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We are developing multi-chroic antenna-coupled Transition Edge Sensor (TES) bolometer detectors for Cosmic Microwave Background (CMB) polarimetry. Multi-chroic detectors increase focal plane area efficiency, and thus the mapping speed per focal plane area, and provide greater discrimination against polarized galactic foregrounds with no increase in weight or cryogenic cost. In each pixel, a silicon lens-coupled dual-polarized sinuous antenna collects photons over a two-octave frequency band. The antenna couples the broadband millimeter wave signal into microstrip transmission lines, and on-chip filter banks split the broadband signal into multiple frequency bands. Separate TES bolometers detect the power in each frequency band and linear polarization state. We will describe the design and performance of these devices and present optical data taken. Our measurements of dual-polarization pixels in multiple frequency bands show beams with percent-level ellipticity, and percent-level cross-polarization leakage. We will also describe the development of large arrays of these multi-chroic pixels. Finally, we will describe kilo-pixel arrays of these detectors planned for the future CMB experiments that will achieve unprecedented mapping speed.

Polarbear-2 (PB-2) is a next-generation receiver that is part of the Simons Array cosmic microwave background (CMB) polarization experiment which is located in the Atacama desert in Northern Chile. The primary scientific goals of the Simons Array are a deep search for the CMB B-mode signature of gravitational waves from inflation and the characterization of large-scale structure using its effect on CMB polarization. The PB-2 receiver will deploy with 1897 dual-polarization sinuous antenna-coupled pixels, each with a directly contacting extended hemispherical silicon lens. Every pixel has dual polarization sensitivity in two spectral bands centered at 95 and 150 GHz, for a total of 7588 transition edge sensor bolometers operating at 270 mK. To achieve the PB-2 detector requirements, we developed a broadband anti-reflection (AR) coating for the extended hemispherical lenses that uses two molds to apply two layers of epoxy, Stycast 1090 and Stycast 2850FT. Our measurements of the absorption loss from the AR coating on a flat surface at cryogenic temperatures show less than 1 % absorption, and the coating has survived multiple thermal cycles. We can control the diameter of the coating within 25 μ m and translation errors are within 25 μ m in all directions, which results in less than 1 % decrease in transmittance. We also find the performance of the AR-coated lens matches very well with simulations.

Prey incorporate information about risk, safety, and the reliability of both of these cues when assessing risk of predation. Here, we report results of an experiment testing avoidance of chemical alarm cues derived from skin extract of blacknose shiners, Notropis heterolepis (BNS), attraction toward a visible shoal of five BNS, and the combination of both, on fishes in Deming Lake where BNS occur. We then repeated the experiment in nearby Budd Lake where BNS do not occur. BNS avoided traps with conspecific alarm cues but did not respond to the presence of BNS shoals. We recorded responses by similar-sized heterospecifics that share predators with BNS to see if they respond to BNS as indicators of risk and safety. Fathead minnows, Pimephales promelas (FHM) avoided traps chemically labeled with BNS alarm cue when a shoal was absent and avoided BNS shoals when traps were labeled with water (control). When both BNS alarm cue and BNS shoal were combined, FHM antipredator response to BNS alarm cue invoked a shoaling response with the BNS shoal in the trap. The more distantly related redbelly dace, Chrosomus eos (RBD), responded weakly to BNS cues in Deming Lake and ignored them in Budd Lake. Non-cyprinid species (brook stickleback Culaea inconstans and pumpkinseed sunfish, Lepomis gibbosus) did not respond to either olfactory or visual cues of BNS in Deming Lake. In Budd Lake, neither avoidance of BNS alarm cue or attraction to BNS shoals surpassed the threshold of statistical significance, indicating a role of ecological familiarity and learned recognition of risk and safety in cross-species reactions to olfactory and visual cues of heterospecifics.Significance statementSmall fish, such as minnows, avoid areas marked by injury-released chemical cues because these cues are released only in the context of predation and are attracted to groups of fish because shoals offer safety from predation. In this study fathead minnows Pimephales promelas (FHM) avoided alarm cue of blacknose shiners Notropis heterolepis (BNS) in Deming Lake where both species occur but not in Budd Lake where BNS do not occur. FHM were not attracted to BNS shoals in either lake. However, when a shoal of BNS was combined with BNS alarm cue a synergism occurred where antipredator responses to BNS alarm cue induced FHM to seek safety by shoaling with BNS shoals. The synergism occurred in Deming Lake where BNS alarm cue and shoals are ecologically familiar but not in Budd Lake where BNS do not occur. These data show that behavioral responses by prey to olfactory and visual cues are tempered by sympatry (ecological familiarity) and confidence in the reliability of those cues.

We are developing multi-chroic antenna-coupled Transition Edge Sensor (TES) focal planes for Cosmic Microwave Background (CMB) polarimetry. In each pixel, a dual polarized sinuous antenna collects light over a two-octave frequency band. Each antenna couples to the telescope with a contacting silicon lens. The antenna couples the broadband RF signal to microstrip transmission lines, and then filter banks split the broadband signal into several frequency bands. A TES bolometer detects the power in each band and polarization. We will describe the design of this device and demonstrate its performance with optical data measured using prototype pixels. Our measurements show low ellipticity beams, low cross-polarization, and properly partitioned bands in banks of 2, 3, and 7 filters. Finally, we will describe how we will upgrade the Polarbear CMB experiment using the focal planes of these detectors to increase the experiment’s mapping speed and its ability to discriminate between the CMB and polarized foregrounds.

