Flux ramp modulation based MHz frequency-division dc-SQUID multiplexer

TL;DR

This paper introduces a MHz frequency-division dc-SQUID multiplexer utilizing flux ramp modulation, enabling simultaneous real-time readout of multiple signals with high bandwidth, suitable for advanced sensing applications.

Contribution

The work presents a novel flux ramp modulation-based MHz frequency-division dc-SQUID multiplexer with a custom high-speed readout system for real-time phase detection.

Findings

Successfully demonstrated simultaneous readout of four signals.

Achieved MHz bandwidth per channel.

Validated the multiplexer with a prototype and custom electronics.

Abstract

We present a MHz frequency-division dc-SQUID multiplexer that is based on flux ramp modulation and a series array of $N$ identical current-sensing dc-SQUIDs with tightly coupled input coil. By running a periodic, sawtooth-shaped current signal through an additional modulation coil being tightly, but non-uniformly coupled to the individual SQUIDs, the voltage drop across the array changes according to the superposition of the flux-to-voltage characteristics of the individual SQUIDs within each cycle of the modulation signal. In this mode of operation, an input signal injected in the input coil of one of the SQUIDs and being quasi-static within a time frame adds a constant flux offset and leads to a phase shift of the associated SQUID characteristics. The latter is inherently proportional to the input signal and can be inferred by channelizing and down-converting the sampled array output voltage. Using a prototype multiplexer as well as a self-developed high-speed readout electronics for real-time phase determination, we demonstrate the simultaneous readout of four signal sources with MHz bandwidth per channel.