Beyond-Ten-Hour Coherence in a Decoherence-Free Trapped-Ion Clock Qubit

TL;DR

This paper demonstrates a trapped-ion qubit system achieving coherence times exceeding ten hours by combining clock states with decoherence-free subspace encoding, surpassing previous experimental limits and approaching the theoretical lifetime of atomic ions.

Contribution

The authors experimentally realize over ten hours of quantum coherence in a trapped-ion system using DFS encoding and clock states, without magnetic shielding or phase stabilization.

Findings

Coherence time of (3.77 +/- 1.09) x 10^4 seconds achieved

DFS encoding effectively rejects microwave phase noise and magnetic fluctuations

Passive error correction enables near-ideal quantum coherence

Abstract

Quantum systems promise to revolutionize information processing science and technology [1-3]. The preservation of quantum coherence, the defining property of qubits, fundamentally constrains the performance of quantum information processing with quantum memories [4]. While trapped atomic ions theoretically support million-year coherence based on spontaneous emission [5-7], experimental demonstrations have reached far less, only about an hour [8-13]. Here we combine clock-state qubits with decoherence-free subspace (DFS) encoding to achieve coherence exceeding ten hours. Using correlation-based phase tracking in 171Yb+ ion pairs sympathetically cooled by 138Ba+ ion, we demonstrate this without magnetic shielding or enhanced microwave phase stabilization that previously limited coherence times. DFS encoding references the qubit phase to the inter-ion energy difference to reject microwave phase noise and common-mode magnetic fluctuations, while clock states provide environmental insensitivity. Throughout measurements extended to 1600 seconds, we observe minimal coherence decay, with exponential fits yielding a coherence time of (3.77 +/- 1.09) x 10^4 seconds. Our results establish DFS encoding as a form of passive error correction that eliminates technical noise constraints, unlocking the million-year coherence potential of atomic ions for scalable quantum information processing.