A three photon noise SIS heterodyne receiver at submillimeter wavelength

An ultra-low noise single sideband SIS receiver has been prepared for radio astronomy at the sub millimeter wavelength lambda approximate to 0.85 mm, The minimum single sideband receiver noise temperature of 48 K corresponds to 3 (h) over bar omega/k or equivalent number of 3 photon of noise. The mi nimum single sideband SIS miser noise temperature is about 20 K, close to 1 .2 (h) over bar omega/k, or one photon of noise. The Nb/AlOx/Nb junctions w ith a Josephson critical current density of 9 KA/cm(2) and with the area of about 0.9 mu m(2) were used. The receiver has been tested at the 30 meter IRAM radio telescope in the wi nter seasons of 1997 and 1998. The observations at the radio telescope are speeded up by a factor of two to three with the new receiver.