289 research outputs found
Optimal fast single pulse readout of qubits
The computer simulations of the process of single pulse readout from the
flux-biased phase qubit is performed in the frame of one-dimensional
Schroedinger equation. It has been demonstrated that the readout error can be
minimized by choosing the optimal pulse duration and the depth of a potential
well, leading to the fidelity of 0.94 for 2ns and 0.965 for 12ns sinusoidal
pulses.Comment: 4 pages, 6 figure
Temperature dependence of coherent oscillations in Josephson phase qubits
We experimentally investigate the temperature dependence of Rabi oscillations
and Ramsey fringes in superconducting phase qubits driven by microwave pulses.
In a wide range of temperatures, we find that both the decay time and the
amplitude of these coherent oscillations remain nearly unaffected by thermal
fluctuations. The oscillations are observed well above the crossover
temperature from thermally activated escape to quantum tunneling for undriven
qubits. In the two-level limit, coherent qubit response rapidly vanishes as
soon as the energy of thermal fluctuations kT becomes larger than the energy
level spacing of the qubit. Our observations shed new light on the origin of
decoherence in superconducting qubits. The experimental data suggest that,
without degrading already achieved coherence times, phase qubits can be
operated at temperatures much higher than those reported till now.Comment: 4 pages, 4 figure
The dust SED in the dwarf galaxy NGC 1569: Indications for an altered dust composition?
We discuss the interpretation of the dust SED from the mid-infrared to the
millimeter range of NGC 1569. The model developed by D\'esert et al. (1990)
including three dust components (Polyaromatic Hydrocarbons, Very Small Grains
and big grains) can explain the data using a realistic interstellar radiation
field and adopting an enhanced abundance of VSGs. A simple three-temperature
model is also able to reproduce the data but requires a very low dust
temperature which is considered to be unlikely in this low-metallicity
starburst galaxy. The high abundance of Very Small Grains might be due to large
grain destruction in supernova shocks. This possibility is supported by ISO
data showing that the emission at 14.3 m, tracing VSGs, is enhanced with
respect to the emission at 6.7 m and 850 m in regions of high star
formation.Comment: 4 pages, conference proceedings paper, "The Spectral Energy
Distribution of Gas-Rich Galaxies: Confronting Models with Data", Heidelberg,
4-8 Oct. 2004, eds. C.C. Popescu & R.J. Tuffs, AIP Conf. Ser., in pres
Molecular Gas in Tidal Dwarf Galaxies: On-going Galaxy Formation
We investigate the process of galaxy formation as can be observed in the only
currently forming galaxies -- the so-called Tidal Dwarf Galaxies, hereafter
TDGs -- through observations of the molecular gas detected via its CO (Carbon
Monoxide) emission. Molecular gas is a key element in the galaxy formation
process, providing the link between a cloud of gas and a {\it bona fide}
galaxy. We have now detected CO in 9 TDGs with an overall detection rate of
80%, showing that molecular gas is abundant in TDGs, up to a few . The CO emission coincides both spatially and kinematically with the
HI emission, indicating that the molecular gas forms from the atomic hydrogen
where the HI column density is high. A possible trend of more evolved TDGs
having greater molecular gas masses is observed, in accord with the
transformation of HI into H. Although uncertainties are still large for
individual objects as the geometry is unknown, we find that the "dynamical"
masses of TDGs, estimated from the CO line widths, do not seem to be greater
than the "visible" masses (HI + H + a stellar component), i.e., TDGs
require no dark matter. We provide evidence that TDGs are self-gravitating
entities, implying that we are witnessing the ensemble of processes in galaxy
formation: concentration of large amounts of gas in a bound object,
condensation of the gas, which is atomic at this point, to form molecular gas
and the subsequent star formation from the dense molecular component.Comment: 8 pages 4 figures, to be published in: Proceedings of the IAU
Symposium 217: Recycling Intergalactic and Interstellar Matte
Enhanced Macroscopic Quantum Tunneling in BiSrCaCuO Intrinsic Josephson Junction Stacks
We have investigated macroscopic quantum tunneling in
BiSrCaCuO intrinsic Josephson junctions at millikelvin
temperatures using microwave irradiation. Measurements show that the escape
rate for uniformly switching stacks of N junctions is about times higher
than that of a single junction having the same plasma frequency. We argue that
this gigantic enhancement of macroscopic quantum tunneling rate in stacks is
boosted by current fluctuations which occur in the series array of junctions
loaded by the impedance of the environment.Comment: 4 pages and 5 figure
Dust in dwarf galaxies: The case of NGC 4214
We have carried out a detailed modelling of the dust heating and emission in
the nearby, starbursting dwarf galaxy NGC 4214. Due to its proximity and the
great wealth of data from the UV to the millimeter range (from GALEX, HST, {\it
Spitzer}, Herschel, Planck and IRAM) it is possible to separately model the
emission from HII regions and their associated photodissociation regions (PDRs)
and the emission from diffuse dust. Furthermore, most model parameters can be
directly determined from the data leaving very few free parameters. We can fit
both the emission from HII+PDR regions and the diffuse emission in NGC 4214
with these models with "normal" dust properties and realistic parameters.Comment: 4pages, 3 figures. To appear in 'The Spectral Energy Distribution of
Galaxies' Proceedings IAU Symposium No 284, 201
Entangling microscopic defects via a macroscopic quantum shuttle
In the microscopic world, multipartite entanglement has been achieved with
various types of nanometer sized two-level systems such as trapped ions, atoms
and photons. On the macroscopic scale ranging from micrometers to millimeters,
recent experiments have demonstrated bipartite and tripartite entanglement for
electronic quantum circuits with superconducting Josephson junctions. It
remains challenging to bridge these largely different length scales by
constructing hybrid quantum systems. Doing this may allow for manipulating the
entanglement of individual microscopic objects separated by macroscopically
large distances in a quantum circuit. Here we report on the experimental
demonstration of induced coherent interaction between two intrinsic two-level
states (TLSs) formed by atomic-scale defects in a solid via a superconducting
phase qubit. The tunable superconducting circuit serves as a shuttle
communicating quantum information between the two microscopic TLSs. We present
a detailed comparison between experiment and theory and find excellent
agreement over a wide range of parameters. We then use the theoretical model to
study the creation and movement of entanglement between the three components of
the quantum system.Comment: 11 pages, 5 figure
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