Thermal magnetic noise in rf SQUIDS coupled to ferromagnetic cores

Journal Article · Wed Mar 01 04:00:00 EST 1989 · J. Appl. Phys.; (United States)

DOI:https://doi.org/10.1063/1.342862· OSTI ID:6404977

Vitale, S; Prodi, G A; Cerdonio, M

We present a simple model for the thermal magnetic noise in a rf SQUID coupled to a ferromagnetic core via a superconducting dc flux transformer. We show that, under conditions that are almost always fulfilled in practice, the coupling to the core can be described in terms of a SQUID frequency-dependent complex inductance L/sub s/ (..omega..). This inductance reduces to an ordinary, frequency-independent real value above a roll-off frequency ..omega../sub c/ . To this inductance, a Nyquist flux noise generator is associated, with spectral density S/sup '//sup 2//sub phi//sub i/(..omega..) = -4k/sub B/T Im(L/sub s/(..omega..))/ ..omega.., where k/sub B/ is the Boltzmann constant, T the temperature, and Im(L/sub s/ (..omega..)) the imaginary part of L/sub s/ (..omega..). If ..omega../sub c/ <<..omega../sub rf/ , with ..omega../sub rf/ the frequency of the rf pump, then the response of the SQUID to low-frequency signals is not modified by the coupling to the core, while the above Nyquist noise acts as an additive input noise. We experimentally demonstrate the model for a SQUID coupled to a toroidal core.

• Research Organization: Dipartimento di Fisica, Universita di Trento, and Istituto Nazionale di Fisica Nucleare, Gruppo di Trento, I-38050, Povo, Trento, Italy
• OSTI ID: 6404977
• Journal Information: J. Appl. Phys.; (United States), Journal Name: J. Appl. Phys.; (United States) Vol. 65:5; ISSN JAPIA
• Country of Publication: United States
• Language: English

Related Subjects

420201* -- Engineering-- Cryogenic Equipment &amp; Devices
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
COUPLING
DATA
ELECTRICAL EQUIPMENT
ELECTRONIC EQUIPMENT
EQUIPMENT
EXPERIMENTAL DATA
FERROMAGNETIC MATERIALS
FLUXMETERS
HYSTERESIS
INFORMATION
MAGNETIC CORES
MAGNETIC FLUX
MAGNETIC MATERIALS
MAGNETIC STORAGE DEVICES
MATERIALS
MATHEMATICAL MODELS
MEASURING INSTRUMENTS
MEMORY DEVICES
MICROWAVE EQUIPMENT
NOISE
NUMERICAL DATA
PERMEABILITY
SQUID DEVICES
SUPERCONDUCTING DEVICES
THEORETICAL DATA
TRANSFORMERS