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The LiteBIRD experiment is an international spaceborne mission, led by JAXA, the Japan Aerospace Exploration Agency, to observe cosmic microwave background (CMB) radiation. The satellite will be deployed to measure and characterize the signature of the primordial gravitational waves from cosmic inflation in the B -mode polarization of the CMB radiation. LiteBIRD will also explore the nature of quantum gravity as well as attempt to detect the recombination peak and reionization peak with greater than 5 σ significance for a tensor-to-scalar value of r  = 0.01. These observations and measurements will take place over 15 separate frequency bands in the range of 34–448 GHz. The 15 frequency channels are separated into three telescopes—low, medium, and high frequency. This paper will describe the process flow developed to fabricate the low frequency detectors, covering bands from 34 to 161 GHz. The detector wafer itself has a device side and a sky side. The device side contains the trichroic polarization sensitive sinuous antennae coupled to transition-edge sensor detectors. The skyside contains the cosmic ray mitigation structure.

The temperature and polarization anisotropies in the Cosmic Microwave Background (CMB) are direct probes into the physics of the early universe. Increasingly sensitive experiments aim to determine the tensor-to-scalar ratio r through measurement of an impossibly faint B-mode polarized signal shrouded by galactic foregrounds. A direct measurement of primordial B-mode polarization will be a measurement of the energy scale of inflation, unlocking an essential piece of the cosmological puzzle. Next-generation CMB experiments employ a large number of highly sensitive detectors in an attempt to find r and further constrain the cosmological parameters. Such a measurement requires not just high sensitivity to the CMB polarized signal, but large experimental bandwidth to characterize the polarized galactic dust and synchrotron radiation foreground signals.For experiments using lenslet-coupled planar antenna detector array designs, reflection off the surface of the lenslet must be minimized over a given bandwidth to maximize the measured CMB signal. To this end, antireflection (AR) coatings for lenslets were developed for 30/40 GHz Simons Observatory low-frequency detectors, along with next-generation prototype coatings for 90/150 and 220/270 GHz arrays. The JAXA-led space-based mission LiteBIRD will utilize lenslet-coupled sinuous antenna arrays and TES bolometers for frequencies ranging from 40-195 GHz, necessitating broadband lenslet AR coatings that are robust to launch vibrations and differential thermal contraction. To meet these requirements, a metamaterial AR surface has been proposed. A metamaterial coating designed for the LiteBIRD LF-3 band has been laser etched onto a flat surface, achieving 98% in-band transmission. A six-axis positioning system is used to etch the metamaterial pattern onto a sphere, and a completed prototype LF-3 lenslet is expected to be etched in late 2023. Details of the metamaterial design and the etch process are discussed. Cosmic rays at the Lagrange point L2 pose a threat to LiteBIRD’s sensitivity, as they produce a white noise component that cannot be fully deconstructed in analysis. To mitigate this cosmic ray white noise component, on-chip mitigations have been developed for the purpose of minimizing thermal diffusion from the silicon detector wafer to the TES bolometer detectors. Lastly, the mechanical design and fabrication of a continuously rotating warm half-wave plate for the POLARBEAR-2a experiment, used to minimize noise in large-angular-scale measurements from atmospheric fluctuations, are discussed.

The Simons Observatory (SO) is a cosmic microwave background (CMB) experiment located in the Atacama Desert in Chile that will make precise temperature and polarization measurements over six spectral bands ranging from 27 to 285 GHz. Three small aperture telescopes (SATs) and one large aperture telescope (LAT) will house ∼ 60,000 detectors and cover angular scales between one arcminute and tens of degrees. We present the performance of the dichroic, low-frequency (LF) lenslet-coupled sinuous antenna transition-edge sensor (TES) bolometer arrays with bands centered at 27 and 39 GHz. The LF focal plane will primarily characterize Galactic synchrotron emission as a critical part of foreground subtraction from CMB data. We will discuss the design, optimization, and current testing status of these pixels.

