Superconducting quantum detectors

Abstract:

We describe the design and expected performance of Clover, a new instrument designed to measure the B-mode polarization of the cosmic microwave background. The proposed instrument will comprise three independent telescopes operating at 90, 150 and 220 GHz and is planned to be sited at Dome C, Antarctica. Each telescope will feed a focal plane array of 128 background-limited detectors and will measure polarized signals over angular multipoles 20 < l < 1000. The unique design of the telescope and careful control of systematics should enable the B-mode signature of gravitational waves to be measured to a lensing-confusion-limited tensor-to-scalar ratio r~0.005.

Abstract:

In this paper we present a novel design of an antenna coupled TES direct detector for high performance applications. In particular, the design of the detector has been optimised to be suitable for the measurement of the weak B-mode signal in the CMB polarization. An important feature of this design is that it employs corrugated horn antennas for coupling the astronomical signal to the detector. This allows us to feed the telescope with a well collimated beam with low sidelobes and cross polarization. The paper contains simulations demonstrating the suitability of individual electromagnetic components to be used in the instrument.

Abstract:

The Quantum Theory of Mixing developed by Tucker provides a solid framework for understanding the behaviour of SIS mixers, and subsequent developments allow the simulation of complete mixer circuits. These methods operate, however, under the assumption of small signal levels, and so neglect the non-linear behaviour of the signal path. The non-linearity of the mixer's response to applied signals is of vital importance to the calibration of SIS receiver systems. We have previously reported(1) a procedure for calculating the full quantum behaviour of tunnel junction circuits under multiple high-level signals, allowing the accurate prediction of the saturation characteristics of SIS mixers. In this paper, we apply our procedure to both an idealized SIS mixer and one of our previously tested 700 GHz finline mixers. We find that the small signal behaviour predicted by our procedure agrees well with other simulation methods, and that the saturation properties of both of these mixers differ from that predicted by previous estimates of saturation behaviour.