Coherence of Symmetry-Protected Rotational Qubits in Cold Polyatomic Molecules

TL;DR

This paper demonstrates long-lived coherence between symmetry-protected rotational states in cold formaldehyde molecules, enabling robust qubits insensitive to external electric and magnetic fields, paving the way for advanced quantum applications.

Contribution

It introduces a method to encode qubits in symmetry-protected rotational states of cold polyatomic molecules, showing their coherence properties and field insensitivity.

Findings

Achieved ~100 μs coherence times in formaldehyde molecules.

Demonstrated insensitivity of qubits to external electric and magnetic fields.

Observed long-lived coherences between symmetry-protected states.

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 (H$_2$CO) inside an electric box and perform a Ramsey-type experiment to observe long-lived (~100 $\mu$s) 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.