A planar cloverleaf antenna for circularly polarized microwave fields in atomic and molecular physics experiments.

The article focuses on the design and experimental characterization of a compact cloverleaf microwave antenna array optimized for precise polarization control in atomic and molecular physics experiments. Comprising four elliptical loop antennas arranged with fourfold rotational symmetry, the planar array operates at 3.47 GHz and enables flexible tuning of microwave polarization, particularly achieving high-purity left-circular polarization. Using ultracold sodium–cesium (NaCs) molecules as quantum sensors positioned 22 mm from the antenna, the study demonstrates a strong microwave coupling with a Rabi frequency of 2π × 46.1 MHz and an electric field amplitude of 33 V/cm, alongside a low polarization ellipticity of approximately 2.3°, indicating effective suppression of unwanted polarization components. The antenna's compact form factor, large optical access, and tunability make it suitable for quantum control applications involving molecular rotational states, atomic hyperfine qubits, and other microwave-regime quantum systems.