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143 results on '"Takayanagi, Hideaki"'

8. Determination of the capacitance o nm scale Josephson junctions

Author

Deppe, Frank, Saito, Shiro, Tanaka, Hirotaka, and Takayanagi, Hideaki

Subjects
Flux (Metallurgy) -- Electric properties, Flux (Metallurgy) -- Research, Josephson junction -- Electric properties, Josephson junction -- Research, Physics
Abstract

Superconducting three-Josephson-junction flux qubits (3JFQB) are possible candidates for the basic elements of a future scalable quantum computer. In this study the capacitance per junction area of junctions used in 3JFQB's are estimated.

Published
2004

39. Carrier flow and nonequilibrium superconductivity in superconductor-based light-emitting diode

Author

Inoue, Ryotaro, Takayanagi, Hideaki, Akazaki, Tatsushi, Tanaka, Kazunori, Sasakura, Hirotaka, and Suemune, Ikuo

Subjects
Superconductivity (cond-mat.supr-con), Condensed Matter::Superconductivity, Condensed Matter - Superconductivity, FOS: Physical sciences
Abstract

Superconductor-based light-emitting diode (superconductor-based LED) in strong light-confinement regime are characterized as a superconductor-based three-terminal device, and its transport properties are quantitatively investigated. In the gate-controlled region, we confirm the realization of new-type Josephson field effect transistor (JoFET) performance, where the channel cross-sectional area of the junction is directly modulated by the gate voltage. In the current-injected region, the superconducting critical current of $\mu$A order in the Josephson junction is found to be modulated by the steady current injection of pA order. This ultrahigh monitoring sensitivity of the radiative recombination process can be explained by taking into account the fact that the energy relaxation of the absorbed photons causes the conversion of superconducting pairs to quasiparticles in the active layer. Using quasiparticle density and superconducting pair density, we discuss the carrier flows together with the non-equilibrium superconductovity in the active layer and the superconducting electrodes, which take place for compensating the conversion.

Published
2013

44. Time evolution and decoherence of entangled states realized in coupled superconducting flux qubits

Author

Mouri, Takuya, Nakano, Hayato, and Takayanagi, Hideaki

Subjects
Superconductivity (cond-mat.supr-con), Condensed Matter - Mesoscale and Nanoscale Physics, Condensed Matter - Superconductivity, Mesoscale and Nanoscale Physics (cond-mat.mes-hall), FOS: Physical sciences, Quantum Physics
Abstract

We study theoretically how decoherence affects superposition states composed of entangled states in inductively coupled two superconducting flux-qubits. We discover that the quantum fluctuation of an observable in a coupled flux-qubit system plays a crucial role in decoherence when the expectation value of the observable is zero. This examplifies that decoherence can be also induced through a quantum mechanically higher-order effect. We also find that there exists a decoherence free subspace for the environment coupled via a charge degree of freedom of the qubit system., 4 pages, 5 figures

Published
2005

46. Single-Shot Readout of Macroscopic Quantum Superposition State in a Superconducting Flux Qubit

Author

Tanaka, Hirotaka, Saito, Shiro, Nakano, Hayato, Semba, Kouichi, Ueda, Masahito, and Takayanagi, Hideaki

Subjects
Superconductivity (cond-mat.supr-con), Computer Science::Emerging Technologies, Condensed Matter::Superconductivity, Condensed Matter - Superconductivity, FOS: Physical sciences, Quantum Physics
Abstract

Single-shot readout experiments were performed on the two lowest-energy states of a superconducting qubit with three Josephson junctions embedded in a superconducting loop. We measured the qubit state via switching current Isw of a current-biased dc-SQUID, a quantum detector surrounding the qubit loop. The qubit signals were measured in a small Isw regime of the SQUID, typically less than 100 nA, where the Isw distribution is particularly narrow. The obtained single-shot data indicate that the qubit state is readout, through the flux generated by the qubit persistent-current, as energy eigenstates rather than current eigenstates., 5 pages, 6 figures

Published
2004

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