Noise and Operational Characteristics of Magnetometers Made from Superconducting-Normal-Superconducting Josephson Junctions

1997 ◽  
Vol 474 ◽  
Author(s):  
D. Reagor ◽  
C. Mombourquette ◽  
J. Decker ◽  
Y. Fan ◽  
M. Hawley ◽  
...  
Keyword(s):  
Geomagnetic Field ◽  
Josephson Junctions ◽  
Quantum Interference ◽  
Applied Field ◽  
Thermal Noise ◽  
Electrical Characteristics ◽  
Noise Characteristics ◽  
Flux Trapping ◽  
Operational Characteristics ◽  
Small Inductance

ABSTRACTWe have fabricated numerous magnetometers using our high temperature superconducting (HTS) Josephson junctions. These Josephson junctions are fabricated in a superconducting-normal-superconducting ramp edge configuration1 with silver doped YBa2Cu3O7 (YBCO) for the superconducting electrodes and PrBa2Cu3O7, (PBCO) for the normal layer. Small inductance quantum interference devices (SQUEDs) made from this junction technology have a transfer function exceeding 150 microvolts per flux quanta and a flux noise of 5×10−6flux quanta per root hertz. In addition, we have established that these junctions have identical electrical characteristics after either a year of storage or repeated thermal cycling. We have also examined the trade-off of 1/f noise versus thermal noise that is obtained as we vary the critical current of the devices.The SQUID magnetometers were made using galvanically coupled input coils. These devices exhibit excellent operational characteristics in the geomagnetic field. They functioned in an unshielded environment for more than 24 hours and operated in a moving dewar (without any feedback fields to compensate the changing applied field) - both without flux trapping. Noise characteristics under these conditions are presented.

EFFECT OF THERMAL NOISE ON THE CURRENT-VOLTAGE CHARACTERISTICS OF JOSEPHSON JUNCTIONS

1996 ◽  
Vol 10 (22) ◽  
pp. 1095-1102 ◽  
Author(s):  
A.K. CHATTAH ◽  
C.B. BRIOZZO ◽  
O. OSENDA ◽  
M.O. CÁCERES
Keyword(s):  
Josephson Junctions ◽  
Thermal Noise ◽  
Planck Equation ◽  
Resonance Problem ◽  
Shapiro Steps ◽  
Periodic Distribution ◽  
Current Voltage ◽  
Current Voltage Characteristics ◽  
Path Integral Method ◽  
Asymptotic Time

We analyze the influence of thermal noise on the Shapiro steps appearing in the current-voltage characteristics of Josephson junctions. We solve the Fokker-Planck equation describing the system by a path integral method in the steepest-descent approximation, previously applied to the stochastic resonance problem. We obtain the Asymptotic Time-Periodic Distribution Pas(ϕ, t), where ϕ∈[0, 2π] and compute from it the voltage [Formula: see text], constructing the I-V characteristics. We find a defined “softening” of the Shapiro steps as temperature increases, for values of the system parameters in the experimentally accessible range.

scholarly journals Influence of Resonances on the Noise Performance of SQUID Susceptometers

Sensors ◽  
2019 ◽  
Vol 20 (1) ◽  
pp. 204 ◽  
Author(s):  
Samantha I. Davis ◽  
John R. Kirtley ◽  
Kathryn A. Moler
Keyword(s):  
Quantum Interference ◽  
Noise Performance ◽  
Superconducting Quantum Interference Device ◽  
Noise Characteristics ◽  
Current Voltage ◽  
Electromagnetic Resonances ◽  
Current Voltage Characteristics ◽  
Local Magnetic Fields ◽  
Scanning Squid ◽  
Further Development

Scanning Superconducting Quantum Interference Device (SQUID) Susceptometry simultaneously images the local magnetic fields and susceptibilities above a sample with sub-micron spatial resolution. Further development of this technique requires a thorough understanding of the current, voltage, and flux ( I V Φ ) characteristics of scanning SQUID susceptometers. These sensors often have striking anomalies in their current–voltage characteristics, which we believe to be due to electromagnetic resonances. The effect of these resonances on the performance of these SQUIDs is unknown. To explore the origin and impact of the resonances, we develop a model that qualitatively reproduces the experimentally-determined I V Φ characteristics of our scanning SQUID susceptometers. We use this model to calculate the noise characteristics of SQUIDs of different designs. We find that the calculated ultimate flux noise is better in susceptometers with damping resistors that diminish the resonances than in susceptometers without damping resistors. Such calculations will enable the optimization of the signal-to-noise characteristics of scanning SQUID susceptometers.

PSIM simulations of a dc SQUID magnetometer

2015 ◽  
Vol 13 (2) ◽  
pp. 298-314 ◽  
Author(s):  
Kehinde Ogunyanda ◽  
Wilfred Fritz ◽  
Robert van Zyl
Keyword(s):  
Quantum Interference ◽  
Thermal Noise ◽  
Squid Magnetometer ◽  
Superconducting Quantum Interference Device ◽  
Test Analysis ◽  
Content Type ◽  
Power Simulation ◽  
Noise Simulation ◽  
Current Characteristics ◽  
Squid Magnetometers

Purpose – This paper aims to report the modelling and simulation work that predicts the behaviours of both a Josephson junction (JJ) and a dc superconducting quantum interference device (SQUID). It is pertinent to predict the SQUID magnetometers’ behaviours via simulations, before subjecting them to real experiments because they are quite expensive to acquire, and can be easily damaged during test analysis. Design/methodology/approach – To achieve this, power simulation (PSIM) was used to model and simulate a JJ, using the basic equation that describes the effective current through it. A dc SQUID magnetometer, which is composed of two JJs, was then modelled and simulated using the modelled JJ. Thermal noise simulation is also included, to observe its effects on the magnetometer’s output. A directly coupled flux-locked loop circuit was later included in the simulation to amplify and linearise the SQUID’s output, which is usually sinusoidal. Findings – When steady bias currents were applied to the JJ, the resulting voltage across it was seen to oscillate. The JJ’s and SQUID’s voltage–current characteristics, and voltage–flux characteristics were also observed in the simulations, and the results respectively agree with the behaviours of a typical JJ and dc SQUID magnetometer. Originality/value – A way of simulating SQUIDs, without a superconducting simulation tool, is presented. The work provides a much simpler way of studying the behaviour of dc SQUID magnetometers, due to the easy accessibility and fast simulation capability of the software used, with an added advantage of being able to simulate the thermal noise effects, without having to import this facility from secondary software.

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