Second-scale rotational coherence and dipolar interactions in a gas of ultracold polar molecules

TL;DR

This paper demonstrates a magic optical trap for ultracold RbCs molecules that achieves long rotational coherence times, enabling control over dipolar interactions for quantum computing and simulation.

Contribution

It introduces a rotationally-magic optical trap that significantly extends coherence times and allows tuning of dipolar interactions in ultracold polar molecules.

Findings

Achieved 0.78 seconds Ramsey coherence time without dipole interactions.

Extended coherence to over 1.4 seconds with spin-echo pulses.

Showed coherence time inversely proportional to dipolar interaction strength.

Abstract

Ultracold polar molecules uniquely combine a rich structure of long-lived internal states with access to controllable long-range, anisotropic dipole-dipole interactions. In particular, the rotational states of polar molecules confined in optical tweezers or optical lattices may be used to encode interacting qubits for quantum computation or pseudo-spins for simulating quantum magnetism. As with all quantum platforms, the engineering of robust coherent superpositions of states is vital. However, for optically trapped molecules, the coherence time between rotational states is typically limited by inhomogeneous light shifts. Here we demonstrate a rotationally-magic optical trap for RbCs molecules that supports a Ramsey coherence time of 0.78(4) seconds in the absence of dipole-dipole interactions. This extends to >1.4 seconds at the 95% confidence level using a single spin-echo pulse. In our magic trap, dipolar interactions become the dominant mechanism by which Ramsey contrast is lost for superpositions that generate oscillating dipoles. By changing the states forming the superposition, we tune the effective dipole moment and show that the coherence time is inversely proportional to the strength of the dipolar interaction. Our work unlocks the full potential of the rotational degree of freedom in molecules for quantum computation and quantum simulation.