A long-lived Zeeman trapped-ion qubit

TL;DR

This paper reports achieving a 2.1-second coherence time for a single trapped calcium ion's electron spin qubit by combining magnetic shielding and permanent magnets, significantly extending qubit coherence durations.

Contribution

The study demonstrates an ultralong coherence time for a simple trapped-ion qubit using magnetic shielding and permanent magnets, surpassing previous results for similar systems.

Findings

Coherence time of 2.1 seconds achieved.

Residual magnetic field fluctuations ≤ 2.7×10⁻¹² T.

Magnetic noise reduced by 20-30 dB with shielding.

Abstract

We demonstrate a coherence time of 2.1(1)~s for electron spin superposition states of a single trapped $^{40}$Ca$^+$ ion. The coherence time, measured with a spin-echo experiment, corresponds to residual rms magnetic field fluctuations $\leq$~2.7$\times$10$^{-12}$~T. The suppression of decoherence induced by fluctuating magnetic fields is achieved by combining a two-layer $\mu$-metal shield, which reduces external magnetic noise by 20 to 30~dB for frequencies of 50~Hz to 100~kHz, with Sm$_2$Co$_{17}$ permanent magnets for generating a quantizing magnetic field of 0.37~mT. Our results extend the coherence time of the simple-to-operate spin qubit to ultralong coherence times which so far have been observed only for magnetic insensitive transitions in atomic qubits with hyperfine structure.