The BICEP/Keck ( BK ) experiment aims to detect the imprint of primordial gravitational waves in the Cosmic Microwave Background polarization , which would be direct evidence of the inflation theory .
While the tensor-to-scalar ratio has been constrained to be r _ { 0.05 } < 0.06 at 95 % c.l. , further improvements on this upper limit are hindered by polarized Galactic foreground emissions and removal of gravitational lensing polarization .
The 30/40 GHz receiver of the BICEP Array ( BA ) will deploy at the end of 2019 and will constrain the synchrotron foreground with unprecedented accuracy within the BK sky patch .
We will show the design of the 30/40 GHz detectors and test results summarizing its performance .
The low optical and atmospheric loading at these frequencies requires our TES detectors to have low saturation power in order to be photon-noise dominated .
To realize the low thermal conductivity required from a 250 mK base temperature , we developed new bolometer leg designs .
We will present the relevant measured detector parameters : G , T _ { c } , R _ { n } , P _ { sat } , and spectral bands , and noise spectra .
We achieved a per bolometer NEP including all noise components of 2.07 \times 10 ^ { -17 } ~ { } { W / \sqrt { Hz } } , including an anticipated photon noise level 1.54 \times 10 ^ { -17 } ~ { } { W / \sqrt { Hz } } .