1,197 research outputs found
Dust during the Reionization
The possibility that population III stars have reionized the Universe at
redshifts greater than 6 has recently gained momentum with WMAP polarization
results. Here we analyse the role of early dust produced by these stars and
ejected into the intergalactic medium. We show that this dust, heated by the
radiation from the same population III stars, produces a submillimetre excess.
The electromagnetic spectrum of this excess could account for a significant
fraction of the FIRAS (Far Infrared Absolute Spectrophotometer) cosmic far
infrared background above 700 micron. This spectrum, a primary anisotropy
() spectrum times the dust emissivity law, peaking in the
submillimetre domain around 750 micron, is generic and does not depend on other
detailed dust properties. Arcminute--scale anisotropies, coming from
inhomogeneities in this early dust, could be detected by future submillimetre
experiments such as Planck HFI.Comment: 6 pages, 8 figures, accepted by A&A; clarifications made, typos
fixed, results more exactly calculate
Controllable coherent population transfers in superconducting qubits for quantum computing
We propose an approach to coherently transfer populations between selected
quantum states in one- and two-qubit systems by using controllable
Stark-chirped rapid adiabatic passages (SCRAPs). These {\it evolution-time
insensitive} transfers, assisted by easily implementable single-qubit
phase-shift operations, could serve as elementary logic gates for quantum
computing. Specifically, this proposal could be conveniently demonstrated with
existing Josephson phase qubits. Our proposal can find an immediate application
in the readout of these qubits. Indeed, the broken parity symmetries of the
bound states in these artificial "atoms" provide an efficient approach to
design the required adiabatic pulses.Comment: 4 pages, 6 figures. to appear in Physical Review Letter
Local transformation of mixed states of two qubits to Bell diagonal states
The optimal entanglement manipulation for a single copy of mixed states of
two qubits is to transform it to a Bell diagonal state. In this paper we derive
an explicit form of the local operation that can realize such a transformation.
The result obtained is universal for arbitrary entangled two-qubit states and
it discloses that the corresponding local filter is not unique for density
matrices with rank and can be exclusively determined for that with
and 4. As illustrations, a four-parameters family of mixed states are explored,
the local filter as well as the transformation probability are given
explicitly, which verify the validity of the general result.Comment: 5 pages, to be published in Phys. Rev.
Anchoring Bias in Online Voting
Voting online with explicit ratings could largely reflect people's
preferences and objects' qualities, but ratings are always irrational, because
they may be affected by many unpredictable factors like mood, weather, as well
as other people's votes. By analyzing two real systems, this paper reveals a
systematic bias embedding in the individual decision-making processes, namely
people tend to give a low rating after a low rating, as well as a high rating
following a high rating. This so-called \emph{anchoring bias} is validated via
extensive comparisons with null models, and numerically speaking, the extent of
bias decays with interval voting number in a logarithmic form. Our findings
could be applied in the design of recommender systems and considered as
important complementary materials to previous knowledge about anchoring effects
on financial trades, performance judgements, auctions, and so on.Comment: 5 pages, 4 tables, 5 figure
Dust Distribution during Reionization
The dust produced by the first generation of stars will be a foreground to
cosmic microwave background. In order to evaluate the effect of this early
dust, we calculate the power spectrum of the dust emission anisotropies and
compare it with the sensitivity limit of the Planck satellite. The spatial
distribution of the dust is estimated through the distribution of dark matter.
At small angular scales () the dust signal is found to be
noticeable with the Planck detector for certain values of dust lifetime and
production rates. The dust signal is also compared to sensitivities of other
instruments. The early dust emission anisotropies are finally compared to those
of local dust and they are found to be similar in magnitude at mm wavelengths.Comment: 6 pages, 6 figures; Typos fixed. Clarifications in the abstract,
sections 2 and 4.1 and fig
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