New tools ‘turn on’ quantum gases of ultracold molecules

False-color image of a gas of potassium-rubidium polar molecules (left) becoming denser and colder in reaching a state called quantum degeneracy (right), in which the individual molecules’ matter waves overlap to create an interdependent system. (Credit: Ye Group/JILA)

JILA researchers have developed tools to “turn on” quantum gases of ultracold molecules, gaining control of long-distance molecular interactions for potential applications such as encoding data for quantum computing and simulations. JILA is a joint institute of the National Institute of Standards and Technology (NIST) and the University of Colorado Boulder.

The new scheme for nudging a molecular gas down to its lowest energy state, called quantum degeneracy, while suppressing chemical reactions that break up molecules finally makes it possible to explore exotic quantum states in which all the molecules interact with one another.

The JILA experiments created a dense gas of about 20,000 trapped potassium-rubidium molecules at a temperature of 250 nanokelvin above absolute zero. Crucially, these molecules are polar, with a positive electric charge at the rubidium atom and a negative charge at the potassium atom. The differences between these positive and negative charges, called electric dipole moments, cause the molecules to behave like tiny compass magnets sensitive to certain forces, in this case electric fields.

When the gas is cooled to near absolute zero, the molecules stop behaving like particles and instead behave like waves that overlap. The molecules stay apart because they are fermions, a class of particles that cannot be in the same quantum state and location at the same time and therefore repel each other. But they can interact at long range through their overlapping waves, electric dipole moments and other features.

The new JILA method can be applied to make ultracold gases out of other types of polar molecules.

Ultracold molecular gases may have many practical uses, including new methods for quantum computing using polar molecules as quantum bits; simulations and improved understanding of quantum phenomena such as colossal magnetoresistance (for improved data storage and processing) and superconductivity (for perfectly efficient electric power transmission); and new tools for precision measurement such as molecular clocks or molecular systems that enable searches for new theories of physics. (NIST)

The paper has been published in Nature.

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