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Zhang, T.*; Tajima, Hiroyuki*; Sekino, Yuta*; Uchino, Shun; Liang, H.*
Communications Physics (Internet), 6, p.86_1 - 86_7, 2023/04
Times Cited Count：1 Percentile：57.37(Physics, Multidisciplinary)We theoretically propose the laser-induced Andreev reflection between two-component Fermi superfluid and normal states via spatially-uniform Rabi couplings. By analyzing the tunneling current between the superfluid and normal states up to the fourth order in the Rabi couplings, we find that the Andreev current exhibits unconventional non-Ohmic transport at zero temperature. Remarkably, the Andreev current gives the only contribution in the synthetic junction system at zero detunings regardless of the ratio of the chemical potential bias to the superfluid gap, which is in sharp contrast to that in the conventional superconductor-normal metal junction. Our result may also pave a way for understanding the black hole information paradox through the Andreev reflection as a quantum-information mirror.
Sekino, Yuta*; Tajima, Hiroyuki*; Uchino, Shun
Physical Review Research (Internet), 5(2), p.023058_1 - 023058_12, 2023/04
We investigate the spectrum of spin conductivity for a miscible two-component Bose-Einstein condensate (BEC) that exhibits spin superfluidity. By using the Bogoliubov theory, the regular part being the spin conductivity at finite ac frequency and the spin Drude weight characterizingthe delta-function peak at zero frequency are analytically computed. We demonstrate that the spectrum exhibits a power-law behavior at low frequency, reflecting gapless density and spin modes specific to the binary BEC. At the phase transition points into immiscible and quantum-dropletstates, the change in quasiparticle dispersion relations modifies the power law. In addition, the spin Drude weight becomes finite, indicating zero spin resistivity due to spin superfluidity. Our results also suggest that the Andreev-Bashkin drag density is accessible by measuring the spin conductivity spectrum.
Sekino, Yuta*; Tajima, Hiroyuki*; Uchino, Shun
Physical Review Research (Internet), 4(4), p.043014_1 - 043014_16, 2022/10
We show that the optical spin conductivity being a small AC response of a bulk spin current and elusive in condensed matter systems can be measured in ultracold atoms. We demonstrate that this conductivity contains rich information on quantum states by analyzing experimentally achievable systems. The obtained conductivity spectra being absent in the Drude conductivity reflect quasiparticle excitations and non-Fermi liquid properties. Unlike its mass transport counterpart, the spin conductivity serves as a probe applicable to clean atomic gases without disorder and lattice potentials. Our formalism can be generalized to various systems such as spin-orbit coupled and nonequilibrium systems.
topological Fermi superfluidsTajima, Hiroyuki*; Sekino, Yuta*; Uchino, Shun
Physical Review B, 105(6), p.064508_1 - 064508_9, 2022/02
Times Cited Count：4 Percentile：56.43(Materials Science, Multidisciplinary)We theoretically investigate optical bulk spin transport properties in a spin- topological Fermi superfluid. We specifically consider a one-dimensional system with an inter-spin 
-wave interaction, which can be realized in ultracold-atom experiments. Developing the BCS-Leggett theory to describe the BCS to Bose-Einstein condensate evolution and the Z
topological phase transition in this system, we show how the spin transport reflects these many-body aspects. We find that the optical spin conductivity, which is a small AC response of a spin current, shows the spin-gapped spectrum in the wide parameter region and the gap closes at the Z topological phase transition point. Moreover, the validity of the low-energy effective model of the Majorana zero mode is discussed along the BCS-BEC evolution in connection with the scale invariance at -wave unitarity.
Ozeki, Ryutaro*; Sekino, Kodai*; Suzuki, Tsuyoshi*; Sawai, Kei*; Takemura, Fumiaki*; Kawabata, Kuniaki; Yamashiro, Hideyuki*
no journal, ,
This paper proposed the browsing system and functions for underwater environmental data gathered by wireless sensor network. The discussions were done for the design approaches and implementation examples with gathered data.
