Interaction of a Laser with a Qubit in Thermal Motion and its Application to Robust and Efficient Readout

TL;DR

This paper investigates how thermal motion affects laser-qubit interactions in trapped ions, developing a model that improves temperature measurement and enhances the robustness of rapid adiabatic passage for quantum control.

Contribution

It introduces an effective Maxwell-Boltzmann theory for thermal fluctuations in ion qubits and demonstrates its experimental validation and application to improve quantum control protocols.

Findings

Accurately measures ion temperature within 2% of Doppler limit.

Validates the model for resonant square pulses and RAP.

Shows improved robustness and efficiency in quantum control.

Abstract

We present a detailed theoretical and experimental study on the optical control of a trapped-ion qubit subject to thermally induced fluctuations of the Rabi frequency. The coupling fluctuations are caused by thermal excitation on three harmonic oscillator modes. We develop an effective Maxwell-Boltzmann theory which leads to a replacement of several quantized oscillator modes by an effective continuous probability distribution function for the Rabi frequency. The model is experimentally verified for driving the quadrupole transition with resonant square pulses. This allows for the determination of the ion temperature with an accuracy of better than 2% of the temperature pertaining to the Doppler cooling limit TD over a range from 0.5TD to 5TD. The theory is then applied successfully to model experimental data for rapid adiabatic passage (RAP) pulses. We apply the model and the obtained experimental parameters to elu- cidate the robustness and efficiency of the RAP process by means of numerical simulations.