Experimental measurements of current-voltage, current-phase, amplitude-frequency, phase-frequency, and signal characteristics of an rf SQUID operating at a frequency of 30 MHz in the nonhysteretic regime (l=2πL 0 I 0/ф0<1) were carried out for the conditionk 2 Ql>1. HereI 0 is the critical current of the weak link,L 0 is the SQUID ring inductance,k is the coefficient of coupling of the SQUID ring to a resonant tank circuit of qualityQ, and ф0 is the magnetic flux quantum. A numerical analysis of the above characteristics for all relevant parameter values close to those occurring under experimental conditions was performed for qualitative comparison with theory. The main difference from the traditional nonhysteretic regime of SQUID operation (k 2 Ql<1,l<1) is the possibility of a strong increase in the magnetic flux-to-voltage transfer coefficients η a and ηθ corresponding to changes in the rf amplitude and the phase. The increase in η is known to reduce the amplifier noise contribution to the SQUID energy resolution. At a temperature of 4.2 K the maximum value of the transfer coefficient was estimated experimentally as η=(3±2)×1012 V/Wb for the single-valued region of the signal characteristics. The results suggest that considerable improvement of rf SQUID resolution is possible in the regimek 2 Ql>1.
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Dmitrenko, I.M., Tsoi, G.M., Shnyrkov, V.I. et al. Rf SQUID in the nonhysteretic regime withk 2 Ql>1. J Low Temp Phys 49, 417–433 (1982). https://doi.org/10.1007/BF00681894
- Transfer Coefficient
- Signal Characteristic
- Magnetic Flux
- Energy Resolution
- Relevant Parameter