Photograph of parallel Josephson junction array integrated with bowtie antenna and rf choke filter. The circuit is composed of 5 identical junctions of embedded in superconductive Nb/SiO/Nb stripline of width . The lengths separating the junctions are , , , and . The trilayer is made of a 200-nm-thick Nb base electrode, 10 nm Al, and 400 nm Nb top electrode. The thickness of the SiO layer, ensuring both electrical insulation of the junctions and dielectric for the stripline, is 250 nm.
Experimental setup to investigate by heterodyne detection the resonances observed in the curve of the five-junction array. Cryostats 1 and 2 contain, respectively, the junction array investigated as a submillimeter-wave source and the twin-junction SIS receiver. They are mutually coupled by quasioptical means. The LO source is a frequency-multiplied Gunn oscillator.
characteristic of the parallel Josephson array measured at . Three resonances appear when an external magnetic field of typically a few Gauss is applied at 0.51, 0.84, and 1.02 mV. The insert shows the rf bandwidths of both the array and the SIS receiver, obtained by FTS. The first and third resonances could emit radiation observable with our heterodyne setup (see Table I).
IF power spectra measured across the 4–8 GHz IF band, showing a beat signal when the solid-state LO is tuned at 494 GHz and the array is biased on the third resonant step at two bias points: (a) 1.01 mV then (b) 1.0 mV . The OFF spectrum corresponds to the array biased outside a resonant step, in the same conditions. Resolution bandwidth is 1 MHz, video bandwidth is 1 kHz, and integration time is 2 s. The results are summarized in Table II.
Same as the previous figure with array now biased on the first resonant step at 0.51 (±0.005) mV (first harmonic at ). The LO is tuned at (a) 490.1, (b) 491.5, and (c) 493.1 GHz.
Resonances in array and corresponding Josephson frequencies, .
Measured and expected IF frequencies.
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