Almost a century ago, physicists Satyendra Nath Bose and Albert Einstein proposed the existence of a state of matter known as Bose-Einstein condensates (BECs). These condensates occur when individual particles condense into an indistinguishable whole at extremely cold temperatures and low densities. Since the experimental realization of BECs in 1995, scientists have been using them to study the world of quantum mechanics. However, creating stable and ultracold molecules to approach a BEC state has been a significant challenge. This article explores the latest breakthrough in the creation of ultracold molecular gases using microwaves, and the potential impact on fundamental physics research.
Researchers at Columbia University, led by physicist Sebastian Will, have made significant strides in the science of ultracold molecular gases. Building upon the work done by researchers in Munich using microwaves to cool fermionic molecules, Will’s team focused on bosonic molecules, a complementary step in the field. In a recent publication in Nature Physics, they demonstrated how microwaves emitted from a custom-built antenna can extend the lifespan of sodium-cesium molecules from milliseconds to over one second. This breakthrough is a critical step towards cooling the molecules and potentially creating a BEC.
The technique employed by Will’s team was initially proposed by Tijs Karman, a theoretical physicist at Radboud University. Microwaves, a form of electromagnetic radiation, induce rotational motion in molecules. In the case of sodium-cesium molecules, microwaves prevent the molecules from sticking to each other and getting lost from the sample. This shielding effect allows the molecules to be subjected to evaporative cooling, similar to blowing on a hot cup of coffee. By removing the hotter molecules, the remaining ones rethermalize to a cooler temperature.
The creation of ultracold sodium-cesium molecules opens up new possibilities for exploring fundamental physics. Sodium-cesium is an interesting molecule due to its bosonic nature and large dipole moment. Unlike fermions, which have half-integer spins, bosons have whole integer spins. This statistical difference leads to contrasting behaviors between the two types of particles. The dipole moment of sodium-cesium, a measure of the difference in electrical charge within the molecule, influences its interactions with other molecules at various distances.
Dipolar interactions between sodium-cesium molecules introduce a level of complexity beyond current experiments that focus on atomic interactions. This unique feature makes ultracold sodium-cesium molecules a promising platform to study new phases of matter and quantum simulations. The dipole moment of sodium-cesium lies between that of magnetic atoms and Rydberg atoms, providing the opportunity to explore uncharted regimes. Magnetic atoms have weak interactions, while Rydberg atoms are short-lived, unstable, and possess interactions that are too strong.
The Will lab’s ultracold sodium-cesium molecules offer numerous avenues for scientific exploration. They present an opportunity to study peculiar types of superfluidity and classical thermodynamics of gases, where molecules interact over long ranges. By tuning into these regimes, the lab hopes to uncover new physics that has yet to be observed in other experiments. The ultracold molecules also have the potential to contribute to advancements in quantum physics research and quantum computing.
The breakthrough achieved by the Will lab in creating ultracold sodium-cesium molecules using microwaves brings scientists closer to realizing Bose-Einstein condensates with molecules. By extending the lifespan of the molecules and dropping the temperature to near the necessary level for BEC formation, the researchers have opened up new possibilities for exploring the microscopic world of quantum mechanics. The unique properties of sodium-cesium molecules, including their large dipole moment, make them a fascinating platform for studying fundamental physics. As the Will lab continues to push the boundaries of ultracold molecular gases, the stage is set for groundbreaking discoveries and a deeper understanding of the complexities of quantum mechanics and quantum simulations.