A Numerical Treatment of the rf SQUID: I. General Properties and Noise Energy |
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Authors: | Reinhold Kleiner Dieter Koelle John Clarke |
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Affiliation: | 1. Physikalisches Institut-Experimentalphysik II, Universit?t Tübingen, 72076, Tübingen, Germany 2. Department of Physics, University of California, 94720-7300, Berkeley, CA, USA 3. Materials Sciences Division, Lawrence Berkeley National Laboratory, 94720, Berkeley, CA, USA
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Abstract: | We investigate the characteristics and noise performance of rf Superconducting Quantum Interference Devices (SQUIDs) by solving
the corresponding Langevin equations numerically and optimizing the model parameters with respect to noise energy. After introducing
the basic concepts of the numerical simulations, we give a detailed discussion of the performance of the SQUID as a function
of all relevant parameters. The best performance is obtained in the crossover region between the dispersive and dissipative
regimes, characterized by an inductance parameter β′
L
≡2π
LI
0/Φ
0≈1; L is the loop inductance, I
0 the critical current of the Josephson junction, and Φ
0 the flux quantum. In this regime, the lowest (intrinsic) values of noise energy are a factor of about 2 above previous estimates
based on analytical approaches. However, several other analytical predictions, such as the inverse proportionality of the
noise energy on the tank circuit quality factor and the square of the coupling coefficient between the tank circuit and the
SQUID loop, could not be well reproduced. The optimized intrinsic noise energy of the rf SQUID is superior to that of the
dc SQUID at all temperatures. Although for technologically achievable parameters this advantage shrinks, particularly at low
thermal fluctuation levels, we give examples for realistic parameters that lead to a noise energy comparable to that of the
dc SQUID even in this regime.
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Keywords: | rf SQUIDs Magnetometer Superconductor Numerical simulations Noise |
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