We are developing multi-band dual-polarized antenna-coupled transition edge sensor (TES) bolometers for observing Cosmic Microwave Background (CMB) polarization anisotropies. We have designed a prototype pixel that uses a dual-polarized log-periodic antenna on a silicon hemispherical lens. Each polarization is coupled onto a separate microstrip transmission line. Microstrip filters are used to divide the broadband output of this antenna into a set of narrow frequency bands centered at 90, 150, and 220 GHz with bandwidths of 20%. We report on the fabrication of these devices as well as the initial optical testing.

The polarbear cosmic microwave background (CMB) polarization experiment has been observing since early 2012 from its 5,200 m site in the Atacama Desert in Northern Chile. polarbear ’s measurements will characterize the expected CMB polarization due to gravitational lensing by large scale structure, and search for the possible B-mode polarization signature of inflationary gravitational waves. polarbear ’s 250 mK focal plane detector array consists of 1,274 polarization-sensitive antenna-coupled bolometers, each with an associated lithographed band-defining filter and contacting dielectric lenslet, an architecture unique in current CMB experiments. The status of the polarbear instrument, its focal plane, and the analysis of its measurements are presented.

We report a measurement of the B-mode polarization power spectrum in the cosmic microwave background (CMB) using the POLARBEAR experiment in Chile. The faint B-mode polarization signature carries information about the Universe's entire history of gravitational structure formation, and the cosmic inflation that may have occurred in the very early Universe. Our measurement covers the angular multipole range 500 < l < 2100 and is based on observations of an effective sky area of 25 square degrees with 3.5 arcmin resolution at 150 GHz. On these angular scales, gravitational lensing of the CMB by intervening structure in the Universe is expected to be the dominant source of B-mode polarization. Including both systematic and statistical uncertainties, the hypothesis of no B-mode polarization power from gravitational lensing is rejected at 97.1% confidence. The band powers are consistent with the standard cosmological model. Fitting a single lensing amplitude parameter A_BB to the measured band powers, A_BB = 1.12 +/- 0.61 (stat) +0.04/-0.12 (sys) +/- 0.07 (multi), where A_BB = 1 is the fiducial WMAP-9 LCDM value. In this expression, \"stat\" refers to the statistical uncertainty, \"sys\" to the systematic uncertainty associated with possible biases from the instrument and astrophysical foregrounds, and \"multi\" to the calibration uncertainties that have a multiplicative effect on the measured amplitude A_BB.

Gravitational lensing due to the large-scale distribution of matter in the cosmos distorts the primordial Cosmic Microwave Background (CMB) and thereby induces new, small-scale \\(B\\)-mode polarization. This signal carries detailed information about the distribution of all the gravitating matter between the observer and CMB last scattering surface. We report the first direct evidence for polarization lensing based on purely CMB information, from using the four-point correlations of even- and odd-parity \\(E\\)- and \\(B\\)-mode polarization mapped over \\(\\sim30\\) square degrees of the sky measured by the POLARBEAR experiment. These data were analyzed using a blind analysis framework and checked for spurious systematic contamination using null tests and simulations. Evidence for the signal of polarization lensing and lensing \\(B\\)-modes is found at 4.2\\(\\sigma\\) (stat.+sys.) significance. The amplitude of matter fluctuations is measured with a precision of \\(27\\%\\), and is found to be consistent with the Lambda Cold Dark Matter (\\(\\Lambda\\)CDM) cosmological model. This measurement demonstrates a new technique, capable of mapping all gravitating matter in the Universe, sensitive to the sum of neutrino masses, and essential for cleaning the lensing \\(B\\)-mode signal in searches for primordial gravitational waves.

The Polarbear Cosmic Microwave Background (CMB) polarization experiment is currently observing from the Atacama Desert in Northern Chile. It will characterize the expected B-mode polarization due to gravitational lensing of the CMB, and search for the possible B-mode signature of inflationary gravitational waves. Its 250 mK focal plane detector array consists of 1,274 polarization-sensitive antenna-coupled bolometers, each with an associated lithographed band-defining filter. Each detector's planar antenna structure is coupled to the telescope's optical system through a contacting dielectric lenslet, an architecture unique in current CMB experiments. We present the initial characterization of this focal plane.

We present the design and characterization of the POLARBEAR experiment. POLARBEAR will measure the polarization of the cosmic microwave background (CMB) on angular scales ranging from the experiment's 3.5 arcminute beam size to several degrees. The experiment utilizes a unique focal plane of 1,274 antenna-coupled, polarization sensitive TES bolometers cooled to 250 milliKelvin. Employing this focal plane along with stringent control over systematic errors, POLARBEAR has the sensitivity to detect the expected small scale B-mode signal due to gravitational lensing and search for the large scale B-mode signal from inflationary gravitational waves. POLARBEAR was assembled for an engineering run in the Inyo Mountains of California in 2010 and was deployed in late 2011 to the Atacama Desert in Chile. An overview of the instrument is presented along with characterization results from observations in Chile.