The Simons Observatory (SO) is a cosmic microwave background (CMB) experiment located in the Atacama Desert in Chile that will make precise temperature and polarization measurements over six spectral bands ranging from 27 to 285 GHz. Three small aperture telescopes (SATs) and one large aperture telescope (LAT) will house \\(\\)60,000 detectors and cover angular scales between one arcminute and tens of degrees. We present the performance of the dichroic, low-frequency (LF) lenslet-coupled sinuous antenna transition-edge sensor (TES) bolometer arrays with bands centered at 27 and 39 GHz. The LF focal plane will primarily characterize Galactic synchrotron emission as a critical part of foreground subtraction from CMB data. We will discuss the design, optimization, and current testing status of these pixels.

LiteBIRD is a JAXA-led strategic large-class satellite mission designed to measure the polarization of the cosmic microwave background and Galactic foregrounds from 34 to 448 GHz across the entire sky from L2 in the late 2020s. The scientific payload includes three telescopes which are called the low-, mid-, and high-frequency telescopes each with their own receiver that covers a portion of the mission's frequency range. The low frequency telescope will map synchrotron radiation from the Galactic foreground and the cosmic microwave background. We discuss the design, fabrication, and characterization of the low-frequency focal plane modules for low-frequency telescope, which has a total bandwidth ranging from 34 to 161 GHz. There will be a total of 4 different pixel types with 8 overlapping bands to cover the full frequency range. These modules are housed in a single low-frequency focal plane unit which provides thermal isolation, mechanical support, and radiative baffling for the detectors. The module design implements multi-chroic lenslet-coupled sinuous antenna arrays coupled to transition edge sensor bolometers read out with frequency-domain mulitplexing. While this technology has strong heritage in ground-based cosmic microwave background experiments, the broad frequency coverage, low optical loading conditions, and the high cosmic ray background of the space environment require further development of this technology to be suitable for LiteBIRD. In these proceedings, we discuss the optical and bolometeric characterization of a triplexing prototype pixel with bands centered on 78, 100, and 140 GHz.

We present a measurement of the gravitational lensing deflection power spectrum reconstructed with two seasons cosmic microwave background polarization data from the POLARBEAR experiment. Observations were taken at 150 GHz from 2012 to 2014 which survey three patches of sky totaling 30 square degrees. We test the consistency of the lensing spectrum with a Cold Dark Matter (CDM) cosmology and reject the no-lensing hypothesis at a confidence of 10.9 sigma including statistical and systematic uncertainties. We observe a value of A_L = 1.33 +/- 0.32 (statistical) +/- 0.02 (systematic) +/- 0.07 (foreground) using all polarization lensing estimators, which corresponds to a 24% accurate measurement of the lensing amplitude. Compared to the analysis of the first year data, we have improved the breadth of both the suite of null tests and the error terms included in the estimation of systematic contamination.

We describe the development of an ambient-temperature continuously-rotating half-wave plate (HWP) for study of the Cosmic Microwave Background (CMB) polarization by the POLARBEAR-2 (PB2) experiment. Rapid polarization modulation suppresses 1/f noise due to unpolarized atmospheric turbulence and improves sensitivity to degree-angular-scale CMB fluctuations where the inflationary gravitational wave signal is thought to exist. A HWP modulator rotates the input polarization signal and therefore allows a single polarimeter to measure both linear polarization states, eliminating systematic errors associated with differencing of orthogonal detectors. PB2 projects a 365-mm-diameter focal plane of 7,588 dichroic, 95/150 GHz transition-edge-sensor bolometers onto a 4-degree field of view that scans the sky at \\(\\) 1 degree per second. We find that a 500-mm-diameter ambient-temperature sapphire achromatic HWP rotating at 2 Hz is a suitable polarization modulator for PB2. We present the design considerations for the PB2 HWP, the construction of the HWP optical stack and rotation mechanism, and the performance of the fully-assembled HWP instrument. We conclude with a discussion of HWP polarization modulation for future Simons Array receivers.

