201 research outputs found
Quasiparticle Dissipation in d-wave Superconductor Phase Qubit
Recent phase sensitive experiments on high Tc superconductors, e.g.,
YBa_2Cu_3O_7 single crystals, have established the d-wave nature of the cuprate
materials. Here we discuss how to make use of d-wave Josephson junctions in the
construction of a phase qubit. We especially focus on the effect of
quasiparticle dissipation on the macroscopic quantum tunneling which
corresponds to the measurement process for the d-wave phase qubit.Comment: 3 pages, 1 figure, The Seventh International Conference on Quantum
Communication, Measurement and Computing, Glasgow, UK, from 25th to 29th July
2004. To appear in the AIP Conference Proceeding
Macroscopic quantum dynamics of pi-junctions with ferromagnetic insulators
We theoretically investigate the macroscopic quantum dynamics of a pi
junction with a superconductor (S) and a multiferroic material or a
ferromagnetic insulator (FI). By deriving the effective action from a
microscopic Hamiltonian, a pi-junction qubit (a S-FI-S superconducting quantum
interference device ring) is proposed. In this qubit, a quantum two-level
system is spontaneously generated and the effect of the quasiparticle
dissipation is found to be very weak. These features make it possible to
realize a quiet qubit with high coherency. We also investigate macroscopic
quantum tunneling (MQT) in current-biased S-FI-S pi junctions and show that the
influence of the quasiparticle dissipation on MQT is negligibly small.Comment: 4 pages, 2 figure
Weight function method for precise determination of top quark mass at Large Hadron Collider
We propose a new method to measure a theoretically well-defined top quark
mass at the LHC. This method is based on the "weight function method," which we
proposed in our preceding paper. It requires only lepton energy distribution
and is basically independent of the production process of the top quark. We
perform a simulation analysis of the top quark mass reconstruction with
pair production and lepton+jets decay channel at the leading order.
The estimated statistical error of the top quark mass is about GeV with
an integrated luminosity of fb at TeV. We also
estimate some of the major systematic uncertainties and find that they are
under good control.Comment: 8 pages, 7 figures, version to appear in PL
Atomic scale 0-pi transition in a high-Tc superconductor/ferromagnetic-insulator/high-T superconductor Josephson junction
We study the Josephson transport in a high-Tc
superconductor/ferromagnetic-insulator(FI)/high-Tc superconductor numerically.
We found the formation of a pi-junction in such systems. More remarkably the
ground state of such junction alternates between 0- and pi-states when
thickness of FI is increasing by a single atomic layer. We propose an
experimental setup for observing the atomic-scale 0-pi transition. Such
FI-based pi-junctions can be used to implement highly-coherent quantum bits.Comment: 4 pages, 3 figure
Theory of Macroscopic Quantum Tunneling and Dissipation in High-Tc Josephson Junctions
We have investigated macroscopic quantum tunneling (MQT) in in-plane high-Tc
superconductor Josephson junctions and the influence of the nodal-quasiparticle
and the zero energy bound states (ZES) on MQT. We have shown that the presence
of the ZES at the interface between the insulator and the superconductor leads
to strong Ohmic quasiparticle dissipation. Therefore, the MQT rate is
noticeably suppressed in comparison with the c-axis junctions in which ZES are
completely absent.Comment: 4 pages. 1 figur
Effect of zero energy bound states on macroscopic quantum tunneling in high-Tc superconductor junctions
The macroscopic quantum tunneling (MQT) in the current biased high-Tc
superconductor Josephson junctions and the effect of the zero energy bound
states (ZES) on the MQT are theoretically investigated. We obtained the
analytical formula of the MQT rate and showed that the presence of the ZES at
the normal/superconductor interface leads to a strong Ohmic quasiparticle
dissipation. Therefore, the MQT rate is noticeably inhibited in compared with
the c-axis junctions in which the ZES are completely absent.Comment: 4 pages, 1 figure, comment and reference about recent experiment
adde
Electron Transport in Magnetic-Field-Induced Quasi-One-Dimensional Electron Systems in Semiconductor Nanowhiskers
Many-body effects on tunneling of electrons in semiconductor nanowhiskers are
investigated in a magnetic quantum limit. We consider the system with which
bulk and edge states coexist. We show that interaction parameters of edge
states are much smaller than those of bulk states and the tunneling conductance
of edge states hardly depends on temperature and the singular behavior of
tunneling conductance of bulk states can be observed.Comment: 4 pages, 4 figure
Numerical study of pi-junction using spin filtering barriers
We numerically investigate the Josephson transport through ferromagnetic
insulators (FIs) by taking into account its band structure. By use of the
recursive Green's function method, we found the formation of the pi junction in
the case of the fully spin-polarized FI (FPFI), e.g., LaBaCuO.
Moreover, the 0-pi transition is induced by increasing the thickness of FPFI.
On the other hand, Josephson current through the Eu chalcogenides shows the pi
junction behavior in the case of the strong d-f hybridization between the
conduction d and the localized f electrons of Eu. Such FI-based Josephson
junctions may become a element in the architecture of future quantum
information devices.Comment: 9 pages, 5 figure
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