Dispersive magnetometry with a quantum limited SQUID parametric amplifier

TL;DR

This paper demonstrates a dispersive SQUID-based magnetometer that achieves quantum-limited sensitivity and tunable bandwidth through parametric amplification, suitable for nanoscale magnetic measurements in the quantum regime.

Contribution

The work introduces a dispersive magnetometer with integrated parametric amplification, achieving high sensitivity and adjustable bandwidth for quantum coherent nanoscale magnetometry.

Findings

Effective flux noise as low as 0.14 μΦ₀/Hz^{1/2}

Bandwidth tunable from 20 MHz to 0.6 MHz

Results match theoretical predictions

Abstract

There is currently fundamental and technological interest in measuring and manipulating nanoscale magnets, particularly in the quantum coherent regime. To observe the dynamics of such systems one requires a magnetometer with not only exceptional sensitivity but also high gain, wide bandwidth and low backaction. We demonstrate a dispersive magnetometer consisting of a two-junction SQUID in parallel with an integrated, lumped-element capacitor. Input flux signals are encoded as a phase modulation of the microwave drive tone applied to the magnetometer, resulting in a single quadrature voltage signal. For strong drive power, the nonlinearity of the resonator results in quantum limited, phase sensitive parametric amplification of this signal, which improves flux sensitvity at the expense of bandwidth. \ Depending on the drive parameters, the device performance ranges from an effective flux noise of 0.29\textbf{}$\mu\Phi_{0}$Hz$^{-\frac{1}{2}}$ and 20 MHz of signal bandwidth to a noise of 0.14 $\mu\Phi_{0}$Hz$^{-\frac{1}{2}}$ and a bandwidth of 0.6 MHz. These results are in excellent agreement with our theoretical model.