On the theory of the symmetrical double SQUID

Boris Chesca

Boris Chesca

Giacomo Trupiano, Elisa Riccardi, Claudio Puglia +5 more

We demonstrate a highly linear superconducting quantum interference device (SQUID) interferometer based on a double-loop (Bi-SQUID) architecture incorporating three superconductor-normal metal-superconductor ( S - N - S ) junctions. Fabricated using niobium-gold technology, the device exhibits robust operation at liquid helium temperatures, with a superconducting transition temperature of 8.5 K. The dc flux-to-voltage transfer function demonstrates sharp, symmetric, and highly linear behavior at temperatures up to 5 K. Bi-SQUIDs featuring our single-element S - N - S design represent an interesting and original approach to this field, as they exhibit a numerically estimated spurious-free dynamic range linearity exceeding 60 dB, achieved in a single element, simplifying the requirements in terms of arrays containing hundreds of junctions. These results highlight the potential of proximity-based Bi-SQUIDs for compact and highly linear cryogenic interferometric devices, motivating future investigations of their dynamic and noise performance for applied implementations such as quantum sensing, magnetometry, and biomedical diagnostics.

J. Vrba, Alistair A. Fife, V. Macura +2 more

A generalized theory of the double-hole SQUID is developed and the importance of the mutual inductive coupling between the SQUID holes is demonstrated. The basic flux periodicity Φeff is found to depend on this inductive coupling and is shown to be within the limits Φ0 ≤ Φeff ≤ 2Φ0 for coupling constant k in the range 1 ≥ k ≥ 0.

N. F. Masharov

A. U. Thomann, V. B. Geshkenbeǐn, G. Blatter