Memory coherence of a sympathetically cooled trapped-ion qubit

TL;DR

This paper demonstrates sympathetic cooling of a trapped-ion qubit with minimal decoherence, achieving near-ground state cooling while preserving qubit coherence, which is crucial for scalable quantum computing.

Contribution

It introduces a method for cooling a trapped-ion qubit using a different isotope as a coolant, maintaining coherence during the process.

Findings

Achieved near-ground state cooling of both axial motional modes.

Maintained qubit coherence with only 3.3% loss per cooling cycle.

Theoretically limits infidelity to about 0.01% per cycle.

Abstract

We demonstrate sympathetic cooling of a 43Ca+ trapped-ion "memory" qubit by a 40Ca+ "coolant" ion near the ground state of both axial motional modes, whilst maintaining coherence of the qubit. This is an essential ingredient in trapped-ion quantum computers. The isotope shifts are sufficient to suppress decoherence and phase shifts of the memory qubit due to the cooling light which illuminates both ions. We measure the qubit coherence during 10 cycles of sideband cooling, finding a coherence loss of 3.3% per cooling cycle. The natural limit of the method is O(0.01%) infidelity per cooling cycle.