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Interferometric Measurement of Magnetic Flux

IP.com Disclosure Number: IPCOM000050568D
Original Publication Date: 1982-Nov-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 2 page(s) / 27K

Publishing Venue

IBM

Related People

Chang, WH: AUTHOR

Abstract

This 3-junction Josephson interferometer is comprised of two superconducting loops which are slightly mismatched in their LI(o) product. This mismatch is about 5%. This slightly asymmetric interferometer is very sensitive to small magnetic fields, and the shift in its threshold curve, due to an input magnetic signal, is a measure of the flux in that signal.

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Interferometric Measurement of Magnetic Flux

This 3-junction Josephson interferometer is comprised of two superconducting loops which are slightly mismatched in their LI(o) product. This mismatch is about 5%. This slightly asymmetric interferometer is very sensitive to small magnetic fields, and the shift in its threshold curve, due to an input magnetic signal, is a measure of the flux in that signal.

Asymmetric interferometer 10 is comprised of two superconducting loops 12 and 14, having slightly different LI(o) products. Josephson junctions J1 and J2 have identical critical currents I(o), while junction J3 has a critical current 2 I(o). A control current I(c) is coupled to both loops 12 and 14 of the interferometer. The control current I(s) is coupled only to loop 14 of the interferometer, and is used to couple the magnetic flux to be measured into the interferometer. A gate current I is provided to the Josephson junctions, and each loop 12 and 14 is tied to a common ground.

When I(s) is not equal to zero, the threshold curves of the interferometer are shifted. The amount of shift is proportional to the ratio of (L3+L4)I(s) over L3+L4- L1-L2. Since delta L can be a fraction of L, say, 5%, an amplification in shift in I(c) is obtained. Using this property, a low magnetic field (proportional to I(s) can be readily measured. By measuring the shift, which is several orders of magnitude larger than I(s), the sensitivity of the measurement is very high.

In a variatio...