Output signal and noise characteristics in RF pumped double SQUIDS

V. I. Shnyrkov, Georgy M. Tsoi

Boris Chesca

Boris Chesca

S. A. Belonogov, Oleg V. Snigirev, S.S. Tinchev +1 more

J Sloggett, David L. Dart, C. P. Foley +3 more

We describe the noise performance of thin-film YBa 2 Cu 3 O 7 RF SQUIDS fabricated on MgO substrates with single step-edge Josephson junctions. A substantial range of noise levels has been observed for devices having similar electrical parameters (inductance, critical current, RF frequency). The best devices have white-noise levels below 10 -4 phi 0 Hz -1/2 when operated at a frequency of 170-200 MHz and have 1/f noise corners of a few hertz. Measurements of the V RF versus L RF characteristics of one SQUID, indicate that intrinsic device noise dominates the measured total noise of these devices. The white noise of all devices exceeds the predictions of the theory of Kurkijarvi at al. by a large factor, apparently because of non-ideal behaviour of step-edge Josephson junctions.

G.S. Krivoy, V. A. Komashko

The dc SQUID had been presented for use in the rf SQUID instead of a weak link. The new device, referred to as “double SQUID”, possesses a large output signal (hundreds of microvolts) in operating in a hysteretic mode. For making an operating mode a double SQUID is coupled to a circuit traditional for rf SQUIDs containing a tank circuit and an rf current pumping generator. The magnetic flux being measured is recognized by the dc SQUID quantization loop which results in changing its critical current. As a result the height of the flat part of the tank circuit I–V characteristics coupled to a double SQUID is modulated. It is this modulation that is the SQUID output signal. The experimental investigations of the double SQUID showed the validity of the assumptions under consideration. Output signals up to 690 μV, noise spectral density ≈2×10−5ϕ0/ Hz 1/2 (ϕ0 is the flux quantum) and energy resolution ≈1.4×10−29 J/Hz have been obtained.