Ultra-Highly Linear Magnetic Flux-to-Voltage response in Proximity-based Mesoscopic bi-SQUIDs

Abstract

Superconducting double-loop interferometers (bi-SQUIDs) have been introduced to produce magnetic flux sensors specifically designed to exhibit ultra-highly linear voltage response as a function of the magnetic flux. These devices are very important for the quantum sensing and for signal processing of signals oscillating at the radio-frequencies range of the electromagnetic spectrum. Here, we report an Al double-loop bi-SQUIDs based on proximitized mesoscopic Cu Josephson junctions. Such a scheme provides an alternative fabrication approach to conventional tunnel junction-based interferometers, where the junction characteristics and, consequently, the magnetic flux-to-voltage and magnetic fluxto-critical current device response can be largely and easily tailored by the geometry of the metallic weak-links. We discuss the performance of such sensors by showing a full characterization of the device switching current and voltage drop vs. magnetic flux for temperatures of operation ranging from 30 mK to ∼ 1 K. The figure of merit of the transfer function and of the total harmonic distortion are also discussed. The latter provides an estimate of the linearity of the flux-to-voltage device response, which obtained values as large as 45 dB. Such a result let us foresee a performance already on pair with that achieved in conventional tunnel junction-based bi-SQUIDs arrays composed of hundreds of interferometers.

Ultra linear magnetic flux-to-voltage conversion in superconducting quantum interference proximity transistors

“…L spans a large interval of values as a function of φ ranging from a minimum of ∼ −20 dB (i. e., the response is strongly non linear) in the surrounding of the extrema of the flux-to-voltage characteristics, to a maximum value as large as ∼ 60 dB around the zeroes. Such performance is equivalent to that of SNS mesoscopic bi-SQUIDs [16] and close to that of arrays of bi-SQUIDs. Interestingly, by changing the value of δ φ , the maximum value of L shifts accordingly.…”

“…For the latter case, response linearity is a major requirement, which is generally improved through external reaction loops [1,3,6] or through the construction of arrays of SQUIDs [7,11], at the cost of a worsening of the operation bandwidth and device integrability. A solution to these restrictions has arisen from the introduction of multi-loop superconducting interferometers, the main types of which are bi-SQUIDs [12][13][14][15][16] and D-SQUIDs [17,18].…”