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A bstract We propose an approach to directly search for light dark matter, such as the axion or the dark photon, by using magnetometry with nitrogen-vacancy centers in diamonds. If the dark matter couples to the electron spin, it affects the evolution of the Bloch vectors consisting of the spin triplet states, which may be detected through several magnetometry techniques. We give several concrete examples with the use of dc and ac magnetometry and estimate the sensitivity on dark matter couplings.

At millimeter wavelengths, the atmospheric emission is circularly polarized owing to the Zeeman splitting of molecular oxygen by the Earth's magnetic field. We report a measurement of the signal in the 150 GHz band using 3 yr of observational data with the Polarbear project. Nonidealities of a continuously rotating half-wave plate (HWP) partially convert circularly polarized light to linearly polarized light. While Polarbear detectors are sensitive to linear polarization, this effect makes them sensitive to circular polarization. Although this was not the intended use, we utilized this conversion to measure circular polarization. We reconstruct the azimuthal gradient of the circular polarization signal and measure its dependency from the scanning direction and the detector bandpass. We compare the signal with a simulation based on atmospheric emission theory, the detector bandpass, and the HWP leakage spectrum model. We find the ratio of the observed azimuthal slope to the simulated slope is 0.92 ± 0.01(stat) ± 0.07(sys). This ratio corresponds to a brightness temperature of 3.8 mK at the effective band center of 121.8 GHz and bandwidth of 3.5 GHz estimated from representative detector bandpass and the spectrum of Zeeman emission. This result validates our understanding of the instrument and reinforces the feasibility of measuring the circular polarization using the imperfection of continuously rotating HWP. Continuously rotating HWP is popular in ongoing and future cosmic microwave background experiments to modulate the polarized signal. This work shows a method for signal extraction and leakage subtraction that can help measure circular polarization in such experiments.

The digital frequency-domain multiplexing technique is widely used for astrophysical instruments with large detector arrays. Detailed detector characterization is required for instrument calibration and systematics control. We conduct the TES complex electrothermal-feedback response measurement with the DfMux readout system as follows. By injecting a single sideband signal, we induce modulation in TES power dissipation over a frequency range encompassing the detector response. The modulated current signal induced by TES heating effect is measured, allowing for the ETF response characterization of the detector. With the injection of an upper sideband, the TES readout current shows both an upper and a lower sideband. We model the upper and lower sideband complex ETF response and verify the model by fitting to experimental data. The model not only can fit for certain physical parameters of the detector, such as loop gain, temperature sensitivity, current sensitivity, and time constant, but also enables us to estimate the systematic effect introduced by the multiplexed readout. The method is therefore useful for in situ detector calibration and for estimating systematic effects during astronomical telescope observations, such as those performed by the upcoming LiteBIRD satellite.

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.

POLARBEAR-2b (PB-2b) is the second receiver in the Simons Array, a cosmic microwave background (CMB) polarization experiment. The Simons Array uses dichroic polarization sensitive lenslet-coupled sinuous antennas and transition-edge sensor (TES) bolometers made of superconducting films. These bolometers are read out with frequency multiplexing electronics. PB-2b contains ∼ 7500 detectors in two bands at 90 and 150 GHz with arcminute resolution. The polarization of these detectors is modulated by a cryogenic continuously rotating half-wave plate. PB-2b was installed on its telescope in 2022 in the Atacama Desert at an altitude of 5.2 km. This paper will detail initial readout commissioning, test of a new loopgain monitoring method, and focusing the optics. Work is ongoing to commission the remaining ambient temperature readout electronics, measure detector time constants, and observe with the cryogenic half-wave plate spinning

