Micromotion minimization using Ramsey interferometry

TL;DR

This paper presents a rapid, precise method using Ramsey interferometry sequences to minimize stray electric fields in ion traps, surpassing previous techniques and enabling improved quantum control and clock synchronization.

Contribution

The authors introduce a novel interferometry-based approach for stray field minimization that is simple, robust, and more precise than existing methods, with applications in quantum metrology and clock synchronization.

Findings

Reduced 2D stray field to (10.5±0.8) mV/m in 11 seconds

Demonstrated quantum-enhanced measurement below standard quantum limit

Achieved micromotion minimization with modest experimental complexity

Abstract

We minimize the stray electric field in a linear Paul trap quickly and accurately, by applying interferometry pulse sequences to a trapped ion optical qubit. The interferometry sequences are sensitive to the change of ion equilibrium position when the trap stiffness is changed, and we use this to determine the stray electric field. The simplest pulse sequence is a two-pulse Ramsey sequence, and longer sequences with multiple pulses offer a higher precision. The methods allow the stray field strength to be minimized beyond state-of-the-art levels, with only modest experimental requirements. Using a sequence of nine pulses we reduce the 2D stray field strength to $(10.5\pm0.8)\,\mathrm{mV\,m^{-1}}$ in $11\,\mathrm{s}$ measurement time. The pulse sequences are easy to implement and automate, and they are robust against laser detuning and pulse area errors. We use interferometry sequences with different lengths and precisions to measure the stray field with an uncertainty below the standard quantum limit. This marks a real-world case in which quantum metrology offers a significant enhancement. Also, we minimize micromotion in 2D using a single probe laser, by using an interferometry method together with the resolved sideband method; this is useful for experiments with restricted optical access. Furthermore, a technique presented in this work is related to quantum protocols for synchronising clocks; we demonstrate these protocols here.