qubit and is well r…
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We develop a coherent beam splitter for single electrons driven through two tunnel-coupled quantum wires by surface acoustic waves (SAWs). The output current through each wire oscillates with gate voltages to tune the tunnel-coupling and potential difference between the wires. This oscillation is assigned to coherent electron tunneling motion that can be used to encode a flying qubit and is well reproduced by numerical calculations of time evolution of the SAW-driven single electrons. The oscillation visibility is currently limited to about 3%, but robust against decoherence, indicating that the SAW-electron can serve as a novel platform for a solid-state flying qubit.
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Submitted 24 April, 2020;
originally announced April 2020.
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Lower critical field measurement of NbN multilayer thin film superconductor at KEK
Authors:
H. Ito,
H. Hayano,
T. Kubo,
T. Saeki,
R. Katayama,
Y. Iwashita,
H. Tongu,
R. Ito,
T. Nagata,
C. Z. Antoine
Abstract:
The multilayer thin film structure of the superconductor has been proposed by A. Gurevich to enhance the maximum gradient of SRF cavities. The lower critical field Hc1 at which the vortex starts penetrating the superconducting material will be improved by coating Nb with thin film superconductor such as NbN. It is expected that the enhancement of Hc1 depends on the thickness of each layer. In orde…
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The multilayer thin film structure of the superconductor has been proposed by A. Gurevich to enhance the maximum gradient of SRF cavities. The lower critical field Hc1 at which the vortex starts penetrating the superconducting material will be improved by coating Nb with thin film superconductor such as NbN. It is expected that the enhancement of Hc1 depends on the thickness of each layer. In order to determine the optimum thickness of each layer and to compare the measurement results with the theoretical prediction proposed by T. Kubo, we developed the Hc1 measurement system using the third harmonic response of the applied AC magnetic field at KEK. For the Hc1 measurement without the influence of the edge or the shape effects, the AC magnetic field can be applied locally by the solenoid coil of 5mm diameter in our measurement system. ULVAC made the NbN-SiO2 multilayer thin film samples of various NbN thicknesses. In this report, the measurement result of the bulk Nb sample and NbN-SiO2 multilayer thin film samples of different thickness of NbN layer will be discussed.
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Submitted 8 July, 2019;
originally announced July 2019.