Measurements of the linewidth of Josephson junction with injectors

 

M. E. Paramonov¹, E. B. Goldobin², V. P. Koshelets¹

¹ Kotel'nikov Institute of Radio Engineering and Electronics of Russian Academy of Sciences, Moscow, Russia

² Tubigen University, Germany

The paper is received on June 3, 2016

Abstract. An integrated microcircuit with a superconducting sub-THz generator based on a distributed Josephson junction with injectors for studying of its spectral characteristics was developed. The principle of operation of the generator is based on flipping a semifluxon that spontaneously appears at the π discontinuity of the Josephson phase artificially created by means of two tiny current injectors. Structurally, the injectors are located in the top layer of Josephson junction manufactured by «overlap» geometry. The generator is connected to the on-chip detector (Josephson tunnel junction superconductor - insulator – superconductor, SIS), via a microstrip line. The estimated radiation power (at the detector) is 8 nW which is comparable with the dc power of 100nW consumed by the generator. Measurements of the linewidth of the generator were performed in a special cryostat for microwave tests. Signal from the reference laboratory microwave synthesizer (frequency approx. 10..12 GHz) was applied to detector. The desired harmonic of the microwave synthesizer was mixed with generator signal on SIS junction. The resulting signal at the difference (intermediate) frequency of about 400 MHz amplified and displayed on the screen of the spectrum analyzer. The measured linewidth was between 1 and 10 MHz, which is is typical for the geometric (Fiske) resonances. We tried to suppress such resonances by placing well-matched microwave transformers at its both ends. In fact, generator with injectors excite Fiske resonances without applying external magnetic field. Dependences of the linewidth on of the generator bias current (with fixed injector current) and a injector current (with fixed bias current) were measured. It is shown that the linewidth of the generator is reduced while moving the operating point up within the Fiske step. It was an ability to shown this stabilization phase generator emission line with injectors. The ability of phase locking of the generator with injectors was demonstrated.

Key words:         tunnel junction superconductor – insulator – superconductor (SIS), SIS – mixer, semifluxon generator, radiation line width.

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