A dispersive nanoSQUID magnetometer for ultra-low noise, high bandwidth flux detection

TL;DR

This paper introduces a dispersive nanoSQUID magnetometer with high sensitivity and wide bandwidth, capable of detecting ultra-low magnetic flux noise with minimal on-chip dissipation, suitable for quantum and classical spin sensing.

Contribution

The work presents a novel dispersive nanoSQUID design with tunable GHz resonant frequency and integrated parametric gain, enhancing flux detection sensitivity and bandwidth.

Findings

Minimum flux noise of 30 nΦ₀/Hz^{1/2}

Bandwidth of 20 MHz, extendable to 60 MHz with a Josephson parametric amplifier

High sensitivity with no on-chip dissipation

Abstract

We describe a dispersive nanoSQUID magnetometer comprised of two variable thickness aluminum weak-link Josephson junctions shunted in parallel with an on-chip capacitor. This arrangement forms a nonlinear oscillator with a tunable 4-8 GHz resonant frequency with a quality factor Q = 30 when coupled directly to a 50 $\Omega$ transmission line. In the presence of a near-resonant microwave carrier signal, a low frequency flux input generates sidebands that are readily detected using microwave reflectometry. If the carrier excitation is sufficiently strong then the magnetometer also exhibits parametric gain, resulting in a minimum effective flux noise of 30 n$\Phi_0$/Hz$^{1/2}$ with 20 MHz of instantaneous bandwidth. If the magnetometer is followed with a near quantum-noise-limited Josephson parametric amplifier, we can increase the bandwidth to 60 MHz without compromising sensitivity. This combination of high sensitivity and wide bandwidth with no on-chip dissipation makes this device ideal for local sensing of spin dynamics, both classical and quantum.