71 research outputs found
Quantum logic gates for coupled superconducting phase qubits
Based on a quantum analysis of two capacitively coupled current-biased
Josephson junctions, we propose two fundamental two-qubit quantum logic gates.
Each of these gates, when supplemented by single-qubit operations, is
sufficient for universal quantum computation. Numerical solutions of the
time-dependent Schroedinger equation demonstrate that these operations can be
performed with good fidelity.Comment: 4 pages, 5 figures, revised for publicatio
Spectroscopy of Three-Particle Entanglement in a Macroscopic Superconducting Circuit
We study the quantum mechanical behavior of a macroscopic, three-body,
superconducting circuit. Microwave spectroscopy on our system, a resonator
coupling two large Josephson junctions, produced complex energy spectra well
explained by quantum theory over a large frequency range. By tuning each
junction separately into resonance with the resonator, we first observe strong
coupling between each junction and the resonator. Bringing both junctions
together into resonance with the resonator, we find spectroscopic evidence for
entanglement between all three degrees of freedom and suggest a new method for
controllable coupling of distant qubits, a key step toward quantum computation.Comment: 4 pages, 3 figure
Mixed-parity superconductivity in centrosymmetric crystals
A weak-coupling formalism for superconducting states possessing both singlet
(even parity) and triplet (odd parity) components of the order parameter in
centrosymmetric crystals is developed. It is shown that the quasiparticle
energy spectrum may be non-degenerate even if the triplet component is unitary.
The superconducting gap of a mixed-parity state may have line nodes in the
strong spin-orbit coupling limit. The pseudospin carried by the superconducting
electrons is calculated, from which follows a prediction of a kink anomaly in
the temperature dependence of muon spin relaxation rate. The anomaly occurs at
the phase boundary between the bare triplet and mixed-parity states. The
stability of mixed-parity states is discussed within Ginzburg-Landau theory.
The results may have immediate application to the superconducting series
Pr(Os,Ru)4Sb12.Comment: 5 pages, 2 figures. Final version accepted to PR
Multilevel effects in the Rabi oscillations of a Josephson phase qubit
We present Rabi oscillation measurements of a Nb/AlOx/Nb dc superconducting
quantum interference device (SQUID) phase qubit with a 100 um^2 area junction
acquired over a range of microwave drive power and frequency detuning. Given
the slightly anharmonic level structure of the device, several excited states
play an important role in the qubit dynamics, particularly at high power. To
investigate the effects of these levels, multiphoton Rabi oscillations were
monitored by measuring the tunneling escape rate of the device to the voltage
state, which is particularly sensitive to excited state population. We compare
the observed oscillation frequencies with a simplified model constructed from
the full phase qubit Hamiltonian and also compare time-dependent escape rate
measurements with a more complete density-matrix simulation. Good quantitative
agreement is found between the data and simulations, allowing us to identify a
shift in resonance (analogous to the ac Stark effect), a suppression of the
Rabi frequency, and leakage to the higher excited states.Comment: 14 pages, 9 figures; minor corrections, updated reference
Trigonometric Parallaxes of Central Stars of Planetary Nebulae
Trigonometric parallaxes of 16 nearby planetary nebulae are presented,
including reduced errors for seven objects with previous initial results and
results for six new objects. The median error in the parallax is 0.42 mas, and
twelve nebulae have parallax errors less than 20 percent. The parallax for
PHL932 is found here to be smaller than was measured by Hipparcos, and this
peculiar object is discussed. Comparisons are made with other distance
estimates. The distances determined from these parallaxes tend to be
intermediate between some short distance estimates and other long estimates;
they are somewhat smaller than estimated from spectra of the central stars.
Proper motions and tangential velocities are presented. No astrometric
perturbations from unresolved close companions are detected.Comment: 24 pages, includes 4 figures. Accepted for A
The USNO-B Catalog
USNO-B is an all-sky catalog that presents positions, proper motions,
magnitudes in various optical passbands, and star/galaxy estimators for
1,042,618,261 objects derived from 3,643,201,733 separate observations. The
data were obtained from scans of 7,435 Schmidt plates taken for the various sky
surveys during the last 50 years. USNO-B1.0 is believed to provide all-sky
coverage, completeness down to V = 21, 0.2 arcsecond astrometric accuracy at
J2000, 0.3 magnitude photometric accuracy in up to five colors, and 85%
accuracy for distinguishing stars from non-stellar objects. A brief discussion
of various issues is given here, but the actual data are available from
http://www.nofs.navy.mil and other sites.Comment: Accepted by Astronomical Journa
The Brown Dwarf Kinematics Project (BDKP) I. Proper Motions and Tangential Velocities for a Large Sample of Late-type M, L and T Dwarfs
We report proper motion measurements for 427 late-type M, L and T dwarfs, 332
of which have been measured for the first time. Combining these new proper
motions with previously published measurements yields a sample of 841 M7-T8
dwarfs. We combined parallax measurements or calculated spectrophotometric
distances and computed tangential velocities for the entire sample. We find
that kinematics for the full and volume-limited 20 pc samples are consistent
with those expected for the Galactic thin disk, with no significant differences
between late-type M, L, and T dwarfs. Applying an age-velocity relation we
conclude that the average kinematic age of the 20 pc sample of ultracool dwarfs
is older than recent kinematic estimates and more consistent with age results
calculated with population synthesis models. There is a statistically distinct
population of high tangential velocity sources whose kinematics suggest an even
older population of ultracool dwarfs belonging to either the Galactic thick
disk or halo. We isolate subsets of the entire sample, including low
surface-gravity dwarfs, unusually blue L dwarfs, and photometric outliers in
J-Ks color and investigate their kinematics. We find that the spectroscopically
distinct class of unusually blue L dwarfs has kinematics clearly consistent
with old age, implying that high surface-gravity and/or low metallicity may be
relevant to their spectral properties. The low surface-gravity dwarfs are
kinematically younger than the overall population, and the kinematics of the
red and blue ultracool dwarfs suggest ages that are younger and older than the
full sample, respectively. We also present a reduced proper motion diagram at
2MASS Ks for the entire population and find that a limit of H_Ks > 18 excludes
M dwarfs from the L and T dwarf population regardless of near-infrared color.Comment: Accepted for publication in the Astronomical Journal, 21 pages text,
12 tables, 12 figure
Review on Superconducting Materials
Short review of the topical comprehension of the superconductor materials
classes Cuprate High-Temperature Superconductors, other oxide superconductors,
Iron-based Superconductors, Heavy-Fermion Superconductors, Nitride
Superconductors, Organic and other Carbon-based Superconductors and Boride and
Borocarbide Superconductors, featuring their present theoretical understanding
and their aspects with respect to technical applications.Comment: A previous version of this article has been published in \" Applied
Superconductivity: Handbook on Devices and Applications \", Wiley-VCH ISBN:
978-3-527-41209-9. The new extended and updated version will be published in
\" Encyclopedia of Applied Physics \", Wiley-VC
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