A single ion as a shot noise limited magnetic field gradient probe

TL;DR

This paper demonstrates a method to measure and compensate magnetic field gradients in ion traps using a single ion, achieving high sensitivity limited by quantum shot noise, which is crucial for scalable ion trap quantum computing.

Contribution

It introduces a technique to measure and correct magnetic field gradients with high precision using a single ion, enabling improved coherence in ion trap quantum computing.

Findings

Achieved magnetic field sensitivity of ΔB/B_0 ~ 5×10^{-7} over 140 μm.

Method can be extended to millimeter ranges with sub-micrometer resolution.

Quantum shot noise is identified as the main limitation in measurement sensitivity.

Abstract

It is expected that ion trap quantum computing can be made scalable through protocols that make use of transport of ion qubits between sub-regions within the ion trap. In this scenario, any magnetic field inhomogeneity the ion experiences during the transport, may lead to dephasing and loss of fidelity. Here we demonstrate how to measure, and compensate for, magnetic field gradients inside a segmented ion trap, by transporting a single ion over variable distances. We attain a relative magnetic field sensitivity of \Delta B/B_0 ~ 5*10^{-7} over a test distance of 140 \micro m, which can be extended to the mm range, still with sub \micro m resolution. A fast experimental sequence is presented, facilitating its use as a magnetic field gradient calibration routine, and it is demonstrated that the main limitation is the quantum shot noise.