Coherence of Symmetry-Protected Rotational Qubits in Cold Polyatomic Molecules

Abstract

Polar polyatomic molecules provide an ideal but largely unexplored platform to encode qubits in rotational states. Here, we trap cold (100–600 mK) formaldehyde (H2CO) inside an electric box and perform a Ramsey-type experiment to observe long-lived (∼100 μs) coherences between symmetry-protected molecular states with opposite rotation but identical orientation, representing a quasi-hidden molecular degree of freedom. As a result, the observed qubit is insensitive to the magnitude of an external electric field and depends only weakly on magnetic fields. Our findings provide a basis for future quantum and precision experiments with trapped cold molecules. Published by the American Physical Society 2025