The Simons Observatory (SO) is a new cosmic microwave background experiment being built on Cerro Toco in Chile, due to begin observations in the early 2020s. We describe the scientific goals of the experiment, motivate the design, and forecast its performance. SO will measure the temperature and polarization anisotropy of the cosmic microwave background in six frequency bands: 27, 39, 93, 145, 225 and 280 GHz. The initial configuration of SO will have three small-aperture 0.5-m telescopes (SATs) and one large-aperture 6-m telescope (LAT), with a total of 60,000 cryogenic bolometers. Our key science goals are to characterize the primordial perturbations, measure the number of relativistic species and the mass of neutrinos, test for deviations from a cosmological constant, improve our understanding of galaxy evolution, and constrain the duration of reionization. The SATs will target the largest angular scales observable from Chile, mapping ~10% of the sky to a white noise level of 2 \\(\\)K-arcmin in combined 93 and 145 GHz bands, to measure the primordial tensor-to-scalar ratio, \\(r\\), at a target level of \\((r)=0.003\\). The LAT will map ~40% of the sky at arcminute angular resolution to an expected white noise level of 6 \\(\\)K-arcmin in combined 93 and 145 GHz bands, overlapping with the majority of the LSST sky region and partially with DESI. With up to an order of magnitude lower polarization noise than maps from the Planck satellite, the high-resolution sky maps will constrain cosmological parameters derived from the damping tail, gravitational lensing of the microwave background, the primordial bispectrum, and the thermal and kinematic Sunyaev-Zel'dovich effects, and will aid in delensing the large-angle polarization signal to measure the tensor-to-scalar ratio. The survey will also provide a legacy catalog of 16,000 galaxy clusters and more than 20,000 extragalactic sources.

We present the first measurement of cross-correlation between the lensing potential, reconstructed from cosmic microwave background (CMB) ıt polarization data, and the cosmic shear field from galaxy shapes. This measurement is made using data from the POLARBEAR CMB experiment and the Subaru Hyper Suprime-Cam (HSC) survey. By analyzing an 11~deg\\(^2\\) overlapping region, we reject the null hypothesis at 3.5\\(\\)\\ and constrain the amplitude of the cross-spectrum to \\(A_ lens=1.70 0.48\\), where \\(A_ lens\\) is the amplitude normalized with respect to the Planck~2018 prediction, based on the flat \\(\\) cold dark matter cosmology. The first measurement of this cross-spectrum without relying on CMB temperature measurements is possible due to the deep POLARBEAR map with a noise level of \\(\\)6\\,\\(\\)K-arcmin, as well as the deep HSC data with a high galaxy number density of \\(n_g=23\\, arcmin^-2\\). We present a detailed study of the systematics budget to show that residual systematics in our results are negligibly small, which demonstrates the future potential of this cross-correlation technique.

The Simons Observatory (SO) will make precise temperature and polarization measurements of the cosmic microwave background (CMB) using a set of telescopes which will cover angular scales between 1 arcminute and tens of degrees, contain over 60,000 detectors, and observe at frequencies between 27 and 270 GHz. SO will consist of a 6 m aperture telescope coupled to over 30,000 transition-edge sensor bolometers along with three 42 cm aperture refractive telescopes, coupled to an additional 30,000+ detectors, all of which will be located in the Atacama Desert at an altitude of 5190 m. The powerful combination of large and small apertures in a CMB observatory will allow us to sample a wide range of angular scales over a common survey area. SO will measure fundamental cosmological parameters of our universe, constrain primordial fluctuations, find high redshift clusters via the Sunyaev-Zel`dovich effect, constrain properties of neutrinos, and trace the density and velocity of the matter in the universe over cosmic time. The complex set of technical and science requirements for this experiment has led to innovative instrumentation solutions which we will discuss. The large aperture telescope will couple to a cryogenic receiver that is 2.4 m in diameter and nearly 3 m long, creating a number of technical challenges. Concurrently, we are designing the array of cryogenic receivers housing the 42 cm aperture telescopes. We will discuss the sensor technology SO will use and we will give an overview of the drivers for and designs of the SO telescopes and receivers, with their cold optical components and detector arrays.