2,788 research outputs found
ARCADE: Absolute Radiometer for Cosmology, Astrophysics, and Diffuse Emission
The Absolute Radiometer for Cosmology, Astrophysics, and Diffuse Emission
(ARCADE) is a balloon-borne instrument designed to measure the temperature of
the cosmic microwave background at centimeter wavelengths. ARCADE searches for
deviations from a blackbody spectrum resulting from energy releases in the
early universe. Long-wavelength distortions in the CMB spectrum are expected in
all viable cosmological models. Detecting these distortions or showing that
they do not exist is an important step for understanding the early universe. We
describe the ARCADE instrument design, current status, and future plans.Comment: 12 pages, 6 figures. Proceedings of the Fundamental Physics With CMB
workshop, UC Irvine, March 23-25, 2006, to be published in New Astronomy
Review
ARCADE 2 Measurement of the Extra-Galactic Sky Temperature at 3-90 GHz
The ARCADE 2 instrument has measured the absolute temperature of the sky at
frequencies 3, 8, 10, 30, and 90 GHz, using an open-aperture cryogenic
instrument observing at balloon altitudes with no emissive windows between the
beam-forming optics and the sky. An external blackbody calibrator provides an
{\it in situ} reference. Systematic errors were greatly reduced by using
differential radiometers and cooling all critical components to physical
temperatures approximating the CMB temperature. A linear model is used to
compare the output of each radiometer to a set of thermometers on the
instrument. Small corrections are made for the residual emission from the
flight train, balloon, atmosphere, and foreground Galactic emission. The ARCADE
2 data alone show an extragalactic rise of mK at 3.3 GHz in addition
to a CMB temperature of K. Combining the ARCADE 2 data with
data from the literature shows a background power law spectrum of [K] from 22 MHz to 10 GHz ( GHz)
in addition to a CMB temperature of K.Comment: 11 pages 5 figures Submitted to Ap
Towards a Re-definition of the Second Based on Optical Atomic Clocks
The rapid increase in accuracy and stability of optical atomic clocks
compared to the caesium atomic clock as primary standard of time and frequency
asks for a future re-definition of the second in the International System of
Units (SI). The status of the optical clocks based on either single ions in
radio-frequency traps or on neutral atoms stored in an optical lattice is
described with special emphasis of the current work at the
Physikalisch-Technische Bundesanstalt (PTB). Besides the development and
operation of different optical clocks with estimated fractional uncertainties
in the 10^-18 range, the supporting work on ultra-stable lasers as core
elements and the means to compare remote optical clocks via transportable
standards, optical fibers, or transportable clocks is reported. Finally, the
conditions, methods and next steps are discussed that are the prerequisites for
a future re-definition of the second
Progress in Atomic Fountains at LNE-SYRTE
We give an overview of the work done with the Laboratoire National de
M\'etrologie et d'Essais-Syst\`emes de R\'ef\'erence Temps-Espace (LNE-SYRTE)
fountain ensemble during the last five years. After a description of the clock
ensemble, comprising three fountains, FO1, FO2, and FOM, and the newest
developments, we review recent studies of several systematic frequency shifts.
This includes the distributed cavity phase shift, which we evaluate for the FO1
and FOM fountains, applying the techniques of our recent work on FO2. We also
report calculations of the microwave lensing frequency shift for the three
fountains, review the status of the blackbody radiation shift, and summarize
recent experimental work to control microwave leakage and spurious phase
perturbations. We give current accuracy budgets. We also describe several
applications in time and frequency metrology: fountain comparisons,
calibrations of the international atomic time, secondary representation of the
SI second based on the 87Rb hyperfine frequency, absolute measurements of
optical frequencies, tests of the T2L2 satellite laser link, and review
fundamental physics applications of the LNE-SYRTE fountain ensemble. Finally,
we give a summary of the tests of the PHARAO cold atom space clock performed
using the FOM transportable fountain.Comment: 19 pages, 12 figures, 5 tables, 126 reference
Quantum Metrology Triangle Experiments: A Status Review
Quantum Metrology Triangle experiments combine three quantum electrical
effects (the Josephson effect, the quantum Hall effect and the single-electron
transport effect) used in metrology. These experiments allow important
fundamental consistency tests on the validity of commonly assumed relations
between fundamental constants of nature and the quantum electrical effects.
This paper reviews the history, results and the present status and perspectives
of Quantum Metrology Triangle experiments. It also reflects on the possible
implications of results for the knowledge on fundamental constants and the
quantum electrical effects.Comment: 36 pages, 8 figure
Advances in Development of Quartz Crystal Oscillators at Liquid Helium Temperatures
This work presents some recent results in the field of liquid helium {bulk
acoustic wave} oscillators. The discussion covers the whole development
procedure starting from component selection and characterization and concluding
with actual phase noise measurements. The associated problems and limitations
are discussed. The unique features of obtained phase noise power spectral
densities are explained with a proposed extension of the Leeson effect.Comment: Cryogenics, 201
Electron Counting Capacitance Standard with an improved five-junction R-pump
The Electron Counting Capacitance Standard currently pursued at PTB aims to
close the Quantum Metrological Triangle with a final precision of a few parts
in 10^7. This paper reports the considerable progress recently achieved with a
new generation of single-electron tunnelling devices. A five-junction R-pump
was operated with a relative charge transfer error of five electrons in 10^7,
and was used to successfully perform single-electron charging of a cryogenic
capacitor. The preliminary result for the single-electron charge quantum has an
uncertainty of less than two parts in 10^6 and is consistent with the value of
the elementary charge.Comment: 16 pages, 9 figures, 1 tabl
BICEP2 II: Experiment and Three-Year Data Set
We report on the design and performance of the BICEP2 instrument and on its
three-year data set. BICEP2 was designed to measure the polarization of the
cosmic microwave background (CMB) on angular scales of 1 to 5 degrees
(=40-200), near the expected peak of the B-mode polarization signature of
primordial gravitational waves from cosmic inflation. Measuring B-modes
requires dramatic improvements in sensitivity combined with exquisite control
of systematics. The BICEP2 telescope observed from the South Pole with a 26~cm
aperture and cold, on-axis, refractive optics. BICEP2 also adopted a new
detector design in which beam-defining slot antenna arrays couple to
transition-edge sensor (TES) bolometers, all fabricated on a common substrate.
The antenna-coupled TES detectors supported scalable fabrication and
multiplexed readout that allowed BICEP2 to achieve a high detector count of 500
bolometers at 150 GHz, giving unprecedented sensitivity to B-modes at degree
angular scales. After optimization of detector and readout parameters, BICEP2
achieved an instrument noise-equivalent temperature of 15.8 K sqrt(s). The
full data set reached Stokes Q and U map depths of 87.2 nK in square-degree
pixels (5.2 K arcmin) over an effective area of 384 square degrees within
a 1000 square degree field. These are the deepest CMB polarization maps at
degree angular scales to date. The power spectrum analysis presented in a
companion paper has resulted in a significant detection of B-mode polarization
at degree scales.Comment: 30 pages, 24 figure
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