Highly-linear flux-to-voltage transducer based on superconducting quantum interference proximity transistors

TL;DR

This paper introduces the bi-SQUIPT, a superconducting flux transducer with enhanced linearity and stability, suitable for scalable quantum electronics, overcoming limitations of traditional SQUIDs.

Contribution

The work demonstrates a bi-SQUIPT device with differential readout that significantly improves linearity and dynamic range over conventional SQUIDs, with low power dissipation and high operational stability.

Findings

Achieved a voltage swing of approximately 120 μV.

Demonstrated a spurious-free dynamic range of up to 60 dB.

Operates stably up to 600 mK.

Abstract

Superconducting quantum interference devices (SQUIDs) are state-of-the-art in ultra-sensitive magnetometry; however, conventional SQUID devices are fundamentally limited by the inherently nonlinear and periodic nature of their transfer function. Although flux-locked loop (FLL) configurations can mitigate this issue, they introduce electronic complexity and bandwidth constraints that hinder scalability in quantum circuits. In this work, we present an experimental demonstration of the bi-SQUIPT, a flux transducer that modulates the density of states in a proximitized superconducting weak link. The device employs a dual-loop architecture with differential readout, which enables cancellation of non-linearities typical of individual elements, achieving a voltage swing of approximately 120 $\mu$V. Measurements yield a spurious-free dynamic range (SFDR) of up to 60 dB, consistent with theoretical predictions and comparable to that of SQUID arrays, while maintaining power dissipation in the femtowatt range. The results further highlight a remarkable operational stability up to 600 mK, positioning the bi-SQUIPT as an enabling technology for high-density cryogenic quantum electronics.