12,684 research outputs found
Suppression of the superconducting energy gap in intrinsic Josephson junctions of single crystals
We have observed back-bending structures at high bias current in the
current-voltage curves of intrinsic Josephson junctions. These structures may
be caused by nonequilibrium quasiparticle injection and/or Joule heating. The
energy gap suppression varies considerably with temperature. Different levels
of the suppression are observed when the same level of current passes through
top electrodes of different sizes. Another effect which is seen and discussed,
is a super-current ``reentrance'' of a single intrinsic Josephson junction with
high bias current.Comment: accepted by Supercond. Sci. and Tech., 200
A conditional quantum phase gate between two 3-state atoms
We propose a scheme for conditional quantum logic between two 3-state atoms
that share a quantum data-bus such as a single mode optical field in cavity QED
systems, or a collective vibrational state of trapped ions. Making use of
quantum interference, our scheme achieves successful conditional phase
evolution without any real transitions of atomic internal states or populating
the quantum data-bus. In addition, it only requires common addressing of the
two atoms by external laser fields.Comment: 8 fig
Reconstruction of the phase of matter-wave fields using a momentum resolved cross-correlation technique
We investigate the potential of the so-called XFROG cross-correlation
technique originally developed for ultrashort laser pulses for the recovery of
the amplitude and phase of the condensate wave function of a Bose-Einstein
condensate. Key features of the XFROG method are its high resolution,
versatility and stability against noise and some sources of systematic errors.
After showing how an analogue of XFROG can be realized for Bose-Einstein
condensates, we illustrate its effectiveness in determining the amplitude and
phase of the wave function of a vortex state. The impact of a reduction of the
number of measurements and of typical sources of noise on the field
reconstruction are also analyzed.Comment: 7 pages; 9 figures; article with higher resolution figures available
from author
Charge Ordered RVB States in the Doped Cuprates
We study charge ordered d-wave resonating valence bond states (dRVB) in the
doped cuprates, and estimate the energies of these states in a generalized model by using a renormalized mean field theory. The long range Coulomb
potential tends to modulate the charge density in favor of the charge ordered
RVB state. The possible relevance to the recently observed
checkerboard patterns in tunnelling conductance in high cuprates is
discussed.Comment: 4 pages, 4 figures, 3 table
Controllable exchange coupling between two singlet-triplet qubits
We study controllable exchange coupling between two singlet-triplet qubits.
We start from the original second quantized Hamiltonian of a quadruple quantum
dot system and obtain the effective spin-spin interaction between the two
qubits using the projection operator method. Under a strong uniform external
magnetic field and an inhomogeneous local micro-magnetic field, the effective
interqubit coupling is of the Ising type, and the coupling strength can be
expressed in terms of quantum dot parameters. Finally, we discuss how to
generate various two-qubit operations using this controllable coupling, such as
entanglement generation, and controlled-NOT gate.Comment: 9 pages, 3 figure
Mesoscopic circuits with charge discreteness:quantum transmission lines
We propose a quantum Hamiltonian for a transmission line with charge
discreteness. The periodic line is composed of an inductance and a capacitance
per cell. In every cell the charge operator satisfies a nonlinear equation of
motion because of the discreteness of the charge. In the basis of one-energy
per site, the spectrum can be calculated explicitly. We consider briefly the
incorporation of electrical resistance in the line.Comment: 11 pages. 0 figures. Will be published in Phys.Rev.
A Variational Expansion for the Free Energy of a Bosonic System
In this paper, a variational perturbation scheme for nonrelativistic
many-Fermion systems is generalized to a Bosonic system. By calculating the
free energy of an anharmonic oscillator model, we investigated this variational
expansion scheme for its efficiency. Using the modified Feynman rules for the
diagrams, we obtained the analytical expression of the free energy up to the
fourth order. Our numerical results at various orders are compared with the
exact and other relevant results.Comment: 9 pages, 3 EPS figures. With a few typo errors corrected. to appear
in J. Phys.
An improved solar wind electron-density model for pulsar timing
Variations in the solar wind density introduce variable delays into pulsar
timing observations. Current pulsar timing analysis programs only implement
simple models of the solar wind, which not only limit the timing accuracy, but
can also affect measurements of pulsar rotational, astrometric and orbital
parameters. We describe a new model of the solar wind electron density content
which uses observations from the Wilcox Solar Observatory of the solar magnetic
field. We have implemented this model into the tempo2 pulsar timing package. We
show that this model is more accurate than previous models and that these
corrections are necessary for high precision pulsar timing applications.Comment: Accepted by ApJ, 13 pages, 4 figure
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