Generation of strong ultralow-phase-noise microwave fields with tunable ellipticity for ultracold polar molecules

TL;DR

This paper reports a robust microwave setup with ultralow phase-noise and tunable ellipticity, enabling precise control and manipulation of ultracold polar molecules for quantum science applications.

Contribution

The authors present a novel microwave system with high electric field strength, ultralow phase-noise, and tunable polarization, optimized for ultracold polar molecule experiments.

Findings

Achieved 6.9 kV/m electric field in near-field from dual-feed waveguide antenna.

Realized Rabi frequency of 71 MHz for sodium-potassium molecular transition.

Prolonged molecular lifetime up to 10 seconds and observed field-linked resonances.

Abstract

Microwave(MW) fields with strong field strength, ultralow phase-noise and tunable polarization are crucial for stabilizing and manipulating ultracold polar molecules, which have emerged as a promising platform for quantum sciences. In this letter, we present the design, characterization, and performance of a robust MW setup tailored for precise control of molecular states. This setup achieves a high electric field intensity of 6.9 kV/m in the near-field from a dual-feed waveguide antenna, enabling a Rabi frequency as high as 71 MHz for the rotational transition of sodium-potassium molecules. In addition, the low noise signal source and controlled electronics provide ultralow phase-noise and dynamically tunable polarization. Narrow-band filters within the MW circuitry further reduce phase-noise by more than 20 dB at 20 MHz offset frequency, ensuring prolonged one-body molecular lifetimes up to 10 seconds. We also show practical methods to measure the MW field strength and polarization using a simple homemade dipole probe, and to characterize phase-noise down to -170 dBc/Hz with a commercial spectrum analyser and a notch filter. Those capabilities allowed us to evaporatively cool our molecular sample to deep quantum degeneracy. Furthermore, the polarization tunability enabled the observation of field-linked resonances and facilitated the creation of field-linked tetramers.These techniques advance the study of ultracold polar molecules and broaden the potential applications of MW tools in other platforms of quantum sciences.