CMB-S4—the next-generation ground-based cosmic microwave background (CMB) experiment—is set to significantly advance the sensitivity of CMB measurements and enhance our understanding of the origin and evolution of the universe. Among the science cases pursued with CMB-S4, the quest for detecting primordial gravitational waves is a central driver of the experimental design. This work details the development of a forecasting framework that includes a power-spectrum-based semianalytic projection tool, targeted explicitly toward optimizing constraints on the tensor-to-scalar ratio, r, in the presence of Galactic foregrounds and gravitational lensing of the CMB. This framework is unique in its direct use of information from the achieved performance of current Stage 2–3 CMB experiments to robustly forecast the science reach of upcoming CMB-polarization endeavors. The methodology allows for rapid iteration over experimental configurations and offers a flexible way to optimize the design of future experiments, given a desired scientific goal. To form a closed-loop process, we couple this semianalytic tool with map-based validation studies, which allow for the injection of additional complexity and verification of our forecasts with several independent analysis methods. We document multiple rounds of forecasts for CMB-S4 using this process and the resulting establishment of the current reference design of the primordial gravitational-wave component of the Stage-4 experiment, optimized to achieve our science goals of detecting primordial gravitational waves for r > 0.003 at greater than 5σ, or in the absence of a detection, of reaching an upper limit of r < 0.001 at 95% CL.

We present a method for precise monitoring of the loop gain of transition edge sensors (TES) under electrothermal feedback. The measurement is implemented on the ICE DfMux electronics and operates simultaneously with Digital Active Nulling (DAN). It uses one additional bias sinusoid per TES and does not require any additional readout channels. The loop gain monitor is being implemented on the Simons Array and is an integral part of the baseline calibration strategy for the upcoming LiteBIRD satellite.

GroundBIRD is a ground-based experiment for a precise observation of the cosmic microwave background (CMB) polarizations. To achieve high sensitivity at large angular scales, we adopt three features in this experiment: fast rotation scanning, microwave kinetic inductance detector (MKID), and cold optics. The rotation scanning strategy has the advantage to suppress 1/ f noise. It also provides a large sky coverage of 40%, which corresponds to the large angular scales of l ∼ 6 . This allows us to constrain the tensor-to-scalar ratio by using low l B-mode spectrum. The focal plane consists of 7 MKID arrays for two target frequencies, 145 GHz and 220 GHz band. There are 161 pixels in total, of which 138 are for 145 GHz and 23 are for 220 GHz. This array is currently under development, and the prototype will soon be evaluated in telescope. The GroundBIRD telescope will observe the CMB at the Teide observatory. The telescope was moved from Japan to Tenerife and is now under test. We present the status and plan of the GroundBIRD experiment.

LiteBIRD is a JAXA-led L-Class mission aimed at the study of B-mode polarization of the cosmic microwave background. Measurements on 15 bandwidth from 34 to 448 GHz are made on two instruments, low-frequency telescope and medium- and high-frequency telescope. To reach the desired sensitivities, more than 4500 transition edge sensors detectors, used on both instruments, will be continuously cooled to 100 mK. The cryogenic design based on shield cooling and mechanical coolers is presented in this paper. Shield cooling will be done with passive cooling and 15 K pulse tube coolers. A single cryogenic chain will cool both instruments. A 4 K stage is cooled by a 4 He Joule–Thomson cooler from Japanese Aerospace Exploration Agency, pre-cooled by Stirling coolers. Multistage adiabatic demagnetization refrigerator will be optimized to provide continuous cooling at 1.75 K, 300 mK and 100 mK with 2.2 µW of cooling power on the latter stage. Seven ADR stages provided by NASA (USA) and CEA (France) are required. Details on the thermal design, preliminary sizing and expected performance are presented.

LiteBIRD is a cosmic microwave background polarization experiment with the goal of measuring the tensor-to-scalar ratio with a total uncertainty of δ r < 0.001 . It will survey the full sky from space for 3 years in 15 frequency bands spanning 34–448 GHz. We are developing detector arrays for the six lowest frequency bands covering 34–99 GHz. The arrays are populated with lenslet-coupled sinuous antennas, triplexer bandpass filters, and transition-edge sensor (TES) bolometers. We have measured the electrical and thermal properties of several TES designs to determine space-optimized parameters. The design balances requirements for low saturation power of the space environment while maintaining a fast time response for use with a continuously rotating half-wave plate. We have achieved detector saturation powers below 1 pW, with time constants faster than 1 ms, at a 100 mK bath temperature measured using both time- and frequency-division multiplexed SQUID readout systems. Using this information, we have fabricated multi-chroic pixels with antenna-coupled space-optimized bolometers.