Superconducting quantum detectors

Abstract:

Several technologies are now being considered for modulating the polarization in various B-mode instruments, including rotating quasioptical half-wave plates in front of the focal plane array, rotating waveguide half-wave plates and Faraday rotators. It is not at all clear that any of these techniques is feasible without heavy penalty in cost or performance. A potentially much more efficient method is to use a pseudo-correlation polarimeter in conjunction with a planar circuit phase switch.We investigate three different devices for use as mm-wave switches, SIS tunnel junctions, capacitively coupled superconducting nanostrips and RF MEMS. The SIS tunnel junction switches operate by switching between two different bias voltages, while the nanostrip switch operates by changing the impedance of a resonant circuit by driving the nanostrip from the superconducting to normal state. In each case the RF signal sees two substantially different complex impedance states, hence could be switched from one transmission line branch to another. In MEMS this is achieved by mechanical movement of one plate of a parallel plate capacitor system. Although RF MEMS have been reported at high microwave and low mm-wave frequencies, in this work we have investigated cryogenic MEMS for operation at high mm-wave frequencies (225 GHz) using superconducting transmission lines.We present and compare designs and simulations of the performance of phase switches based on all three switching C, technologies, as well as preliminary experimental results for each of the switches. Finally we also present designs of phase shift circuits that translates the on/off switching into phase modulation.

Abstract:

ClOVER is an experiment which aims to detect the signature of gravitational waves from inflation by measuring the B-mode polarization of the cosmic microwave background. CLOVER consists of three telescopes operating at 97, 150, and 220 GHz. The 97-GHz telescope has 160 horns in its focal plane while the 150 and 220-GHz telescopes have 256 horns each. The horns are arranged in a hexagonal array and feed a polarimeter which uses finline-coupled TES bolometers as detectors. To detect the two polarizations the 97-GHz telescope has 320 detectors while the 150 and 220-GHz telescopes have 512 detectors each. To achieve the required NEPs the detectors are cooled to 100 mK for the 97 and 150-GHz polarimeters and 230 mK for the 220-GHz polarimeter. Each detector is fabricated as a single chip to guarantee fully functioning focal planes. The detectors are contained in linear modules made of copper which form split-block waveguides. The detector modules contain 16 or 20 detectors each for compatibility with the hexagonal arrays of horns in the telescopes' focal planes. Each detector module contains a time-division SQUID multiplexer to read out the detectors. Further amplification of the multiplexed signals is provided by SQUID series arrays. The first prototype detectors for ClOVER operate with a bath temperature of 230 mK and are used to validate the detector design as well as the polarimeter technology. We describe the design of the ClOVER detectors, detector blocks, and readout, and give an update on the detector development.

Abstract:

The ClOVER instrument (described elsewhere in this volume) is being built to measure the B-mode polarisation of the Cosmic Microwave Background. Each of the 256 pixels is made up a pseudo-correlation receiver that can be realised using either waveguide or microstrip technology. In this work we present a design study for a possible waveguide-based solution. Each of the individual components has been optimised using electromagnetic finite-element modelling software (HFSS).

Abstract:

We present a new, fully-funded ground-based instrument designed to measure the B-mode polarization of the Cosmic Microwave Background (CMB). The concept is based on three independent subsystems operating at 90, 150 and 220 GHz, each comprising a telescope and a focal plane of horn-coupled background-limited bolometers. This highly-sensitive experiment, planned to be based at Dome C station in Antarctica, is optimised to produce very low systematic effects. It will allow the detection of the CMB polarization over angular multipoles 20 < l < 1000 accurately enough to measure the B-mode signature from gravitational waves to a lensing-confusion-limited tensor-to-scalar ratio r similar to 0.005.