Highly sensitive polarimetric camera (B-BOP) for the SPICA mission.

The Space Infrared telescope for Cosmology and Astrophysics (SPICA) mission has just been selected by the European Space Agency as one of the three candidate missions to be further studied for the medium size mission M5. B-BOP, formerly named POL, is one of the three scientific instruments of SPICA which aims, among other scientific goals, to map the galactic filamentary structures and their associated magnetic fields. With a novel interlaced-shaped design, B-BOP will contain 1344 pixels, operating within a temperature range of 50-100 mK, covering a 2.6 arcmin field of view, and delivering imaging polarimetry in three spectral bands: 100 µm, 200 µm, and 350 µm simultaneously. In this paper, we investigate by numerical simulations the mechanical, electromagnetic, and thermoelectric behaviors of B-BOP detectors and predict for the three bands (i) a sufficient mechanical stability, (ii) a good electromagnetic absorption higher than 95%, (iii) a high response value better than 1011 V/W, and (iv) especially a very low noise equivalent power reaching 1 aW/Hz1/2 at 50 mK.

Thermal and quantum depletion of superconductivity in narrow junctions created by controlled electromigration.

Superconducting nanowires currently attract great interest due to their application in single-photon detectors and quantum-computing circuits. In this context, it is of fundamental importance to understand the detrimental fluctuations of the superconducting order parameter as the wire width shrinks. In this paper, we use controlled electromigration to narrow down aluminium nanoconstrictions. We demonstrate that a transition from thermally assisted phase slips to quantum phase slips takes place when the cross section becomes less than ∼150 nm(2). In the regime dominated by quantum phase slips the nanowire loses its capacity to carry current without dissipation, even at the lowest possible temperature. We also show that the constrictions exhibit a negative magnetoresistance at low-magnetic fields, which can be attributed to the suppression of superconductivity in the contact leads. These findings reveal perspectives of the proposed fabrication method for exploring various fascinating superconducting phenomena in atomic-size contacts.