Towards Improved Quantum Simulations and Sensing with Trapped 2D Ion Crystals via Parametric Amplification

TL;DR

This paper demonstrates motional parametric amplification in 2D ion crystals, enhancing spin-motion coupling and sensing sensitivity, with potential applications in quantum simulation and precision measurement.

Contribution

It introduces and experimentally validates protocols for motional squeezing via parametric amplification in large 2D ion crystals, improving coherence and sensitivity in quantum experiments.

Findings

Achieved 5.4 dB motional squeezing below ground state.

Predicted 10 dB sensitivity enhancement for displacement measurements.

Calibrated parametric coupling strength for continuous squeezing.

Abstract

Improving coherence is a fundamental challenge in quantum simulation and sensing experiments with trapped ions. Here we discuss, experimentally demonstrate, and estimate the potential impacts of two different protocols that enhance, through motional parametric excitation, the coherent spin-motion coupling of ions obtained with a spin-dependent force. The experiments are performed on 2D crystal arrays of approximately one hundred $^9$Be$^+$ ions confined in a Penning trap. By modulating the trapping potential at close to twice the center-of-mass mode frequency, we squeeze the motional mode and enhance the spin-motion coupling while maintaining spin coherence. With a stroboscopic protocol, we measure $5.4 \pm 0.9$ dB of motional squeezing below the ground-state motion, from which theory predicts a $10$ dB enhancement in the sensitivity for measuring small displacements using a recently demonstrated protocol [Science $\textbf{373}$, 673 (2021)]. With a continuous squeezing protocol, we measure and accurately calibrate the parametric coupling strength. Theory suggests this protocol can be used to improve quantum spin squeezing, limited in our system by off-resonant light scatter. We illustrate numerically the trade-offs between strong parametric amplification and motional dephasing in the form of center-of-mass frequency fluctuations for improving quantum spin squeezing in our set-up.