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Low Temperature Physics

Controlled Stochastic Amplification of a Weak Signal in a Superconducting Quantum Interferometer

Oleg G. Turutanov, V. Yu. Lyakhno, M. E. Pivovar, V. I. Shnyrkov

Published Jan 1, 2019• 3 citations
Publisher

Abstract

In a single-junction niobium superconducting quantum interferometer (RF SQUID loop), a weak low-frequency harmonic signal is amplified when quasi-white Gaussian noise magnetic flux is applied to the loop; such amplification is due to stochastic resonance (SR). We have experimentally shown that if the suboptimal flux noise intensity is insufficient for SR, the mean rate of transitions between the metastable states of the loop, and thus the signal gain, can be controlled by an additional deterministic alternating magnetic flux with frequency being much higher than that of the useful signal to provide the maximal possible gain. The frequency characteristics of a multi-tone composite signal amplification in the cases of controlled stochastic amplification and “pure” SR are compared to each other.

DOI
10.1063/1.5082311

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In a single-junction niobium superconducting quantum interferometer (RF SQUID loop), a weak low-frequency harmonic signal is amplified when quasi-white Gaussian noise magnetic flux is applied to the loop; such amplification is due to stochastic resonance (SR). We have experimentally shown that if the suboptimal flux noise intensity is insufficient for SR, the mean rate of transitions between the metastable states of the loop, and thus the signal gain, can be controlled by an additional deterministic alternating magnetic flux with frequency being much higher than that of the useful signal to provide the maximal possible gain. The frequency characteristics of a multi-tone composite signal amplification in the cases of controlled stochastic amplification and “pure” SR are compared to each other.
The features of the response of a single-junction superconducting quantum interferometer to a low-frequency harmonic signal in the presence of noise and a high-frequency electromagnetic field are investigated through numerical solution of the equations of motion. It is shown that in this situation a system described by a double-well potential will display stochastic-parametric amplification of weak harmonic signals owing to the cooperative effects of noise and the high-frequency field. The gain is a nonmonotonic function of the amplitude of the high-frequency field and the variance of the noise flux and passes through a maximum. A detailed numerical analysis of the dependence of the gain on the noise intensity and on the frequency and amplitude of the high-frequency field is carried out in the stochastic, parametric, and stochastic-parametric amplification regimes. It is shown that at optimal amplitude of the high-frequency field the gain for a weak harmonic signal reaches rather high values (10–30). The specific properties of stochastic-parametric amplification are discussed, and the possible applications of this effect for constructing input circuits of detectors based on SQUIDs with registration of weak narrow-band information signals are considered.
This paper proposes one of possible solutions to arrange the weak continuous measurements of the state of the flux qubit based on a superconducting interferometer ring, with a stochastic amplifier which provides the minor back action.The amplifier exploits the stochastic resonance (SR) effect and is embodied as a superconducting interferometer ring incorporating the four-terminal (4-t) Josephson junction . The two leads of the 4-t Josephson junction are closed by the amplifier-interferometer ring while the rest two are connected to the superconducting magnetic antenna (flux transformer) that senses the flux qubit state. In this arrangement, a variation of the qubit flux which corresponds to a certain qubit state superposition results in a change in the antenna loop current. Further, the stochastic amplifier gain, as it will be shown below, depends on the antenna loop current thus monitoring the cubit state.
The superconducting quantum interferometer with two quantization loops, the so-called double SQUID, or D-SQUID, is a modification of the well-known rf SQUID. The modification consists of a replacement of the one junction of the rf SQUID by a superconducting loop with two Josephson junctions. This device can be used to transform the weak magnetic flux applied to the loop with junctions to a voltage across the tank circuit inductively coupled to the other loop. As has previously been shown in experiments [G. S. Krivoy and H. Koch, J. Appl. Phys. 74, 2925 (1993)], D-SQUIDs have an extremely large output signal swing up to 1 mV and a transfer function of several mV/(h/2e). In this paper, a D-SQUID theory using a numerical and an analytical approach is developed. The theoretical results are compared with the above-mentioned experiments.