Experimental realization of a 218-ion multi-qubit quantum memory

TL;DR

This paper demonstrates a multi-ion quantum memory with over 200 ions in a cryogenic environment, achieving long coherence times and highlighting the importance of sympathetic cooling for stable, long-term quantum information storage.

Contribution

It reports the first stable trapping of over 200 ions and the demonstration of long coherence times, combining multi-qubit capacity with extended storage duration.

Findings

Coherence time of hundreds of milliseconds for individual ions.

Sympathetic cooling is essential for long-term multi-qubit storage.

Stable trapping of above 200 ions in a cryogenic setup.

Abstract

Storage lifetime and capacity are two important factors to characterize the performance of a quantum memory. Here we report the stable trapping of above 200 ions in a cryogenic setup, and demonstrate the combination of the multi-qubit capacity and long storage lifetime by measuring the coherence time of randomly chosen ions to be on the order of hundreds of milliseconds. We apply composite microwave pulses to manipulate qubit states globally for efficient characterization of different storage units simultaneously, and we compare the performance of the quantum memory with and without the sympathetic cooling laser, thus unambiguously show the necessity of sympathetic cooling for the long-time storage of multiple ionic qubits.